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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.

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.

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.

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 active galactic nuclei characterized by ultra-luminous broad-band, non-thermal radio to gamma-ray continuum radiation, and by irregular, rapid flux variability across wavebands. They are divided into two subclasses: BL Lac objects and flat spectrum radio quasars (FSRQs). A primary method employed to probe our understanding of these objects is to study their spectral energy distributions (SEDs). Until recently, however, studies of blazar SEDs have been hindered by an insufficient number of simultaneous observations across the spectrum, a critical deficiency with such variable objects. In this thesis, I discuss the data accumulated by an international, long-term, 35-blazar monitoring program led by the Boston University blazar group. By systematically processing these data, I produce SEDs using measurements obtained on average within nine hours per epoch. Sufficient measurements exist within the data set to study the sources in differing states of activity. I propose a definition of quiescent and active states, and extract measurements for epochs during which the sources were either quiescent or active in the gamma-ray regime. For these epochs, I measure the spectral slopes and statistically analyze the relationships between slopes at the different frequency regimes. While the subclasses exhibit some distinct characteristics in the optical and gamma-ray indices when quiescent, these distinctions are significantly less pronounced when the objects are active. The spectral indices for the FSRQs steepen when active in the optical, flatten in the gamma-ray, and remain flat and stable in the X-ray. Generally, BL Lacs exhibit less pronounced changes between states than do the FSRQs.

The extragalactic gamma-ray sky is dominated by blazars, active galactic nuclei (AGN) with a relativistic jet that is closely aligned with the line of sight. Galaxies develop an active nucleus if the central supermassive black hole (BH) accretes large amounts of ambient matter and magnetic flux. The inflowing mass accumulates around the plane perpendicular to the accretion flow's angular momentum. The flow is heated through viscous friction and part of the released energy is radiated as blackbody or non-thermal radiation, with luminosities that can dominate the accumulated stellar luminosity of the host galaxy. A fraction of the accretion flow luminosity is reprocessed in a surrounding field of ionised gas clouds. These clouds, revolving around the central BH, emit Doppler-broadened atomic emission lines. The region where these broad-line-emitting clouds are located is called broad-line region (BLR). About one in ten AGN forms an outflow of radiation and relativistic particles, called a relativistic jet. According to the Blandford-Znajek mechanism, this is facilitated through electromagnetic processes in the magnetosphere of a spinning BH. The latter induces a magnetospheric poloidal current circuit, generating a decelerating torque on the BH and inducing a toroidal magnetic field. Consequently, rotational energy of the BH is converted to Poynting flux streaming away mainly along the rotational axis and starting the jet. One possibility for particle acceleration near the jet base is realised by magnetospheric vacuum gaps, regions temporarily devoid of plasma, such that an intermittent electric field arises parallel to the magnetic field lines, enabling particle acceleration and contributing to the mass loading of the jets. Magnetised structures, containing bunches of relativistic electrons, propagate away from the galactic nucleus along the jets. Assuming that these electrons emit synchrotron radiation and that they inverse-Compton (IC) up-scatter abundant target photons, which can either be the synchrotron photons themselves or photons from external emitters, the emitted spectrum can be theoretically determined. Additionally taking into account that these emission regions move relativistically themselves and that the emission is Doppler-boosted and beamed in forward direction, the typical two-hump spectral energy distribution (SED) of blazars is recovered. There are however findings that challenge this well-established model. Short-time variability, reaching down to minute scales at very high energy gamma rays, is today known to be a widespread phenomenon of blazars, calling for very compact emission regions. In most models of such optically thick emission regions, the gamma-ray flux is usually pair-absorbed