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1
Lima, I. J., G. J. M. Luna, K. Mukai, et al. "Symbiotic stars in X-rays." Astronomy & Astrophysics 689 (September 2024): A86. http://dx.doi.org/10.1051/0004-6361/202449913.
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White dwarf symbiotic binaries are detected in X-rays with luminosities in the range of 1030–1034 ergs s−1. Their X-ray emission arises either from the accretion disk boundary layer, from a region where the winds from both components collide, or from nuclear burning on the surface of the white dwarf (WD). In our continuous effort to identify X-ray-emitting symbiotic stars, we studied four systems using observations from the Neil Gehrels Swift Observatory and XMM-Newton satellites in X-rays and from Transiting Exoplanet Survey Satellite (TESS) in the optical. The X-ray spectra were fit with absorbed optically thin thermal plasma models that are either single- or multitemperature with kT < 8 keV for all targets. Based on the characteristics of their X-ray spectra, we classified BD Cam as possible β-type, V1261 Ori and CD −27 8661 as δ-type, and confirmed NQ Gem as β/δ-type. The δ-type X-ray emission most likely arises from the boundary layer of the accretion disk, while in the case of BD Cam, its mostly soft emission originates from shocks, possibly between the red giant and WD and disk winds. In general, we find that the observed X-ray emission is powered by accretion at a low accretion rate of about 10−11 M⊙ yr−1. The low ratio of X-ray to optical luminosities, however indicates that the accretion-disk boundary layer is mostly optically thick and tends to emit in the far or extreme UV. The detection of flickering in optical data provides evidence of the existence of an accretion disk.
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Ögelman, H., J. Krautter, and K. Beuermann. "Exosat Observations of X-Rays from Classical Novae during Outburst Stage." International Astronomical Union Colloquium 93 (1987): 279. http://dx.doi.org/10.1017/s0252921100104981.
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AbstractThe initial discovery of soft X-rays from Nova Muscae 1983 was followed by eight additional observations of the three brightest novae whose outburst stage coincided with the lifetime of EXOSAT satellite; namely three more observations of Nova Muscae 1983, three observations of Nova Vulpeculae 1984 # 1 (PW Vul), and two observations of Nova Vulpeculae 1984 # 2. Through these observations we sampled the soft X-ray light curve of classical novae from optical maximum to ~ 900 days after. The observations seem best explained by the constant bolometric luminosity model of a hot white dwarf remnant. Although the measurements suffer from limited statistics, very broad energy bandpass, and incomplete sampling of any single nova, their constraints on the theories of nova outburst are significant. One constraint is that the lifetime of the white dwarf remnant in Nova Muscae 1983 is ~ 2 to 3 years, which leads to the conclusion that the burned envelope mass Mburn should be of the order of . The second constraint is that the maximum temperature, of the white dwarf remnant should approximately be within 200 000 K to 400 000 K. We estimate that a white dwarf remnant evolving like the central star of a planetary nebula, with core mass of 0.8 to 0.9 M⊙, core luminosity of ~ 2 × 104L⊙, and envelope mass of 10−6M⊙, can explain the general characteristics of the X-ray measurements for Nova Muscae 1983. In order to have ≥ 1.1 M⊙ core mass, estimated from the early observations of bolometric luminosity in the UV to infrared range, a wind with Ṁ ≤ 5 × 10−7M⊙yr−1 appears to be necessary. The few observations of Nova Vulpeculae 1984 # 1 and Nova Vulpeculae 1984 # 2 , during the first year after outburst, give a risetime and intensity that is consistent with a constant bolometric luminosity model.
3
Balman, S. "Inner Disk Structure of Dwarf Novae in the Light of X-Ray Observations." Acta Polytechnica CTU Proceedings 2, no. 1 (2015): 116–22. http://dx.doi.org/10.14311/app.2015.02.0116.
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Diversity of the X-ray observations of dwarf nova are still not fully understood. I review the X-ray spectral characteristics of dwarf novae during the quiescence in general explained by cooling flow models and the outburst spectra that show hard X-ray emission dominantly with few sources that reveal soft X-ray/EUV blackbody emission. The nature of aperiodic time variability of brightness of dwarf novae shows band limited noise, which can be adequately described in the framework of the model of propagating fluctuations. The frequency of the break (1-6 mHz) indicates inner disk truncation of the optically thick disk with a range of radii (3.0-10.0)×109 cm. The RXTE and optical (RTT150) data of SS Cyg in outburst and quiescence reveal that the inner disk radius moves towards the white dwarf and receeds as the outburst declines to quiescence. A preliminary analysis of SU UMa indicates a similar behaviour. In addition, I find that the outburst spectra of WZ Sge shows two component spectrum of only hard X-ray emission, one of which may be fitted with a power law suggesting thermal Comptonization occuring in the system. Cross-correlations between the simultaneous UV and X-ray light curves (XMM −Newton) of five DNe in quiescence show time lags in the X-rays of 96-181 sec consistent with travel time of matter from a truncated inner disk to the white dwarf surface. All this suggests that dwarf novae and other plausible nonmagnetic systems have truncated accretion disks indicating that the disks may be partially evaporated and the accretion may occur through hot (coronal) flows in the disk.
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Mukhopadhyay, Banibrata, and Mukul Bhattacharya. "Formation, Possible Detection and Consequences of Highly Magnetized Compact Stars." Particles 5, no. 4 (2022): 493–513. http://dx.doi.org/10.3390/particles5040037.
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Over the past several years, there has been enormous interest in massive neutron stars and white dwarfs due to either their direct or indirect evidence. The recent detection of gravitational wave event GW190814 has confirmed the existence of compact stars with masses as high as ∼2.5–2.67 M⊙ within the so-called mass gap, indicating the existence of highly massive neutron stars. One of the primary goals to invoke massive compact objects was to explain the recent detections of over a dozen Type Ia supernovae, whose peculiarity lies with their unusual light curve, in particular the high luminosity and low ejecta velocity. In a series of recent papers, our group has proposed that highly magnetised white dwarfs with super-Chandrasekhar masses can be promising candidates for the progenitors of these peculiar supernovae. The mass-radius relations of these magnetised stars are significantly different from those of their non-magnetised counterparts, which leads to a revised super-Chandrasekhar mass-limit. These compact stars have wider ranging implications, including those for soft gamma-ray repeaters, anomalous X-ray pulsars, white dwarf pulsars and gravitational radiation. Here we review the development of the subject over the last decade or so, describing the overall state of the art of the subject as it stands now. We mainly touch upon the possible formation channels of these intriguing stars as well as the effectiveness of direct detection methods. These magnetised stars can have many interesting consequences, including reconsideration of them as possible standard candles.
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MIRZA, BABUR M. "GRAVITOMAGNETIC RESONANCE SHIFT DUE TO A SLOWLY ROTATING COMPACT STAR." International Journal of Modern Physics D 13, no. 02 (2004): 327–33. http://dx.doi.org/10.1142/s0218271804004463.
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The effect of a slowly rotating mass on a forced harmonic oscillator with two degrees of freedom is studied in the weak field approximation. It is found that according to the general theory of relativity there is a shift in the resonant frequency of the oscillator which depends on the density and rotational frequency of the gravitational source. The proposed shift is quite small under normal physical situations however it is estimated that for compact X-ray sources such as white dwarfs, pulsars and neutron stars the shift is quite appreciable.
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Jinzhong, Liu, and Zhang Yu. "A binary population synthesis study on gravitational wave sources." Proceedings of the International Astronomical Union 11, A29B (2015): 365–66. http://dx.doi.org/10.1017/s1743921316005548.
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AbstractGravitational waves (GW) are a natural consequence of Einstein's theory of gravity (general relativity), and minute distortions of space-time. Gravitational Wave Astronomy is an emerging branch of observational astronomy which aims to use GWs to collect observational data about objects such as neutron stars and black holes, about events such as supernovae and about the early universe shortly after the big bang.This field will evolve to become an established component of 21st century multi-messenger astronomy, and will stand shoulder-to-shoulder with gamma-ray, x-ray, optical, infrared and radio astronomers in exploring the cosmos. In this paper, we state a recent theoretical study on GW sources, and present the results of our studies on the field using a binary population synthesis (BPS) approach, which was designed to investigate the formation of many interesting binary-related objects, including close double white dwarfs, AM CVn stars, ultra-compact X-ray binaries(UCXBs), double neutron stars, double stellar black holes. Here we report how BPS can be used to determine the GW radiation from double compact objects.
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Oks, Eugene. "Review of recent advances in the analytical theory of Stark broadening of spectral lines in plasmas: applications to laboratory discharges and astrophysical plasmas." Journal of Physics: Conference Series 2439, no. 1 (2023): 012009. http://dx.doi.org/10.1088/1742-6596/2439/1/012009.
