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Dissertations / Theses on the topic 'Gamma-ray blazars'
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McKenny, Joy Martina. "Observations of southern hemisphere gamma ray emitting blazars." Thesis, Durham University, 2003. http://etheses.dur.ac.uk/3695/.
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This thesis details observations of three Southern hemisphere blazars PKS 2155-304 PKS 2005-489 and PKS 0548-322 using the University of Durham Mark 6 Telescope between 1996 and 1999. The nature of blazars and the physical processes responsible for very high energy emission are also discussed. A signal above 700 GeV was observed from PKS 2155-304 between 1996 and 1997 but not in 1998 and 1999. One plausible explanation for this is a reduction in sensitivity of the Mark 6.Evidence for variability of high energy emission from PKS 2155-304 was search for but no firm conclusion was reached. Upper limits to emission from PKS 2005-489 and PKS 0548-322 were determined. Gamma ray observations for all three objects were tested for correlation with near simultaneous 2-10 keV X-ray emission (taken using the ASM onboard RXTE). No strong evidence for correlation was found. It is worth noting however that gamma ray emission from PKS 2155-304 was detected when the X-ray emission was greatest. No constraints could be made on models of gamma ray production from blazars. No models were excluded. Future observations with the new generation of gamma ray telescopes such as H.E.S.S. and CANGAROO will allow more detailed investigation of these objects and many others and their variability while multiwavelength observations will determine the nature of the acceleration processes at work.
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Harris, Jonathan Daniel. "Physics from the gamma-ray spectra of blazars." Thesis, Durham University, 2014. http://etheses.dur.ac.uk/11446/.
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Blazars are numerous and often bright sources of cosmic γ-rays with several hundred such objects currently detected in this regime. However, there are several outstanding issues surrounding them. For example, it is uncertain exactly where in the kiloparsec- scale blazar jet γ-rays are produced and what the physical mechanisms responsible for the emission are. This thesis is an investigation in the physics and astronomy that can be learnt from studying the γ-ray energy spectra of blazars. Two studies are presented analysing bright blazars with the Fermi-Large Area Telescope (LAT). From the smooth spectral curvature seen in many of the objects and the lack of sharp spectral breaks it is concluded that the emission region is likely beyond the radius of the broad line region of 0.1 pc. It is seen that nearby confusing objects can lead to apparent breaks being ob- served in the spectra. However, a light curve analysis is performed of the bright blazar 3C 454.3 and it is seen that spectral breaks do sometimes occur when the object is in high flux states. From the shift in the peak of the γ-ray emission it is concluded that the high flux states are caused by an increase in the Lorentz factor of the emission region or by changes in the population of electrons in the emission region, but the origin of the breaks remains unexplained. Finally, a study is presented examining the effect that hypothetical axions or axion-like particles (ALPs) would have on the spectra if these particles should exist. It is found that under the right conditions a sudden flux boost could appear in the spectrum at a few TeV. The chances of the future Cherenkov Telescope Array (CTA) detecting the effects of photon-ALP mixing in AGN spectra is considered through simu- lated observations. These effects potentially present themselves in the spectra two ways: firstly the aforementioned flux boost and secondly due to the fact that the existence of ALPs could mitigate the pair absorption that γ-rays undergo when they traverse inter- galactic space. It is concluded that CTA will have good prospects of either detecting these effects or else, if no effect is seen, setting limits on the mass and coupling constant that ALPs could have.
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Dickinson, Mark R. "Very high energy gamma ray observations of southern hemisphere blazars." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/4705/.
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This thesis is concerned with very high energy γ-ray observations of blazars observable from the southern hemisphere. The data presented were obtained using the recently deployed University of Durham Mark 6 high sensitivity Čerenkov telescope. Chapters 1 and 2 are introductory; the subjects of γ-ray astronomy, extensive air showers, Čerenkov light production, the development of the atmospheric Čerenkov technique and the current status of TeV astronomy are discussed. Chapter 3 introduces the telescopes operated by the University of Durham. The Mark 6 telescope, designed to have a low threshold energy and a high resolution imaging system, is discussed in detail. Chapter 4 presents the calibration and analysis techniques routinely applied to data obtained with the Mark 6 telescope. The chapter concludes with a set of moment parameter selections designed to reject a significant fraction of the cosmic ray cascades, while retaining the majority of γ-rays cascades. These selections have resulted in a 5σ detection of PSR 1706-44. Chapter 5 discusses active galactic nuclei and in particular blazars. Topics included are recent high energy observations; the differences between the radio/X-ray selected BL Lacs and flat spectrum radio quasars; the infrared background; high energy flux variability and γ-ray production mechanisms within these objects. The chapter concludes with a list of possible very high energy γ-ray emitting blazars observable with the Mark 6 Čerenkov telescope. Chapter 6 presents the results from four of these very high-energy γ-ray blazar candidates; PKS 0548-322, PKS 1514-24, PKS 2005-489 and PKS 2155-304. There is no evidence for γ-ray emission from these sources, either in the form of a steady flux or variable activity. Three sigma integral flux upper limits above 300 GeV are produced for these objects and the implications of these observations are discussed. The conclusions are presented in Chapter 7 as well as ideas for future work.
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Healey, Stephen Edward. "Multiwavelength studies of gamma-ray blazars over the entire sky /." May be available electronically:, 2009. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Bastin, Fane Troy. "A multiwavelength investigation of blazar-type active galactic nuclei." Thesis, University of Canterbury. Department of Physics and Astronomy, 2013. http://hdl.handle.net/10092/11302.
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A multiwavelength investigation is conducted for nineteen blazar-type active galactic nuclei. Studies of variability timescales and flux duty cycles are performed at x- and gamma-rays for each source, with the relationship between flux and spectral index also being probed at gamma wavelengths. The correlation between these two energy ranges is also investigated, by utilising the Discrete Correlation Function with both one and ten day binning. The sources were chosen for their availability over a range of different x- and gamma-ray data sources: observations utilised include 0.2 - 150 keV x-ray data from the Swift mission and 200 MeV- 300 GeV gamma-ray data from the Fermi mission.
Daily-binned Fermi data is used to calculate the smallest rise and decay e-folding times in gamma for each source. The results range from 0.4 to 21 days, corresponding to limits on the size of the gamma emission region ranging from Rd^-1 = 4.39 x 10^12 to Rd^-1 = 5.14 x 10^14 m.
Flux duty cycles for fourteen sources are created from Fermi data, with six displaying structure at high fluxes that indicate flaring states have occured. Five of these six sources also display clear flares in their light curves, confirming these results. The relationship between the flux and the spectral index shows eight of nineteen sources exhibit harder-when-brighter behaviour. Four of these eight have been previously confirmed to display such behaviour.
Results from the Discrete Correlation Function show a correlation at a time lag of ~ 600 days for H 1426+428, of uncertain origin. Gaussian functions are fitted to possible near-zero peaks in 3C 66A, 3C 454.3 and Mrk 421, which could be indicative of a synchrotron self-Compton component to the emission of these objects.
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Calle, PeÌrez Ignacio de la. "Detection of high energy gamma rays from X-ray selected blazars." Thesis, University of Leeds, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270857.
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Nandikotkur, Giridhar. "Tracking spectral changes in blazars with the energetic gamma ray experiment telescope (EGRET)." College Park, Md.: University of Maryland, 2007. http://hdl.handle.net/1903/7747.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.<br>Thesis research directed by: Dept. of Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Roustazadeh, Sheikhyousefi Parisa. "Pair Cascades in Blazars and Radio Galaxies." Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1327333900.
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Wagner, Robert Marcus. "Measurement of very high energy gamma-ray emission from four blazars using the MAGIC telescope and a comparative blazar study." [S.l.] : [s.n.], 2006. http://mediatum2.ub.tum.de/doc/604099/document.pdf.
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Wagner, Robert M. "Very High Blazar Astrophysics : Measurement of Very High Energy Gamma-Ray Emission from Four Blazars Using the MAGIC Telescope and a Comparative Blazar Study /." Fischbachtal, Odenw : HARLAND media, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=3001678&prov=M&dok_var=1&dok_ext=htm.
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Grube, Jeffrey. "X-ray and Gamma-ray Study of TeV Blazars with RXTE, XMM-Newton, and the Whipple 10 m Telescope." Thesis, University of Leeds, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485170.
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This thesis presents long-tenn X-ray and TeV y-ray observations from 2000 to 2006 of three TeV blazar type Active Galactic Nuclei (AGN): Mrk 421, Mrk 501, and H1426i428. Standard emission models for TeV blazars predict correlated and highly variable X-ray and TeV y-ray radiation from accelerated electrons in a jet orientated along our line of sight By using a large sample . of near simultaneous observations, this thesis examines potential flux and spectral correlations between the X-ray and TeV y-ray energy bands. Joint nightly observations ofMrk 421 with the X-ray instrument RXTEPCA, and at 0.5-10 TeV y-ray energies with the Whipple 10 m telescope during periods ranging from a week to 6 months revealed complicated, high amplitude flaring. Spectral variability was investigated for the rising and decay phases of large isolated day timescale flares. Generally, the X-ray and TeV y-ray spectra hardened with increasing integral flux, but a consistent spectral evolution was not shown between individual flares. Absorption of the TeV y-ray energy spectrum by the extragalactic background light (EBL) was corrected for. During a large flare in \. March 2001; tentative evidence was found for a highly curved intrinsic TeV y-ray energy spectrum peaking at 0.85 ± 0.22 TeV simultaneous to a curved X-ray spectruI)1 peaking at 2.14 ± 0.19 keY. RXTEPCA and Whipple io m campaigns on Mrk 501 and H1426i428 showed significant X-ray spectral variability, however the TeV y-ray integral flux remained near the detection limit of the Whipple 10 m. The broadband 0.6-20 keY X-ray spectrum of the 3 TeV blazars was investigated with XMM-Newton and RXTE peA observations. In addition to simultaneous day timescale variability, the large sample of Whipple 10 m observations from 2000 to 2006 allowed for a detailed study of long-tenn y-ray variability. For Mrk 421, a weak correlation, with large spread is shown for the Whipple 10 m integral flux above 0.6 TeV and RXTEASM X-ray rate on month timescales. From 2001 to 2006, Mrk 501 was recorded by the Whipple 10 m in a low flux state of 27% of the integral flux from the Crab nebula supernova remnant. In July 2005, the MAGIC telescope recorded large TeV y-ray flaring in Mrk 501 by a factor> 3 of the Crab nebula flux. This high flux state occured after the Whipple 10 m observing period on Mrk 501 in June 2005, and so could not be verified in this work. The detection of H1426-t428 at TeV y-ray energies by the Whipple 10 m in 2001 is confirmed in this work, however the source was not detected again by the Whipple 10 m over a 5 year period. The detailed study ofTeV blazar X-ray and y-ray variability in this work highlights the need for high sensitivity observations to better resolve complicated and unpredictable flaring states.
