Thesis (Ph. D.)--University of Adelaide, 2003. / Title from title screen. Description based on contents viewed Apr. 21, 2005. Includes bibliographical references.

No description available.

We investigate the multiwavelength behaviour of the high-energy peaked BL Lac object (HBL) Mrk 421 at redshift z = 0.031 in the period 2007-2015. We use optical photometric, spectroscopic, and polarimetric data and near-infrared data obtained by 35 observatories participating in the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT), as well as by the Steward Observatory Support of the Fermi Mission. We also employ high-energy data from the Swift (UV and X-rays) satellite to study correlations among emission in different bands.

We report on long-term multiwavelength monitoring of blazar Mrk 421 by the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope (GASP-WEBT) collaboration and Steward Observatory, and by the Swift and Fermi satellites. We study the source behaviour in the period 2007-2015, characterized by several extreme flares. The ratio between the optical, X-ray and gamma-ray fluxes is very variable. The gamma-ray flux variations show a fair correlation with the optical ones starting from 2012. We analyse spectropolarimetric data and find wavelength-dependence of the polarization degree (P), which is compatible with the presence of the host galaxy, and no wavelength dependence of the electric vector polarization angle (EVPA). Optical polarimetry shows a lack of simple correlation between P and flux and wide rotations of the EVPA. We build broad-band spectral energy distributions with simultaneous near-infrared and optical data from the GASP-WEBT and ultraviolet and X-ray data from the Swift satellite. They show strong variability in both flux and X-ray spectral shape and suggest a shift of the synchrotron peak up to a factor of similar to 50 in frequency. The interpretation of the flux and spectral variability is compatible with jet models including at least two emitting regions that can change their orientation with respect to the line of sight.