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Abstract We present an overview of latest advances in the analytical theory of Stark broadening of spectral lines and their applications to various types of laboratory and astrophysical plasmas. They include: 1) in-depth study of intra-Stark spectroscopy in the x-ray range in relativistic laser-plasma interactions; 2) effect of diamagnetism on the number of observable hydrogen lines in plasmas; 3) influence of magnetic-field-caused modifications of trajectories of plasma electrons on the width of hydrogen/deuterium spectral lines: applications to white dwarfs; 4) Stark broadening of hydrogen/deuterium spectral lines by a relativistic electron beam: analytical results and applications to magnetic fusion; 5) counterintuitive dependence of the dynamical Stark width of hydrogenic spectral lines on the electron density.
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Melrose, DB, and WEP Padden. "Comptonisation of Radiation Below the Cyclotron Frequency in a Strong Magnetic Field." Australian Journal of Physics 39, no. 6 (1986): 961. http://dx.doi.org/10.1071/ph860961.
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We present new equations describing the Thomson scattering of the o-mode and z-mode in a strongly magnetised plasma, valid below the fundamental cyclotron frequency. Scattering by nonrelativistic thermal electrons leads to a frequency diffusion equation for the more strongly scattered o-mode and this equation is effectively the Kompaneets equation with cross section 2/ 15th of the Thomson' cross section. Transfer of the photons tends to be dominated by the less strongly scattered z-mode; an o-mooe photon is scattered occasionally into a z-mode photon, which then diffuses rapidly due to its large mean free path before being scattered back into an o-mode photon. Our results should have applications in X-ray pulsars and 'Y-ray burst sources, as well as magnetic white dwarfs occurring in cataclysmic variables.
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Antokhina, E. A., and I. I. Antokhin. "DETERMINATION OF THE CLOSE BINARY SYSTEMS PARAMETERS BY SYNTHESIS METHODS: FROM WHITE DWARFS TO WOLF–RAYET STARS AND BLACK HOLES." Астрономический журнал 100, no. 9 (2023): 772–84. http://dx.doi.org/10.31857/s0004629923090013.
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Synthesis methods for light and radial velocity curves are currently one of the main tools for studying close binary systems (CBS). The paper gives a brief overview of the history and development of the methods and their implementations at the SAI MSU, where a set of computer programs has been created to analyze observations of various types of CBS. As a demonstration, we present the results of the analysis by our algorithms of three interesting CBSs at different evolutionary stages. An analysis of the unusual light curves of the recently discovered pre-cataclysmic binary GPX-TF16E-48 was performed using the Roche model with spots on the normal star. The X-ray light curves of the microquasar SS433 were analyzed in a model with a precessing accretion disk. Thanks to the photometric data obtained from space, the highly elliptical Wolf–Rayet binary WR22 was studied in the Roche model accounting for the absorption in the powerful wind of the Wolf–Rayet star. As a result of this detailed analysis of the light curves and involving spectroscopic information, the parameters of the CBSs and their components were found. The paper is based on a talk presented at the astrophysical memorial seminar “Novelties in Understanding the Evolution of Binary Stars”, dedicated to the 90th anniversary of Professor M.A. Svechnikov.
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Wang, Joan Jing, and Hsiang-Kuang Chang. "Can SGRs/AXPs Originate from Neutron Star Binaries?" Physics Research International 2014 (August 21, 2014): 1–8. http://dx.doi.org/10.1155/2014/375624.
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Soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are two groups of enigmatic objects, which have been extensively investigated in past few decades. Based on the ample information about their timing behaviors, spectra, and variability properties, it was proposed that SGRs/AXPs are isolated neutron stars (NSs) with extremely strong magnetic fields, the so-called magnetars. Nonetheless, some alternative models are probably equally convincing such as those proposing that they are accreting NSs with a fall-back disk or rotation-powered magnetized and massive white dwarfs. The nature and nurture of SGRs/AXPs remain controversial. In this paper, we propose that SGRs/AXPs can, alternatively, originate from normal NSs in binary systems, which resorts to the reexplosion of normal NS induced by instant contraction of the massive star envelope in a Thorne-Żytkow object (TZO). The spin-period clustering is due to either the brake of a slowly rotating envelope or the frictional drag during the common-envelope phase.
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Doikov, D. N., and A. V. Yushchenko. "THE POSIBILITY OF TRIPLE DETONATION IN WHITE DWARFS." Odessa Astronomical Publications 34 (December 3, 2021): 40–47. http://dx.doi.org/10.18524/1810-4215.2021.34.244285.
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The induced γ-ray emissions are considered in contact cataclysmic binary systems with strong magnetic fields near white dwarfs and companion’s stars’ components. He-C-O atoms in white dwarf’s atmospheres collide with flows falling to poles as a magnetic column. Near white dwarf’s surface the falling flows with speed reaches 3 ∙ 10 6 m /s and creates sufficient conditions for nuclear γ-radiation emission. The cross sections of nuclear γ-radiation emission are presented in 0.1 – 150 MeV energy intervals depending on the colliding atoms and particles. The mass loss from binary components is of the order of ̇ ≈ (10 −11 − 10 −7 )Msun. We considered the collisions of p – He, α – He, p – C, α – C, p – N, α – N, p – O, α – O, C – He, C – C, C – N, C – O, N – He, N – C, N – N, N – O, O – He, O – C, O – N, and O – O types. Monochromatic energy luminosities Lγ in the above energy intervals for different modes in cataclysmic systems were calculated taking into account the loss of mass M , chemical composition and dynamics of fluxes incident on the magnetic poles. We found the dependencies between Lγ and chemical composition and calibrated the synthetic γ-spectra in the above pointed energy intervals. It has been concluded that power flyers are detected from p-p detonation in surface layers in white dwarf’s atmospheres. From calculation we estimated that p-p detonation time scale is in frame of the 0.07-0.1 sec. From which it is concluded that in some surface p-p explosions in the column of the magnetic field are produce significant number of positrons who has a sufficient probability to inject beyond the atmosphere of a white dwarf. It has been shown that the induce γ-ray spectroscopy together with positron spectroscopy are opens new possibilities for diagnostics of the flayers in AM Her polar system. The mechanism of triple detonation, which leads to the explosion of type I supernovae, is proposed. In this context, it is assumed that SN I type explosions occur in white dwarfs with masses not reaching the Chandrasekhar limit. The neutron formation in the matter that are in an explosive state after p-p detonation is considered separately.
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Ye, Claire S., Kyle Kremer, Scott M. Ransom, and Frederic A. Rasio. "Lower-mass-gap Black Holes in Dense Star Clusters." Astrophysical Journal 975, no. 1 (2024): 77. http://dx.doi.org/10.3847/1538-4357/ad76a0.
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Abstract The existence of compact stellar remnants in the mass range 2–5 M ⊙ has long been debated. This so-called lower-mass gap (LMG) was initially suggested by the lack of low-mass X-ray binary observations with accretors about 2–5 M ⊙, but it has recently been called into question following newer observations, including an LMG candidate with a millisecond pulsar (MSP) companion in the dense globular cluster NGC 1851. Here, we model NGC 1851 with a grid of similar dense star clusters utilizing the state-of-the-art Monte Carlo N-body code Cluster Monte Carlo, and we specifically study the formation of LMG black holes (BHs). We demonstrate that both massive star evolution and dynamical interactions can contribute to forming LMG BHs. In general, the collapse of massive remnants formed through mergers of neutron stars (NSs) or massive white dwarfs produces the largest number of LMG BHs among all formation channels. However, in more massive clusters, supernova core collapse can contribute comparable numbers. Our NGC 1851-like models can reproduce MSP—LMG BH binaries similar to the observed system. Additionally, the LMG BHs can also become components of dynamically assembled binaries, and some will be in merging BH–NS systems similar to the recently detected gravitational wave source GW230529. However, the corresponding merger rate is probably ≲1 Gpc−3 yr−1.
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Campana, Sergio, Luigi Stella, Sandro Mereghetti, and Domitilla de Martino. "A universal relation for the propeller mechanisms in magnetic rotating stars at different scales." Astronomy & Astrophysics 610 (February 2018): A46. http://dx.doi.org/10.1051/0004-6361/201730769.
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Accretion of matter onto a magnetic, rotating object can be strongly affected by the interaction with its magnetic field. This occurs in a variety of astrophysical settings involving young stellar objects, white dwarfs, and neutron stars. As matter is endowed with angular momentum, its inflow toward the star is often mediated by an accretion disc. The pressure of matter and that originating from the stellar magnetic field balance at the magnetospheric radius: at smaller distances the motion of matter is dominated by the magnetic field, and funnelling towards the magnetic poles ensues. However, if the star, and thus its magnetosphere, is fast spinning, most of the inflowing matter will be halted at the magnetospheric radius by centrifugal forces, resulting in a characteristic reduction of the accretion luminosity. The onset of this mechanism, called the propeller, has been widely adopted to interpret a distinctive knee in the decaying phase of the light curve of several transiently accreting X-ray pulsar systems. By comparing the observed luminosity at the knee for different classes of objects with the value predicted by accretion theory on the basis of the independently measured magnetic field, spin period, mass, and radius of the star, we disclose here a general relation for the onset of the propeller which spans about eight orders of magnitude in spin period and ten in magnetic moment. The parameter-dependence and normalisation constant that we determine are in agreement with basic accretion theory.
