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Medin, Zach, Marina von Steinkirch, Alan C. Calder, Christopher J. Fontes, Chris L. Fryer, and Aimee L. Hungerford. "MODEL ATMOSPHERES FOR X-RAY BURSTING NEUTRON STARS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/624031.
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The hydrogen and helium accreted by X-ray bursting neutron stars is periodically consumed in runaway thermonuclear reactions that cause the entire surface to glow brightly in X-rays for a few seconds. With models of the emission, the mass and radius of the neutron star can be inferred from the observations. By simultaneously probing neutron star masses and radii, X-ray bursts (XRBs) are one of the strongest diagnostics of the nature of matter at extremely high densities. Accurate determinations of these parameters are difficult, however, due to the highly non-ideal nature of the atmospheres where XRBs occur. Observations from X-ray telescopes such as RXTE and NuStar can potentially place strong constraints on nuclear matter once uncertainties in atmosphere models have been reduced. Here we discuss current progress on modeling atmospheres of X-ray bursting neutron stars and some of the challenges still to be overcome.
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Gregory, Scott G. "T Tauri stars : mass accretion and X-ray emission." Thesis, St Andrews, 2007. http://hdl.handle.net/10023/336.
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Massa, Derek, Lidi Oskinova, Raman Prinja, and Richard Ignace. "Coordinated UV and X-Ray Spectroscopic Observations of the O-type Giant ξ Per: The Connection between X-Rays and Large-scale Wind Structure." Digital Commons @ East Tennessee State University, 2019. https://dc.etsu.edu/etsu-works/5501.
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We present new, contemporaneous Hubble Space Telescope STIS and XMM-Newton observations of the O7 III(n)((f)) star ξ Per. We supplement the new data with archival IUE spectra, to analyze the variability of the wind lines and X-ray flux of ξ Per. The variable wind of this star is known to have a 2.086-day periodicity. We use a simple, heuristic spot model that fits the low-velocity (near-surface) IUE wind line variability very well, to demonstrate that the low-velocity absorption in the new STIS spectra of N iv λ1718 and Si iv λ1402 vary with the same 2.086-day period. It is remarkable that the period and amplitude of the STIS data agree with those of the IUE spectra obtained 22 yr earlier. We also show that the time variability of the new XMM-Newton fluxes is also consistent with the 2.086-day period. Thus, our new, multiwavelength coordinated observations demonstrate that the mechanism that causes the UV wind line variability is also responsible for a significant fraction of the X-rays in single O stars. The sequence of events for the multiwavelength light-curve minima is Si iv λ1402, N iv λ1718, and X-ray flux, each separated by a phase of about 0.06 relative to the 2.086-day period. Analysis of the X-ray fluxes shows that they become softer as they weaken. This is contrary to expectations if the variability is caused by periodic excess absorption. Furthermore, the high-resolution X-ray spectra suggest that the individual emission lines at maximum are more strongly blueshifted. If we interpret the low-velocity wind line light curves in terms of our model, it implies that there are two bright regions, i.e., regions with less absorption, separated by 180°, on the surface of the star. We note that the presence and persistence of two spots separated by 180° suggest that a weak dipole magnetic field is responsible for the variability of the UV wind line absorption and X-ray flux in ξ Per.
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Kastner, Joel H., David A. Principe, Kristina Punzi, Beate Stelzer, Uma Gorti, Ilaria Pascucci, and Costanza Argiroffi. "M STARS IN THE TW HYA ASSOCIATION: STELLAR X-RAYS AND DISK DISSIPATION." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621232.
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To investigate the potential connection between the intense X-ray emission from young low-mass stars and the lifetimes of their circumstellar planet-forming disks, we have compiled the X-ray luminosities (L-X) of M stars in the similar to 8 Myr old TW Hya Association (TWA) for which X-ray data are presently available. Our investigation includes analysis of archival Chandra data for the TWA binary systems TWA 8, 9, and 13. Although our study suffers from poor statistics for stars later than M3, we find a trend of decreasing L-X/L-bol with decreasing T-eff for TWA M stars, wherein the earliest-type (M0-M2) stars cluster near log(L-X/L-bol) approximate to -3.0 and then log(L-X/L-bol) decreases, and its distribution broadens, for types M4 and later. The fraction of TWA stars that display evidence for residual primordial disk material also sharply increases in this same (mid-M) spectral type regime. This apparent anticorrelation between the relative X-ray luminosities of low-mass TWA stars and the longevities of their circumstellar disks suggests that primordial disks orbiting early-type M stars in the TWA have dispersed rapidly as a consequence of their persistent large X-ray fluxes. Conversely, the disks orbiting the very lowest-mass pre-MS stars and pre-MS brown dwarfs in the Association may have survived because their X-ray luminosities and, hence, disk photoevaporation rates are very low to begin with, and then further decline relatively early in their pre-MS evolution.
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Güver, Tolga, Feryal Özel, Herman Marshall, Dimitrios Psaltis, Matteo Guainazzi, and Maria Díaz-Trigo. "SYSTEMATIC UNCERTAINTIES IN THE SPECTROSCOPIC MEASUREMENTS OF NEUTRON STAR MASSES AND RADII FROM THERMONUCLEAR X-RAY BURSTS. III. ABSOLUTE FLUX CALIBRATION." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621974.
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Many techniques for measuring neutron star radii rely on absolute flux measurements in the X-rays. As a result, one of the fundamental uncertainties in these spectroscopic measurements arises from the absolute flux calibrations of the detectors being used. Using the stable X-ray burster, GS 1826-238, and its simultaneous observations by Chandra HETG/ACIS-S and RXTE/PCA as well as by XMM-Newton EPIC-pn and RXTE/PCA, we quantify the degree of uncertainty in the flux calibration by assessing the differences between the measured fluxes during bursts. We find that the RXTE/PCA and the Chandra gratings measurements agree with each other within their formal uncertainties, increasing our confidence in these flux measurements. In contrast, XMM-Newton EPIC-pn measures 14.0 +/- 0.3% less flux than the RXTE/PCA. This is consistent with the previously reported discrepancy with the flux measurements of EPIC-pn, compared with EPIC MOS1, MOS2, and ACIS-S detectors. We also show that any intrinsic time-dependent systematic uncertainty that may exist in the calibration of the satellites has already been implicity taken into account in the neutron star radius measurements.
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Watson, Casey Richard. "The cosmological X-ray evolution of stars, AGN, and galaxies." The Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=osu1148410557.
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González, Galán Ana. "Fundamental properties of High Mass X-ray Binaries." Doctoral thesis, Universidad de Alicante, 2014. http://hdl.handle.net/10045/41723.
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The aim of this thesis is to characterise a sample of High Mass X-ray Binaries (HMXBs) formed by: IGR J00370+6122, XTE J1855-026, AX J1841.0-0535 and AX J1845.0-0433. These objects are composed of pulsars (rotating neutron stars) accreting material from the wind of their supergiant companions. The X-rays are produced in the interaction of the accreted material with the strong gravitational field of the neutron star that accelerates this material and heats it up to ~ 107 K. The study of HMXBs has strong implications in several areas of Physics and Astrophysics. They contain neutron stars whose study is essential to constrain the equation of state of nuclear dense matter, and provides insights on the astrophysical models of core collapse and Supernovae explosions. HMXBs considered as a population give information on the properties of the galaxy. In addition they are excellent test-beds to study accretion physics and outflows. The X-ray behaviour of these systems determines the class of system (classical HMXBs, Supergiant Fast X-ray Transients, Be/X-ray Binaries). The differences in the X-ray emission are supposed to be due to the different properties of the binary systems, such as the orbital properties, the magnetic field of the neutron star or the spectral type of the donor star. HMXBs in this thesis are wind-fed systems, therefore, the properties of the wind (which depend on the spectral type) and the interaction of this wind with the gravitational field of the compact object are key elements to understand the X-ray emission. Therefore, in this thesis an orbital solution for each target of study has been determined using optical spectra of the donor star. Moreover, to check if wind variability is related to the orbit of the binary system, analysis of Ha variations have been carried out. Furthermore, in the case of IGR J00370+6122 and XTE J1855-026 we have obtained an atmosphere model for each of the donor stars allowing us to characterise the atmospheres of these stars, and consequently to determine physical parameters such as the Teff or the log g. Finally publicly available X-ray light curves have been analysed to study the X-ray emission of the different sources against their orbital periods. As a general conclusion, it seems there is a continuum of properties of these systems more than a strict classification. A combination of factors, of which some of them could be unknown, might be the cause of their different X-ray flux behaviours. The outline of this thesis is as follows: the scientific context is given in Chapter 1 an overview of the analysis performed for each of the sources of study is presented in Chapter 2; Chapter 3 is dedicated to the description of a pipeline optimised for the reduction of FRODOSpec spectra of obscured red sources (donor stars of the targets of study); Chapters (4, 5 and 6) present the characterization of the four sources in this thesis, which are different kind of wind-fed systems; and finally general conclusions and future work are given in Chapter 7.
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Toalá, Jesus A., Lidia M. Oskinova, and Richard Ignace. "On the Absence of Non-thermal X-Ray Emission around Runaway O Stars." Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etsu-works/2687.
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Theoretical models predict that the compressed interstellar medium around runaway O stars can produce high-energy non-thermal diffuse emission, in particular, non-thermal X-ray and γ-ray emission. So far, detection of non-thermal X-ray emission was claimed for only one runaway star, AE Aur. We present a search for non-thermal diffuse X-ray emission from bow shocks using archived XMM-Newton observations for a clean sample of six well-determined runaway O stars. We find that none of these objects present diffuse X-ray emission associated with their bow shocks, similarly to previous X-ray studies toward ζ Oph and BD+43°3654. We carefully investigated multi-wavelength observations of AE Aur and could not confirm previous findings of non-thermal X-rays. We conclude that so far there is no clear evidence of non-thermal extended emission in bow shocks around runaway O stars.
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Ignace, Richard, Z. Damrau, and K. T. Hole. "Variability in X-ray Line Ratios in Helium-Like Ions of Massive Stars: The Wind-Driven Case." Digital Commons @ East Tennessee State University, 2019. https://dc.etsu.edu/etsu-works/5500.
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Context. High spectral resolution and long exposure times are providing unprecedented levels of data quality of massive stars at X-ray wavelengths.
Aims. A key diagnostic of the X-ray emitting plasma are the fir lines for He-like triplets. In particular, owing to radiative pumping effects, the forbidden-to-intercombination line luminosity ratio, R = f∕i, can be used to determine the proximity of the hot plasma to the UV-bright photospheres of massive stars. Moreover, the era of large observing programs additionally allows for investigation of line variability.
Methods. This contribution is the second to explore how variability in the line ratio can provide new diagnostic information about distributed X-rays in a massive star wind. We focus on wind integration for total line luminosities, taking account of radiative pumping and stellar occultation. While the case of a variable stellar radiation field was explored in the first paper, the effects of wind variability are emphasized in this work.