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Rani, Bindu [Verfasser], Anton J. [Akademischer Betreuer] Zensus, and Andreas [Akademischer Betreuer] Eckart. "Broad-band study of selected Gamma-ray active blazars / Bindu Rani. Gutachter: Anton J. Zensus ; Andreas Eckart." Köln : Universitäts- und Stadtbibliothek Köln, 2014. http://d-nb.info/1047666480/34.
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Palma, Cruz Norman I. "Multiwavelength Analysis of the Gamma-Ray Blazar PKS 0528+134 in Quiescence." Ohio University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1289321486.
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Valverde, Quispe Janeth Veronica. "New insights on the nature of blazars from a decade of multi-wavelength observations : Discovery of a very large shift of the synchrotron peak frequency, long-term optical-gamma-ray flux correlations, and rising flux trend in the BL Lac 1ES 1215+303." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX013.
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Les blazars sont connus pour leur variabilité sur une large gamme d'échelles de temps à toutes les longueurs d'onde; et leur classification (en quasars radio à spectre plat, BL Lac à basse fréquence crête, intermédiaire ou haute fréquence; FSRQ, LBL, IBL, HBL, pour ses sigles en anglais) est basée sur des caractéristiques spectrales à large bande qui ne considèrent pas la source comme étant, éventuellement, dans différentes états d'activité. Récemment, il a été proposé de classer les blazars en fonction de la cinématique de leurs caractéristiques radio. La plupart des études sur les blazars à rayons gamma TeV se concentrent sur des échelles de temps courtes, en particulier pendant les éruptions, en raison de la rareté des campagnes d'observation ou de l'existence relativement récente de détecteurs spécialisés suffisamment sensibles.Avec une décennie d'observations du Fermi-LAT, VERITAS, Je présente une étude approfondie de la variabilité à long terme multi longueurs d'onde du blazar 1ES 1215+303, des rayons gamma à la radio. Cet ensemble de données sans précédent révèle de multiples éruptions de rayons gamma fortes et une augmentation à long terme de la ligne de base des rayons gamma et du flux optique de la source sur une période de dix ans, ce qui se traduit par une corrélation linéaire entre ces deux bandes d'énergie sur une décennie. Des comportements HBL typiques sont identifiés dans la morphologie radio de la source. Cependant, des analyses de la distribution d'énergie spectrale à large bande à différents états de flux de la source, révèlent un déplacement extrême de l'énergie de la fréquence de crête du synchrotron de l'IR aux rayons X mous; indiquant que la source présente les caractéristiques IBL pendant les états de repos et le comportement HBL pendant les états éruptifs. Un modèle synchrotron self-Compton à deux composantes est utilisé pour décrire ce changement spectaculaire.Un cadre détaillé de l'analyse des données de l'instrument Fermi-LAT est fourni et pourrait servir de guide aux chercheurs intéressés par ce domaine. Je présente les efforts approfondis de validation des méthodes utilisées et les contrôles d'intégrité des résultats effectués. Une description des analyses de niveau supérieur est fournie, comme la sélection des éruptions et la recherche d'un comportement plus dur quand plus lumineux dans les données de Fermi-LAT, l'analyse de corrélation croisée et de variabilité à plusieurs longueurs d'onde; la recherche de tendances, log-normalité et variabilité, la caractérisation des éruptions et des distributions spectrales d'énergie, et la recherche d'observations Fermi-LAT - VERITAS simultanées. Ce sont le cœur de ce travail de doctorat.Les différentes méthodes appliquées et présentées dans ce travail fournissent un panorama complet et détaillé de la nature complexe de ce blazar et peuvent même remettre en question notre système de classification actuel. De plus, ce travail fournit une illustration du type d'analyses à long terme que les futurs instruments d'imagerie atmosphérique, tels que le Cherenkov Telescope Array, non seulement permettront mais pourrait même d'améliorer<br>Blazars are known for their variability on a wide range of timescales at all wavelengths; and their classification (into flat spectrum radio quasars, low-, intermediate- or high-frequency-peaked BL Lac; FSRQ, LBL, IBL, HBL) is based on broadband spectral characteristics that do not consider the source being at, possibly, different states of activity. Recently, it was proposed that blazars could be classified according to the kinematics of their radio features. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares, due to the scarcity of observational campaigns or due to the relatively young existence of specialized, sensitive enough detectors.With a decade of observations from the Fermi-LAT and VERITAS, I present an extensive study of the long-term multi-wavelength variability of the blazar 1ES 1215+303 from gamma-rays to radio. This unprecedented data set reveals multiple strong gamma-ray flares and a long-term increase in the gamma-ray and optical flux baseline of the source over the ten-year period, which results in a linear correlation between these two energy bands over a decade. Typical HBL behaviors are identified in the radio morphology of the source. However, analyses of the broadband spectral energy distribution at different flux states of the source, unveil an extreme shift in energy of the synchrotron peak frequency from IR to soft X-rays; indicating that the source exhibits IBL characteristics during quiescent states and HBL behavior during high states. A two-component synchrotron self-Compton model is used to describe this dramatic change.A detailed framework of the analysis of the data from the Fermi-LAT instrument is provided, and could serve as a guideline for researchers interested in this field. I present the thorough efforts that were employed in validating the methods used and the sanity checks that were performed on the results obtained. A description of the higher-level analyses are provided, including the flare-selection algorithms, the search for harder-when-brighter behavior in the Fermi-LAT data, the multi-wavelength cross-correlation and variability analysis, the search for trends, log-normality and variability, the characterization of flares and of the spectral energy distributions, and the search for simultaneousFermi-LAT - VERITAS observations. These are the heart of this PhD work.The different methods applied and presented in this work provide a complete and detailed panorama of the intricate nature of this blazar, and possibly even challenge our current classification scheme. Moreover, this work provides an illustration of the type of long-term analyses that future imaging atmospheric instruments, such as the Cherenkov Telescope Array, will not only allow but potentially improve
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Minutilli, Loreta. "Fermi blazars as candidate neutrino emitters: a study of temporal coincidence with IceCube events." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/22554/.
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Multimessenger astronomy provides a unique tool for exploring the universe at the highest energies: the association between neutrinos and their astrophysical sources would constitute a powerful probe of the high-energy sky.
In 2017, the neutrino event IceCube-170922A was found to be coincident in arrival time and direction with an enhanced γ-ray activity from the blazar TXS 0506+056 at redshift z ∼ 0.34, and it was associated to this source at the 3σ confidence level. This discovery motivates further research in the field of the blazar-neutrino connection.
In this work, the temporal coincidence between the arrival times of IceCube
neutrinos and the γ-ray (0.1 − 300 GeV) emission from a sample of Fermi-detected blazars is investigated. The spatial coincidence for the same sample had been investigated in a previous reference work.
Different criteria for the definition of the flaring state of a source were adopted depending on the blazar class (HBL/IBL or LBL) and a subsample of 4 flare-neutrino coincident blazars was selected.
A statistical test was performed on each class separately in order to assess the nature of the observed coincidences. An interesting excess was found for the class of HBLs/IBLs while no excess was observed for the LBLs.
I discussed the implications of these results for the blazar neutrino connection and the future perspectives for this work.
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Giomi, Matteo. "A catalog of variable high-energy gamma-ray sources and prospects for polarization measurement with the Fermi Large Area Telescope." Doctoral thesis, Humboldt-Universität zu Berlin, 2017. http://dx.doi.org/10.18452/18596.
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Das Fermi Large Area Telescope (LAT) ist ein satellitengestütztes Gammastrahlungs-Teleskop zur Messung von Gammastrahlung im Energiebereich zwischen ∼ 30 MeV und mehreren hundert GeV. Der Nachweis extraterrestrischer Gammastrahlung in diesem Energiebereich erlaubt Rückschlüsse auf die astrophysikalischen Quellen der Gammastrahlung und Beschleunigungsmechanismen kosmischer Strahlung mit Energien zwischen 1 GeV und ∼ 10 TeV. Die Beobachtung von Quellen während Phasen vorübergehend erhöhter Gammastrahlungslüsse (‘Flares’) ermöglicht dabei eine besonders empfindliche Untersuchung der Produktionsmechanismen kosmischer Strahlung in den Quellen, da die Eigenschaften kürzlich beschleunigter Teilchen unmittelbar studiert werden können.
Der Hauptteil dieser Dissertation stellt das neueste Verzeichnis zeitlich variabler Gammastrahlungsquellen über 100 MeV vor, den zweiten ‘Fermi All-sky Variability Analysis’ Katalog (2FAV). Der 2FAV Katalog enthält über 4500 Flares, welche in den ersten 7.4 Jahren der LAT Datennahme auf einem hohen Vertrauensniveau gemessen und an 518 verschiedenen Himmelspositionen beobachtet wurden. 441 dieser Quellpositionen im 2FAV können Aktiven Galaktischen Kernen (AGN) zugeordnet werden. Die verbleibenden 77 Quellpositionen besitzen keine sichere Entsprechung in anderen Verzeichnissen von Gammastrahlungs- oder Blazarquellen und stellen möglicherweise neue Gammastrahlungsquellen dar. Bei der Untersuchung der Spektren der 2FAV Flares, welche sogenannten ‘Flat-Spectrum’ Radioquasaren (FSRQ) - eine Unterklasse der AGN - zugeordnet werden können, wurde durchweg ein härteres Gammastrahlungsspektrum während Phasen erhöhter Gammastrahlungsemission beobachtet. Zudem wurde eine Untergrenze in der Verteilung der spektralen Exponenten, Γ ≳ 1.5, in der Stichprobe der untersuchten Flares festgestellt. Unter der Annahme eines einfachen leptonischen Modells und dass die Verteilung beschleunigter Teilchen im Inertialsystem der Quelle isotrop ist, folgt daraus, dass die Energiespektren der kosmischen Strahlung, welche die Gammastrahlungs-Flares verursachen, mit dN/dE ∝ E −2 oder stärker abfallen.