exponentially, without considering the cascade evolving from the pair-produced electrons. From the observed flux, it is often concluded that emission emanates from larger distances where the region is optically thin, especially from outside of the BLR. Only in few blazars gamma-ray attenuation associated with pair absorption in the BLR was clearly reported. With the advent of sophisticated high-energy or very high energy gamma-ray detectors, like the Fermi Large Area Telescope or the Major Atmospheric Gamma-ray Imaging Cherenkov telescopes, besides the extraordinarily fast variability spectral features have been found that cannot be explained by conventional models reproducing the two-hump SED. Two such narrow spectral features are discussed in this work. For the nearby blazar Markarian 501, hints to a sharp peak around 3 TeV have been reported from a multi-wavelength campaign carried out in July 2014, while for 3C 279 a spectral dip was found in 2018 data, that can hardly be described with conventional fitting functions. In this work it is examined whether these spectral peculiarities of blazar jet emission can be explained, if the full radiation reprocessing through an IC pair cascade is accounted for. Such a cascade is the multiple concatenation of IC scattering events and pair production events. In the cascades generally considered in this work, relativistic electrons and high-energy photons are injected into a fixed soft target photon field. A mathematical description for linear IC pair cascades with escape terms is delivered on the basis of preliminary works. The steady-state kinetic equations for the electrons and for the photons are determined, whereby it is paid attention to an explicit formulation and to motivating the correct integration borders of all integrals from kinematic constraints. In determining the potentially observable gamma-ray flux, both the attenuated injected flux and the flux evolving as an effect of IC up-scattering, pair absorption and escape are incorporated, giving the emerging spectra very distinct imprints. Much effort is dedicated to the numerical solution of the electrons' kinetic equation via iterative schemes. It is explained why pointwise iteration from higher to lower Lorentz factors is more efficient than iterating the whole set of sampling points. The algorithm is parallelised at two positions. First, several workers can perform pointwise iterations simultaneously. Second, the most demanding integral is cut into a number of part integrals which can be determined by multiple workers. Through these measures, the Python code can be readily applied to simulate steady-state IC pair cascades with escape. In the case of Markarian 501 the developed framework is as follows. The AGN hosts an advection-dominated accretion flow with a normalised accretion rate of several \(10^{-4}\) and an electron temperature near \(10^{10}\) K. On the one hand, the accretion flow illuminates the few ambient gas clouds with approximate radius \(10^{11}\) m, which reprocess a fraction 0.01 of the luminosity into hydrogen and helium emission lines. On the other hand, the gamma rays from the accretion flow create electrons and positrons in a sporadically active vacuum gap in the BH magnetosphere. In the active gap, a power of roughly 0.001 of the Blandford-Znajek power is extracted from the rotating BH through a gap potential drop of several \(10^{18}\) V, generating ultra-relativistic electrons, which subsequently are multiplied by a factor of about \(10^6\) through interaction with the accretion flow photons. This electron beam propagates away from the central engine and encounters the photon field of one passing ionised cloud. The resulting IC pair cascade is simulated and the evolving gamma-ray spectrum is determined. Just above the absorption troughs due to the hydrogen lines, the spectrum exhibits a narrow bump around 3 TeV. When the cascaded emission is added to the emission generated at larger distances, the observed multi-wavelength SED including the sharp peak at 3 TeV is reproduced, underlining that radiation processes beyond conventional models are motivated by distinct spectral features. The dip in the spectrum of 3C 279 is addressed by a similar cascade model. Three types of injection are considered, varying in the ratio of the photon density to the electron density and varying in the spectral shape. The IC pair cascade is assumed to happen either in the dense BLR photon field with a luminosity of several \(10^{37}\) W and a radial size of few \(10^{14}\) m or in the diluted photon field outside of the BLR. The latter scenario is however rejected as the spectral slope around several 100 MeV and the dip at few 10 GeV cannot