Results. We formulate an expression for the ratio of line luminosities f∕i that closely resembles the classic expression for the on-the-spot result. While there are many ways to drive variability in the line ratio, we use variable mass loss as an illustrative example for wind integration, particularly since this produces no variability for the on-the-spot case. The f∕i ratio can be significantly modulated owing to evolving wind properties. The extent of the variation depends on how the timescale for the wind flow compares to the timescale over which the line emissivities change.
Conclusions. While a variety of factors can ellicit variable line ratios, a time-varying mass-loss rate serves to demonstrate the range of amplitude and phased-dependent behavior in f∕i line ratios. Importantly, we evaluate how variable mass loss might bias measures of f∕i. For observational exposures that are less than the timescale of variable mass loss, biased measures (relative to the time-averaged wind) can result; if exposures are long, the f∕i ratio is reflective of the time-averaged spherical wind.
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MAZZOLA, Simona Michela. "Accretion onto Neutron Stars: spectral and timing investigation of Low Mass X-ray Binaries." Doctoral thesis, Università degli Studi di Palermo, 2021. http://hdl.handle.net/10447/500712.
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Ignace, Richard, K. T. Hole, Lidia M. Oskinova, and J. P. Rotter. "An X-Ray Study of Two B+B Binaries: AH Cep and CW Cep." Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etsu-works/2683.
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AH Cep and CW Cep are both early B-type binaries with short orbital periods of 1.8 days and 2.7 days, respectively. All four components are B0.5V types. The binaries are also double-lined spectroscopic and eclipsing. Consequently, solutions for orbital and stellar parameters make the pair of binaries ideal targets for a study of the colliding winds between two B stars. Chandra ACIS-I observations were obtained to determine X-ray luminosities. AH Cep was detected with an unabsorbed X-ray luminosity at a 90% confidence interval of erg s−1, or , relative to the combined Bolometric luminosities of the two components. While formally consistent with expectations for embedded wind shocks, or binary wind collision, the near-twin system of CW Cep was a surprising nondetection. For CW Cep, an upper limit was determined with , again for the combined components. One difference between these two systems is that AH Cep is part of a multiple system. The X-rays from AH Cep may not arise from standard wind shocks nor wind collision, but perhaps instead from magnetism in any one of the four components of the system. The possibility could be tested by searching for cyclic X-ray variability in AH Cep on the short orbital period of the inner B stars.
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Smith, Nathan, Charles D. Kilpatrick, Jon C. Mauerhan, Jennifer E. Andrews, Raffaella Margutti, Wen-Fai Fong, Melissa L. Graham, et al. "Endurance of SN 2005ip after a decade: X-rays, radio and Hα like SN 1988Z require long-lived pre-supernova mass-loss." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/623937.
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Supernova (SN) 2005ip was a Type IIn event notable for its sustained strong interaction with circumstellar material (CSM), coronal emission lines and infrared (IR) excess, interpreted as shock interaction with the very dense and clumpy wind of an extreme red supergiant. We present a series of late- time spectra of SN 2005ip and a first radio detection of this SN, plus late-time X-rays, all of which indicate that its CSM interaction is still strong a decade post- explosion. We also present and discuss new spectra of geriatric SNe with continued CSM interaction: SN 1988Z, SN 1993J and SN 1998S. From 3 to 10 yr post- explosion, SN 2005ip's Ha luminosity and other observed characteristics were nearly identical to those of the radio- luminous SN 1988Z, and much more luminous than SNe 1993J and 1998S. At 10 yr after explosion, SN 2005ip showed a drop in Ha luminosity, followed by a quick resurgence over several months. We interpret this Ha variability as ejecta crashing into a dense shell located less than or similar to 0.05 pc from the star, which may be the same shell that caused the IR echo at earlier epochs. The extreme Ha luminosities in SN 2005ip and SN 1988Z are still dominated by the forward shock at 10 yr post- explosion, whereas SN 1993J and SN 1998S are dominated by the reverse shock at a similar age. Continuous strong CSM interaction in SNe 2005ip and 1988Z is indicative of enhanced mass- loss for similar to 10(3) yr before core collapse, longer than Ne, O or Si burning phases. Instead, the episodic mass- loss must extend back through C burning and perhaps even part of He burning.
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Leto, P., Corrado Trigilio, Lidia M. Oskinova, Richard Ignace, C. S. Buemi, G. Umana, A. Ingallinera, H. Todt, and F. Leone. "The Detection of Variable Radio Emission from the Fast Rotating Magnetic Hot B-Star HR 7355 and Evidence for Its X-Ray Aurorae." Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etsu-works/2695.
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In this paper we investigate the multiwavelengths properties of the magnetic early B-type star HR7355. We present its radio light curves at several frequencies, taken with the Jansky Very Large Array, and X-ray spectra, taken with the XMM X-ray telescope. Modeling of the radio light curves for the Stokes I and V provides a quantitative analysis of the HR7355 magnetosphere. A comparison between HR7355 and a similar analysis for the Ap star CUVir, allows us to study how the different physical parameters of the two stars affect the structure of the respective magnetospheres where the non-thermal electrons originate. Our model includes a cold thermal plasma component that accumulates at high magnetic latitudes that influences the radio regime, but does not give rise to X-ray emission. Instead, the thermal X-ray emission arises from shocks generated by wind stream collisions close to the magnetic equatorial plane. The analysis of the X-ray spectrum of HR7355 also suggests the presence of a non-thermal radiation. Comparison between the spectral index of the power-law X-ray energy distribution with the non-thermal electron energy distribution indicates that the non-thermal X-ray component could be the auroral signature of the non-thermal electrons that impact the stellar surface, the same non-thermal electrons that are responsible for the observed radio emission. On the basis of our analysis, we suggest a novel model that simultaneously explains the X-ray and the radio features of HR7355 and is likely relevant for magnetospheres of other magnetic early type stars.
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Corcoran, Michael, Joy Nichols, H. Pablo, Tomer Shenar, Andy Pollock, W. Waldron, A. Moffat, et al. "A Coordinated X-ray and Optical Campaign of the Nearest Massive Eclipsing Binary, δ Ori Aa: I. Overview of the X-ray Spectrum." Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etsu-works/6238.
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We present an overview of four deep phase-constrained Chandra HETGS X-ray observations of δ Ori A. Delta Ori A is actually a triple system that includes the nearest massive eclipsing spectroscopic binary, δ Ori Aa, the only such object that can be observed with little phase-smearing with the Chandra gratings. Since the fainter star, δ Ori Aa2, has a much lower X-ray luminosity than the brighter primary (δ Ori Aa1), δ Ori Aa provides a unique system with which to test the spatial distribution of the X-ray emitting gas around δ Ori Aa1 via occultation by the photosphere of, and wind cavity around, the X-ray dark secondary. Here we discuss the X-ray spectrum and X-ray line profiles for the combined observation, having an exposure time of nearly 500 ks and covering nearly the entire binary orbit. The companion papers discuss the X-ray variability seen in the Chandra spectra, present new space-based photometry and ground-based radial velocities obtained simultaneously with the X-ray data to better constrain the system parameters, and model the effects of X-rays on the optical and UV spectra. We find that the X-ray emission is dominated by embedded wind shock emission from star Aa1, with little contribution from the tertiary star Ab or the shocked gas produced by the collision of the wind of Aa1 against the surface of Aa2. We find a similar temperature distribution to previous X-ray spectrum analyses. We also show that the line half-widths are about 0.3−0.5 times the terminal velocity of the wind of star Aa1. We find a strong anti-correlation between line widths and the line excitation energy, which suggests that longer-wavelength, lower-temperature lines form farther out in the wind. Our analysis also indicates that the ratio of the intensities of the strong and weak lines of Fe XVII and Ne X are inconsistent with model predictions, which may be an effect of resonance scattering.
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Taverna, Roberto. "Polarized emission from highly-magnetized neutron stars." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424483.
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The study of magnetars, the anomalous X-ray pulsars (AXPs) and the soft gamma repeaters (SGRs), and of X-ray Dim Isolated Neutron Stars (XDINSs) is of particular relevance, since these objects exhibit the strongest magnetic fields ever observed in the universe (10^13-10^15 G) and represent the only laboratories where physics in the presence of such strong magnetic fields can be tested. Until now, these peculiar neutron stars have been investigated through spectroscopic and timing measurements, which led to validate the theoretical models developed to explain their phenomenology, as in the case of the "twisted magnetosphere'' model for magnetars or the different surface emission models for XDINSs. Nevertheless, this kind of analysis alone is far from providing complete information. In this respect, X-ray polarimetry may disclose an entirely new approach in the study of highly magnetized neutron stars. Radiation emitted in the presence of strong magnetic fields, in fact, is expected to be highly polarized; polarization measurements provide two additional observables, the linear polarization fraction and the polarization angle, that can unambiguously determine the model parameters also when spectral analysis alone fails. The polarization signal that an observer at infinity would collect, however, do not necessary coincide with model predictions for the polarization at the surface, due to the effects of quantum electrodynamics in the highly magnetized vacuum around the star, coupled with the rotation of the Stokes parameters in the plane perpendicular to the line of sight, induced by the non-uniform magnetic field. In this thesis I present the results of the numerical codes I developed to simulate the polarization pattern, both at the surface and as observed at infinity, of the radiation emitted from highly magnetized, isolated neutron stars, using as templates the bright AXP 1RXS J170849.0-400910 and the XDINS RX J1856.5-3754. I demonstrate that polarization measurements can indeed provide key information about the physical and geometrical properties of these sources, allowing to directly test theoretical models. This work is also relevant in view of the launch of new-generation X-ray polarimeters, currently under development, like the X-ray Imaging Polarimeter Explorer (XIPE). For this reason, I also compare theoretical models with XIPE simulated observations, in order to show how polarization measurements can be used to extract the values of magnetospheric parameters and viewing angles.Lo studio delle magnetars, anomalous X-ray pulsars (AXPs) e soft gamma repeaters (SGRs), e delle X-ray Dim Isolated Neutron Stars (XDINSs) è di particolare rilevanza, dal momento che questi oggetti mostrano i più forti campi magnetici mai osservati nell'universo (10^13-10^15 G) e rappresentano i soli laboratori dove la fisica in presenza di campi magnetici così forti può essere testata. Fino ad ora, queste particolari stelle di neutroni sono state studiate attraverso misure spettroscopiche e di timing, che hanno portato a corroborare i modelli teorici formulati per spiegare la loro fenomenologia, come nel caso del "twisted magnetosphere'' model per le magnetars o dei diversi modelli di emissione superficiale per le XDINSs. Cionondimeno, questa analisi da sola non riesce a fornire informazioni complete. A questo riguardo, la polarimetria X può svelare un approccio completamente nuovo nello studio delle stelle di neutroni altamente magnetizzate. La radiazione emessa in presenza di forti campi magnetici, infatti, è attesa essere altamente polarizzata; le misure di polarizzazione forniscono due osservabili aggiuntivi, la frazione di polarizzazione lineare e l'angolo di polarizzazione, che possono determinare senza ambiguità i parametri dei modelli anche quando la sola analisi spettrale si dimostra insufficiente. Il segnale di polarizzazione che un osservatore riceve all'infinito, tuttavia, non coincide necessariamente con ciò che i modelli predicono per la polarizzazione alla superficie, a causa degli effetti dell'elettrodinamica quantistica nel vuoto fortemente magnetizzato attorno alla stella, accoppiato con la rotazione dei parametri di Stokes nel piano perpendicolare alla linea di vista, indotta dal campo magnetico non uniforme. In questa tesi presento i risultati dei codici numerici che ho sviluppato per simulare il pattern di polarizzazione, sia alla superficie che all'infinito, della radiazione emessa da stelle di neutroni isolate altamente magnetizzate, usando come modelli la luminosa AXP 1RXS 170849.0-400910 e la XDINS RX J1856.5-3754. Dimostrerò che le misure di polarizzazione possono effettivamente fornire informazioni cruciali sulle proprietà fisiche e geometriche di queste sorgenti, permettendo di testare direttamente i modelli teorici. Questo lavoro è inoltre rilevante in vista del lancio di polarimetri X di nuova generazione, attualmente in fase di sviluppo, come l'X-ray Imaging Polarimetry Explorer (XIPE). Per questa ragione, confronterò i modelli teorici con osservazioni simulate di XIPE, allo scopo di mostrare come le misure di polarizzazione possono essere utilizzate per estrarre i valori dei parametri relativi alla magnetosfera e gli angoli di vista.