Eine andere Möglichkeit, die Beschleunigungsmechanismen kosmischer Strahlung zu untersuchen, ist die Messung der Polarisation der begleitenden Gammastrahlung. Der letzte Teil dieser Dissertation enthält eine vorläufige Studie zur Messbarkeit linearer Polarisation astrophysikalischer Gammastrahlung mit dem LAT-Instrument. Bei Konversion hochenergetischer Photonen in Elektron-Positron-Paare verursacht eine lineare Polarisation der Gammastrahlung eine Modulation des Azimutwinkels der Ebenen, in denen die Elektron-Positron-Paare erzeugt wurden. Obwohl der LAT ursprünglich nicht als Polarimeter konzipiert wurde, ermöglicht das Instrument eine Messung dieser Modulation für niederenergetische Primärteilchen (≲ 200 MeV), welche in den Silikonschichten des Detektors konvertieren. Eine Auswahl solcher Ereignisse, selektiert durch Algorithmen überwachten maschinelles Lernens (‘supervised machine learning’), wird verwendet um die statistischen und systematischen Messunsicherheiten abzuschätzen, denen eine Messung unterworfen ist. Werden allein statistische Unsicherheiten berücksichtigt, ist der LAT in der Lage, einen Polarisationsgrad von 30−50% der Gammastrahlungsflüsse vom Vela-Pulsar und vom Krebs-Pulsarwindnebels nach einer Beobachtungszeit von zehn Jahren auf einem Vertrauensniveau von 5σ nachzuweisen. Werden zusätzlich systematische Unsicherheiten berücksichtigt, wird abgeschätzt, dass ein Polarisationsgrad von ∼ 46% auf einem Vertrauensniveau von 5σ nachweisbar ist, indem eine Auswahl von AGN als unpolarisierte Testprobe verwendet und mit umfangreichen Monte-Carlo Simulationen verglichen wird. Die Analyse in dieser Dissertation berücksichtigt zum ersten Mal sämtliche Aspekte einer polarization-sensitiven Ereignissrekonstruktion und dienst damit als Grundlage für zukünftige Nachweisversuche der Polarisation astrophysikalischer Gammastrahlung mit dem LAT.<br>The Fermi Large Area Telescope (LAT) is a space-based pair-conversion telescope sensitive to gamma rays with energies from ∼ 30 MeV to several hundreds of GeV. Observing gamma rays in this energy range, we gain information on the sources and acceleration mechanisms of cosmic rays (CRs) of energies from ∼ 1 GeV to ∼ 10 TeV. Studying the emission of gamma-ray sources during periods of enhanced activity (flares) provides a sensitive probe of the production mechanisms of CRs, as it makes it possible to investigate the distributions of the freshly-accelerated particles.
The main part of this work presents the latest catalog of variable gamma-ray sources above 100 MeV, the second Fermi All-sky Variability Analysis catalog (2FAV). The 2FAV catalog contains more than 4500 flares detected at high significance in the first 7.4 years of LAT observations and the 518 sources from which these flares originate. Probable counterparts, mostly active galactic nuclei (AGN), have been found for 441 sources in the 2FAV. The remaining 77 sources have no reliable counterparts in other gamma-ray or blazar catalogs; they are potentially new gamma-ray sources. Studying the spectra of the 2FAV flares, we observe a harder-when-brighter behavior for the entire sample of flares associated with lat spectrum radio quasars, a class of AGN. We also observe a minimum value in the distribution of the photon index Γ of the flares, corresponding to Γ ≳ 1.5. In a simple leptonic scenario, assuming that the distribution of accelerated particles is isotropic in the source reference frame, this limit on the spectral hardness implies that the spectra of the accelerated particles responsible for the lare is never harder than dN/dE ∝ E −2.
Another way to probe the environments where CRs are accelerated is by measuring the polarization of the gamma rays. A preliminary study of the LAT sensitivity to linear polarization of astrophysical gamma-rays is presented in the last part of this thesis. In the pair-production regime, linear polarization of the gamma-rays induces a modulation in the azimuthal angle of the planes where the electron-positron pairs are produced. Although not designed as a polarimeter, the LAT has the potential to measure this modulation using low energy (≲ 200 MeV) events converting in the silicon detector layers of its tracker. A selection of these events using supervised machine learning algorithms is presented and used as a basis to estimate the statistical and systematic uncertainties afecting the measurement. Considering only statistical uncertainties, a degree of polarization of ∼ 30−50% could be detected at the 5σ confidence level for the Vela pulsar and the Crab pulsar-wind nebula after 10 years of observation. By including systematic uncertainties, a 5σ sensitivity limit corresponding to a polarization degree of ∼ 46% is estimated, using a stack of AGN as an unpolarized test source and comparing the data with detailed Monte Carlo simulations. This analysis addresses for the first time all the steps of a real measurement and can therefore provide the basis for future measurements of gamma-ray polarization with the LAT.
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Organokov, Mukharbek. "ANTARES search for high-energy neutrinos from TeV-emitting blazars, Markarian 421 and 501, in coïncidence with HAWC gamma-ray tiares." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAE039.
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Les neutrinos sont des messagers uniques pour détecter les phénomènes violents de l’Univers. Les sources potentielles de neutrinos cosmiques sont, par exemple, les Noyaux Actifs de Galaxie (NAGs), ou les sursauts gammas. Dans le cas d’un accélérateur astrophysique de rayons cosmiques hadroniques, la production de neutrinos s’accompagne éventuellement d’émissions gammas de haute énergie. La recherche des coïncidences entre des neutrinos de haute énergie détectés avec le télescope à neutrinos ANTARES et des photons gamma captés par l’observatoire HAWC est présentée. La recherche dans une fenêtre temporelle particulière réduit le bruit de fond de manière significative dans les données du télescope à neutrinos et augmente donc le potentiel de découverte. Dans cette thèse, les résultats de la recherche de neutrinos détectés en corrélation avec un signal gamma en provenance de 2 NAG particulier, Markarian 421 et Markarian 501, sont présentés. En tant que blazars les plus proches de la Terre, ils constituent d’excellentes sources pour tester le scénario de connexion blazar-neutrinos, en particulier lors de leurs "bouffées" d’activités (flares) pour lesquelles la recherche de neutrinos en fonction du temps peut présenter une probabilité de détection plus élevée<br>Neutrinos are unique messengers for detecting violent phenomena in the Universe. Potential sources of cosmic neutrinos are, for example, Active Galactic Nuclei (AGNs) or Gamma-Ray Bursts (GRBs). In the case of hadronic cosmic rays acceleration, the production of neutrinos is possibly accompanied by high-energy gamma-ray emissions. The search for coincidences between high-energy neutrinos detected by the ANTARES neutrino telescope and gamma-rays detected by the HAWC gamma-ray observatory is presented. Searching in a particular time window significantly reduces the background noise in the neutrino data and thus increases the discovery potential. In this thesis, the results of a search for neutrinos detected in correlation with a gamma-ray signal from two particular AGNs, Markarian 421 and Markarian 501, are presented. As the blazars closest to Earth, they are excellent sources for testing the blazar-neutrino connection scenario, especially during the increase of their activities (flares) in which the search for neutrinos may have a higher detection probability
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Valtonen-Mattila, Nora. "High Energy gamma-ray behavior of a potential astrophysical neutrino source : The case of TXS 0506+056." Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-90569.
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Blazars are a type of Active Galaxy that emit strong astrophysical jets. The association of a HE gamma-ray flare from the blazar TXS 0506+056 to the IceCube-170922A neutrino event in 2017, opened the possibility to a link between these two events. In this thesis, we will look at the HE gamma-ray behavior of TXS 0506+056 using data obtained from the Fermi-LAT by taking into account the other set of neutrino events associated with this source from 2014-2015. We will investigate whether both neutrino events present with comparable HE gamma-ray behavior by analyzing the lightcurves and the spectra for a quiet state, the 2014-2015 period, and the flare centered around the neutrino event from 2017. The results of the analysis performed in this thesis show no strong indication of a change in the gamma-ray behaviour in these potential neutrino detections.
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D'Antonio, Daniele. "A wide frequency study of the spectral properties of cores and lobes of radio galaxies." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14083/.
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Low-frequency radio arrays are opening a new window for the study of the sky, to characterise both new phenomena and already known classes of sources. In our work, we characterise the spectral properties of the blazar population at low radio frequency, compare the radio and high energy properties of the gamma-ray blazar population, and search for radio counterparts of the unidentified gamma-ray sources.
In a previous work (Giroletti et al. 2016), the 6100 square degrees Murchison Widefield Array Commissioning Survey catalogue (MWACS) was cross-correlated with the third catalogue of gamma-ray active galactic nuclei detected by Fermi (3LAC). In this Thesis, we cross-correlate the 24831 square degrees Galactic and Extragalactic All-sky MWA (GLEAM) with the same Fermi catalogue. By comparison to MWACS, GLEAM does not only have a larger sky area, but also a better
sensitivity and a wider spectral coverage. The fraction of gamma-ray blazars detected in GLEAM grows to 78%, compared to 35% found in MWACS.