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Mukai, Koji, and Kristiina Byckling. "The White Dwarf Mass versus X-Ray Temperature Relationship of Dwarf Novae, Revisited." Research Notes of the AAS 6, no. 3 (2022): 65. http://dx.doi.org/10.3847/2515-5172/ac618b.
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Abstract Most methods used to determine the white dwarf mass in non-magnetic cataclysmic variables are subject to large systematic errors. X-ray spectroscopy has the potential to enable mass estimation with a good accuracy, when calibrated against accurate and reliable values. This is now possible thanks to the work of Pala et al., who estimated the white dwarf masses for 43 cataclysmic variables relying in part on Gaia distances. In this research note we provide a brief update on the X-ray temperature versus white dwarf mass relationship using the X-ray spectroscopy results of Byckling et al. compared against the results of Pala et al., thereby putting the X-ray spectroscopy method on a securer footing.
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Cavallo, Rob, Keith A. Arnaud, and Virginia Trimble. "An upper limit to coronal X-rays from single, magnetic white dwarfs." Journal of Astrophysics and Astronomy 14, no. 3-4 (1993): 141–43. http://dx.doi.org/10.1007/bf02702364.
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Lu, Wenbin, Paz Beniamini, and Pawan Kumar. "Implications of a rapidly varying FRB in a globular cluster of M81." Monthly Notices of the Royal Astronomical Society 510, no. 2 (2021): 1867–79. http://dx.doi.org/10.1093/mnras/stab3500.
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ABSTRACT A repeating source of fast radio bursts (FRBs) is recently discovered from a globular cluster of M81. Association with a globular cluster (or other old stellar systems) suggests that strongly magnetized neutron stars, which are the most likely objects responsible for FRBs, are born not only when young massive stars undergo core-collapse, but also by mergers of old white dwarfs. We find that the fractional contribution to the total FRB rate by old stellar populations is at least a few per cent, and the precise fraction can be constrained by FRB searches in the directions of nearby galaxies, both star-forming and elliptical ones. Using very general arguments, we show that the activity time of the M81-FRB source is between 104 and 106 yr, and more likely of the order of 105 yr. The energetics of radio outbursts put a lower limit on the magnetic field strength of 10$^{13}\,$G, and the spin period $\gtrsim 0.2\,$s, thereby ruling out the source being a milli-second pulsar. The upper limit on the persistent X-ray luminosity (provided by Chandra), together with the high FRB luminosity and frequent repetitions, severely constrains (or rules out) the possibility that the M81-FRB is a scaled-up version of giant pulses from Galactic pulsars. Finally, the 50-ns variability time of the FRB light curve suggests that the emission is produced in a compact region inside the neutron star magnetosphere, as it cannot be accounted for when the emission is at distances $\gtrsim 10^{10}\rm \, cm$.
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Arnaud, Keith A., Vladimir V. Zhelezniakov, and Virginia Trimble. "Coronal X rays from single, magnetic white dwarfs - A search and probable detection." Publications of the Astronomical Society of the Pacific 104 (April 1992): 239. http://dx.doi.org/10.1086/132983.
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Greiner, J., C. Maitra, F. Haberl, et al. "A helium-burning white dwarf binary as a supersoft X-ray source." Nature 615, no. 7953 (2023): 605–9. http://dx.doi.org/10.1038/s41586-023-05714-4.
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AbstractType Ia supernovae are cosmic distance indicators1,2, and the main source of iron in the Universe3,4, but their formation paths are still debated. Several dozen supersoft X-ray sources, in which a white dwarf accretes hydrogen-rich matter from a non-degenerate donor star, have been observed5 and suggested as Type Ia supernovae progenitors6–9. However, observational evidence for hydrogen, which is expected to be stripped off the donor star during the supernova explosion10, is lacking. Helium-accreting white dwarfs, which would circumvent this problem, have been predicted for more than 30 years (refs. 7,11,12), including their appearance as supersoft X-ray sources, but have so far escaped detection. Here we report a supersoft X-ray source with an accretion disk whose optical spectrum is completely dominated by helium, suggesting that the donor star is hydrogen-free. We interpret the luminous and supersoft X-rays as resulting from helium burning near the surface of the accreting white dwarf. The properties of our system provide evidence for extended pathways towards Chandrasekhar-mass explosions based on helium accretion, in particular for stable burning in white dwarfs at lower accretion rates than expected so far. This may allow us to recover the population of the sub-energetic so-called Type Iax supernovae, up to 30% of all Type Ia supernovae13, within this scenario.
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Traulsen, I., K. Reinsch, and A. D. Schwope. "Probing the Accretion Processes in Soft X-Ray Selected Polars." Acta Polytechnica CTU Proceedings 2, no. 1 (2015): 76–80. http://dx.doi.org/10.14311/app.2015.02.0076.
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High-energy data of accreting white dwarfs give access to the regime of the primary accretion-induced energy release and the different proposed accretion scenarios. We perform XMM-Newton observations of polars selected due to their ROSAT hardness ratios close to -1.0 and model the emission processes in accretion column and accretion region. Our models consider the multi-temperature structure of the emission regions and are mainly determined by mass-flow density, magnetic field strength, and white-dwarf mass. To describe the full spectral energy distribution from infrared to X-rays in a physically consistent way, we include the stellar contributions and establish composite models, which will also be of relevance for future X-ray missions. We confirm the X-ray soft nature of three polars.
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ANDRUCHOW, ILEANA, NICOLA MASETTI, DOMITILLA DE MARTINO, SERGIO A. CELLONE, ELENA MASON, and JEAN-MARC BONNET-BIDAUD. "SPIN PERIODICITY MEASUREMENTS OF WHITE DWARFS HOSTED IN SOUTHERN HARD X–RAY INTERMEDIATE POLAR CANDIDATES." International Journal of Modern Physics D 19, no. 06 (2010): 797–803. http://dx.doi.org/10.1142/s0218271810016610.
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Thanks to the combination of hard X–ray data afforded with the INTEGRAL satellite and optical spectroscopy at various telescopes, a number of new, possibly magnetic, Cataclysmic Variables (CVs) has been recently discovered. We here report on the preliminary analysis of B-band optical photometry performed with the 2.15m "Jorge Sahade" telescope at CASLEO (Argentina) on 5 CVs discovered at hard X–rays with INTEGRAL and which show features of a magnetic white dwarf (WD) in their optical spectra. The aim of these observations is to derive the orbital periods of these systems and the spin periodicity of their accreting WD.
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AHLUWALIA, D. V. "ON QUANTUM NATURE OF BLACK-HOLE SPACETIME: A POSSIBLE NEW SOURCE OF INTENSE RADIATION." International Journal of Modern Physics D 08, no. 05 (1999): 651–57. http://dx.doi.org/10.1142/s0218271899000456.
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Atoms and the planets acquire their stability from the quantum mechanical incompatibility of the position and momentum measurements. This incompatibility is expressed by the fundamental commutator [x, px]=iℏ, or equivalently, via the Heisenberg's uncertainty principle Δx Δ px~ℏ. A further stability-related phenomenon where the quantum realm plays a dramatic role is the collapse of certain stars into white dwarfs and neutron stars. Here, an intervention of the Pauli exclusion principle, via the fermionic degenerate pressure, stops the gravitational collapse. However, by the neutron-star stage the standard quantum realm runs dry. One is left with the problematic collapse of a black hole. This essay is devoted to a concrete argument on why the black-hole spacetime itself should exhibit a quantum nature. The proposed quantum aspect of spacetime is shown to prevent the general-relativistic dictated problematic collapse. The quantum nature of black-hole spacetime is deciphered from a recent result on the universal equal-area spacing [Formula: see text] for black holes. In one interpretation of the emergent picture, an astrophysical black hole can fluctuate to [Formula: see text] time its classical size, and thus allow radiation and matter to escape to the outside observers. These fluctuations I conjecture provide a new source, perhaps beyond Hawking radiation, of intense radiation from astrophysical black holes and may be the primary source of observed radiation from those galactic cores what carry black hole(s). The presented interpretation may be used as a criterion to choose black holes from black hole candidates.
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Titarchuk, Lev, and Elena Seifina. "How to distinguish white dwarf and neutron star X-ray binaries during their X-ray outbursts?" World journal of physics 02, no. 01 (2024): 110–42. http://dx.doi.org/10.56439/wjp/2024.1111.