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Oskinova, Lidia M., David P. Huenemoerder, Wolf-Rainer Hamann, Tomer Shenar, A. A. C. Sander, Richard Ignace, H. Todt, and R. Hainich. "On the Binary Nature of Massive Blue Hypergiants: High-resolution X-Ray Spectroscopy Suggests That Cyg OB2 12 is a Colliding Wind Binary - IOPscience." Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etsu-works/2688.
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The blue hypergiant Cyg OB2 12 (B3Ia+) is a representative member of the class of very massive stars in a poorly understood evolutionary stage. We obtained its high-resolution X-ray spectrum using the Chandra observatory. PoWR model atmospheres were calculated to provide realistic wind opacities and to establish the wind density structure. We find that collisional de-excitation is the dominant mechanism depopulating the metastable upper levels of the forbidden lines of the He-like ions Si xivand Mg xii. Comparison between the model and observations reveals that X-ray emission is produced in a dense plasma, which could reside only at the photosphere or in a colliding wind zone between binary components. The observed X-ray spectra are well-fitted by thermal plasma models, with average temperatures in excess of 10 MK. The wind speed in Cyg OB2 12 is not high enough to power such high temperatures, but the collision of two winds in a binary system can be sufficient. We used archival data to investigate the X-ray properties of other blue hypergiants. In general, stars of this class are not detected as X-ray sources. We suggest that our new Chandra observations of Cyg OB2 12 can be best explained if Cyg OB2 12 is a colliding wind binary possessing a late O-type companion. This makes Cyg OB2 12 only the second binary system among the 16 known Galactic hypergiants. This low binary fraction indicates that the blue hypergiants are likely products of massive binary evolution during which they either accreted a significant amount of mass or already merged with their companions.
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Sasmaz, Mus Sinem. "X-ray And Timing Properties Of Anomalous X-ray Pulsar 1e 2259+586." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/3/12608625/index.pdf.
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In this thesis, we present the spectral and timing variabilities of anomalous X-ray pulsar 1E 2259+586 observed with European Photon Imaging PN Camera (EPIC PN) on board X-ray Multi Mirror Mission (XMM), Proportional Counter Array (PCA) on board Rossi X-ray Timing Explorer (RXTE) and Advanced CCD Imaging Spectrometer (ACIS) on board Chandra X-ray Observatory.
We presented the results of spectral analysis of 2000 January 11 ACIS observation. Pulse phase spectroscopy was performed on two XMM observations before and after the outburst. Pulse profiles of two XMM observations before the outburst and three XMM observations after the outburst were studied. Results are consistent with the those presented by Patel et al. (2001) and Woods et al. (2004).
We searched for the spectral variations versus spin rate during the outburst. Long-term spectral, frequency and spin-down rate variations are presented between 1996 and 2006 including 98 RXTE and 4 XMM observations. However, except outburst region (Woods et al. 2004) no significant spectral and spin rate variabilities were seen. Around the outburst region we confirmed the spectral hardening with increasing spin rate and flux.
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Igance, Richard. "Modeling X-ray Emission Line Profiles from Massive Star Winds - A Review." Digital Commons @ East Tennessee State University, 2016. https://dc.etsu.edu/etsu-works/2686.
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The Chandra and XMM-Newton X-ray telescopes have led to numerous advances in the study and understanding of astrophysical X-ray sources. Particularly important has been the much increased spectral resolution of modern X-ray instrumentation. Wind-broadened emission lines have been spectroscopically resolved for many massive stars. This contribution reviews approaches to the modeling of X-ray emission line profile shapes from single stars, including smooth winds, winds with clumping, optically thin versus thick lines, and the effect of a radius-dependent photoabsorption coefficient.
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BASSI, Tiziana. "Accretion and ejection in transient black hole binaries: the case of GRS 1716-249." Doctoral thesis, Università degli Studi di Palermo, 2020. http://hdl.handle.net/10447/401924.
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I buchi neri transienti (BHT) sono tra le sorgenti con emissione ai raggi X più luminose della galassia. Grazie all’elevato flusso in banda X e alla loro alta variabilità temporale. queste sorgenti offrono un’opportunità unica per studiare la fisica dell’accrescimento in straordinareie condizioni fisiche. I BHT mostrano episodici outburst caratterizzati da diverse luminosità in banda X e γ, diverse forme spettrali e proprietà della variabilità temporale. L’obiettivo di questa tesi è lo studio della geometria, dei meccanismi e dei processi fisici coinvolti nell’emissione del buco nero transiente GRS 716-249. Di seguito presento l’analisi spettrale e temporale delle osservazioni della GRS 1716-249 ai raggi X effettuate con il satellite Neil Gehrels Swift bservatory durante l’outburst verificatosi nel 2016-2017. Questi dati mi hanno permesso di studiare l’evoluzione dei parametri fisici durante tutta la durata dell’outburst e di studiare come varia la geometria della materia in accrescimento attraverso le transizioni spettrali. In particolare, coerentemente con lo scenario del disco di accrescimento troncato in cui il disco si avvicina all’oggetto compatto durante l’evoluzione dell’outburst, ho osservato che il disco di accrescimento della GRS 1716-249 potrebbe aver raggiunto l’ultima orbita stabile mentre la sorgente si trovava nello stato hard intermedio. Grazie al monitoraggio radio effettuato durante l’outburst ho potuto localizzare la sorgente sulla sempre più popolata correlazione radio/X degli "outliers" (o radioquieti) nel piano delle luminosità radio/X. Successivamente, mi sono concentrata sull’emissione ai raggi X/γ della sorgente. Questo mi ha permesso di osservare un eccesso nell’emissione alle alte energie, sopra a 200 keV, in aggiunta allo spettro di Comptonizzazione termica, nello spettro della GRS 1716-249. L’origine di questa componente può essere dovuta a processi di Compton inverso tra i fotoni soft del disco d’accrescimento e una popolazione di elettroni non-termici nella corona, o all’emissione di sincrotrone prodotta dagli elettroni energetici nel getto. Inizialmente ho modellando lo spettro X/γ della sorgente con modelli ibridi di Comptonizazione termica/non-termica: EQPAIR e BELM. In particolare, utilizzando BELM ho potuto stimare un limite superiore sull’intensità del campo magnetico nella corona. Infine, ho considerato la possibilità che l’eccesso di energia alle ate energie sia dovuto all’emissioni del jet. A tale scopo, ho prodotto la distribuzione d’energia spettrale della GRS 1716-249 usando le osservazioni multi-banda (dalla banda radio ai raggi γ) eseguite quando la sorgente era nello stato hard. Il flusso di accrescimento l’ho modellato con un modello di disco irradiato unito ad un modello di Comptonizzazine, mentre l’emissione del getto l’ho modellata con il modello Internal Schock Emission Model (ISHEM). Questo modello assume che le fluttuazioni di velocità del getto siano guidate dalla variabilità
delle proprietà temporali del disco di accrescimento. Sebbene (ISHEM riproduce i dati radio e soft γ della sorgente GRS 1716-249, i risultati favoriscono lo scenario di Comptonizazione non termica nel flusso di accrescimento rispetto all’emissione di sincrotrone del getto oltre 200 keV.Black hole transients (BHTs) are among the brightest X-ray sources in the Galaxy. Thanks to their high X-ray flux and short variability time scales they offer a unique opportunity to study the physics of the accretion under extraordinary physical conditions. These sources show episodic outbursts characterised by different X/γ-ray luminosities, spectral shapes and timing properties. The aim of this thesis is the understanding of the geometry, mechanisms and physical processes playing a role in the bright black hole X-ray transient GRS 1716-249. I present the spectral and timing analysis of X-ray observations performed with the Neil Gehrels Swift Observatory on GRS 1716-249 during the 2016-2017 outburst. These data gave me the opportunity to study the evolution of physical parameters and geometry variation of the accreting matter through the spectral transitions during the whole outburst. I found that the accretion disc could have reached the inner stable circular orbit during the hard intermediate state, coherently with the truncated accretion disc scenario in which the disc moves closer to the compact object. Then, the radio monitoring performed during the outburst let me locate the source on the ever more populated radio-quiet branch on the radio/X-ray luminosity plane. Thereafter, focusing on the soft γ-ray emission of the source, I observed a high energy excess, above 200 keV, in addition to the thermal Comptonisation spectrum. This component could be originate either through inverse Compton of the soft photons by non-thermal electrons in the corona, or from synchrotron emission of energetic electrons in the jet. First, I fitted the broad band X/γ-ray spectrum of GRS 1716-249 with hybrid Comptonisation thermal/non-thermal models: EQPAIR and BELM. Using BELM I obtained an upper limit on the magnetic field intensity in the corona. Finally, I investigated the possible origin of this high energy excess as due to jet emission. To this aim, I computed the Spectral Energy Distribution of GRS 1716-249 with the multi-wavelength observations (from the radio band to γ-rays) performed. I modelled the accretion flow with an irradiated disc plus Comptonisation model and the jet emission with the internal shock emission model (ISHEM). This model assumes that the jet velocity fluctuations are directly driven by the variability of X-ray timing proprieties of the accretion flow. Even though ISHEM reproduces the radio and soft γ-ray data of GRS 1716-249, the results seem to disfavour the jet scenario for the excess above 200 keV, in favour of non-thermal Comptonisation process.
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Lau, Ryan M., Mansi M. Kasliwal, Howard E. Bond, Nathan Smith, Ori D. Fox, Robert Carlon, Ann Marie Cody, et al. "RISING FROM THE ASHES: MID-INFRARED RE-BRIGHTENING OF THE IMPOSTOR SN 2010da IN NGC 300." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/624070.