BL Lacertae objects belong to the most luminous sources in the Universe. They represent a subclass of active galactic nuclei with a spectrum that is dominated by non-thermal emission, extending from radio wavelengths to tera electronvolt (TeV) energies. The emission is strongly variable on time scales of years down to minutes, and arises from relativistic jets pointing at small angles to the line of sight of the observer, which is the reason for naming them “blazars”. Blazars are the dominant extragalactic source class in the radio, microwave and gamma-ray regime, are prime candidates for the origin of the Cosmic Rays and excellent laboratories to study black hole and jet physics as well as relativistic effects. Despite more than 20 years of observational efforts, the physical mechanisms driving their emission are not yet fully understood. So far, studies of their broad-band continuum emission were mostly concentrated on bright, flaring states. However, for a better understanding of the central engine powering the jets, the bias from flux-limited observations of the past must be overcome and their long-term average continuum spectral energy distributions (SEDs) must be determined. This work presents the first simultaneous multi-wavelength campaigns from the radio to the TeV regime of two high-frequency peaked BL Lacertae objects known to emit at TeV energies. The first source, 1ES 1011+496, was observed between February and May 2008, the second one, 1ES 2344+514, between September 2008 and February 2009. The extensive observational campaigns were organised independently from an external trigger for the presence of a flaring state. Since the duty cycle of major flux outbursts is known to be rather low, the campaigns were expected to yield SEDs representative of the long-term average emission. Central for this thesis is the analysis of data obtained with the MAGIC Cherenkov telescope, measuring energy spectra and light curves from ~0.1 to ~10 TeV. For the remaining instruments, observation time was proposed and additional data was organised by collaboration with the instrument teams by the author of this work. Such data was obtained mostly in a fully reduced state. Individual light curves are investigated as well as combined in a search for inter-band correlations. The data of both sources reveal a notable lack of a correlation between the emission at radio and optical wavelengths, indicating that the radio and short-wavelength emission arise in different regions of the jet. Quasi-simultaneous SEDs of two different flux states are observationally determined and described by a one-zone as well as a self-consistent two-zone synchrotron self-Compton model. First approaches to model the SEDs by means of a Chi2 minimisation technique are briefly discussed. The SEDs and the resulting model parameters, characterising the physical conditions in the emission regions, are compared to archival data. Though the models can describe the data well, for 1ES 1011+496 the model parameters indicate that in addition to the synchrotron and inverse-Compton emission of relativistic electrons, emission due to accelerated protons seems to be required. The SEDs of 1ES 2344+514 reveal one of the lowest activity states ever detected from the source. Despite that, the model parameters are not indicative of a distinct quiescent state, which may be caused by the degeneracy of the different parameters in one-zone models. Moreover, indications accumulate that the radiation can not be attributed to a single emission region. The results disfavour some of the current blazar classification schemes and the so-called “blazar sequence”, emphasising the need for a more realistic explanation of the systematics of the blazar SEDs in terms of fundamental parameters. / BL Lacertae-Objekte sind mit die leuchtkräftigsten Quellen im Universum. Sie stellen eine Unterklasse der Galaxien mit aktiven Kernen dar. Ihr Spektrum erstreckt sich von Radio-Wellenlängen bis in den Tera-Elektronvolt (TeV)-Bereich und ist dominiert durch nicht-thermische Strahlung. Ihre Emission is stark variabel, auf Zeitskalen von Jahren bis Minuten, und entsteht in relativistischen Jets, welche mit einem geringen Winkel zur Sichtlinie beobachtet werden. Daher werden diese Objekte “Blazare” genannt. Blazare sind die dominierende extragalaktische Quellpopulation im Radio-, Mikrowellen- und Gamma-Regime, gehören zu den favorisierten Quellen der Kosmischen Strahlung und bieten ausgezeichnete Bedingungen, um die Physik schwarzer Löcher, Jets sowie relativistische Effekte zu untersuchen. Trotz mehr als 20 Jahre andauernder Beobachtungen sind die physikalischen Mechanismen, welche für die Emission verantwortlich sind, noch nicht völlig verstanden. Bisher konzentrierten sich die Untersuchungen der Breitband-Kontinuumsstrahlung der Quellen hauptsächlich auf deren helle Ausbrüche. Um jedoch die zentrale Komponente der Jetenergetik zu verstehen, muss die in der Vergangenheit aufgebaute Tendenz zu flusslimitierten Beobachtungen überwunden werden, und die über lange Zeiträume gemittelten spektralen Energieverteilungen bestimmt werden. Die vorliegende Arbeit präsentiert die ersten simultanen Multiwellenlängenkampagnen vom Radio- bis in den TeV-Bereich für zwei BL Lacertaue Objekte, welche als TeV-Emitter bekannt sind. Die erste der beiden Quellen, 1ES 1011+496, wurde zwischen Februar und Mai 2008 beobachtet, 1ES 2344+514, die zweite Quelle, von September 2008 bis Februar 2009. Die umfangreichen Beobachtungskampagnen wurden unabhängig von externen Benachrichtigungen über hohe Flusszustände organisiert. Da starke Ausbrüche der Quellen relativ selten sind, wurde von den Kampagnen erwartet, dass eine spektrale Energieverteilung erbringen würden, welche repräsentativ für ein Langzeitmittel der Emission wäre. Die Analyse der Daten des MAGIC-Cherenkov-Teleskops, welches im Bereich von ~0.1 – 10 TeV beobachtet, nahm in dieser Arbeit ein zentrale Rolle ein. Daten der übrigen Instrumente wurde entweder über Anträge auf Beobachtungszeit oder Kooperationen mit den Instrumententeams vom Autor dieser Arbeit eingeworben. Entsprechende Daten wurden hauptsächlich in einer finalen Form übermittelt. In dieser Arbeit werden die individuellen Lichtkurven untersucht sowie für die Suche nach Korrelationen zwischen den verschiedenen Bändern verwendet. Für beide Quellen konnte keine Korrelation zwischen dem Radio- und optischen Bereich gefunden werden, was darauf hindeutet, dass deren Strahlung in unterschiedlichen Regionen des Jets produziert wird. Mit Hilfe der gewonnenen Daten wurden quasi-simultane spektrale Energieverteilungen in je zwei unterschiedlichen Flusszuständen ermittelt und mit Hilfe eines Ein-Zonen sowie eines selbst-konsistenten Zwei-Zonen-Synchrotron-Selbst-Compton-Modells beschrieben. Erste Versuche, die Energieverteilungen mit Hilfe einer Chi2-Minimisierungsstrategie zu untersuchen werden kurz erläutert. Die gewonnen Modellparameter, welche die physikalischen Eigenschaften der Emissionsregionen charakterisieren, werden mit Archivdaten verglichen. Obwohl die Modelle die spektralen Energieverteilungen gut beschreiben können, deuten die Modellparameter darauf hin, dass neben der Synchrotron- und invers-Compton-Strahlung relativistischer Elektronen auch Protonen zur Emission beitragen. Im Fall von 1ES 2344+514 konnte einer der niedrigsten jemals gemessenen Flusszustände beobachtet werden, welcher jedoch nicht durch Modellparameter gegeben ist, die auf einen Grundzustand der Quelle hindeuten würden. Eine Ursache hierfür könnte in der Entartung der Modellparameter der ein-Zonen-Modelle liegen. Zusätzlich zeichnet sich ab, dass mehrere Regionen für die beobachtete Emission verantwortlich sind. Die gewonnenen Ergebnisse sind schwer mit aktuellen Szenarien der Klassifikation der Blazare sowie der sogenannten “Blazar-Sequenz” vereinbar. Diese Erkenntnisse verdeutlichen, dass eine realistischere, auf grundlegenden Parametern basierende Interpretation der Systematiken der spektralen Energieverteilungen von Nöten ist.