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We present spectral signatures of neutron stars (NSs) and white dwarfs (WDs) hosted in accreting X-ray binaries that can be easily identified in X-ray observations. We perform spectral and timing analysis of 4U 1636–53 and SS Cygni, as typical representatives of such NS and WD binaries, based on their X-ray observations by RXTE, ASCA, Suzaku and BeppoSAX. As a result, we formulate a criterion that makes it easy to distinguish NS from WD in such binaries: NS X-rays exhibits quasi-stable behavior with the index Γ → 2 and is characterized by quasi periodic oscillations (QPOs) at 𝜈𝑄𝑃𝑂 > 0.5 Hz, although WD X-rays is stable with Γ → 1.85 and is accompanied by QPOs at 𝜈𝑄𝑃𝑂 < 0.05 Hz during source outbursts. In addition, we revealed that in 4U 1636–53 the mHz QPOs anti-correlate with the temperature, 𝑇𝑒 of the corona around a NS. This allowed us to associate mHz-QPOs with the corona dynamics during outburst cycle. The above index effect, now well established for 4U 1636–53 and SS Cygni using extensive observations, has previously been found in other low-mass X-ray NS and WD binaries and agrees well with the criterion for distinguishing NSs and WDs presented here.
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Ögelman, Hakki. "Recent and Future X-ray Observations of Classical Novae During the Outburst Stage." International Astronomical Union Colloquium 122 (1990): 148–54. http://dx.doi.org/10.1017/s0252921100068470.
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The discovery of soft X-rays from Nova GQ Mus with the EXOSAT satellite has added an important channnel to the observational information on classical novae during the outburst stage (Ögelman, Beuermann, and Krautter 1984). With peak luminosities in excess of 1038 erg s−1 and total liberated energies of more than 1045 erg, novae constitute the second most energetic outburst phenomena in the galactic population exceeded only by supernovae (see Gallagher and Starrfield, 1978; Truran, 1982 for a review of the observations and theory). Regardless of the details of the outburst, objects of the size of white dwarfs (~ 109 cm) radiating close to Eddington luminosities (~ 1038 erg s−1 ) should emit soft X-rays provided that the envelope is sufficiently transparent. In addition, the ejected shell, moving at velocities around 1000 km s−1, is capable of shocking the circumstellar medium to X-ray temperatures.
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Orio, M. "X-Ray Observations of Classical and Recurrent Novae in Outburst." International Astronomical Union Colloquium 194 (July 2004): 182–86. http://dx.doi.org/10.1017/s0252921100152406.
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AbstractI review X-ray observations of classical and recurrent novae in outburst, some of them recently done with Chandra and XMM-Newton for 12 objects. Significant X-ray flux is emitted by the nova shell, with a peak luminosity up to Lx = 1035 erg s–1 in the 0.2-10 keV range. In recurrent nova systems, or in novae hosting a red giant, the source of X-rays may be previous circumstellar matter shocked by the nova wind. However, for most classical novae, X-rays originate inside the nebula ejected in the outburst. The data indicate a very high fraction of shocked material, and a non-smooth, varying wind outflow. A nebular emission line spectrum is also observed at late phases. In about half of the observed novae, the central white dwarf appears as a very luminous supersoft X-ray source for 1 to 9 years after the outburst. It is the best type of object to study the characteristics of shell hydrogen burning on white dwarfs in single degenerate systems. Still incomplete statistics indicate that the duration of the supersoft X-ray phase is peaked around ≃2 years. The correlation of the X-ray light curve with the nova properties is not quite clear. Recently, “template grating spectra” with high S/N have been obtained for V4743 Sgr. The X-ray light curve of this nova reveals a rich and complex power spectrum, with signatures of non-radial g-mode oscillations of the white dwarf. The oscillations and the spectra allow to determine the properties of the shell hydrogen burning white dwarf.
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Hameury, J. M., J. P. Lasota, C. Knigge, and E. G. Körding. "Hystereses in dwarf nova outbursts and low-mass X-ray binaries." Astronomy & Astrophysics 600 (April 2017): A95. http://dx.doi.org/10.1051/0004-6361/201629953.
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Context. The disc instability model (DIM) successfully explains why many accreting compact binary systems exhibit outbursts during which their luminosity increases by orders of magnitude. The DIM correctly predicts which systems should be transient and works regardless of whether the accretor is a black hole, a neutron star, or a white dwarf. However, it has been known for some time that the outbursts of X-ray binaries, which contain neutron-star or black-hole accretors, exhibit hysteresis in the X-ray hardness-intensity diagram (HID). More recently, it has been shown that the outbursts of accreting white dwarfs also show hysteresis, but in a diagram combining optical, EUV, and X-ray fluxes. Aims. We examine the nature of the hysteresis observed in cataclysmic variables and low-mass X-ray binaries. Methods. We used our disc evolution code for modelling dwarf nova outbursts, and constructed the hardness intensity diagram as predicted by the disc instability model. Results. We show explicitly that the standard DIM, modified only to account for disc truncation, can explain the hysteresis observed in accreting white dwarfs, but cannot explain that observed in X-ray binaries. Conclusions. The spectral evidence for the existence of different accretion regimes or components (disc, corona, jets, etc.) should only be based on wavebands that are specific to the innermost parts of the discs, i.e. EUV and X-rays; this task is difficult because of interstellar absorption. The existing data, however, indicate that a hysteresis is in the EUV – X-ray domain is present in SS Cyg.
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Burdge, Kevin B., Kareem El-Badry, Saul Rappaport, et al. "Orbital Decay in an Accreting and Eclipsing 13.7 Minute Orbital Period Binary with a Luminous Donor." Astrophysical Journal Letters 953, no. 1 (2023): L1. http://dx.doi.org/10.3847/2041-8213/ace7cf.
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Abstract We report the discovery of ZTF J0127+5258, a compact mass-transferring binary with an orbital period of 13.7 minutes. The system contains a white dwarf accretor, which likely originated as a post–common envelope carbon–oxygen (CO) white dwarf, and a warm donor (T eff,donor = 16,400 ± 1000 K). The donor probably formed during a common envelope phase between the CO white dwarf and an evolving giant that left behind a helium star or white dwarf in a close orbit with the CO white dwarf. We measure gravitational wave–driven orbital inspiral with ∼51σ significance, which yields a joint constraint on the component masses and mass transfer rate. While the accretion disk in the system is dominated by ionized helium emission, the donor exhibits a mixture of hydrogen and helium absorption lines. Phase-resolved spectroscopy yields a donor radial velocity semiamplitude of 771 ± 27 km s−1, and high-speed photometry reveals that the system is eclipsing. We detect a Chandra X-ray counterpart with L X ∼ 3 × 1031 erg s−1. Depending on the mass transfer rate, the system will likely either evolve into a stably mass-transferring helium cataclysmic variable, merge to become an R CrB star, or explode as a Type Ia supernova in the next million years. We predict that the Laser Space Interferometer Antenna (LISA) will detect the source with a signal-to-noise ratio of 24 ± 6 after 4 yr of observations. The system is the first LISA-loud mass-transferring binary with an intrinsically luminous donor, a class of sources that provide the opportunity to leverage the synergy between optical and infrared time domain surveys, X-ray facilities, and gravitational-wave observatories to probe general relativity, accretion physics, and binary evolution.
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Mohanty, S. "Magnetospheric accretion & outflows in stars & brown dwarfs: theories and observational constraints." Proceedings of the International Astronomical Union 5, H15 (2009): 753. http://dx.doi.org/10.1017/s1743921310011385.
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The manner in which young classical T Tauri stars (cTTs) and brown dwarfs accrete gas from their surrounding disks and simultaneously drive jets and outflows is central to star and planet formation and angular momentum evolution, but remains an ill-understood and hotly debated subject. One of the central concerns is the stellar field geometry: while analytic theories assume an idealized stellar dipole, T Tauri fields are observed to be complex multipolar beasts. I present an analytic generalization of the X-wind theory to include such fields. Independent of the precise field geometry, the generalized model makes a unique prediction about the relationship between various cTTs observables. I show that this prediction is supported by observations of accretion rate, hot spot size, stellar rotation and field strength from stellar to brown dwarf masses, including recent detailed spectropolarimetric measurements. I also discuss the unique insights offered by recent magnetic field measurements on accreting brown dwarfs: while they agree with the accretion theory above, they also pose a puzzle for magnetic field generation theory. Resolving this conundrum promises to illuminate our general picture of accretion and angular momentum transport in fully convective objects.
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Singh, K. K., P. J. Meintjes, and K. K. Yadav. "Properties of white dwarf in the binary system AR Scorpii and its observed features." Modern Physics Letters A 36, no. 13 (2021): 2150096. http://dx.doi.org/10.1142/s0217732321500966.