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We present multi-epoch mid-infrared (IR) photometry and the optical discovery observations of the "impostor" supernova (SN) 2010da in NGC. 300 using new and archival Spitzer Space Telescope images and ground-based observatories. The mid-infrared counterpart of SN. 2010da was detected as Spitzer Infrared Intensive Transient Survey (SPIRITS). 14bme in the SPIRITS, an ongoing systematic search for IR transients. Before erupting on 2010 May 24, the SN. 2010da progenitor exhibited a constant mid-IR flux at 3.6 and only a slight similar to 10% decrease at 4.5 mu m between 2003 November and 2007 December. A sharp increase in the 3.6 mu m flux followed by a rapid decrease measured similar to 150 days before and similar to 80 days after the initial outburst, respectively, reveal a mid-IR counterpart to the coincident optical and high luminosity X-ray outbursts. At late times, after the outburst (similar to 2000 days), the 3.6 and 4.5 mu m emission increased to over a factor of two. times the progenitor flux and is currently observed (as of 2016 Feb) to be fading, but still above the progenitor flux. We attribute the re-brightening mid-IR emission to continued dust production and increasing luminosity of the surviving system associated with SN. 2010da. We analyze the evolution of the dust temperature (T-d similar to 700-1000 K), mass (Md similar to 0.5-3.8 x. 10(-7) M circle dot), luminosity (L-IR similar to 1.3-3.5 x 10(4) L circle dot), and the equilibrium temperature radius (R-eq similar to 6.4-12.2 au) in order to resolve the nature of SN. 2010da. We address the leading interpretation of SN. 2010da as an eruption from a luminous blue variable high-mass X-ray binary (HMXB) system. We propose that SN. 2010da is instead a supergiant (sg)B[e]-HMXB based on similar luminosities and dust masses exhibited by two other known sgB[e]-HMXB systems. Additionally, the SN. 2010da progenitor occupies a similar region on a mid-IR color-magnitude diagram (CMD) with known sgB[e] stars in the Large Magellanic Cloud. The lower limit estimated for the orbital eccentricity of the sgB[e]-HMXB (e > 0.82) from X-ray luminosity measurements is high compared to known sgHMXBs and supports the claim that SN. 2010da may be associated with a newly formed HMXB system.
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Yukita, M., A. Ptak, A. E. Hornschemeier, D. Wik, T. J. Maccarone, K. Pottschmidt, A. Zezas, et al. "Identification of the Hard X-Ray Source Dominating the E > 25 keV Emission of the Nearby Galaxy M31." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623858.
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We report the identification of a bright hard X-ray source dominating the M31 bulge above 25 keV from a simultaneous NuSTAR-Swift observation. We find that this source is the counterpart to Swift J0042.6+4112, which was previously detected in the Swift BAT All-sky Hard X-ray Survey. This Swift BAT source had been suggested to be the combined emission from a number of point sources; our new observations have identified a single X-ray source from 0.5 to 50 keV as the counterpart for the first time. In the 0.5-10 keV band, the source had been classified as an X-ray Binary candidate in various Chandra and XMM-Newton studies; however, since it was not clearly associated with Swift J0042.6+4112, the previous E < 10 keV observations did not generate much attention. This source has a spectrum with a soft X-ray excess (kT similar to 0.2 keV) plus a hard spectrum with a power law of Gamma similar to 1 and a cutoff around 15-20 keV, typical of the spectral characteristics of accreting pulsars. Unfortunately, any potential pulsation was undetected in the NuSTAR data, possibly due to insufficient photon statistics. The existing deep HST images exclude high-mass (> 3 M-circle dot) donors at the location of this source. The best interpretation for the nature of this source is an X-ray pulsar with an intermediate-mass (< 3 M-circle dot) companion or a symbiotic X-ray binary. We discuss other possibilities in more detail.
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van, Haaften Lennart M., Thomas J. Maccarone, Paul H. Sell, J. Christopher Mihos, David J. Sand, Arunav Kundu, and Stephen E. Zepf. "An Excess of Low-mass X-Ray Binaries in the Outer Halo of NGC 4472." IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/626536.
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We present new Chandra observations of the outer halo of the giant elliptical galaxy NGC 4472 (M49) in the Virgo Cluster. The data extend to 130 kpc (28'), and have a combined exposure time of 150 ks. After identifying optical counterparts using the Next Generation Virgo Cluster Survey to remove background active galactic nuclei and globular cluster (GC) sources, and correcting for completeness, we find that the number of field low-mass X-ray binaries (LMXBs) per unit stellar V-band light increases significantly with the galactocentric radius. Because the flux limit of the complete sample corresponds to the Eddington limit for neutron stars in NGC 4472, many of the similar to 90 field LMXBs in this sample could host black holes. The excess of field LMXBs at large galactocentric radii may be partially caused by natal kicks on black holes and neutron stars in binary systems in the inner part of the galaxy. Furthermore, because the metallicity in the halo of NGC 4472 strongly decreases toward larger galactocentric radii, the number of field LMXBs per unit stellar mass is anticorrelated with metallicity, opposite to what is observed in GCs. Another way to explain the spatial distribution of field LMXBs is therefore a reversed metallicity effect, although we have not identified a mechanism to explain this in terms of stellar and binary evolution.
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Leto, P., Courtney Trigilio, Lidia M. Oskinova, Richard Ignace, C. S. Buemi, G. Umana, A. Ingallinera, et al. "A Combined Multiwavelength VLA/ALMA/Chandra Study Unveils the Complex Magnetosphere of the B-Type Star HR5907." Digital Commons @ East Tennessee State University, 2018. https://dc.etsu.edu/etsu-works/2682.
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We present new radio/millimeter measurements of the hot magnetic star HR 5907 obtained with the VLA and ALMA interferometers. We find that HR 5907 is the most radio luminous early type star in the cm–mm band among those presently known. Its multi-wavelength radio light curves are strongly variable with an amplitude that increases with radio frequency. The radio emission can be explained by the populations of the non-thermal electrons accelerated in the current sheets on the outer border of the magnetosphere of this fast-rotating magnetic star. We classify HR 5907 as another member of the growing class of strongly magnetic fast-rotating hot stars where the gyro-synchrotron emission mechanism efficiently operates in their magnetospheres. The new radio observations of HR 5907 are combined with archival X-ray data to study the physical condition of its magnetosphere. The X-ray spectra of HR 5907 show tentative evidence for the presence of non-thermal spectral component. We suggest that non-thermal X-rays originate a stellar X-ray aurora due to streams of non-thermal electrons impacting on the stellar surface. Taking advantage of the relation between the spectral indices of the X-ray power-law spectrum and the non-thermal electron energy distributions, we perform 3-D modelling of the radio emission for HR 5907. The wavelength-dependent radio light curves probe magnetospheric layers at different heights above the stellar surface. A detailed comparison between simulated and observed radio light curves leads us to conclude that the stellar magnetic field of HR 5907 is likely non-dipolar, providing further indirect evidence of the complex magnetic field topology of HR 5907.
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Chadney, J. M., T. T. Koskinen, M. Galand, Y. C. Unruh, and J. Sanz-Forcada. "Effect of stellar flares on the upper atmospheres of HD 189733b and HD 209458b." EDP SCIENCES S A, 2017. http://hdl.handle.net/10150/626411.
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Stellar flares are a frequent occurrence on young low-mass stars around which many detected exoplanets orbit. Flares are energetic, impulsive events, and their impact on exoplanetary atmospheres needs to be taken into account when interpreting transit observations. We have developed a model to describe the upper atmosphere of extrasolar giant planets (EGPs) orbiting flaring stars. The model simulates thermal escape from the upper atmospheres of close-in EGPs. Ionisation by solar radiation and electron impact is included and photo-chemical and diffusive transport processes are simulated. This model is used to study the effect of stellar flares from the solar-like G star HD 209458 and the young K star HD 189733 on their respective planets, HD 209458b and HD 189733b. The Sun is used as a proxy for HD 209458, and is an element of Eridani, as a proxy for HD 189733. A hypothetical HD 209458b-like planet orbiting the very active M star AU Microscopii is also simulated. We find that the neutral upper atmosphere of EGPs is not significantly affected by typical flares on HD 209458 and HD 189733. Therefore, stellar flares alone would not cause large enough changes in planetary mass loss to explain the variations in HD 189733b transit depth seen in previous studies, although we show that it may be possible that an extreme stellar proton event could result in the required mass loss. Our simulations do however reveal an enhancement in electron number density in the ionosphere of these planets, the peak of which is located in the layer where stellar X-rays are absorbed. Electron densities are found to reach 2.2 to 3.5 times pre-flare levels and enhanced electron densities last from about 3 to 10 h after the onset of the flare, depending on the composition of the ionospheric layer. The strength of the flare and the width of its spectral energy distribution affect the range of altitudes in the ionosphere that see enhancements in ionisation. A large broadband continuum component in the XUV portion of the flaring spectrum in very young flare stars, such as AU Mic, results in a broad range of altitudes a ff ected in planets orbiting this star. Indeed, as well as the X-ray absorption layer, the layer in which EUV photons are absorbed is also strongly enhanced.
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RIGOSELLI, MICHELA. "X-ray emission from the magnetic polar caps of old rotation-powered pulsars." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/277373.
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Le stelle di neutroni sono il risultato dell'evoluzione di stelle massive dopo l'esplosione di supernova. Il progetto di questa Tesi di PhD consiste nello studio dell'emissione di raggi X da parte di stelle di neutroni isolate di età superiore a 100000 anni. Sono stati analizzati dati provenienti dal satellite XMM-Newton (ESA). Per estrarre la miglior informazione possibile dai dati, ho implementato un metodo di maximum likelihood (ML) e l'ho utilizzato per estrarre spettri e profili pulsati di pulsar vecchie in banda X, che poi sono stati analizzati con raffinati di emissione.
La Tesi è strutturata come segue: nei primi tre capitoli illustro le proprietà principali delle stelle di neutroni, con particolare attenzione ai processi termici e non termici che producono raggi X. I raggi X non termici sono prodotti da particelle relativistiche accelerate da campi elettromagnetici; una frazione di queste particelle viene accelerata verso la superficie della stella, e riscalda le zone delle calotte polari magnetiche. La componente termica, che può essere prodotta dall'intera superficie o da una parte, viene solitamente descritta come un corpo nero; tuttavia, la presenza di intensi campi magnetici superficiali influenza le proprietà della materia, e la radiazione emessa è ampiamente anisotropa.
Nel Capitolo 4 descrivo come ho generato spettri e profili pulsati sintetici, utilizzando modelli di emissione che considerano calotte polari ricoperte di un'atmosfera di idrogeno magnetizzata. Mi sono basata su un software esistente che, dato un certo set di parametri relativi alle proprietà fisiche della stella, stima l'intensità della radiazione prodotta. Successivamente, esso somma i contributi degli elementi di superficie che sono visibili all'osservatore alle differenti fasi di rotazione. Quindi, nel Capitolo 5 descrivo come ho implementato un software di analisi che si basa sul metodo di ML. Dato un certo modello, esso stima i parametri più probabili che ricostruiscono i dati osservati, nella fattispecie il numero di conteggi relativo alla sorgente e al background. Ho validato il metodo e dimostrato che esso è particolarmente efficace per sorgenti deboli, quali sono la maggior parte delle pulsar vecchie.