Thanks to the spectral coverage of GLEAM and of other existing radio surveys, we studied the blazar spectral properties at low (~200MHz), mid (~1GHz), and high frequency (20GHz with the Australia Telescope 20GHz, AT20G). Compact cores and extended lobes have different spectral properties: at low frequency we can study the extended emission, while at high frequency we can study the core. Therefore, determining blazar spectra in different frequency regimes helps us to disentangle the different contributions of the two components, and provide a proxy for the core dominance. The core dominance of an object is a test for the Unified Model for AGN. Also, it is possible to observe the core emission, using an optimal angular resolution. So we used the FIRST survey, with an angular resolution of 5 arcsec. Therefore we estimated the core dominance.
Moreover, we created a simulation of 20000 radio sources to verify our results.
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Couturier, Camille. "Invariance de Lorentz et Gravité Quantique : contraintes avec des sources extragalactiques variables observées par H.E.S.S. et Fermi-LAT." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066555/document.
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Des modèles de Gravité Quantique (QG) prédisent une violation de l'invariance de Lorentz (LIV), se manifestant par une dispersion de la lumière dans le vide. Si un tel effet existe, des photons d'énergies différentes émis en même temps par une source distante sont détectés sur Terre à des moments différents. Les émissions transitoires à (très) hautes énergies provenant de sources astrophysiques lointaines, comme les sursauts gamma (GRBs) et les blazars sont utilisées pour contraindre cet effet LIV. Cet ouvrage présente les études menées avec deux télescopes gamma majeurs : H.E.S.S. -- pour lequel une étude de la qualité des données étalonnées a été réalisée -- et Fermi-LAT. Les énergies et les temps d'arrivée de photons individuels ont été utilisés pour contraindre le paramètre de dispersion dans le vide ainsi que l'échelle d'énergie E_QG à laquelle des effets LIV peuvent apparaitre. La méthode de maximum de vraisemblance est décrite, avec une étude détaillée des systématiques. Une modification dans le cas de fond non négligeable est appliquée aux données de l'éruption d'un blazar observé par H.E.S.S. : les limites obtenues sur E_QG sont moins contraignantes que les meilleures limites précédentes, mais elles se trouvent à un redshift non couvert à ce jour. Quatre GRBs observés par Fermi-LAT ont aussi été analysés, en déterminant la courbe de lumière de deux manières : ajustements gaussiens et estimation par densité de noyaux. Les meilleures limites sur E_QG pour le cas linéaire/subluminal sont obtenus avec GRB090510 : E_QG,1 > 7,6 E_Planck. Des limites plus robustes, tenant compte des effets intrinsèques à la source, ont également été produites<br>Some Quantum Gravity (QG) theories allow for a violation of Lorentz invariance (LIV), manifesting as a dependence on the velocity of light in vacuum on its energy. If such a dependence exists, then photons of different energies emitted together by a distant source will arrive at the Earth at different times. (Very) high energy transient emissions from distant astrophysical sources such as Gamma-ray Bursts (GRBs) and blazars can be used to search for and constrain LIV. This work presents the studies obtained with two leading Gamma-ray telescopes: H.E.S.S. -- for which a study of the quality of the calibrated data was performed -- and Fermi-LAT. The energies and arrival times of individual photons were used to constrain the vacuum dispersion parameter and the energy scale EQG at which QG effects causing LIV may arise. The maximum likelihood method is described, with detailed studies of the systematics. A modification for a non-negligible background is provided and applied to the data of an AGN flare observed by H.E.S.S.: the obtained limits on the QG energy scale are less constraining than the previous best limits obtained with blazars; yet, the new limits lie a redshift range not covered this far. Four bright and quasi background-free GRBs observed by the Fermi-LAT were also analysed, with two different template light curve determinations -- Gaussian fits and Kernel Density Estimates. The best limits on the E_QG scale for the linear/subluminal case are from the shortest burst, GRB090510: E_QG,1 > 7.6 E_Planck. More robust limits, considering the intrinsic effects possibly occurring at the source, were also derived
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Uellenbeck, Malwina [Verfasser], Wolfgang [Akademischer Betreuer] Rhode, and Carsten [Gutachter] Westphal. "Study of extragalactic very high energy gamma ray sources : Monitoring and discoveries of blazars with the MAGIC telescopes / Malwina Uellenbeck. Betreuer: Wolfgang Rhode. Gutachter: Carsten Westphal." Dortmund : Universitätsbibliothek Dortmund, 2013. http://d-nb.info/1106333381/34.
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Escande, Lise. "Variabilité des blazars détectés par le télescope spatial Fermi-LAT : étude de 3C 454.3 et développement d’une méthode de génération de courbes de lumière optimisées." Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14565/document.
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Dédié à l'étude du ciel en rayons gamma, le satellite Fermi comporte à son bord le Large Area Telescope (LAT), sensible au rayonnement gamma de 20 MeV à 300 GeV. Les données recueillies par le LAT depuis son lancement en 2008 ont permis de multiplier par 10 le nombre de noyaux actifs de galaxie (NAG) détectés dans le domaine du GeV. Les rayons gamma observés dans les NAGs proviennent de processus énergétiques faisant intervenir des particules chargées de très haute énergie. Ces particules sont confinées dans un jet de plasma magnétisé qui prend sa source dans une région proche du trou noir supermassif habitant la zone centrale de la galaxie hôte. Ce jet s’éloigne à des vitesses aussi élevées que 0.9999c, formant dans de nombreux cas des lobes radio sur des échelles du kiloparsec voire du mégaparsec. Les NAGs dont le jet fait un angle faible avec la ligne de visée sont appelés blazars. La combinaison de cette très faible inclinaison du jet par rapport à la ligne de visée et de vitesses d’éjection relativistes donne lieu à des effets relativistes : mouvements apparents superluminiques, amplification de la luminosité et modification des échelles de temps. Les blazars sont caractérisés par une extrême variabilité à toutes les longueurs d’onde, sur des échelles de temps allant de quelques minutes à plusieurs mois. Une étude temporelle et spectrale du plus brillant d'entre ceux détectés par le LAT, 3C 454.3, a été réalisée afin de contraindre les modèles d'émission. Une nouvelle méthode de génération de courbes de lumière à échantillonnage adaptatif est également proposée dans cette thèse. Celle-ci permet d'extraire le maximum d'information des données du LAT quel que soit l'état de flux de la source<br>The Fermi Gamma-ray Space Telescope was launched on 2008 June 11, carrying the Large Area Telescope(LAT), sensitive to gamma-rays in the 20 MeV – 300 GeV energy range. The data collected since then allowed to multiply by a factor of 10 the number of Active Galactic Nuclei (AGN) detected in the GeV range. Gamma-rays observed in AGNs come from energetic precesses bringing into play very high energy charged particles. These particles are confined in a magnetized plasma jet rising in a region close to the supermassive black hole in the center of the host galaxy. This jet moves away with velocities as high as 0.9999c, forming in many cases radio lobes on kiloparsec or even megaparsec scales. Among the AGNs, those whose jet inclination angle to the line of sight is small are called blazars. The combination of this small inclination angle with relativistic ejection speeds leds to relativistic effects : apparent superluminal motions, amplification of the luminosity and modification of the time scales. Blazars are characterized by extreme variability at all wavelengths, on time scales from a few minutes to several months. A temporal and spectral study of the most luminous of those detected by the LAT, 3C 454.3, was done so as to constrain emission models. A new method for generating adaptive-binning lightcurves is also suggested in this thesis. It allows to extract the maximum of information from the LAT data whatever the flux state of the source
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Zefi, Floriana. "Gamma-ray flux variation studies from the blazar B2 1215+30 with the Fermi-LAT and the Crab Nebula with the H.E.S.S. experiment." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS587/document.