Zsfassung in dt. Sprache. - Würzburg, Univ., Diss., 2008

Thesis ( Ph.D.). / Written for the Dept. of Physics. Title from title page of PDF (viewed 2009/06/11). Includes bibliographical references.

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.

La présente thèse porte sur quatre aspects différents de l’astronomie des hautes énergies.La première partie de ma thèse est dédiée à un développement instrumental pour les télescopes Cherenkov imageurs, le système de déclenchement de niveau 2 du télescope de 28 mètres du réseau H.E.S.S. (High Energy Stereoscopic System). Mon travail s’est focalisé sur l’invention d’algorithmes et les simulations Monte-Carlo du système de déclenchement, ainsi que la comparaison de la reconstruction au niveau de la carte de déclenchement à la reconstruction ”hors-ligne” (Moudden,Barnacka, Glicenstein et al. 2011a; Moudden, Venault, Barnacka et al. 2011b). Je décris le système et j’évalue ses performances.Le réseau H.E.S.S. a observé le blazar PKS1510-089. La deuxième partie de ma thèse traite de l’analyse des données et la modélisation de l’émission large bande de ce blazar. C’est un exemple de quasar radio à spectre plat (FSRQ), pour lequel il n’est attendu aucune émission aux très hautes énergiesJ’ai modélisé les données observées pendant un "flare” de PKS1510-089. Ce modèle est basé sur un scénario de choc interne à une zone.Le troisième chapitre de ma thèse est une étude d’un autre phénomène affectant potentiellement les blazars observés par FERMI-LAT: l’effet de lentille gravitationnelle fort. Cette partie de ma thèse montre le premier indice de présence d’un effet de lentille gravitationnelle dans le domaine des photons de haute énergie. Cet indice provient de l’observation d’un écho dans la courbe de lumière du blazar distant PKS1830-211, qui est une lentille gravitationnelle connue. Les méthodes d’estimation des retards temporels dans les systèmes de lentille gravitationnelles reposent sur la corrélation croisée des courbes de lumière individuelles. Dans l’analyse présentée dans cette thèse, j’ai utilisé des photons de 300 MeV à 30 GeV détectés par l’instrument FERMI-LAT. L’instrument FERMI-LAT ne peut pas séparer spatialement les images des lentilles gravitationnelles fortes connues. La courbe de lumière observée est donc la superposition des courbes de lumière des images individuelles. Les données du FERMI-LAT ont l’avantage d’être des séries temporelles régulièrement espacées,avec un bruit de photons très bas. Cela permet d’utiliser directement les méthodes de transformées de Fourier. Un retard temporel entre les images compactes de PKS1830-211 a été recherché par deux méthodes : une méthode d’auto-corrélation et la méthode du ”double spectre”. La méthode du double spectre fournit un signal de 27 ± 0.6jours (statistique) avec une significativité de 4.2 σ. Ce résultat est compatible avec ceux de Lovell et al (1998) et Wiklind et Combes (2001).La dernière partie de ma thèse est consacrée à un effet de lentille différent, le ”femtolensing”. La recherche d’effets de femtolensing a été utlisée pour obtenir des limites sur l’abondance de trous noirs primordiaux. Celle-ci a été contrainte de manière significative dans un large domaine de masses. Les limites les moins contraignantes ont été établies pour les objets de faible masse, pour lesquels la détection représente un défi expérimental. J’ai utilisé les sursauts gamma de redshift connus d´etectés par le Fermi Gamma Ray Burst Monitor (GBM) pour rechercher d’éventuels effets de femtolensing produits par des objets compacts sur la ligne de visée. L’absence de ces effets de femtolensing montre que des trous noirs primordiaux de masse comprises entre 5×10^17 et 10^20 g ne constituent pas une fraction importante de la matière noire. J’ai effectué mes études de thèse en co-tutelle entre le Centre Astronomique Nicolaus Copernicus de l’académie des sciences polonaise, à Varsovie et l’Institut de Recherches sur les Lois fondamentales de l’Univers du CNRS à Saclay, en France. / This thesis presents the study of four aspects of high energy astronomy.The first part of my thesis is dedicated to an aspect of instrument development for imaging atmospheric Cherenkov telescopes, namely the Level 2 trigger system of the High Energy Stereoscopic System (H.E.S.S.). My work on the project focused on the algorithm development and the Monte Carlo simulations of the trigger system and overall instrument (Moudden, Barnacka, Glicenstein et al. 2011a; Moudden, Venault, Barnacka et al. 2011b). The hardware implementation of the system is described andits expected performances are then evaluated. The H.E.S.S. array has been used to observe the blazar PKS 1510-089.The second part of my thesis deals with the data analysis and modeling of broad-band emission of this particular blazar. In part II of my thesis, I am presenting the analysis of the H.E.S.S. data: the light curve and spectrum of PKS 1510-089, together with the FERMI data and a collection of multi-wavelength data obtained with various instruments. I am presenting the model of PKS 1510-089 observations carried out during a flare recorded by H.E.S.S.. The model is based on a single zone internal shock scenario.The third part of my thesis deals with blazars observed by the FERMI-LAT, but from the point of view of other phenomena: a strong gravitational lensing. This part of my thesis shows the first evidence for gravitational lensing phenomena in high energy gamma-rays. This evidence comes from the observation of a gravitational lens system induced echo in the light curve of the distant blazar PKS 1830-211. Traditionalmethods for the estimation of time delays in gravitational lensing systems rely on the cross-correlation of the light curves from individual images. In my thesis, I used 300 MeV-30 GeV photons detected by the Fermi-LAT instrument. The FERMI-LAT instrument cannot separate the images of known lenses. The observed light curve is thus the superposition of individual image light curves. The FERMI-LAT instrument has the advantage of providing long, evenly spaced, time series with very low photonnoise. This allows to use directly Fourier transform methods. A time delay between the two compact images of PKS 1830-211 has been searchedfor both by the autocorrelation method and a new method: the “double power spectrum”. The double power spectrum shows a 4.2 σ evidence for a time delay of 27.1±0.6 days (Barnacka et al. 2011), consistent with the results from Lovell et al. (1998) and Wiklind & Combes (2001).The last part of my thesis concentrates on another lensing phenomena called ”femtolensing”. The search for femtolensing effects has been used to derive limits on the primordial black holes abundance. The abundance of primordial black holes is currently significantly constrained in a wide range of masses. The weakest limits are established for the small mass objects, where the small intensity of the associated physical phenomenon provides a challenge for current experiments. I have usedgamma-ray bursts with known redshifts detected by the FERMI Gamma-ray Burst Monitor (GBM) to search for the femtolensing effects caused by compact objects. The lack of femtolensing detection in the GBM data provides new evidence that primordial black holes in the mass range 5 × 10^17 – 10^20 g do not constitute a major fraction of dark matter (Barnacka et al. 2012). My Ph.D. studies have been carried out jointly between the Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences, in Warsaw in Poland and the IRFU institute of the Commissariat à l’énergie atomique et aux énergies alternatives(CEA) Saclay in France.