Successivamente, ho applicato i metodi finora descritti ad alcune pulsar vecchie. Nel Capitolo 6 riporto l'analisi di PSR J0726-2612, una pulsar radio che ha alcune delle caratteristiche delle XDINSs: un periodo di rotazione lungo, un intenso campo magnetico, ed emissione X termica. Grazie ad un'analisi congiunta dello spettro e del profilo pulsato, ho mostrato che la presenza di impulsi radio in PSR J0726-2612, così come la loro assenza nelle XDINSs, potrebbe essere dovuta ad un'orientazione differente rispetto all'osservatore. Nel Capitolo 7 presento il caso di PSR B0943+10, una pulsar con emissione X sia termica sia non termica ma che, nonostante sia un rotatore allineato, ha una grande frazione pulsata. Sono riuscita a riappacificare i due diversi aspetti grazie ad un'attenta analisi di ML e all'intrinseca anisotropia dell'emissione termica prodotta da un'atmosfera magnetizzata. Nel Capitolo 8 ho invece applicato il metodo di ML su sette pulsar poco brillanti, delle quali quattro avevano diverse analisi già pubblicate in letteratura, ma con risultati discordanti, mentre le altre tre non erano ancora state rivelate in banda X. Ho trovato tracce evidenti di emissione termica solo in due oggetti, più un accenno nello spettro pulsato di un terzo oggetto.
Infine, ho considerato tutte le pulsar vecchie che emettono raggi X termici e ho confrontato le misure di temperatura, raggio e luminosità alle aspettative dei modelli teorici. In particolare, ho scoperto che le aree di emissione sono generalmente in accordo con quelle previste dal modello di dipolo magnetico rotante, purché vengano considerati anche effetti di proiezione geometrica e modelli di emissione realistici, quali appunto i modelli di atmosfera magnetizzata.Neutron stars are the remnants of massive stars whose cores collapse during the supernova explosions. The project of this PhD Thesis consisted in the study of the X-ray emission from isolated neutron stars older than about 100000 years. The work was based mainly on data obtained with the XMM-Newton satellite (ESA). To extract the best possible information from the data, I implemented a maximum likelihood (ML) technique and used it to derive the X-ray spectra and pulse profiles of several old pulsars, that were then studied with state-of-the-art models of X-ray emission. The Thesis is structured as follows: in the first three chapters I outline the main properties of neutron stars, with a major focus on the thermal and nonthermal processes that produce X-rays. The nonthermal X-rays are produced by relativistic particles accelerated by rotation-induced electric fields and moving along the magnetic field lines. A fraction of these particles is accelerated backward and returns on the stellar surface, heating the magnetic polar caps. The thermal component, that can be produced by the whole stellar surface or by small hot spots, can be described, in a first approximation, by a blackbody. However, the presence of intense surface magnetic fields strongly affects the properties of matter, and the emergent radiation is widely anisotropic. In Chapter 4, I describe how I generated synthetic spectra and pulse profiles using thermal emission models that consider polar caps covered by a magnetized hydrogen atmosphere or with a condensed iron surface. I relied on an existing software that, given a set of stellar parameters, evaluates the emerging intensity of the radiation. A second software, which I adapted on the sources I analyzed in the Thesis, collects the contribution of surface elements which are in view at different rotation phases from a stationary observer. Then, in Chapter 5, I describe how I implemented an analysis software that relies on the ML method. It estimates the most probable number of source and background counts by comparing the spatial distribution of the observed counts with the expected distribution for a point source plus an uniform background. I demonstrated that the ML method is particularly effective for dim sources, as most old pulsars are. Subsequently, I applied the methods described above to some old pulsars. In Chapter 6, I report the analysis of PSR J0726-2612, a radio pulsars that shares some properties with the radio-silent XDINSs, as the long period, the high magnetic field, and the thermal X-ray emission from the cooling surface. Thanks to an in-depth analysis of the combined spectrum and pulse profile, I showed that the presence of radio pulses from PSR J0726-2612, as well as the absence from the XDINSs, might simply be due to different viewing geometries. In Chapter 7, I present the case of PSR B0943+10, a pulsar with a nonthermal and thermal X-ray spectrum but that, despite being an aligned rotator, has a large pulsed fraction. I could reconcile the two opposite properties analyzing with the ML the spectrum and the pulse profile, and considering the magnetic beaming of a magnetized atmosphere model, that well fits the thermal component. In Chapter 8, I applied the ML method to seven old and dim pulsars, of which four had controversial published results, and three were so far undetected. I found convincing evidence of thermal emission only in the phase-averaged spectrum of two of them, plus a hint for a thermal pulsed spectrum in a third object. Finally, I considered all the old thermal emitters and I compared their observed temperatures, radii and luminosities to the expectations of the current theoretical models for these objects. In particular, I found that the emitting area are generally in agreement with the polar cap regions evaluated in a dipole approximation, if the combined effects of geometry projections plus realistic thermal models (as the magnetic atmosphere) are taken into account.
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Bassi, Tiziana. "Accrétion et éjection dans les systèmes binaires X transitoires à trous noirs : le cas de GRS 1716-249." Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30019.
Full textAbstract:
Les transitoires à trou noir (BHT) sont parmi les sources X les plus brillantes de la galaxie. Grace à leur flux X intense et leur variabilité rapide, elles offrent une opportunité unique d'étudier la physique de l'accrétion dans des conditions physiques extrêmes. Ces sources présentent des éruptions épisodiques caractérisées par différents niveaux de luminosité en rayons X et gamma, différentes formes spectrales et propriété de variabilité temporelle. Le but de cette thèse est de mieux comprendre la géométrie, les mécanismes et les processus physiques jouant un rôle dans la transitoire X à trou noir brillante GRS 1716-249. Je présente l'analyse spectrale et temporelle des observations de GRS 1716-249 en rayons X effectuées avec l'Observatoire Neil Gehrels Swift durant son éruption de 2016-2017. Ces données m'ont permis d'étudier l'évolution des paramètres physique pendant toute la durée de l'éruption ainsi que les changements de géométrie de la matière accrétante durant les transitions spectrales. Je montre que le disque d'accrétion pourrait avoir atteint la dernière orbite circulaire stable pendant l'état dur intermédiaire. Ceci est en accord avec le modèle de disque tronqué dans lequel bord interne du disque se rapproche de l'objet compact. De plus, le suivi de la source en ondes radio, effectué pendant l'éruption, me permet de placer la source sur la branche radio faible de la correlation des luminosités radio et X. Par la suite, je me concentre sur l'émission en rayons gamma mous de la source. Un excès à haute énergie est détecté au dessus de 200 keV par rapport au spectre de Comptonization thermique. L'origine de cette composante pourrait être l'émission Compton inverse par des électrons non-thermiques dans la couronne, ou l'émission synchrotron d'electron relativistes dans le jet. Je commence par fitter le spectre large bande X/gamma de GRS 1716-249 avec des modèles de Comptonization hybride thermique/non-thermique : eqpair et belm. Les ajustements spectraux avec belm me donnent une limite supérieure sur l'intensité du champs magnétique dans la couronne. Je considère ensuite la possibilité que l'excès à haute énergie soit d au jet. Dans ce but, j'ai produit une distribution spectrale d'énergie s'étendant de la radio jusqu'au rayons gamma. J'ajuste ces données avec un modèle de disque d'accrétion irradié plus Comptonization pour simuler l'émission du flot d'accrétion, et un modèle de shock internes pour l'émission du jet (ishem).[...]Black hole transients (BHTs) are among the brightest X-ray sources in the Galaxy. Thanks to their high X-ray flux and short variability time scales they offer a unique opportunity to study the physics of the accretion under extraordinary physical conditions. These sources show episodic outbursts characterised by different X/gamma-ray luminosities, spectral shapes and timing properties. The aim of this thesis is the understanding of the geometry, mechanisms and physical processes playing a role in the bright black hole X-ray transient GRS 1716-249. I present the spectral and timing analysis of X-ray observations performed with the Neil Gehrels Swift Observatory on GRS 1716-249 during the 2016-2017 outburst. These data gave me the opportunity to study the evolution of physical parameters and geometry variation of the accreting matter through the spectral transitions during the whole outburst. I found that the accretion disc could have reached the inner stable circular orbit during the hard intermediate state, coherently with the truncated accretion disc scenario in which the disc moves closer to the compact object. Then, the radio monitoring performed during the outburst let me locate the source on the ever more populated radio-quiet branch on the radio/X-ray luminosity plane. Thereafter, focusing on the soft gamma-ray emission of the source, I observed a high energy excess, above 200 keV, in addition to the thermal Comptonisation spectrum. This component could be originate either through inverse Compton of the soft photons by non-thermal electrons in the corona, or from synchrotron emission of energetic electrons in the jet. First, I fitted the broad band X/gamma-ray spectrum of GRS 1716-249 with hybrid Comptonisation thermal/non-thermal models: eqpair and belm. Using belm I obtained an upper limit on the magnetic field intensity in the corona. Finally, I investigated the possible origin of this high energy excess as due to jet emission. To this aim, I computed the Spectral Energy Distribution of GRS 1716-249 with the multi-wavelength observations (from the radio band to gamma-rays) performed. I modelled the accretion flow with an irradiated disc plus Comptonisation model and the jet emission with the internal shock emission model (ishem). This model assumes that the jet velocity fluctuations are directly driven by the variability of X-ray timing proprieties of the accretion flow. Even though ishem reproduces the radio and soft gamma-ray data of GRS 1716-249, the results seems to disfavour the jet scenario for the excess above 200 keV, in favour of non-thermal Comptonisation process
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Hubrig, S., M. Schöller, A. Kholtygin, H. Tsumura, A. Hoshino, S. Kitamoto, L. Oskinova, Richard Ignace, H. Todt, and I. Ilyin. "New Multiwavelength Observations of the Of?p Star CPD -28◦ 2561." Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etsu-works/6241.
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A rather strong mean longitudinal magnetic field of the order of a few hundred gauss was detected a few years ago in the Of?p star CPD −28° 2561 using FORS2 (FOcal Reducer low dispersion Spectrograph 2) low-resolution spectropolarimetric observations. In this work, we present additional low-resolution spectropolarimetric observations obtained during several weeks in 2013 December using FORS 2 mounted at the 8-m Antu telescope of the Very Large Telescope (VLT). These observations cover a little less than half of the stellar rotation period of 73.41 d mentioned in the literature. The behaviour of the mean longitudinal magnetic field is consistent with the assumption of a single-wave variation during the stellar rotation cycle, indicating a dominant dipolar contribution to the magnetic field topology. The estimated polar strength of the surface dipole Bd is larger than 1.15 kG. Further, we compared the behaviour of the line profiles of various elements at different rotation phases associated with different magnetic field strengths. The strongest contribution of the emission component is observed at the phases when the magnetic field shows a negative or positive extremum. The comparison of the spectral behaviour of CPD −28° 2561 with that of another Of?p star, HD 148937 of similar spectral type, reveals remarkable differences in the degree of variability between both stars. Finally, we present new X-ray observations obtained with the Suzaku X-ray Observatory. We report that the star is X-ray bright with log LX/Lbol ≈ −5.7. The low-resolution X-ray spectra reveal the presence of a plasma heated up to 24 MK. We associate the 24 MK plasma in CPD −28° 2561 with the presence of a kG strong magnetic field capable to confine stellar wind.