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The binary system AR Scorpii hosts an M-type main sequence cool star orbiting around a magnetic white dwarf in the Milky Way Galaxy. The broadband non-thermal emission over radio, optical and X-ray wavebands observed from AR Scorpii indicates strong modulations on the spin frequency of the white dwarf as well as the spin-orbit beat frequency of the system. Therefore, AR Scorpii is also referred to as a white dwarf pulsar wherein a fast spinning white dwarf star plays very crucial role in the broadband non-thermal emission. Several interpretations for the observed features of AR Scorpii appear in the literature without firm conclusions. In this paper, we investigate connection between some of the important physical properties like spin-down power, surface magnetic field, equation of state, temperature and gravity associated with the white dwarf in the binary system AR Scorpii and its observational characteristics. We explore the plausible effects of white dwarf surface magnetic field on the absence of substantial accretion in this binary system and also discuss the gravitational wave emission due to magnetic deformation mechanism.
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Doikov, Marko D. "THE PROBLEM OF OBTAINING COMBINED GAMMA AND OPTICAL DETECTORS FOR THE REGISTRATION OF FAST NUCLEAR PROCESSES." Odessa Astronomical Publications 36 (December 4, 2023): 42–50. http://dx.doi.org/10.18524/1810-4215.2023.36.290774.
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The physical and technical aspects of the registration of fast physical processes involving nuclear transformations with the help of binary detectors in the γ-and optical ranges are considered We chose a semiconducting perovskite crystal CsPbBr3 as the main element of the detector. Have been presented with geometrical and technologically usable parameters of the CsPbBr3 crystal for its implementations in nuclear medicine, geophysics and astrophysics. One of the objects that allow testing of the developed high-speed spectrographic equipment are lightning discharges in the atmospheres of planets, including the Earth. The thermonuclear nature of γ-bursts detected during thunderstorms was revealed by their spectra. The paper shows the role of the corresponding channels involving high-energy protons and α-particles, leading to the formation of 116C, 137 N, 158O isotopes. The registration of the γ-spectrum of the flash and its evolution allowed to estimate the character, energy and time scales of the processes necessary for the design and manufacture of multipurpose measuring complexes by us. The inclusion of γ-spectra in the consideration allowed to estimate the correlation between the maximum currents of particles and the productivity of γ-rays. In the experiments planned by us, the magnetic field fluctuations caused by currents are simultaneously recorded by highly sensitive magnetic field detectors. The height of the building of the Faculty of Physics in Smolyan, Bulgaria, is 900 meters above sea level. This makes it possible to place the measuring complex as close as possible to the sources of hard radiation and to carry out easurements in the immediate vicinity. Unlike distant space objects, the perovskite detector registers the positions themselves. This makes it possible to use the methods of positron γ-spectroscopy and accurately determine the parameters of local currents. The technological parameters of the device were determined. A simulation model was created in Simulink MATLAB, LabVIEW with synchronization of the operation of the listed spectrographs. The characteristic shape of the signal formed by individual γ-quanta with the parameters of the Gaussian function and the total number of these quanta are calculated. The degree of mathematical blinding of neighboring Gaussian functions and its influence on the structure of the final spectrogram in the form of an autocorrelation function is estimated. The similarity of the time scales of thermonuclear explosion processes on white dwarfs (WD) and the processes of synthesis of 116C, 137 N and 158O isotopes in the flash head is determined. It is concluded that it is expedient to create a robotic network of lightning observation stations similar to the meteor patrol at the I. I. Mechnikov National University of Ukraine.
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KING, A. R. "Accretion onto the White Dwarf and X-Ray Production in Nonmagnetic Cataclysmic Variables." Annals of the New York Academy of Sciences 470, no. 1 Twelfth Texas (1986): 320–30. http://dx.doi.org/10.1111/j.1749-6632.1986.tb47982.x.
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Bednarek, W., and A. Śmiałkowski. "High-energy neutrinos from fast winds in novae." Monthly Notices of the Royal Astronomical Society 511, no. 3 (2022): 3339–45. http://dx.doi.org/10.1093/mnras/stac243.
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ABSTRACT We discuss a scenario in which TeV neutrinos are produced during explosions of novae. It is argued that hadrons are accelerated to very high energies in the inner part of a nova wind, as a result of reconnection of the strong magnetic field of a white dwarf. Hadrons are expected to interact efficiently with a dense matter of the wind, either already during the acceleration process or during their advection with the equatorial wind. We calculate the neutrino spectra and estimate the muon neutrino event rates in the IceCube telescope, in the case of a few novae. In general, those event rates are unlikely to be detected with the present neutrino detectors. However, for a favourable location of the observer, some neutrino events might be detected not only from the class of novae recently detected in the GeV γ-rays by the Fermi-LAT (Large Area Telescope), but also from novae not detected in γ-rays. The GeV γ-ray emission observed from novae cannot originate in terms of the model discussed here, since protons are accelerated within a few stellar radii of the white dwarf, i.e. in the region in which GeV γ-rays are expected to be severely absorbed in the interactions with the radiation field and the matter of the wind.
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Hutchinson, I. B., R. S. Warwick, and R. Willingale. "Mapping Cool Gas in the ISM with ROSAT." International Astronomical Union Colloquium 166 (1997): 283–86. http://dx.doi.org/10.1017/s0252921100071128.
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AbstractWe have investigated the distribution of cool gas within the local interstellar medium (<150 pc) using data derived from both the ROSAT X-ray and EUV all-sky surveys. The EUV/X-ray spectra for a sample of 89 white dwarf stars and 200 active late-type stars have been analysed to give an estimate of the gas column density along each object’s line of sight. In order to extend the sky coverage we have also included in the analysis 190 late-type stars detected only in the X-ray band. The derived NHI measurements confirm the size of the local low density bubble as typically 50-100 pc and also show that in the general direction of Loop I there is a substantial excess of absorption at a range of distances from 10-150 pc.
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Chan, Alex C. H., and K. L. Li. "A Possible Orbital Period of MAXI J0158-744." Research Notes of the AAS 8, no. 1 (2024): 32. http://dx.doi.org/10.3847/2515-5172/ad2264.
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Abstract Optical Gravitational Lensing Experiment (OGLE) has observed Monitor of All-sky X-ray Image J0158-744 for at least 10 yr since the X-ray/optical burst in 2011, which is a Be+ White Dwarf Supersoft source. By analyzing the OGLE light curve, we noticed that the optical brightness was changing periodically, indicating a possible orbital period of 439 − 80 + 114 days.
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Hayashi, Takayuki, Hideyuki Mori, Koji Mukai, Yukikatsu Terada, and Manabu Ishida. "Gravitational Redshift Detection from the Magnetic White Dwarf Harbored in RX J1712.6–2414." Astrophysical Journal 953, no. 1 (2023): 30. http://dx.doi.org/10.3847/1538-4357/acd001.
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Abstract Gravitational redshift is a fundamental parameter that allows us to determine the mass-to-radius ratio of compact stellar objects, such as black holes, neutron stars, and white dwarfs (WDs). In the X-ray spectra of the close binary system, RX J1712.6−2414, obtained from the Chandra High Energy Transmission Grating observation, we detected significant redshifts for characteristic X-rays emitted from hydrogen-like magnesium, silicon (ΔE/E rest ∼ 7 × 10−4), and sulfur (ΔE/E rest ∼ 15 × 10−4) ions, which are over the instrumental absolute energy accuracy (ΔE/E rest ∼ 3.3 × 10−4). Considering some possible factors, such as Doppler shifts associated with the plasma flow, systemic velocity, and optical depth, we concluded that the major contributor to the observed redshift is the gravitational redshift of the WD harbored in the binary system, which is the first gravitational redshift detection from a magnetic WD. Moreover, the gravitational redshift provides us with a new method of WD mass measurement by invoking the plasma-flow theory with strong magnetic fields in close binaries. Regardless of large uncertainty, our new method estimated the WD mass to be M WD > 0.9 M ⊙.
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Cheong 張, Patrick Chi-Kit 志杰, Tetyana Pitik, Luís Felipe Longo Micchi, and David Radice. "Gamma-Ray Bursts and Kilonovae from the Accretion-induced Collapse of White Dwarfs." Astrophysical Journal Letters 978, no. 2 (2025): L38. https://doi.org/10.3847/2041-8213/ada1cc.