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Les expériences actuelles en astronomie gamma sont le satellite Fermi-LAT et les expériences au sol tel que H.E.S.S., VERITAS et MAGIC. La surveillance des sources d’énergie très élevées indique une physique diversifiée. Afin d’étudier la forme la plus énergétique de radiation et les phénomènes les plus violents qui se déroulent dans l’Univers, l’analyse des sources individuelles est importante. Les BL Lac, un type de galaxie active, constituent la classe de source extragalactique la plus abondante détecté dans les énergies du GeV au TeV, tandis que le nébuleuses de vent de Pulsar sont la classe la plus peuplée dans le plan galactique. Ces deux types de sources ont des émissions variables de rayons gamma.Dans cette thèse, la variabilité de l'objet BL Lac B2 1215 + 30 est étudiée avec les données du satellite Fermi-LAT. Une grande variation de flux, détectée par Fermi-LAT en février 2014, est simultanée avec un éruption très lumineux observé au TeV par l'expérience VERITAS. En collaboration avec la collaboration VERITAS, la variabilité du flux de rayons gamma a été utilisée pour établir des contraintes sur la taille de la région d'émission et sur le facteur Doppler. La variabilité à long terme, en utilisant près de neuf ans de données de Fermi-LAT de 100 MeV jusqu'à 500 GeV, a permis de détecter plusieurs flares. L'étude de la variabilité du flux indique un comportement quasi périodique avec une période de jours.Ensuite, la variabilité du flux de l’un des objets les plus étudié, la Nébuleuse du Crabe, au TeV est étudiée avec dix ans d'observation de l'expérience H.E.S.S. Le spectre de la nébuleuse du crabe est mesuré de 280 GeV jusqu'à 62 TeV. Ceci est la première mesure qui s'étend à ces très hautes énergies. Considérée comme une “chandelle standard” en astronomie gamma, la nébuleuse du crabe est une source utilisée pour l'étalonnage et l'étude des instruments. L’observation de variations du flux au GeV par le satellite Fermi-LAT a par conséquent été une découverte inattendue. Ces variations de flux au GeV ont motivé la recherche de variations de flux au TeV en utilisant les données de l'expérience H.E.S.S. La position de la nébuleuse de crabe dans l'hémisphère nord et la localisation de H.E.S.S. en Namibie rendent cette enquête complexe en raison des importantes erreurs systématiques introduites par des conditions d'observation non optimales. Le travail sur la nébuleuse du crabe montre que la prise en compte de la transparence atmosphérique pour l'étude de l'évolution du flux avec le temps résulte en une réduction des effets systématiques. Aucune variation de flux n'a été observée à des énergies supérieures à 1 TeV dans les données de H.E.S.S. I. Une autre variation de flux au GeV signalée par le Fermi-LAT en octobre 2016 par télégramme astronomique, a été étudiée avec H.E.S.S. II. Cette analyse a montré que le GeV éruption a duré pendant un mois, et le flux avec H.E.S.S. a une variance excessive de 15 %. Cela devrait être comparé à l'incertitude systématique de 20 % fréquemment citée par H.E.S.S<br>The current state-of-the-art experiments in gamma-ray astronomy are the Fermi-LAT in space and the ground-based H.E.S.S., VERITAS and MAGIC experiments. The monitoring of the very-high-energy gamma-ray emitting sources indicates the diverse physics taking place in astrophysical environments. To study the most energetic form of radiation and the most violent phenomena taking place in the Universe, individual source analyses are important. BL Lac objects, a subcategory of active galaxies, are the most abundant source class detected both in the GeV andTeV energies, while pulsar wind nebulae represent the most numerous identified source class in the galactic plane. Both source classes exhibit gamma-ray flux variations.In this thesis, the gamma-ray variability of the BL Lac object B2 1215+30 is presented with Fermi-LAT data. A bright flare, with 16 times the average quiescent flux, was detected in February 2014.In collaboration with the VERITAS experiment, the gamma-ray variability was investigated over five decades in energy. This work resulted in the detection of a luminous flare, seen simultaneously in GeV and TeV energies by both instruments. These results were used to set constraints on the size of the emission region and on the Doppler factor of the relativistic jet. Additionally, the long-term variability was studied using nine years of Fermi-LAT data. This brought out new flux enhancements, which characterize the long-term lightcurve from 100 MeV up to 500 GeV. Other striking characteristics are a steady linear increase of the yearly average flux, together with a hardening of the spectral index. The investigation of the light curve indicates a hint of quasi-periodic behavior with a period of around 1083±32 days.This work includes spectrum and flux variability studies for the well-studied but ever-surprising Crab Nebula at TeV energies with more than a decade of H.E.S.S. observations. The spectrum measured in this work goes from 280 GeV to 62 TeV, making this the first measurement tha textends to such very-high-energies. Considered as a standard candle for ground-based gamma-ray astronomy, the Crab Nebula is also used for calibration and instrument studies. The detection of GeV flares by the Fermi-LAT were unexpected and motivated the search of flux variations at TeVenergies with the H.E.S.S. experiment. The position of the Crab Nebula in the northern hemisphere makes this investigation challenging due to the large systematic uncertainties introduced by the non-optimal observation conditions. This work showed that the systematic uncertainties can be reduced by taking into account the atmospheric transparency. No flux variations were found at energies above 1 TeV from the H.E.S.S. I data. A flare reported by the Fermi-LAT in October 2016 was also investigated. This analysis showed the GeV flare lasting for one month, while the flux withH.E.S.S. II had an excess variance of 15 %. This should be compared to the commonly quoted 20% systematic uncertainty by H.E.S.S. experiment
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Eichmann, Björn [Verfasser], Wolfgang [Akademischer Betreuer] Rhode, and Reinhard [Akademischer Betreuer] Schlickeiser. "Leptonic and hadronic radiation production in flaring blazars : A theoretical analysis of the temporal development of the emergent synchrotron, gamma ray and neutrino intensity / Björn Eichmann. Betreuer: Wolfgang Rhode. Gutachter: Reinhard Schlickeiser." Dortmund : Universitätsbibliothek Dortmund, 2012. http://d-nb.info/1099295351/34.
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Dmytriiev, Anton. "Exploring active galactic nuclei at extreme energies : analysis and modeling of multi-wavelength flares and preparation of CTA." Thesis, Université de Paris (2019-....), 2020. https://theses.md.univ-paris-diderot.fr/Dmytriiev_Anton_va2.pdf.
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De nombreuses questions liées à la physique des jets des Noyaux Actifs de Galaxies restent ouvertes. Une classe particulière d’AGN, les blazars, a un jet pointant vers la Terre. Une telle orientation du jet nous permet de sonder une riche variété de phénomènes physiques mal compris sur les écoulements relativistes. Les blazars montrent une émission non thermique, provenant du jet, qui est très variable sur tout le spectre électromagnétique, des radiofréquences aux rayons gamma du TeV. Le flux d’énergie peut augmenter d’un ordre de grandeur sur des échelles de temps aussi courtes que quelques minutes, un phénomène appelé “sursaut” (flare), et aussi longues que des mois ou même des années. Malgré la quantité croissante de données disponibles sur plusieurs longueurs d’onde (multi-wavelength, MWL), l’origine et les mécanismes physiques derrière les sursauts fréquemment observés dans les blazars ne sont toujours pas bien compris. De nombreuses tentatives ont été faites pour décrire les flares avec différents modèles d’émission, mais les propriétés détaillées de l’évolution temporelle des flux dans différentes bandes spectrales restent difficiles à reproduire. Afin d’identifier les processus physiques impliqués lors des sursauts de blazars, j’ai développé un code radiatif polyvalent, basé sur un traitement dépendant du temps de l’accélération des particules, de l’échappement et du refroidissement radiatif. Le code calcule l’évolution dans le temps de la fonction de distribution des électrons dans la zone d’émission du blazar et le spectre de l’émission Synchrotron Self-Compton (SSC) par ces électrons. J’ai appliqué le code à un sursaut multi-lambda géant du blazar Mrk 421, représentant de la classe des BL Lacertae, qui est le sursaut le plus brillant détecté jusqu’ici en provenance de cette source. Dans notre approche, nous considérons le sursaut comme une perturbation modérée de l’état de flux stationnaire et recherchons des interprétations avec un nombre minimum de paramètres libres. En conséquence, j’ai développé un nouveau scénario physique de l’activité observé pendant le sursaut, qui décrit l’ensemble des données, comprenant des spectres à l’état haut de la source dans différentes gammes d’énergie, et des courbes de lumière multi-lambda du domaine optique aux rayons gamma VHE. Dans ce scénario, le processus déclenchant le sursaut est l’accélération des particules par un processus de type Fermi du second ordre, dû à la turbulence qui emerge au voisinage de la région d’émission stationnaire du blazar. Dans cette thèse, j’ai également effectué une analyse des données du High Energy Stereoscopic System (H.E.S.S.) de deux sursauts géants du blazar 3C 279, représentant de la classe des Flat Spectrum Radio Quasars (FSRQ). Enfin, j’ai contribué à la préparation du Cherenkov Telescope Array (CTA), qui est un observatoire de rayons gamma au sol de nouvelle génération, dont l’entrée en service est prévue à partir de 2022. L’instrument, qui est actuellement en cours de développement, aura des performances considérablement améliorées par rapport aux Imaging Atmospheric Cherenkov Telescopes (IACTs) qui sont actuellement en fonctionnement, y compris une couverture spectrale sans précédent de quelques dizaines de GeV à ~300 TeV. Dans le cadre du CTA, j’ai effectué des simulations de performances optiques du Gamma-Ray Cherenkov Telescope (GCT), l’un des trois modèles proposés de télescopes de petite taille (SST) pour CTA. De plus, en utilisant les observations d’étoiles brillantes effectuées par le prototype de télescope installé sur le site de l’Observatoire de Paris à Meudon, j’ai étudié l’effet de la micro-rugosité des miroirs du télescope sur la fonction d’étalement du point (PSF) et calculé le niveau de qualité de polissage des miroirs requis pour optimiser les performances<br>Many questions related to the physics of jets of Active Galactic Nuclei remain open. A particular subclass of AGN, blazars, have a jet pointing towards the Earth. Such suitable orientation of the jet allows us to probe a rich variety of poorly understood physical phenomena related to relativistic outflows. Blazars show non-thermal emission, originating from the jet, which is highly variable across the entire electromagnetic spectrum, from radio frequencies to TeV gamma-rays. The energy flux can enhance by an order of magnitude on time-scales as short as minutes, a phenomenon referred to as a “flare”, and as long as months or even years. Despite the growing amount of available multi-wavelength (MWL) data, the origin and the physical mechanisms behind the frequently observed flaring events in blazars are still not well understood. Many attempts have been made to describe the flares with different emission models, but detailed properties of flux variation patterns (light curves) in different wavebands remain difficult to reproduce. In order to identify physical processes that are involved during blazar outbursts, I have developed a versatile radiative code, based on a time-dependent treatment of particle acceleration, escape and radiative cooling. The code computes time evolution of the distribution function of electrons in the blazar emitting zone and the spectrum of the Synchrotron Self-Compton (SSC) emission by these electrons. I applied the code to a giant MWL flare of the blazar Mrk 421, a representative of the BL Lacertae class, which is the brightest VHE flare ever detected from this source. In our approach, we consider the flare as a moderate perturbation of the quiescent state and search for interpretations with a minimum number of free parameters. As a result, I developed a novel physical scenario of the flaring activity that describes the data set, comprising spectra in the high state of the source in different energy ranges, and MWL light curves from the optical domain to the VHE gamma-ray band. In this scenario, the process initiating the outburst is the second-order Fermi acceleration of particles due to turbulence arising in the vicinity of the blazar stationary emission region. In this thesis, I also performed analysis of High Energy Stereoscopic System (H.E.S.S.) data of two giant flares of the blazar 3C 279, a representative of the Flat Spectrum Radio Quasars (FSRQ) class. Finally, I contributed to preparation of Cherenkov Telescope Array (CTA), which is a new-generation ground-based gamma-ray observatory, expected to start operations in 2022. The instrument, which is presently under development, will have greatly improved performance compared to currently operating Imaging Atmospheric Cherenkov Telescopes (IACTs), including unprecedented spectral coverage from a few tens of GeV to ~300 TeV. In the context of CTA, I performed simulations of the optical performance of the Gamma-Ray Cherenkov Telescope (GCT), one of the three proposed designs of Small-Size Telescopes (SST) for CTA. Also, using the observations of bright stars done by the telescope prototype installed on the site of Paris Observatory in Meudon, I studied the effect of micro-roughness of the telescope mirrors on the point spread function (PSF) and calculated the level of the mirror polishing quality required to optimize the performances
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Buckman, Benjamin Jerome. "Cosmic-Ray Emission as a Window into Extragalactic Environments: Starburst Galaxies & Blazars." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1595554171852752.