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Oskinova, Lidia M., Richard Ignace, and D. P. Huenemoerder. "X-ray Diagnostics of Massive Star Winds." Digital Commons @ East Tennessee State University, 2016. https://dc.etsu.edu/etsu-works/2703.
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Observations with powerful X-ray telescopes, such as XMM-Newton and Chandra, significantly advance our understanding of massive stars. Nearly all early-type stars are X-ray sources. Studies of their X-ray emission provide important diagnostics of stellar winds. High-resolution X-ray spectra of O-type stars are well explained when stellar wind clumping is taking into account, providing further support to a modern picture of stellar winds as non-stationary, inhomogeneous outflows. X-ray variability is detected from such winds, on time scales likely associated with stellar rotation. High-resolution X-ray spectroscopy indicates that the winds of late O-type stars are predominantly in a hot phase. Consequently, X-rays provide the best observational window to study these winds. X-ray spectroscopy of evolved, Wolf-Rayet type, stars allows to probe their powerful metal enhanced winds, while the mechanisms responsible for the X-ray emission of these stars are not yet understood.
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PAPITTO, ALESSANDRO. "Analysis of the rotational behaviour and evolutionary scenarios of Accreting Millisecond Pulsars." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2009. http://hdl.handle.net/2108/812.
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In questo studio viene presentata un'analisi
dell'evoluzione rotazionale ed orbitale delle Pulsar X al millisecondo (AMSP). Queste sorgenti sono delle stelle di neutroni (NS) che emettono energia in raggi X accrescendo la materia trasferita da una stella compagna, tramite un disco di accrescimento. Poichè le AMSP poseggono una magnetosfera che interrompe il flusso di materia nel disco prima della superficie, concentrando l'accrescimento nelle vicinanze dei poli magnetici, l'emissione X è pulsata al periodo di rotazione della stella, che è di qualche millisecondo per una AMSP.
Il mio progetto di ricerca si basa sull'utilizzo di questa proprietà fondamentale per valutare la reazione della NS all'accrescimento di materia. Infatti le particelle di un disco di accrescimento posseggono un elevato momento angolare specifico, specialmente nelle vicinanze della NS; quando la materia viene accresciuta il suo momento angolare viene rilasciato alla stella, che tende quindi ad accellerare. E' proprio questo meccanismo che ha condotto le AMSP alla estrema velocità di rotazione attuale (un decimo della velocità della luce). Avendo a disposizione un tale orologio solidale alla stella, ho utilizzato le pulsazioni X provenienti dalla superficie per misurare le piccole variazioni della frequenza di rotazione della NS mentre accresce massa. Se ne trae quindi una misura delle coppie che agiscono su di essa e la stima delle grandezze che le regolano, principalmente il tasso di accrescimento di massa e l'intensità del campo magnetico della NS.
Tali misure sono estremamente delicate, specialmente nel caso delle AMSP. Infatti queste sorgenti accrescono massa al più per qualche mese ed, a causa dell'elevata inerzia di una NS, la variazione di frequenza attesa è solamente di poche parti su dieci miliardi. Innanzi tutto le tecniche standard di timing sono state quindi adattate al caso particolare di questi oggetti, permettendo per la prima volta una misura affidabile del loro stato rotazionale. Sono state prese in considerazione sei delle dieci AMSP scoperte sin ora. In particolare, le due alle quali mi sono dedicato maggiormente mostrano adeguatamente come il semplice schema di accellerazione della NS delineato sopra non valga in ogni caso, e come una AMSP possa anche decelerare durante l'accrescimento. La causa di tale decelerazione è individuata dalla teoria dell'accrescimento nell'interazione tra il campo magnetico e il disco di accrescimento, interazione che può quindi rallentare la stella specialmente se questa ruota molto rapidamente. In questo lavoro mostro come questi rallentamenti vengono effettivamente osservati e come consentano di ottenere stime del campo magnetico della NS.
Gli elementi basilari delle teorie dell'accrescimento su un rotatore veloce sono stati testati non solo sulla base dei risultati dell'analisi temporale. Si mostra infatti come le attese teoriche siano supportate anche alla luce dell'informazione spettrale. In particolare l'osservazione di una AMSP mostra la presenza di una riga del ferro molto larga nel suo spettro in raggi X. Essendo la regione interna del disco di accrescimento l'unica possibile regione di formazione di una riga così larga, è stato possibile misurare, per la prima volta nel caso di una pulsar, l'estensione del bordo interno del disco. Il valore misurato è perfettamente in accordo con il ristretto intervallo permesso dalla teoria, rappresentando così una verifica fondamentale della sua consistenza.
L'analisi temporale consente inoltre di valutare l'evoluzione orbitale del sistema binario al quale appartiene la NS. Nell'unico caso di un sistema che abbia mostrato più di un episodio di attività, si è trovata evidenza di una evoluzione molto più rapida di quella attesa. Questo comportamento può essere spiegato solo in termini di rilevanti perdite di massa, massa che porta con sé la quantità di momento angolare necessaria per rendere conto dell'evoluzione misurata. Ciò supporta inoltre l'ipotesi che tali perdite di massa siano dovute all'accensione di una pulsar alimentata dalla rotazione durante le sue fasi di quiete del sistema. Questo può in definitiva essere considerato uno dei pochi casi astrofisici in cui viene osservata in tempo reale un'evoluzione altamente non conservativa.
I risultati presentati in questa tesi coprono quindi molti aspetti della fisica di questi sistemi, mostrando come l'unione dell'analisi temporale e spettrale possa fornire una gran quantità di informazioni su questi sistemi estremi e per certi versi sconcertanti. In definitiva sono state confermate le attese teoriche di base sull'accrescimento su NS veloci, ma si aprono anche diverse questioni che promettono di gettare maggiore luce sulla fisica dell'ambiente immediatamente circostante la stella e sull'effettiva linea evolutiva delle AMSP.I present in this study an analysis of the spin and orbital evolution of Accreting Millisecond Pulsars (AMSP). These sources are neutron stars (NS) emitting X-rays because of the accretion of mass transferred by a nearby companion star through an accretion disc. As AMSP owns a magnetosphere that truncates the disc before the NS, thus channelling accreted matter in the vicinity of the magnetic poles, their X-ray emission is pulsed at the NS spin period, which is of few milliseconds in an AMSP. My scientific project relies on the use this invaluable property to evaluate the rotational reaction of the NS to the accretion of mass. As a matter of fact, mass orbiting in an accretion disc has a large specific angular momentum especially close to the NS; when this matter is accreted, it releases its angular momentum to the NS that is therefore expected to accelerate. It is indeed through this mechanism that AMSP have been spun up to their extreme rotational velocities (up to 0.1 times the speed of light in vacuum). I therefore used the X-ray pulsations coming from the NS surface as a clock to precisely measure the tiny variations of the accretor spin frequency as it accretes. This is ultimately a measure of the accretion torques acting on the NS and allows a model dependent estimate of the physical quantities regulating these torques, mainly the rate at which mass is accreted on the NS and the magnetic field straight. Such measurements can be very tricky especially for AMSP. They accrete mass for at most few months, and because of to the large inertia of a NS, the expected frequency variations are of only few parts on ten billions. Standard timing techniques were therefore first tailored to the particular case of these sources, allowing for the first time reliable estimates of their spin state. Six among the ten AMSP discovered so far are considered in this work. In particular, the two sources I focused on the most show how the simple picture of the NS spin-up outlined above does not hold in every case, as the outcome of the accretion can also be the deceleration of the NS. The reason for this behaviour is interpreted by the accretion theory in terms of the interaction between the magnetic field and the accretion disc. This interaction may then brake of the compact object especially if it is very fast. I show in this work how these spin-down are effectively observed and how this allows an estimate of the NS magnetic field. The basics of the accretion picture onto a fast object are tested not only on the basis of a temporal analysis. I show in fact how the spectral information also supports the theoretical expectations. In particular a high spectral resolution observation of a AMSP shows the presence of a broadened iron line in its X-ray spectrum. The only viable location for the formation of a line so broadened is the inner part of the accretion disc, thus allowing for the first time the measure of the size of the inner disc rim of a pulsar. This measure is perfectly consistent with the small range allowed by theory, thus representing a fundamental test of their consistency. Temporal analysis also allows to enlighten the evolution of the binary system the NS belongs to. In the only case of a system which recurred more than once, we could find evidence of a faster than expected evolution. We interpret such behaviour as an indication of relevant mass lost which carries away the angular momentum needed to match the observations. This supports the hypothesis that a rotation powered pulsar switches on during the quiescent phases of the binary. Moreover, this observation can be considered as one of the few astrophysical cases in which a highly non conservative evolution was directly observed. The results presented in this thesis cover many aspects of the physics of these fast accretors, and show how X-ray temporal and spectral analysis can jointly supply a wealth of information on the physical state of these extreme and puzzling systems. These results confirm the basic theoretical expectations but open also several issues which are very promising to shed some light in particular on the environment surrounding these fast rotating NS and on their actual evolutionary progeny.
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Telleschi, Alessandra Silvia. "Coronal evolution of solar-like stars : X-ray spectroscopy of stars in star-forming regions and the solar neighborhood /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17018.
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Gonzalez, Marjorie. "X-ray observations of young neutron stars." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18813.