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Abstract We present the first seconds-long 2D general relativistic neutrino magnetohydrodynamic simulations of accretion-induced collapse (AIC) in rapidly rotating, strongly magnetized white dwarfs (WDs), which might originate as remnants of double-WD mergers. This study examines extreme combinations of magnetic fields and rotation rates, motivated both by the need to address the limitations of 2D axisymmetric simulations and to explore the physics of AIC under rare conditions that, while yet to be observationally confirmed, may be consistent with current theoretical models and account for unusual events. Under these assumptions, our results demonstrate that, if realizable, such systems can generate relativistic jets and neutron-rich outflows with properties consistent with long gamma-ray bursts (LGRBs) accompanied by kilonovae, such as GRB 211211A and GRB 230307A. These findings highlight the potential role of AIC in heavy r-process element production and offer a framework for understanding rare LGRBs associated with kilonova emission. Longer-duration 3D simulations are needed to fully capture magnetic field amplification, resolve instabilities, and determine the fate of the energy retained by the magnetar at the end of the simulations.
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Orio, M., H. Ögelman, and S. Balman. "The ROSAT observations of classical novae." International Astronomical Union Colloquium 158 (1996): 289. http://dx.doi.org/10.1017/s0252921100038872.
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We observed a number of classical and recurrent novae in the Galaxy and the LMC with the ROSAT X-ray telescope and searched the archival data for other serendipitous observations. Preliminary results show that only 9 out of 37 observed objects were bright enough in X-rays to be detected with ROSAT, either in outburst or at quiescence.Three basic mechanisms can cause X-ray emission from classical or re-current novae. The first is hot hydrogen burning in a thin shell of the remnant envelope left on the white dwarf after the nova explosion. Hydrogen burning post-novae should be blackbody like emitters at nearly Eddington luminosity (as per the ‘supersoft’ X-ray sources). In our sample, only GQ Mus (Nova Mus 1983, see Ögelman et al. 1993; Shanley et al. 1995) and V1974 Cyg 1992 (Krautter et al. 1996) had these characteristics. Remarkably, among 10 LMC novae that had an outburst in the last 47 yr none was detected as a ‘supersoft’ X-ray source. The 3 σ upper limits for the black-body temperatures of the post-nova white dwarfs are mainly in the range 20… 30 eV. A post-nova can also emit X-rays because of shocks occurring in the ejected shell (e.g. O’Brien et al. 1994). Three out of four classical novae that were observed in outburst displayed a hard X-ray component in the ROSAT energy band, which might be due to a shocked shell. Finally, X-ray emission is expected from quiescent nearby novae because of accretion. Only four nearby accreting sources were detected; the ROSAT upper limits for the non-detected quiescent novae are Lx < 1031… 1032 ergs−1, assuming a thermal plasma at kT = a few keV.
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Sivaram, C. "Some constraints on quasar progenitors and quasar evolution." Symposium - International Astronomical Union 119 (1986): 417–18. http://dx.doi.org/10.1017/s0074180900153136.
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There is strong evidence that quasars are powered by the gravitational energy released by in fall of matter into a compact supermassive object which is most likely a black hole with mass M>106 to 109MO. The question then arises as to how such massive black holes came to be formed. What sort of objects were the progenitors? While looking for an answer we have to bear in mind another bit of intriguing evidence that even high Z quasars show lines of heavier elements (Oxygen, magnesium, etc) with solar abundances, strongly suggesting that matter had already undergone nuclear processing at even earlier epochs. Again even the oldest stars in our galaxy show evidence of metal content. All this suggests that atleast part of the metal content could have been generated by pregalactic supermassive stars, sometimes referred to as Pop.III objects. Such stars with masses ranging from 102–106 M⊙ could have formed in clusters consisting of about a few hundred or thousand of these objects at Z ⋍ 10. Now objects >106 M⊙ would have central temperatures not high enough for nuclear reactions the reason being a well known instability of general relativistic origin which is reached when GM/R⋍9c2/16 (M⊙/M)½; MO ⋍M⊙ giving rise to a maximum central temperature Tc reached at the instability, i.e. just before collapse. This is given by Tc = 2×1013/(M/MO) giving Tmax = 107K (necessary for CNO reactions) for M ⋍ 106M⊙ and for M> 106 M⊙, Tc is too low. It is believed that 10−5 of the primordial material might have been processed in Pop III objects which would have undergone nuclear reactions and evolved over some fraction of a Salpeter time, cσT/4πGmp ⋍ 108 yrs; (σT = Thompson cross section, mp is proton mass)., producing heavier elements in the process. It turns out that objects of mass M <300 M⊙ can explode and scatter the heavy elements. For instance a 116 M⊙ oxgen core of a 200MO object can completely disrupt and the evolution of such objects can explain anomalies like the O/Fe enrichment in metal poor stars and the G dwarf problem. Again there can be substantial mass loss from these superstars (a typical empirical relation like M ⋍ (tD/tKH)¼. L/GM/R (where tD is the dynamical time, and tKH is the Kelvin-Helmholtz scale, L is the luminosity) predicting · ≈ 10−3MO/yr) again leading to enrichment of the medium. Stars >300 MO do not explode but would collapse. The relaxation time scale for a cluster of these objects is again 5×108 to 109 yrs, so that they would all collapse to form a central black hole of M ∼ 108 −109 MO, the surrounding earlier ejected matter enriched in heavier elements being now accreted onto it. There would have been atleast a few times 108 of these black holes formed. Assuming near Eddington luminosity the rate of accretion given by ·(t) ⋍ 8πGM(t)/kc⋍16πG2M2(t)X ρ(t)V/c4, ρ(t) being a function of Z) would put a constraint on when Pop III stars formed and accreted enough matter to trigger quasar activity as quasars do not seem to be present before z = 4. This gives the result that they could not have formed before z ⋍8–10. Another possibility of forming a central black hole is by the collapse of a dense star cluster (consisting mainly of neutron stars or white dwarfs), the central relaxation time is tR∼VC3 / mc21n(0.4 Nc) ∼109yr. One obtains the result that for a core of compact stars to evolve to a relativistic state in a Hubble time it should have a minimal velocity dispersion given by Vc (min)⋍ 103(mc) (1-A/B) (7-3A/B)km/s, A, B are constants. This corresponds to clusters roughly having 107–109 compact stars and the gravitational collapse of such a cluster would then lead to black holes in the required mass range. An observed example is the central 3.5 pc core of NGC 4151 which has a mean stellar density of 2×108 M pc−3 corresponding to V ⋍ 103 km/s. As the central black hole grows the relative tidal force decreases and quasar activity can stop when the hole can no longer break up stars. (Tidal break up is also producing and scattering heavy elements.) For a central black hole accreting white dwarfs M <106MO and for it to break up neutron stars M <2 · 103MO. The break up of a neutron star by such a hole would give a burst of energy ∼1052ergs/sec which has so far not been recorded in any quasar or AGN, the upper limit to the luminosity being ∼1049 ergs/s. This may be indirect evidence that the mass of the central black hole is well above 104 MO in all cases. It is a pleasure to thank Professor Martin Rees for valuable discussions.
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Oskinova, Lidia M., Vasilii V. Gvaramadze, Götz Gräfener, Norbert Langer, and Helge Todt. "X-rays observations of a super-Chandrasekhar object reveal an ONe and a CO white dwarf merger product embedded in a putative SN Iax remnant." Astronomy & Astrophysics 644 (December 2020): L8. http://dx.doi.org/10.1051/0004-6361/202039232.
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The merger of two white dwarfs (WDs) is a natural outcome of the evolution of many binary stars. Recently, a WD merger product, IRAS 00500+6713, was identified. IRAS 00500+6713 consists of a central star embedded in a circular nebula. The analysis of the optical spectrum of the central star revealed that it is hot, hydrogen, and helium free, and it drives an extremely fast wind with a record breaking speed. The nebula is visible in infrared and in the [O III] λ5007 Å line images. No nebula spectroscopy was obtained prior to our observations. Here we report the first deep X-ray imaging spectroscopic observations of IRAS 00500+6713. Both the central star and the nebula are detected in X-rays, heralding the WD merger products as a new distinct type of strong X-ray sources. Low-resolution X-ray spectra reveal large neon, magnesium, silicon, and sulfur enrichment of the central star and the nebula. We conclude that IRAS 00500+6713 resulted from a merger of an ONe and a CO WD, which supports earlier suggestion for a super-Chandrasekhar mass of this object. X-ray analysis indicates that the merger was associated with an episode of carbon burning and possibly accompanied by an SN Iax. In X-rays, we observe the point source associated with the merger product while the surrounding diffuse nebula is a supernova remnant. IRAS 00500+6713 will likely terminate its evolution with another peculiar Type I supernova, where the final core collapse to a neutron star might be induced by electron captures.
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Guerrero, Martín A. "X-ray observations of central stars of planetary nebulae and their winds." Proceedings of the International Astronomical Union 7, S283 (2011): 204–10. http://dx.doi.org/10.1017/s1743921312010964.