Blazars are variable emitters across all wavelengths over a wide range of timescales, from months down to minutes. It is therefore essential to observe blazars simultaneously at different wavelengths, especially in the X-ray and gamma-ray bands, where the broadband spectral energy distributions usually peak. In this work, we report on three " target-of-opportunity" observations of Mrk 421, one of the brightest TeV blazars, triggered by a strong flaring event at TeV energies in 2014. These observations feature long, continuous, and simultaneous exposures with XMM-Newton (covering the X-ray and optical/ultraviolet bands) and VERITAS (covering the TeV gamma-ray band), along with contemporaneous observations from other gamma-ray facilities (MAGIC and Fermi-Large Area Telescope) and a number of radio and optical facilities. Although neither rapid flares nor significant X-ray/TeV correlation are detected, these observations reveal subtle changes in the X-ray spectrum of the source over the course of a few days. We search the simultaneous X-ray and TeV data for spectral hysteresis patterns and time delays, which could provide insight into the emission mechanisms and the source properties (e. g., the radius of the emitting region, the strength of the magnetic field, and related timescales). The observed broadband spectra are consistent with a one-zone synchrotron self-Compton model. We find that the power spectral density distribution at greater than or similar to 4 x 10(-4) Hz from the X-ray data can be described by a power-law model with an index value between 1.2 and 1.8, and do not find evidence for a steepening of the power spectral index (often associated with a characteristic length scale) compared to the previously reported values at lower frequencies.