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The extreme physical properties of neutron stars make them efficient emitters at all wavelengths of the electromagnetic spectrum and, traditionally, they have been extensively studied at radio wavelengths. The neutron stars with the highest estimated magnetic fields (so-called "magnetars") have remarkably different characteristics from the rest of the population: they emit no persistent radio emission but show large amounts of high-energy radiation that is thought to be powered by their large magnetic fields. For this thesis we have studied the X-ray emission properties of various types of young neutron stars, discovering unusual characteristics, constraining long-term behaviour and finding associated nebulae. We have observed the neutron stars PSR B0154+61 and PSR J1119-6127, which have high magnetic fields but otherwise emit normal radio emission. For the latter, unusual thermal X-ray emission was discovered that points to the possible effects of a magnetic field on the surface. Also, this source now represents the youngest neutron star from which thermal emission from the surface has been detected. However, we find no evidence for clear magnetar-like characteristics in these sources. The reason for this discrepancy, as yet unclear and a matter of debate, poses a great challenge to our understanding of the evolution of neutron stars and their emission mechanisms. We have also studied the long-term properties of the "anomalous X-ray pulsar" 4U 0142+61, thought to be a magnetar. We find that changes are present in almost all of its emission characteristics over the last 7 years. The observed changes agree with the general predictions made by the magnetar model of such sources. However, the details of these changes suggest that further work is still needed on the expected emission from these objects. In addition, neutron stars are seen to power extended structures, called pulsar wind nebulae (PWNe), which can radiate large amounts of high-energy emission. HeLes propriétés extrêmes des étoiles à neutrons font de ces objets compacts des émetteurs efficaces dans toutes les longueurs d'ondes du spectre électromagnétique. Cependant, elles ont historiquement été étudiées principalement dans les ondes radios. Les étoiles à neutrons ayant un fort champ magnétique (appelées "magnétars") ont des caractéristiques remarquablement différentes du reste de la population: elles n'émettent pas d'ondes radios mais elles présentent de grandes quantités de radiations à haute énergie causées par le champ magnétique. Pour ce projet, nous avons étudié les propriétés des rayons X provenant de différents types de jeunes étoiles à neutrons, découvert des caractéristiques inattendues, contraint le comportement à long terme et enfin trouvé des nébuleuses associés aux étoiles à neutrons. Tout d'abord, nous avons observé les étoiles à neutrons PSR B0154+61 et PSR J1119-6127. Ces deux objets ont un fort champ magnétique mais ils émettent cependant des ondes radios normales. Pour la seconde, des émissions de rayons X thermiques ont également été découvertes, ce qui suggère les possibles effets du champ magnétique sur la surface. Aussi, cette source est maintenant la plus jeune étoile à neutrons émettant une radiation thermique depuis sa surface. Il n'y a cependant aucune preuve permettant d'associer ces sources aux caractéristiques des magnétars. La raison de cette différence, toujours incomprise et sujette à de nombreux débats, pose un énorme défi à notre compréhension de l'évolution des étoiles à neutrons et de leurs mécanismes d'émission. Ensuite, nous avons également étudié les propriétés à long terme du "pulsar anormal à Rayons X" 4U 0142+61, que l'on pense être un magnétar. Nous trouvons des changements de presque toutes ces caractéristiques d'émission sur les 7 dernières années. Les variations observées sont en accord avec les prédictions suggérées par$
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Baskill, Darren Stuart. "X-ray properties of cataclysmic variable stars." Thesis, University of Leicester, 2003. http://hdl.handle.net/2381/30669.
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In this thesis, I study the entire sample of non-magnetic cataclysmic variables observed with the Japanese satellite ASCA, presenting a detailed analysis of the spectral and temporal behaviour of these twenty-nine targets. The spectral analysis indicates that all the targets in the ASCA sample appear to be X-ray under-luminous, with only three possible exceptions. This indicates that energy is being lost from the accretion disk in a non-radiative way. Since a third of the observations require additional absorption above that expected from interstellar alone, both the X-ray under-luminosity and the excess absorption observed spectrally may be attributed to the existence of accretion disk-winds. The spectral analysis also indicates that the under-lying spectra of all non-magnetic cataclysmic variables may be more complicated than at first thought, since those spectra containing the highest number of counts require more sophisticated multi-temperature modelling of the X-ray source. Further spectra results suggests that there may be some previously unidentified magnetic systems in the ASCA sample. Such systems give away their identity through having a much harder spectrum than the non-magnetic systems, and both LS Peg and V426 Oph should be considered as weakly magnetic candidates. The temporal analysis reveals other unusual members. SS Cyg appears to be unusually faint during an observation made during quiescence, and a four-fold difference is observed in VW Hyi during two optically quiescent states, suggesting that the inner disk behaves almost independently of the outer disk. ASCA observations caught Z Cam during both an optical outburst, and during the transition to another outburst. The unique transition observation shows the X-ray count rate falling by a factor of three as the source becomes optically thick. High levels of absorption are detected in the X-ray spectra throughout both the outburst and transitional observations, greater than that expected from interstellar absorption alone.
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Oskinova, Lidi, and Richard Igance. "X-ray Diagnostics of Massive Star Winds." Digital Commons @ East Tennessee State University, 2017. https://www.amzn.com/1107170060.
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Nichols, Joy, D. Huenemoerder, Michael Corcoran, W. Waldron, Y. Nazé, Andy Pollock, A. Moffat, et al. "A Coordinated X-Ray and Optical Campaign of the Nearest Massive Eclipsing Binary, δ Orionis Aa: II. X-Ray Variability." Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etsu-works/6237.
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We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral data set of the δ Ori Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of ≈ 479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range of 5–25 Å is confirmed, with a maximum amplitude of about ±15% within a single ≈ 125 ks observation. Periods of 4.76 and 2.04 days are found in the total X-ray flux, as well as an apparent overall increase in the flux level throughout the nine-day observational campaign. Using 40 ks contiguous spectra derived from the original observations, we investigate the variability of emission line parameters and ratios. Several emission lines are shown to be variable, including S xv, Si xiii, and Ne ix. For the first time, variations of the X-ray emission line widths as a function of the binary phase are found in a binary system, with the smallest widths at ϕ = 0.0 when the secondary δ Ori Aa2 is at the inferior conjunction. Using 3D hydrodynamic modeling of the interacting winds, we relate the emission line width variability to the presence of a wind cavity created by a wind–wind collision, which is effectively void of embedded wind shocks and is carved out of the X-ray-producing primary wind, thus producing phase-locked X-ray variability. Based on data from the Chandra X-ray Observatory and the MOST satellite, a Canadian Space Agency mission, jointly operated by Dynacon Inc., the University of Toronto Institute of Aerospace Studies, and the University of British Columbia, with the assistance of the University of Vienna.
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Oskinova, Lidia, Yael Nazé, Helge Todt, David Huenemoerder, Richard Ignace, Swetlana Hubrig, and Wolf-Rainer Hamann. "Discovery of X-ray Pulsations from a Massive Star." Digital Commons @ East Tennessee State University, 2014. https://dc.etsu.edu/etsu-works/6240.
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X-ray emission from stars much more massive than the Sun was discovered only 35 years ago. Such stars drive fast stellar winds where shocks can develop, and it is commonly assumed that the X-rays emerge from the shock-heated plasma. Many massive stars additionally pulsate. However, hitherto it was neither theoretically predicted nor observed that these pulsations would affect their X-ray emission. All X-ray pulsars known so far are associated with degenerate objects, either neutron stars or white dwarfs. Here we report the discovery of pulsating X-rays from a non-degenerate object, the massive B-type star ξ1 CMa. This star is a variable of β Cep-type and has a strong magnetic field. Our observations with the X-ray Multi-Mirror (XMM-Newton) telescope reveal X-ray pulsations with the same period as the fundamental stellar oscillations. This discovery challenges our understanding of stellar winds from massive stars, their X-ray emission and their magnetism.
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Krauss, Miriam Ilana. "X-ray spectroscopy of neutron star low-mass X-ray binaries." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/45408.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2007.Includes bibliographical references (p. 133-150).
In this thesis, I present work spanning a variety of topics relating to neutron star lowmass X-ray binaries (LMXBs) and utilize spectral information from X-ray observations to further our understanding of these sources. First, I give an overview of important X- ray astrophysics relevant to the work I present in subsequent chapters, as well as information about the X-ray observatories from which I obtained my data. In the next three chapters, I consider spectra-both high- and low-resolution--of accretion-powered millisecond X-ray pulsars, a unique and relatively new class of objects. In addition to analysis of the pulsar XTE J1814-338, I compare a broader sample of pulsars with a sample of atoll sources in order to better understand why the latter class do not contain persistently pulsating neutron stars. In particular, I test the hypothesis that pulsations in the atoll sources are suppressed by a high-optical- depth scattering region. Using X-ray color-color diagrams to define a selection criterion based on spectral state, I analyze Rossi X-ray Timing Explorer (RXTE) spectra from all the sources, and use a Comptonization model to obtain measurements of their optical depths. I then discuss efforts to spatially resolve X-ray jets from the accretion-powered millisecond pulsar SAX J1808.4-3658 and the Z source XTE J1701-462. Each was observed by the Chandra X-ray Observatory to produce a high-spatial-resolution image. This work was motivated in part by my analysis of XTE J1814-338, which found an apparent excess of infrared flux which could be attributed to jet emission. Next, I discuss the measured temperatures of thermonuclear X-ray bursts. The detection of line features in these bursts, and hence from the surfaces of neutron stars, has been an important goal for high-resolution X-ray spectroscopy. A measurement of the wavelengths of identified line features would yield a measurement of the neutron star's gravitational redshift, which would help constrain current models for the neutron star equation of state.
(cont.) Although such a measurement has been made for one source, other searches have not been able to repeat this measurement. I consider the effects of burst temperature on the formation of discrete spectral features, using a large sample of bursts observed by the RXTE PCA. Finally, I present analysis of high-resolution Chandra HETG spectra of a sample of Galactic LMXBs. High-resolution spectra are able to resolve line features, such as the prominent Ne and O emission lines in the ultracompact X-ray binary 4U 1626-67. They also allow for more precise measurements of photoelectric absorption edges, which can otherwise hinder the determination of continuum spectral components, particularly in the lower-energy spectral regions.
by Miriam Ilana Krauss.
Ph.D.
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Hamaguchi, Kenji. "X-ray Study of the Intermediate Mass Young Stars Herbig Ae/Be Stars." 京都大学 (Kyoto University), 2001. http://hdl.handle.net/2433/150824.
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Fleming, Thomas Anthony. "Optical analysis of an x-ray selected sample of stars." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184366.
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I analyse an x-ray selected sample of 128 late-type (F-M) stars. These stars were identified as optical counterparts to serendipitous x-ray detections made by the Einstein Observatory Extended Medium Sensitivity Survey. Once identified as x-ray sources, the stars were reobserved with an extensive program of optical observations consisting of high- and low-resolution spectroscopy and photometry. Spectral types, luminosity classes, absolute magnitudes, distances, x-ray luminosities, projected rotation rates (v sin i), radial velocities, and binary status have been determined for the sample. I find that Lₓ is correlated with v sin i for single stars. However, Lₓ does not correlate with Ω sin i, which leads me to believe that the correlation seen with v sin i is actually a correlation with radius. Indeed, Lₓ correlates strongly with radius (color, mass) for main sequence stars. This result provides a plausibility argument for rotational saturation in the coronae of late-type stars. Since this sample is flux limited, I use sky coverage and sensitivity information from the Einstein Observatory to calculate the bright end of the x-ray luminosity function for late-type stars. It appears that previously calculated luminosity functions from optically selected samples have underestimated the number of x-ray bright F and G dwarfs. I have also discovered 8 previously uncatalogued M dwarfs within 25 pc of the sun. My sample includes only M dwarfs of spectral type M5 and earlier, 93% of which are "emission" stars (i.e. type Me V), as well as two pre-main sequence M stars. Arguments involving kinematics and stellar rotational velocities are used to estimate the age of these x-ray "bright" M dwarfs; they appear to be quite young (≤ 1-3 x 10⁹ yrs). Since the local space density of x-ray "bright" M dwarfs increases with mass, I infer a longer activity timescale for lower masses. M dwarfs later than M5 lie below the sample's x-ray sensitivity limit. An upper limit of log Lₓ = 27.45 is put on their coronal emission. I also present H(α) and Ca II K line fluxes for most members of the M dwarf sample and show that the H(α) and Ca II K luminosities do indeed correlate with Lₓ. However, these chromospheric luminosities are weaker functions of rotation than Lₓ and may, in fact, represent saturated levels of activity. My results are consistent with the hypothesis that the chromosphere is heated by x-rays from the overlying corona. Finally, I discuss two unusual members of the sample which are attractive candidates for the recently proposed class of FK Comae stars.