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AbstractThe photospheric emission from the hottest central stars of planetary nebulae (CSPNe) is capable to extend into the X-ray domain, with emission peaking at 0.1-0.2 keV and vanishing above 0.4 keV. Unexpected, intriguing hard X-ray emission with energies greater than 0.5 keV has been reported for several CSPNe and for a number of white dwarfs (WDs). Different mechanisms may be responsible for the hard X-ray emission from CSPNe and WDs: coronal emission from a late-type companion, shocks in fast winds as in OB stars, leakage from underneath the star photosphere, or accretion of material from a disk, a companion star, or the circumstellar medium. Therefore, the hard X-ray emission associated with CSPNe may have significant implications for our understanding of the formation of PNe: binary companions, disks, and magnetic fields are thought to play a major role in the shaping of PNe, whereas clumping in the stellar wind may have notable effects in the PN evolution by modifying the stellar mechanical energy output. Here I present the results of different observational efforts to search for hard X-ray emission from CSPNe and discuss the different mechanisms for the production of hard X-rays.
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Zhang, Shu-Rui, Yan Luo, Xiao-Jun Wu, Jian-Min Wang, Luis C. Ho, and Ye-Fei Yuan. "Electromagnetic signatures of white dwarf collisions in AGN discs." Monthly Notices of the Royal Astronomical Society 524, no. 1 (2023): 940–51. http://dx.doi.org/10.1093/mnras/stad1855.
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ABSTRACT In the inner region of the disc of an active galactic nucleus (AGN), the collision of two white dwarfs (WDs) through Jacobi capture might be inevitable, leading to a Type Ia supernova (SN Ia) explosion. This transient event, influenced by the disc gas and the gravity of the supermassive black hole (SMBH), exhibits distinct characteristics compared with normal SNe Ia. The energy of the explosion is mainly stored in the ejecta in the form of kinetic energy. Typically, the ejecta is not decelerated effectively by the AGN disc and rushes rapidly out of the AGN disc. However, under the influence of the SMBH, most of the ejecta falls back toward the AGN disc. As the fallback ejecta becomes more dispersed, it interacts with the disc gas, converting its kinetic energy into thermal energy. This results in a high-energy transient characterized by a rapid initial rise followed by a decay with L∝t−2.8. The time-scale of the transient ranges from hours to weeks, depending on the mass of the SMBH. This process generates high-energy radiation spanning from hard X-rays to the soft γ range. Additionally, the subsequent damage to the disc may result in changing-look AGNs. Moreover, the falling back of SNe Ia ejecta on to the AGN disc significantly increases the metallicity of the AGN and can even generate heavy elements within AGN discs.
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Koyama, Katsuji, and Masayoshi Nobukawa. "Origin and Composition of the Galactic Diffuse X-Ray Emission Spectra by Unresolved X-Ray Sources." Astrophysical Journal 961, no. 2 (2024): 205. http://dx.doi.org/10.3847/1538-4357/ad0dff.
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Abstract Galactic diffuse X-ray emission (GDXE) can be spatially segmented into Galactic center X-ray emission (GCXE), Galactic ridge X-ray emission (GRXE), and Galactic bulge X-ray emission (GBXE). The X-ray spectra of GDXE are expressed by the assembly of compact X-ray sources, which are either white dwarfs (WDs) or X-ray active stars consisting of binaries with late-type stars. WDs have either a strong magnetic field or a weak magnetic field. WDs and X-ray active stars are collectively called compact X-ray stars. However, spectral fittings by the assembly of all compact X-ray stars for GCXE, GRXE, and GBXE are rejected, leaving significant excess near the energies of the Kα, Heα, and Lyα lines. These excesses are found in the collisional ionization equilibrium (CIE) plasma. Thus, the spectra of GRXE and GBXE are improved by adding CIE supernova remnants (SNRs). However, the GCXE spectrum is still unacceptable, with significant data excess due to radiative recombination emission (recombining plasma (RP)). The GCXE fit is then significantly improved by adding aged RP-SNRs. Aged RP-SNRs are made by a past big flare of Sgr A* emitting either hard X-rays or low-energy cosmic rays. The big flares may excite Fe and Ni atoms in cold diffuse gas (cold matter (CM)) and emit fluorescent X-ray lines. The CIE-SNRs, RP-SNRs, and CM are called diffuse X-ray sources. This paper presents the spectral fits by the assembly of all the compact and diffuse X-ray sources together with high-quality spectra and a combined fit among all the GDXE of GCXE, GRXE, and GBXE. This provides the first scenario to quantitatively and comprehensively predict the origin of the GDXE spectra.
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Carvalho, G. A., and S. Pilling. "X-ray photolysis of CH3COCH3 ice: implications for the radiation effects of compact objects towards astrophysical ices." Monthly Notices of the Royal Astronomical Society 498, no. 1 (2020): 689–701. http://dx.doi.org/10.1093/mnras/staa2501.
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ABSTRACT In this study, we employed broad-band X-rays (6–2000 eV) to irradiate the frozen acetone CH3COCH3, at the temperature of 12 K, with different photon fluences up to 2.7 × 1018 photons cm−2. Here, we consider acetone as a representative complex organic molecule (COM) present on interstellar ice grains. The experiments were conduced at the Brazilian Synchrotron facility (LNLS/CNPEN) employing infrared spectroscopy (FTIR) to monitor chemical changes induced by radiation in the ice sample. We determined the effective destruction cross-section of the acetone molecule and the effective formation cross-section for daughter species. Chemical equilibrium, obtained for fluence 2 × 1018 photons cm−2, and molecular abundances at this stage were determined, which also includes the estimates for the abundance of unknown molecules, produced but not detected, in the ice. Time-scales for ices, at hypothetical snow line distances, to reach chemical equilibrium around several compact and main-sequence X-ray sources are given. We estimate time-scales of 18 d, 3.6 and 1.8 months, 1.4 × 109–6 × 1011 yr, 600 and 1.2 × 107 yr, and 107 yr, for the Sun at 5 au, for O/B stars at 5 au, for white dwarfs at 1 LY, for the Crab pulsar at 2.25 LY, for Vela pulsar at 2.25 LY, and for Sagittarius A* at 3 LY, respectively. This study improves our current understanding about radiation effects on the chemistry of frozen material, in particular, focusing for the first time, the effects of X-rays produced by compact objects in their eventual surrounding ices.
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Thomas, H. C., and K. Beuermann. "Distribution and Space Density of Soft X-ray Emitting Polars in the Solar Neighbourhood." International Astronomical Union Colloquium 166 (1997): 247–50. http://dx.doi.org/10.1017/s0252921100071062.
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The ROSAT All Sky Survey (RASS) was the first one performed with an imaging telescope in the soft X-ray regime and has led to the discovery of numerous new objects whose emission is dominated by soft X-rays. Among these are white dwarfs and a subclass of the cataclysmic variables (CVs), the Polars or AM Herculis binaries. From a pre-ROSAT census of only 17, the number of known sources of this class has increased to some 55 (Beuermann and Thomas 1993, Beuermann 1997). Distances or lower limits to the distance are available for some 35 of these, based on the detection or non-detection of the TiO-Features in their optical red spectra. The derived distances range from below 100 pc up to ~ 600 pc, implying that many of these objects are located within the “Local Bubble” of low gas density in interstellar space. As the soft X-ray emission can be reasonably well represented by blackbody emission with a typical temperature of kTbb ≃ 25 eV, spectral fits to the ROSAT PSPC spectra from either the All-Sky-Survey (RASS) or from subsequent pointed ROSAT observations allow to determine the foreground absorption column density in the direction of the polars.
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Misra, D., T. Fragos, T. M. Tauris, E. Zapartas, and D. R. Aguilera-Dena. "The origin of pulsating ultra-luminous X-ray sources: Low- and intermediate-mass X-ray binaries containing neutron star accretors." Astronomy & Astrophysics 642 (October 2020): A174. http://dx.doi.org/10.1051/0004-6361/202038070.