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Spingola, Cristiana. "Radio follow-up of the gamma-ray flaring gravitational lens B0218+357." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7230/.
Full textAbstract:
B0218+357 è un blazar soggetto al lensing che si trova a z=0.944. Questo sistema
consiste in due componenti compatte (A e B) e un anello di Einstein. Recentemente è stato
associato ad una sorgente gamma soggetta a burst osservata con il satellite Fermi-LAT. Questo
blazar ha mostrato una forte variabilità in banda γ da agosto a settembre del 2012. Gli
episodi di variabilità osservati hanno consentito di misurare per la prima volta in banda gamma il
ritardo temporale previsto dalla teoria del lensing gravitazionale. Le osservazioni in banda gamma sono state seguite da un programma di monitoring con il Very Long Baseline Array (VLBA) in banda radio con lo scopo di verificare l’esistenza di una correlazione tra l’emissione nelle
due bande.
In questa Tesi tali osservazioni radio sono state analizzate con lo scopo di studiare la
variabilità di B0218+357 e, quindi, attestare la connessione tra l’emissione alle alte energie
e quella in banda radio. L’obiettivo principale di questo lavoro di Tesi è quello di studiare
l’evoluzione della densità di flusso, dell’indice spettrale e della morfologia delle immagini A
e B e delle loro sottocomponenti.
I dati analizzati sono stati ottenuti con l’interferometro VLBA a tre frequenze di osser-
vazione: 2.3, 8.4 GHz (4 epoche con osservazioni simultanee alle due frequenze) e 22 GHz
(16 epoche). Le osservazioni hanno coperto un periodo di circa due mesi, subito successivo al flare in banda gamma. La riduzione dei dati è stata effettuata con il pacchetto AIPS. Dall’analisi delle immagini, nella componente B è possibile riconoscere la tipica struttura nucleo-getto chiaramente a tutte e tre le frequenze, invece nella componente A questa struttura è identificabile solo a 22 GHz. A 2.3 e 8.4 GHz la risoluzione
non è sufficiente a risolvere nucleo e getto della componente A e l’emissione diffusa risulta
dominante. Utilizzando il metodo dello stacking sulle immagini a 2.3 GHz, è stato possibile rivelare
le parti più brillanti dell’Einstein ring associato a questa sorgente. Questo è stato possibile
poiché la sorgente non ha mostrato alcun segno di variabilità significativa né di struttura né
di flusso nelle componenti.
Quindi dall’analisi delle curve di luce delle due componenti A e B non è emersa una
variabilità significativa chiaramente associabile al flare osservato in banda gamma. Per verificare
questo risultato, le curve di luce ottenute sono state confrontate con le osservazioni del radio
telescopio OVRO (15 GHz) nel periodo corrispondente alle nostre osservazioni. La curva di
luce OVRO è risultata in pieno accordo con le curve di luce ottenute durante questo lavoro
di tesi e ha confermato che B0218+257 non ha mostrato un’importante attività radio nel
periodo delle osservazioni VLBA.
In definitiva, la mancanza di variabilità radio associata a quella osservata nei raggi gamma
può essere dovuta al fatto che la regione in cui si è originato il flare gamma è otticamente spessa
alle lunghezze d’onda radio, oppure non esiste una precisa correlazione tra le due emissioni,
rimanendo quindi un problema aperto da investigare.
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Griffiths, Scott Tyler. "Exploring the limits of Lorentz invariance with VERITAS gamma-ray observations of Markarian 421." Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/1847.
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The search for a theory of quantum gravity has persisted through the last century. Although many beautiful theories such as string theory and loop quantum gravity have been proposed, experimental evidence to support or refute these theories has been difficult to obtain. Searching for Lorentz invariance violation (LIV) is one of a limited number of experimental tests which can be used to search for evidence of quantum gravity since new physics may only be observable at energies well beyond those present in the most energetic astrophysical objects, which are far greater than the energies accessible in a terrestrial laboratory.
One method of searching for LIV is to look for energy-dependent time delays in the arrival of high-energy photons from distant astrophysical sources. We search for Lorentz invariance violation (LIV) using VERITAS, an imaging atmospheric Cherenkov telescope (IACT) located in southern Arizona. Significant TeV gamma ray flaring activity was detected from the blazar Markarian 421 on the night of February 17, 2010 (MJD 55244), which presented a good opportunity to search for delays in the energetic emission. We demonstrate the performance of two different dispersion estimation algorithms and apply these algorithms to our data to search for LIV. We find that while the emission from Markarian 421 contains significant variability, a necessary condition for an LIV detection, the presence of a constant background flux severely limits our sensitivity. We expect our findings to be useful for guiding future LIV studies, especially those using IACT data.
In the latter part of this work we discuss the alignment of ground-based gamma-ray telescopes and present a digital autocollimator which will be used in the alignment system of a next-generation IACT. The configuration of our autocollimator enables measurement of the angle formed between the planar surface of a distant reflector and the line of sight over a range of ±0.126° with a precision better than 5 arcsec. We present a detailed description of the instrument and its data acquisition software that was used during laboratory testing.
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Pia, Valerio. "Calcolo del flusso di raggi-γ del Blazar PKS B1424-418". Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/12048/.
Full textAbstract:
Lo scopo di questo lavoro è quello di analizzare i dati raccolti dal Large Area Telescope a bordo del satellite Fermi con l'obiettivo di ricavare il flusso di raggi-γ, di energia compresa tra 100 MeV e 300 GeV, prodotti dal Blazar PKS B1424-418 in un periodo compreso tra l'1 Gennaio 2012 e il 4 Settembre 2016. Secondo alcuni modelli questo blazar potrebbe essere
infatti la prima sorgente di Ultra High Energy Cosmic Ray associata sperimentalmente all'emissione di neutrini.
L'analisi dei dati è effettuata tramite il pacchetto di software Fermi Science Tools.
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Giavitto, Gianluca. "Observing the VHE Gamma Ray Sky with the MAGIC Telescopes: the Blazar B3 2247+381 and the Crab Pulsar." Doctoral thesis, Universitat Autònoma de Barcelona, 2013. http://hdl.handle.net/10803/116193.
Full textAbstract:
El objetivo de esta tesis es ampliar nuestra comprensión de la física de dos
clases de fuentes astrofísicas entre las más importantes emisoras de radiación
no-térmica: blazars y púlsares. En particular, la tesis relata sobre la
observación del blazar B3 2247 381 y el púlsar del Cangrejo.
Este estudio se llevó a cabo mediante la medición de rayos gamma por encima de
~50 GeV con los telescopios MAGIC.
Las dos clases de fuentes incluidas en esta tesis no están fuertemente
relaccionadas, sin embargo, representan dos ejemplos interesantes de cómo
observaciones de rayos gamma en una gama de energía cerca del umbral de MAGIC
puedan conducir a avances en la comprensión de los mecanismos de emisión, y a
veces a descubrimientos sorprendentes.
Los blazares son galaxias activas con un chorro relativista propulsado por su
agujero negro central y dirigido hacia el observador. La emisión de rayos gammas
procede de partículas cargadas aceleradas en el chorro.
El tipo de partículas aceleradas, la posición de la emisión y el mecanismo de
aceleración son algunas de las preguntas abiertas sobre los blazars. Además, su
observación puede proporcionar límites sobre la luz de fondo extragaláctica
(EBL), importante para comprender la formación y evolución de las primeras
galaxias.
B3 2247+381 ya se observó con MAGIC en el modo monoscópico en 2006, pero no fue
detectado. En 2009, el comienzo de las observaciones estereoscópicas mejoró la
sensibilidad de MAGIC, y se propuso su re-observación. Se detectó en Octubre de
2010, conseguentemente se determinó su espectro por encima de 200 GeV. No se
encontró variabilidad.
Esta evidencia, junto con las observaciones en otras longitudes de onda, se
interpretó mediante un simple modelo Synchrotron Self Compton (SSC) a una zona
con parámetros similares a los adoptados por otros blazars.
Aunque B3 2247+381 no sea una fuente sorprendente,estos resultados conferman de
la validez de modelo SSC y amplian la base de datos disponibles para estudios de
EBL y de población.
Los púlsares son estrellas de neutrones altamente magnetizadas, que girando
emiten pulsos de radiación electromagnética en todas las longitudes de onda.
Hasta hace poco, no se había detectado ningun púlsar por encima de 100 GeV, de
acuerdo con la las predicciones del modelo “outer gap” (OG) de un corte
exponencial en el espectro de energía alrededor de algunos GeV.
MAGIC observó el púlsar del Cangrejo entre 2009 y 2011, recogiendo 73 horas de
datos stereo de buena calidad. Un plug-in para el software de timing TEMPO2 fue
escrito para calcular las fases de los succesos mediante efemérides radio. La
análisis fue adaptada para obtener un bajo umbral de energía.
Una pulsación significativa (>6.8 sigma) se detectó en el rango de energía
46-416 GeV. La curva de luz presenta dos picos (P1 y P2), en línea con los de
energías más bajas, pero más estrechos y con proporción P1/P2 de 0,5.
Los espectros de energía resueltos en fase continuan como una ley de potencia
con un índice espectral de ~-4 hasta las energías más altas, en fuerte
desacuerdo con todas predicciones. Un modelo OG ampliado interpreta esta emisión
como procedente de inverse Compton scattering por pares secundarios y terciarios
sobre fotones IR/UV. Otras explicaciones existen, algunas predicen
características espectrales comprobables con más observaciones. Queda para
averiguar si el Púlsar del Cangrejo es único en su clase o si la emisión de
rayos gamma hasta centenares de GeV está presente en otros púlsares.
Durante el transcurso de esta tesis también he trabajado activamente en el
para la actualización de la camera y del sistema de lectura de datos de
MAGIC, que asegurará observaciones más eficientes y más estables.<br>The goal of this thesis is to expand our understanding of the physics of two
astrophysical source classes amongst the most prominent emitters of non-thermal
radiation: blazars and pulsars. In particular, the thesis reports the
observation of the blazar B3 2247+381 and the Crab pulsar.