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Edwards, Philip Gregory. "A search for ultra high energy gamma ray emission from binary X-ray systems." Title page, contents and summary only, 1988. http://web4.library.adelaide.edu.au/theses/09PH/09phe266.pdf.
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Hodgkin, Simon T. "EUV and X-ray observations of late-type stars." Thesis, University of Leicester, 1995. http://hdl.handle.net/2381/35914.
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In this thesis I describe a number of projects arising from the ROSAT mission, inspired by a desire to understand better the activity of late-type stars from studies of their coronal EUV and X-ray emission. A brief introduction summarises some of the most important work on cool star coronas. The second chapter describes the mechanisms by which X-rays are produced in coronal plasmas. I also discuss the ROSAT mission, its instrumentation and applicability for observing cool stars. In Chapter 3 I describe the discovery of one of the brightest sources in the EUV sky, the hot white dwarf companion to HD 33959C. I discuss the importance of such binaries for the determination of more accurate measurements of mass, radius and distance than is possible for isolated white dwarfs. Chapter 4 is a WFC survey of all known late-type stars within 25 parsecs of the Sun. I construct and discuss the first ever EUV luminosity functions for such a sample and show that stars in interacting binaries are more active than single stars. In Chapters 5 and 6 I present a deep PSPC survey of the Hyades, comprising 11 overlapping pointings. In Chapter 5 I derive the Hyades dK and dM X-ray luminosity functions down to Lx ~ 5 x 1027 erg s-1. In Chapter 6 I investigate the X-ray spectra of the more luminous Hyads, both non-parametrically using hardness ratios, and parametrically using simple one-temperature and two-temperature fits to the data. Flares were observed in VB 50 and VA 334; both stars show increases in temperature and emission measure during the flaring episodes. In Chapter 7 I summarise my conclusions and discuss projects which arise from the work presented in this thesis. Finally I describe some of the impacts that we may expect to see from three future missions, JET-X, AXAF and XMM.
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Huenemoerder, David, L. Oskinova, W. Hamann, Richard Ignace, H. Todt, and W. Waldron. "X-Ray Line Emission from Weak Wind O-Stars." Digital Commons @ East Tennessee State University, 2011. https://dc.etsu.edu/etsu-works/6278.
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The action of X-rays is commonly invoked to explain the wind properties of low-luminosity O-type stars. These stars have significantly smaller mass loss rates than predicted radiation-driven wind theories. In this respect they may resemble the first generation of supermassive stars in the early universe which presumably had weak winds due to their low metallicity. We present the high-resolution X-ray spectrum of a weak-wind star, mu Col, and discuss the potential for X-ray emission line strengths and profiles to discriminate among proposed mechanisms for the generation of X-rays in stellar winds, and in resolving the weak-wind problem.
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Balogh, Michael Lajos. "The recent star formation history of galaxies in X-ray clusters." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0004/NQ40452.pdf.
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Negueruela, Ignacio. "Observational constraints on Be/x-ray binary models." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242871.
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Roche, Paul. "Multi-wavelength studies of the high mass X-ray binaries X persei (4U0352+309) and OAO1657-415." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239680.
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Reynolds, Alastair P. "A spectroscopic study of high mass X-ray binaries." Thesis, University of St Andrews, 1992. http://hdl.handle.net/10023/14509.
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Observations of four massive x-ray binary stars are presented, based on data accumulated between February 1989 and August 1991. Using modern techniques of spectroscopic data analysis, velocity curves are derived for three of these systems. Two of these curves (SMC X-1, QV Nor) yield very precise mass estimates for the component stars, while the third (Cen X-3) offers a constraint on the possible masses. The fourth system (X Per) is not shown to exhibit periodic variations, despite an extensive study conducted over more than two years. For the two systems that yielded precise masses, the component neutron stars are shown to lie within the theoretical mass range based on theories of their formation via the supernova explosion of a helium star in a close binary system. This is a marked improvement on previous studies where both stars had estimated masses which lay well outside of the expected range. The derivation of these masses incorporates the use of non-Keplerian velocity corrections, arising from the non-spherical, asymmetrically illuminated primary stars. A study of the line profiles showed that the temperatures around both primary stars were consistent with the parameters in these calculations. For the third system, the inaccuracy of the published ephemeris resulted in a lack of observations at the times of maximum and minimum velocity. The semi-amplitude is thus not well constrained, but it is shown that the observations are consistent with the assumption of a normal mass neutron star secondary. The system is shown to have undergone a gradual decrease in its orbital period which follows a parabolic trend, suggesting substantial mass-transfer. For the fourth system, a periodicity analysis of 130 spectroscopic velocity measurements of a Be star, via Fouriergram and string-length techniques, failed to highlight any strong periodicity. The scatter in the data appears larger than would be expected for a non-variable B star. The absence of periodic velocity variations at the expected period is discussed in terms of the binarity (or otherwise) of the Be star. A transition from Be to shell-star or ordinary B star phase occurred during the study, which is not evident from the spectral variations observed in the blue.
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Bowden, Christopher Charles Geoffrey. "A search for TeV gamma ray emission from X-ray binary stars." Thesis, Durham University, 1993. http://etheses.dur.ac.uk/5631/.
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This work is concerned with the detection of pulsed TeV gamma ray emission from a number of X-ray binary systems by the use of the atmospheric Cerenkov technique. Chapters 1 and 2 give an overview of the development of gamma ray astronomy, with emphasis placed on progress made in the detection of TeV gamma rays by their Cerenkov radiation in the atmosphere. Chapters 3 and 4 describe the University of Durham atmospheric Cerenkov telescopes, which were used to make the observations reported in this work, and the standard data processing and analysis procedures adopted. The main part of the thesis deals with the application of these techniques to observations of five X-ray binaries. After a review of the properties of such objects in Chapter 5, Chapters 6 and 7 deal specifically with the results for two of the systems considered to be among the most likely candidates to give a detectable TeV photon flux; Centaurus X-3 and Vela X-1. A study of all data recorded on Cen X-3 over the course of six years suggests the presence of a weak gamma ray flux pulsed at the X-ray period. Previous reports of stronger emission near the ascending node of the orbit are confirmed here. For Vela X-1, the analysis of a dataset recorded during a single dark moon interval reveals evidence for two short outbursts of pulsed TeV gamma ray emission. Chapter 8 reports the series of observations made of SMC X-1, 4U1626-67 and X0G21-72, and upper limits are placed on the TeV gamma ray emission from each. Finally, the results reported here are compared with the predictions of a number of theoretical models, some of which are found to give good agreement with the limits and detections derived in this work. A discussion of the status of this field and future observational prospects is also given.
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Naylor, Timothy. "High inclination X-ray and cataclysmic binaries." Thesis, University of Oxford, 1987. http://ora.ox.ac.uk/objects/uuid:c932bc88-4a04-4e08-9ea5-db7178a3dd0b.
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An introduction is given to the fields of X-ray and cataclysmic binaries, low mass X-ray binaries (LMXBs) and globular clusters. New observations of the W Vir star AC5 (=V86) are used show that it is probably the source of Hα emission previous authors have found in core of the globular cluster M15. The first phase resolved optical spectroscopy of AC211, the optical counterpart of the X-ray source in M15, are presented, and its binary period discovered to be 9.l±0.5 hours. A re-analysis of archive ultraviolet (UV) spectra of M15, shows spectral features which are attributed to AC211. These observations are combined with those of other authors, to prove AC211 is probably an "accretion disc corona" (ADC) source. After reviewing the superoutbursts of the SU UMa class of dwarf novae, X-ray, UV, optical and infrared observations of the SU UMa star OY Car are used to show that during superoutburst there is extensive vertical structure in its accretion disc, similar to that in the ADC and "dipping" LMXBs. Archive UV data from the 1978 outburst of WZ Sge shows that it had similar vertical structure. UV observations presented of EX Hya during a bright outburst may have the same explanation. From the OY Car data, a temperature and area for the region which produces the "superhump" light are derived, of 8 OOOK and -1020cm2, respectively. It is found that during OY Car's superoutburst, the size of the 0-C variations of the eclipse timings are significantly smaller than was previously thought, and that it has an extended X-ray source whose size is comparable to the binary separation. The results are discussed with respect to models of the superhump phenomena in SU UMa stars, and possible causes of vertical disc structure in X-ray and cataclysmic binaries.
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Ignace, Richard, W. Waldron, and N. Cassinelli. "X-ray Emissions from Clump Bowshocks in Massive Star Winds." Digital Commons @ East Tennessee State University, 2012. https://dc.etsu.edu/etsu-works/6277.
Full textAbstract:
Clumped structures in wind flows have substantially altered our interpretations of multiwavelength data for understanding mass loss from massive stars. Embedded wind shocks have long been the favored explanation for the hot plasma production and X-ray generation in massive star winds. This contribution reports on line profile shapes fromthe clump bowshock model and summarizes the temperature and emission measure distributions throughout the wind for this model with a focus on results that can be tested against observations.The authors acknowledge funding support for this work from a NASA grant(NNH09CF39C
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Huenemoerder, David P., K. G. Gayley, Wolf-Rainer Hamann, Richard Ignace, J. S. Nichols, Lidia M. Oskinova, A. M. T. Pollock, Nobert S. Schulz, and Tomer Shenar. "Probing Wolf–Rayet Winds: Chandra/HETG X-Ray Spectra of WR 6." Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etsu-works/2692.
Full textAbstract:
With a deep Chandra/HETGS exposure of WR 6, we have resolved emission lines whose profiles show that the X-rays originate from a uniformly expanding spherical wind of high X-ray-continuum optical depth. The presence of strong helium-like forbidden lines places the source of X-ray emission at tens to hundreds of stellar radii from the photosphere. Variability was present in X-rays and simultaneous optical photometry, but neither were correlated with the known period of the system or with each other. An enhanced abundance of sodium revealed nuclear-processed material, a quantity related to the evolutionary state of the star. The characterization of the extent and nature of the hot plasma in WR 6 will help to pave the way to a more fundamental theoretical understanding of the winds and evolution of massive stars.
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Machin, Graham. "Cataclysmic variables in globular clusters and low mass X-ray binaries." Thesis, University of Oxford, 1990. http://ora.ox.ac.uk/objects/uuid:9cddbf39-034d-4d33-ad98-eecbe9bd60a7.
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