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Context. Ultra-luminous X-ray sources (ULXs) are those X-ray sources located away from the centre of their host galaxy with luminosities exceeding the Eddington limit of a stellar-mass black hole (LX > 1039 erg s−1). Observed X-ray variability suggests that ULXs are X-ray binary systems. The discovery of X-ray pulsations in some of these objects (e.g. M82 X-2) suggests that a certain fraction of the ULX population may have a neutron star as the accretor. Aims. We present systematic modelling of low- and intermediate-mass X-ray binaries (LMXBs and IMXBs; donor-star mass range 0.92–8.0 M⊙ and neutron-star accretors) to explain the formation of this sub-population of ULXs. Methods. Using MESA, we explored the allowed initial parameter space of binary systems consisting of a neutron star and a low- or intermediate-mass donor star that could explain the observed properties of ULXs. These donors are transferring mass at super-Eddington rates while the accretion is limited locally in the accretion disc by the Eddington limit. Thus, our simulations take into account beaming effects and also include stellar rotation, tides, general angular momentum losses, and a detailed and self-consistent calculation of the mass-transfer rate. Results. Exploring the initial parameters that lead to the formation of neutron-star ULXs, we study the conditions that lead to dynamical stability of these systems, which depends strongly on the response of the donor star to mass loss. Using two values for the initial neutron star mass (1.3 M⊙ and 2.0 M⊙), we present two sets of mass-transfer calculation grids for comparison with observations of NS ULXs. We find that LMXBs/IMXBs can produce NS-ULXs with typical time-averaged isotropic-equivalent X-ray luminosities of between 1039 and 1041 erg s−1 on a timescale of up to ∼1.0 Myr for the lower luminosities. Finally, we estimate their likelihood of detection, the types of white-dwarf remnants left behind by the donors, and the total amount of mass accreted by the neutron stars. Conclusions. We show that observed super-Eddington luminosities can be achieved in LMXBs/IMXBs undergoing non-conservative mass transfer while assuming geometrical beaming. We also compare our results to the observed pulsating ULXs and infer their initial parameters. Our results suggest that a large subset of the observed pulsating ULX population can be explained by LMXBs/IMXBs in a super-Eddington mass-transfer phase.
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Doroshenko, V., A. Santangelo, V. F. Suleimanov, and S. S. Tsygankov. "An observational argument against accretion in magnetars." Astronomy & Astrophysics 643 (November 2020): A173. http://dx.doi.org/10.1051/0004-6361/202038948.
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The phenomenology of anomalous X-ray pulsars is usually interpreted within the paradigm of very highly magnetized neutron stars, also known as magnetars. According to this paradigm, the persistent emission of anomalous X-ray pulsars (AXPs) is powered by the decay of the magnetic field. However, an alternative scenario in which the persistent emission is explained through accretion is also discussed in literature. In particular, AXP 4U 0142+61 has been suggested to be either an accreting neutron star or a white dwarf. Here, we rule out this scenario based on the observed X-ray variability properties of the source. We directly compare the observed power spectra of 4U 0142+61 and of two other magnetars, 1RXS J170849.0−400910 and 1E 1841−045 with that of the X-ray pulsar 1A 0535+262, and of the intermediate polar GK Persei. In addition, we include a bright young radio pulsar PSR B1509-58 for comparison. We show that, unlike accreting sources, no aperiodic variability within the expected frequency range is observed in the power density spectrum of the magnetars and the radio pulsar. Considering that strong variability is an established feature of all accreting systems from young stellar objects to super-massive black holes and the absence of the variability reports from other magnetars, we conclude that our results also indicate that magnetars, in general, are not powered by accretion.
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Lobato, Ronaldo V., Jaziel G. Coelho, and M. Malheiro. "Ultra-high energy cosmic rays from white dwarf pulsars and the Hillas criterion." Journal of Physics: Conference Series 861 (June 2017): 012005. http://dx.doi.org/10.1088/1742-6596/861/1/012005.
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Armstrong, Isabella, Berkin Gurbuz, David Curtin, and Christopher D. Matzner. "Electromagnetic Signatures of Mirror Stars." Astrophysical Journal 965, no. 1 (2024): 42. http://dx.doi.org/10.3847/1538-4357/ad283c.
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Abstract Mirror stars are a generic prediction of dissipative dark matter (DM) models, including minimal atomic DM and twin baryons in the mirror twin Higgs model. Mirror stars can capture regular matter from the interstellar medium through extremely suppressed kinetic mixing interactions between the regular and the dark photon. This accumulated “nugget” will draw heat from the mirror star core and emit highly characteristic X-ray and optical signals. In this work, we devise a general parameterization of mirror star nugget properties that is independent of the unknown details of mirror star stellar physics, and use the Cloudy spectral synthesis code to obtain realistic and comprehensive predictions for the thermal emissions from optically thin mirror star nuggets. We find that mirror star nuggets populate an extremely well-defined and narrow region of the Hertzsprung–Russell diagram that only partially overlaps with the white dwarf population. Our detailed spectral predictions, which we make publicly available, allow us to demonstrate that optically thin nuggets can be clearly distinguished from white dwarf stars by their continuum spectrum shape, and from planetary nebulae and other optically thin standard sources by their highly exotic emission-line ratios. Our work will enable realistic mirror star telescope searches, which may reveal the detailed nature of DM.
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Šimon, Vojtech. "NON-THERMAL EMISSION FROM CATACLYSMIC VARIABLES: IMPLICATIONS ON ASTROPARTICLE PHYSICS." Acta Polytechnica 53, A (2013): 595–600. http://dx.doi.org/10.14311/ap.2013.53.0595.
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We review the lines of evidence that some cataclysmic variables (CVs) are the sources of non-thermal radiation. It was really observed in some dwarf novae in outburst, a novalike CV in the high state, an intermediate polar, polars, and classical novae (CNe) during outburst. The detection of this radiation suggests the presence of highly energetic particles in these CVs. The conditions for the observability of this emission depend on the state of activity, and the system parameters. We review the processes and conditions that lead to the production of this radiation in various spectral bands, from gamma-rays including TeV emission to radio. Synchrotron and cyclotron emissions suggest the presence of strong magnetic fields in CV. In some CVs, e.g. during some dwarf nova outbursts, the magnetic field generated in the accretion disk leads to the synchrotron jets radiating in radio. The propeller effect or a shock in the case of the magnetized white dwarf (WD) can lead to a strong acceleration of the particles that produce gamma-ray emission via pi0 decay; even Cherenkov radiation is possible. In addition, a gamma-ray production via pi0 decay was observed in the ejecta of an outburst of a symbiotic CN. Nuclear reactions during thermonuclear runaway in the outer layer of the WD undergoing CN outburst lead to the production of radioactive isotopes; their decay is the source of gamma-ray emission. The production of accelerated particles in CVs often has episodic character with a very small duty cycle; this makes their detection and establishing the relation of the behavior in various bands difficult.
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Klement, Robert, Thomas Rivinius, Douglas R. Gies, et al. "The CHARA Array Interferometric Program on the Multiplicity of Classical Be Stars: New Detections and Orbits of Stripped Subdwarf Companions." Astrophysical Journal 962, no. 1 (2024): 70. http://dx.doi.org/10.3847/1538-4357/ad13ec.
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Abstract Rapid rotation and nonradial pulsations enable Be stars to build decretion disks, where the characteristic line emission forms. A major but unconstrained fraction of Be stars owe their rapid rotation to mass and angular momentum transfer in a binary. The faint, stripped companions can be helium-burning subdwarf OB-type stars (sdOBs), white dwarfs (WDs), or neutron stars. We present optical/near-infrared Center for High Angular Resolution Astronomy (CHARA) interferometry of 37 Be stars selected for spectroscopic indications of low-mass companions. From multiepoch H- and/or K-band interferometry plus radial velocities and parallaxes collected elsewhere, we constructed 3D orbits and derived flux ratios and absolute dynamical masses of both components for six objects, quadrupling the number of anchor points for evolutionary models. In addition, a new wider companion was identified for the known Be + sdO binary 59 Cyg, while auxiliary Very Large Telescope Interferometer/GRAVITY spectrointerferometry confirmed circumstellar matter around the sdO companion to HR 2142. On the other hand, we failed to detect any companion to the six Be stars with γ Cas–like X-ray emission, with sdOB and main-sequence companions of the expected spectroscopic mass being ruled out for the X-ray-prototypical stars γ Cas and π Aqr, leaving elusive WDs as the most likely companions, as well as a likely explanation of the X-rays. No low-mass main-sequence close companions were identified for the other stars.
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Feigelson, Eric D. "Do neutron stars produce jets?" Canadian Journal of Physics 64, no. 4 (1986): 474–78. http://dx.doi.org/10.1139/p86-087.
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The evidence for jets emanating from neutron stars is reviewed. Isolated radio pulsars do not appear to produce collimated outflows. A few supernova remnants, notably the Crab nebula, exhibit jetlike protrusions at their outer boundaries. These are probably "blowouts" of the plasma in the remnant rather than true jets from a neutron star. However, several cases of degenerate stars in X-ray binary systems do make jets. SS433 has twin precessing jets moving outward at v ~ 0.26c, and Sco X-1 has radio lobes with v ~ 0.0001c. Cyg X-3 appears to eject synchrotron plasmoids at high velocities. Other X-ray binaries associated with variable radio sources are discussed; some are interesting candidates for collimated outflow. G109.1-1.0 is an X-ray binary in a supernova remnant that may have radio or X-ray jets. It is not clear in all these cases, however, that the compact object is a neutron star and not a black hole or white dwarf.A tentative conclusion is reached that isolated neutron stars do not produce jets, but degenerate stars in accreting binary systems can. This suggests that the presence of an accretion disk, rather than the characteristics of an isolated pulsar's dipole magnetosphere, is critical in making collimated outflows.