This study was carried out by measuring gamma-ray emission above ~50 GeV from
these sources with the MAGIC telescopes.
The two source classes covered in this thesis are not closely related,
however they represent two interesting examples of how gamma-ray observations
between 50 and few hundreds of GeV, an energy range close to the threshold of
MAGIC, can lead to advancements in the understanding of the emission mechanisms,
and sometimes to surprising discoveries.
Blazars are a type of active galaxies with a relativistic jet powered by their
central black hole and directed towards the observer. Gamma-ray emission
originates from charged particles accelerated in the jet.
The nature of the accelerated particles, the position of the emission and the
acceleration mechanism are some of the open questions about blazars.
Furthermore, their observation can provide indirect limits on the extragalactic
background light (EBL), important for understanding early galaxy formation and
evolution.
B3 2247+381 was observed already by MAGIC in monoscopic mode in 2006, but eluded
detection. In 2009, the commencement of stereoscopic observations enhanced the
sensitivity of MAGIC, so it was proposed for re-observation. It was detected in
October 2010, leading to the determination of its spectrum above 200 GeV. No
significant variability could be found.
This evidence, together with observations at other wavelengths, is interpreted
using a simple one-zone Synchrotron Self Compton (SSC) model, with parameters
similar to those adopted for other blazars.
Even if B3 2247+381 was not a surprising source, these results confirm the
validity of SSC models and enlarge the data base to be used in EBL and blazar
population studies.
Pulsars are highly magnetized, rotating neutron stars that emit periodic
radiation at all wavelengths. Until recently, no pulsar was detected above 100
GeV, in agreement with the “outer gap” (OG) model predictions of an exponential
cutoff in the energy spectrum at few GeV. For the Crab pulsar however, the
presence of said cutoff was questioned in 2010 by MAGIC monoscopic measurement.
MAGIC observed the Crab pulsar in stereoscopic mode between 2009 and 2011,
collecting 73 hours of good quality data. A plug-in for the TEMPO2 timing
software was written to calculate the event phases using radio ephemerides. The
analysis cuts were customized to obtain the lowest energy threshold possible.
A significant pulsation (>6.8 sigma) was detected in the energy range 46 - 416 GeV.
The folded light curve shows two peaks (P1 and P2), aligned with the ones at
lower energies, but narrower and with P1/P2 ratio of ~0.5.
The phase-resolved gamma-ray energy spectra continue as a power-law with a
spectral index ~-4 up to the highest energies, in stark disagreement with all
predictions. An extended OG model interprets this emission as high-altitude
inverse Compton scattering of secondary and tertiary pairs on IR/UV photons.
Other explanations exists, some predicting spectral features testable with
further MAGIC observations. It remains to be understood if the Crab pulsar is
unique in its kind or if gamma-ray emission up to hundreds of GeV is present in
other pulsars.
During the course of this thesis I was also actively involved the work for the
MAGIC camera and readout upgrade, which will assure more efficient and stabler
observations in the future.
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Bollström, Nadja. "A gamma-ray study of a highly variable blazar : The Fermi-LAT analysis and the modeling of the FSRQ PKS 1510–089." Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-104617.
Full textAbstract:
The subject of this thesis is the analysis and modeling of the active galactic nucleus PKS 1510-089. The aim is to present a thorough background of active galactic nuclei combined with the analysis and modeling of a specific active galactic nucleus. The results will then be linked to previous research and theories about active galactic nuclei. The data used in the analysis were retrieved from the Fermi Gamma-ray Space Telescope. A light curve analysis that extended over 12 years provided knowledge about variability and presented four interesting flaring periods. The four periods underwent a spectral analysis, and the results showed that a log parabolic curvature could best describe all four periods. The last step before the modeling was to create spectral energy distributions for all four periods to retrieve spectral points from wavelengths other than those available from Fermi. Unfortunately, there were only sufficient data for one period. That period was later used in the modeling and resulted in a well-fitted external Compton model, which was compared, with relatively good results, with previous research.
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Berger, Karsten. "Discovery and Characterization of the first Low-Peaked and Intermediate-Peaked BL Lacertae Objects in the Very High Energy Gamma-Ray Regime." kostenfrei, 2009. http://www.opus-bayern.de/uni-wuerzburg/volltexte/2009/3743/.
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Caneva, Gessica De. "Studies of active galactic nuclei with the MAGIC telescopes." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17179.
Full textAbstract:
Schwerpunkt dieser Arbeit ist die Emission von hochenergetischer Gammastrahlung aus Aktiven Galaxienkernen, anhand von Beobachtungen mit den MAGIC Teleskopen. Aktive Galaxien entstehen durch die Freisetzung von Gravitationsenergie der Stellarmaterie, die in das zentrale Schwarze Loch fällt. Zwei diametral entgegengesetzte Jets strömen aus dem Kern. Falls einer von diesen Jets zum Beobachter zeigt, wird der aktive Galaxienkern als Blazar bezeichnet. In dieser Doktorarbeit wird die Analyse der MAGIC Beobachtungen von drei Blazaren präsentiert: der bisher unbekannte hochenergetische Blazar 1ES 1727+502 und die bekannten Objekte 3C 279 und PKS 1510-089. Die Quelle 1ES 1727+502 gehört zu der Unterklasse der BL Lac Objekte, die die zahlenmässig größte Klasse an extragalaktischen hochenergetische Objekten ist. Diese Entdeckung beweist, wie wichtig es ist, mehrere und verschiedene Kriterien für die Auswahl von Objekten zu benutzen. Der Blazar 1ES 1727+502 wurde aus einem X-ray Katalog ausgesucht, die Datennahme war unabhängig von dem Aktivitätsstatus der anderen Energiebänder. Die Blazare 3C 279 und PKS 1510-089 gehören zu der Unterklasse des Flat Spectrum Radio Quasars. Es gibt nur drei bekannte Flat Spectrum Radio Quasare. Die Entdeckung von Flat Spectrum Radio Quasaren ist schwierig, weil im leisen Zustand der hochenergetische Fluss niedrig ist. Während eines Flares steigt der Fluss in sehr kurzer Zeit um mehrere Größenordnungen an, deswegen ist die Beobachtung eines Flares schwer zu realisieren aber physikalisch äußerst interessant. Die MAGIC Beobachtungen sind mit Messungen aus anderen Energiebändern kombiniert. Mögliche Interpretationen des beobachteten Verhaltens werden diskutiert. Die Ergebnisse werden erläutert und mit historischen Beobachtungen verglichen. Die offenen Fragen und Probleme, die Ziel zukünftiger Studien sein sollen, werden am Schluss hervorgehoben.<br>This PhD thesis addresses the problem of understanding the very high energy emission from active galactic nuclei as detected with the MAGIC telescopes. Active galactic nuclei are galaxies powered by the release of gravitational energy of stellar material falling into a black hole, located in their core. Two opposed jets extend from the central region outwards, if one of the them points towards the observer, the source is called a blazar. In this thesis the analysis of MAGIC observations of three different blazars is presented: the newly discovered very high energy blazar 1ES 1727+502, and the two known objects 3C 279 and PKS 1510-089. The source 1ES 1727+502 belongs to the subclass of BL Lac objects, the most numerous class of extragalactic very high energy emitters. This source was selected for observations from an X-ray catalogue and was observed even if no high activity states were reported at lower energies. For this reason, this discovery proves the importance of using several criteria for the selection of very high energy observation targets. The other two objects, 3C 279 and PKS 1510-089, belong to the subclass of flat spectrum radio quasars. We count only three representatives of this class in the very high energy domain. Their detection is critical because during quiescent states they have low flux levels at very high energies. During flaring states, flat spectrum radio quasars exhibit flux enhancements of orders of magnitudes and short time scales. Observations during such states, difficult to catch, are interesting because extreme processes are taking place. Very high energy observations of these three objects are complemented with measurements at lower energies and interpretations of the observed behaviours are discussed. The results are compared with historical observations, highlighting open questions and problems which should be addressed by future studies.
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Richards, Joseph Lee. "The Radio Variability of Gamma-Ray Blazars." Thesis, 2012. https://thesis.library.caltech.edu/6945/1/richards_joseph_l_2012_thesis.pdf.
Full textAbstract:
Since late 2007, we have regularly monitored over 1100 systematically selected blazars at 15 GHz using the Owens Valley Radio Observatory 40 m radio telescope. The number of sources in the program has grown to nearly 1600, including all the active galactic nuclei associated with Fermi Large Area Telescope (LAT) gamma-ray point source detections north of our declination limit of -20°. Here, we describe the first 42 months of this program, including the design and implementation of an automated data reduction pipeline and a MySQL database system for storing the reduced data and intermediate data products. Using the "intrinsic modulation index," a maximum-likelihood method, we estimate the variability amplitudes for 1413 sources from their radio light curves and compare the properties of physically defined subpopulations of the sample. We find that, among our preselected sample, gamma-ray-loud blazars detected by the LAT are significantly more variable at 15 GHz, attributable to a difference in variability between the gamma-ray-loud and gamma-ray-quiet flat spectrum radio quasars. The BL Lacertae objects in the samples do not show this division in variability amplitudes. In the first two years of our program, a 3σ-significant difference between variability amplitudes for sources at redshift z ≥ 1 and for sources at z < 1 was found. This difference is found no longer to be significant in the full 42-month data set, particularly after we apply an analysis method to account for the effect of cosmological time dilation.
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Max-Moerbeck, Astudillo Walter Kennerth. "The Relationship Between the Radio and Gamma-Ray Emission of Blazars." Thesis, 2013. https://thesis.library.caltech.edu/7784/1/thesis.pdf.
Full textAbstract:
<p>Blazars are active galaxies with a jet closely oriented to our line of sight. They are powerful, variable emitters from radio to gamma-ray wavelengths. Although the general picture of synchrotron emission at low energies and inverse Compton at high energies is well established, important aspects of blazars are not well understood. In particular, the location of the gamma-ray emission region is not clearly established, with some theories favoring a location close to the central engine, while others place it at parsec scales in the radio jet.</p>
<p>We developed a program to locate the gamma-ray emission site in blazars, through the study of correlated variations between their gamma-ray and radio-wave emission. Correlated variations are expected when there is a relation between emission processes at both bands, while delays tell us about the relative location of their energy generation zones. Monitoring at 15 GHz using the Owens Valley Radio Observatory 40 meter telescope started in mid-2007. The program monitors 1593 blazars twice per week, including all blazars detected by the Fermi Gamma-ray Space Telescope (Fermi) north of -20 degrees declination. This program complements the continuous monitoring of gamma-rays by Fermi.</p>
<p>Three year long gamma-ray light curves for bright Fermi blazars are cross-correlated with four years of radio monitoring. The significance of cross-correlation peaks is investigated using simulations that account for the uneven sampling and noise properties of the light curves, which are modeled as red-noise processes with a simple power-law power spectral density. We found that out of 86 sources with high quality data, only three show significant correlations (AO 0235+164, B2 2308+34 and PKS 1502+106). Additionally, we find a significant correlation for Mrk 421 when including the strong gamma-ray/radio flare of late 2012. In all four cases radio variations lag gamma-ray variations, suggesting that the gamma-ray emission originates upstream of the radio emission. For PKS 1502+106 we locate the gamma-ray emission site parsecs away from the central engine, thus disfavoring the model of Blandford and Levinson (1995), while other cases are inconclusive. These findings show that continuous monitoring over long time periods is required to understand the cross-correlation between gamma-ray and radio-wave variability in most blazars.</p>
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Bhattacharya, Debbijoy. "Origin Of The Extragalactic Gamma-Ray Background." Thesis, 2008. http://etd.iisc.ernet.in/handle/2005/2252.
Full textAbstract:
It is evident that the origin of EGRB is not well established. In this thesis I examine the unresolved discrete origin of EGRB. The contribution from normal galaxies, starburst galaxies and AGNs to the EGRB is examined. The second chapter includes the methodology used to find the contributions from different source classes. In the third chapter the contribution from normal and starburst galaxies is discussed. A methodology is developed to derive the contribution from normal and starburst galaxies to the EGRB considering all the major γ-ray production processes in these galaxies. The calculations in this thesis consider the detailed γ-ray measurements of our galaxy(Hunter etal.1997) to derive suitable scaling relations to extend the analysis beyond the Milky Way. It is assumed that all normal and starburst galaxies also have similar γ-ray spectra. A relationship is derived between the γ-ray luminosity and SFR of a normal galaxy. Infrared luminosity of a normal galaxy is used as a tracer of SFR of that galaxy (Kewley et al.2002). For starburst galaxies, the contribution depends on the relative ratio(β)of cosmic-ray enhancement per SFR w.r.t the Milky Way. To find the proportionality constants between cosmic-ray production rate and SFR of starburst galaxies, M82 has been taken as a standard.
Contribution from FSRQs and BL Lacs to the EGRB is discussed in the fourth chapter. FSRQs and BL Lacs are considered as separate source classes, and their luminosity functions are constructed separately from the recent identifications of EGRET sources(Sowards-Emmerd,Romani&Michelson2003 and Sowards-Emmerd et al.2004) which almost doubled the blazers count than that used by Chiang & Mukher-jee(1998).
Radio-loud AGNs with all possible jet to line-of-sight angle (SSRQs, FR IIs, FR Is) are termed here off-axis AGNs. It is considered that SSRQs and FSRQs and FR IIs are from one parent population, BL Lacs and FR Is are from another parent population. The scenario considered includes an AGN jet which slows down as it moves away from the central source. The contributions from these AGNs (relative to the FSRQs and BL Lacs contribution) are discussed in chapter five. Chapter six briefly summarised the findings from the thesis.
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Zacharopoulou, Olga [Verfasser]. "On the origin of the unusually hard γ-ray [gamma-ray] spectra of TeV blazars / put forward by Olga Zacharopoulou". 2010. http://d-nb.info/1009928805/34.
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Wagner, Robert Marcus [Verfasser]. "Measurement of very high energy gamma-ray emission from four blazars using the MAGIC telescope and a comparative blazar study / Robert Marcus Wagner." 2006. http://d-nb.info/98518826X/34.
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Eggen, Joseph. "Optical Polarimetry and Gamma-Ray Observations of a Sample of Radio-Loud Narrow Line Seyfert 1 Galaxies." 2014. http://scholarworks.gsu.edu/phy_astr_diss/70.
Full textAbstract:
The recent discovery of a new population of Active Galactic Nuclei (AGN) – the Radio Loud Narrow Line Seyfert 1 (RL NLS1) galaxies – at g-ray energies by Fermi has prompted intense interest among researchers, as evidence mounts that these objects may in fact compose a new class of blazars. If RL NLS1s are indeed a new class of blazars, or at least analogous to them, then the detection of certain blazar-like properties would be expected. These properties include significant variability at all wavelengths across the electromagnetic spectrum and on timescales from minutes to years, significant & variable polarization in the radio and optical regimes, significant & variable high-energy emissions (especially in the g-ray regime), and a double-peaked structure of their spectral energy distributions.
This dissertation seeks to characterize several of these properties for RL NLS1s as a class. These include the degree to which these objects are polarized and the variability of this property, the detection and characterization of these sources at g-ray energies with the Large Area Telescope aboard the Fermi spacecraft, and the degree to which these properties are interdependent. A photopolarimetric survey (the first of its kind for this class of objects) and g-ray monitoring program were conducted by the author in order to obtain the data necessary for this project. The measurements obtained via these observations are used to characterize this interesting class of objects with respect to a sample of blazars. In general, it was found that the polarizations of these objects fall between radio-quiet NLS1s and FSRQ-type blazars, and were most similar to HBL-type blazars. The 7 RL NLS1s in this sample that had been detected above a Test Statistic (TS) of 25 by Fermi/LAT were most similar to FSRQs, while 9 objects detected in the interval 9 < TS < 25 shared several properties with HBLs. Two RL NLS1s - J1443+4725 and J1644+2619 - are identified as high-confidence (TS > 25) g-ray sources for the first time, bringing the total number of members of this class firmly detected at g-ray energies to 8. The gamma-ray spectra of RL NLS1s are similar to FSRQs, though some have steeper spectra.
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Swaby, David. "Flasher calibration of the T1 and T2 CANGAROO telescopes and TeV gamma ray observation of Markarian 421 and EXO 055625-3838.6 BL Lacertae blazars." Thesis, 2010. http://hdl.handle.net/2440/66096.
Full textAbstract:
Calibration tests were made on the T1 and T2 telescopes of the CANGAROO collaboration in 2001 to 2003, using a custom-made LED light flasher apparatus to test the two (T1 and T2) telescope responses to a fixed amplitude light signal. The flasher apparatus was set up (a kilometre distance from the telescopes), to trigger the telescopes with a 10 nanosecond or 20 nanosecond pulse width flash, running at a rate of 1 kilohertz. Measurement of the light intensity of the flasher was achieved by using a custom-made PIN diode monitor coupled to the flasher output. After data analysis, it was found that the principal flasher signal amplitude variation (from month to month) as measured by a telescope, was due to errors in the encoders upon slewing and parking the telescope. This effect was found and measured by taking the two dimensional cross-correlation of the flasher pixel images (acquired in the camera of the two telescopes), taken monthly. Measurement of the T1 telescope energy threshold was attempted, using cosmic ray showers at the zenith, on two separate occasions. Finally, 2313.9 on-source minutes of data on the HBL Lac. blazar, Markarian 421 data was acquired by T1 in 2001 to 2003, and 1013 on-source minutes of data on the BL Lac. blazar EXO 055625-3838.6 were acquired in 2002 and 2003, by T1. From alpha plot distributions (where alpha ≤ 40°), it was found that the TeV gamma ray signal significance for Markarian 421 was 2.8 σ (in 2001-03); 3.3 σ (in 2001) and 0.4 σ (upper limit in 2002-03). Furthermore, from (alpha < 20°) to maximize signal over noise, the significance for Markarian 421 was found to be 3.5 σ (2001-03); 3.5 σ (in 2001) and 1.2 σ (upper limit in 2002-03). The TeV gamma ray signal significance (where alpha ≤ 20°), was 2.2 σ for EXO 055625-3838.6 over 2002-03.<br>Thesis (M.Sc.) -- University of Adelaide, School of Chemistry and Physics, 2010
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Brill, Aryeh Louis. "Advancing Blazar Science with Very-High-Energy Gamma-Ray Telescopes." Thesis, 2021. https://doi.org/10.7916/d8-jznf-8e64.
Full textAbstract:
Blazars, active galactic nuclei with relativistic jets pointed almost directly at Earth, are powerful and highly variable sources of nonthermal electromagnetic radiation, including very-high-energy gamma rays. We can detect these gamma rays with arrays of imaging atmospheric Cherenkov telescopes (IACTs), including the Very Energetic Radiation Imaging Telescope Array System (VERITAS) and the upcoming Cherenkov Telescope Array (CTA). After reviewing the science of blazars and the methods used by IACTs, we investigate how gamma-ray variability can provide insight into blazars' physical properties while also complicating efforts to understand these sources as a population.
We first present a study of three flaring blazars observed with VERITAS and analyze these sources' spectral and variability characteristics, taking into account data at other wavebands, including that of the Large Area Telescope aboard the Fermi space telescope (Fermi-LAT). Next, after laying out how observing biases and intrinsic variability can confound blazar population studies with IACTs, we propose methods to account for these effects, and use simulated data to report expectations for a blazar luminosity function measurement with VERITAS. Sophisticated new instruments and data analysis methods can further expand the frontier of gamma-ray blazar science. To that end, we design a camera software system to enable safer and more efficient operations of a next-generation IACT being developed for CTA, the prototype Schwarzschild-Couder Telescope (pSCT). Finally, we develop methods to apply deep neural networks to the analysis of IACT data and employ these methods to reject background events detected by simulated arrays of IACTs.