be reconciled within this model. The radiation cascaded in the BLR can explain the observational data, irrespective of the assumed injected rate. It is therefore concluded that for this period of gamma-ray emission, the radiation production happens at the edge of the BLR of 3C 279. Both investigations show that IC pair cascades can account for fine structure seen in blazar SEDs. It is insufficient to restrict the radiation transport to pure exponential absorption of an injection term. Pair production and IC up-scattering by all generations of photons and electrons in the optically thick regime critically shape the emerging spectra. As the advent of future improved detectors will provide more high-precision spectra, further observations of narrow spectral features can be expected. It seems therefore recommendable to incorporate cascading into conventional radiation production models or to extend the model developed in this work by synchrotron radiation. / Beobachtet man das Firmament im Licht der Gammastrahlung, stellen Blasare die Mehrzahl extragalaktischer Objekte dar. Blasare sind aktive Galaxienkerne mit einem relativistischen Jet, der entlang der Sichtlinie ausgerichtet ist. Galaxien haben einen aktiven Kern, wenn das zentrale supermassereiche Schwarze Loch große Mengen an Umgebungsmaterie und magnetischem Fluss akkretiert. Die nach Innen strömende Masse sammelt sich nahe der Ebene an, die senkrecht zum Drehimpuls des Akkretionsflusses steht. Das akkretierte Material wird durch viskose Reibung aufgeheizt und ein Teil der freigesetzten Energie wird als Schwarzkörper- oder nicht-thermische Strahlung abgestrahlt, deren Leuchtkraft die gesamte stellare Leuchtkraft der Wirtsgalaxie übertreffen kann. Ein Teil der Leuchtkraft des Akkretionsflusses wird in einem umgebenden Feld von ionisierten Gaswolken reprozessiert. Diese Wolken, die um das zentrale Schwarze Loch kreisen, emittieren Doppler-verbreiterte Emissionslinien. Den Teil des aktiven Galaxienkerns, in dem sich diese Wolken befinden, bezeichnet man als BLR (englisch: broad-line region). Ihr Abstand zum zentralen Schwarzen Loch beträgt typischerweise etwa 0,1 pc. Etwa einer von zehn aktiven Galaxienkernen bildet einen Ausfluss von Strahlung und relativistischen Teilchen aus, einen sogenannten relativistischen Jet. Dies wird gemäß dem Blandford-Znajek-Mechanismus durch elektromagnetische Prozesse in den Magnetosphären rotierender Schwarzer Löcher bewerkstelligt. Letztere induzieren einen poloidalen magnetosphärischen Stromkreis, der ein abbremsendes Drehmoment auf das Schwarze Loch ausübt und ein toroidales Magnetfeld erzeugt. Folglich wird die Rotationsenergie des Schwarzen Lochs in Poynting-Fluss umgewandelt, der hauptsächlich entlang der Rotationsachse abfließt und den Jet entstehen lässt. Durch Prozesse, die noch nicht eindeutig identifiziert wurden, werden geladene Teilchen in der Nähe der Jetbasis beschleunigt. Eine Möglichkeit dafür ist Teilchenbeschleunigung in magnetosphärischen Vakuum-Lücken. Dies sind Regionen, die vorübergehend nahezu frei von Plasma sind, sodass zeitweise ein elektrisches Feld parallel zu den Magnetfeldlinien entsteht, das die Teilchenbeschleunigung ermöglicht und zur Aufladung der Jets mit massebehafteten Teilchen beiträgt. Magnetisierte Strukturen, die relativistische Elektronen enthalten, bewegen sich entlang der Jets vom Galaxienkern weg. Unter der Annahme, dass diese Elektronen Synchrotronstrahlung aussenden und dass sie vorhandenen weichen Photonen, die entweder die Synchrotronphotonen selbst oder Photonen von externen Emittern sein können, durch inverse Compton-Streuung höhere Energien verleihen, kann das emittierte Spektrum berechnet werden. Berücksichtigt man zusätzlich, dass sich diese Emissionsgebiete selbst relativistisch bewegen und dass die Emission Doppler-verstärkt ist und bevorzugt in Vorwärtsrichtung abgestrahlt wird, erhält man die typische zweihöckrige spektrale Energieverteilung von Blasaren. Es gibt jedoch Erkenntnisse, die dieses bewährte Modell in Frage stellen. Kurzzeit-Variabilität, die bei sehr hochenergetischer Gammastrahlung bis zu Minuten-Skalen hinunterreicht, ist ein weit verbreitetes Phänomen bei Blasaren und setzt sehr kompakte Emissionsregionen voraus. In den meisten Modellen für solche optisch dicken Emissionsregionen wird der Gammastrahlenfluss durch Paarbildung lediglich exponentiell absorbiert, ohne die Kaskade zu berücksichtigen, die sich durch die erzeugten Elektronen entwickelt. Aus den Beobachtungen wird oft gefolgert, dass die Emission aus optisch dünnen Regionen bei größeren Entfernungen stammt, insbesondere von außerhalb der BLR. Nur bei wenigen Blasaren wurde eine Abschwächung der Gammastrahlung durch Absorption in der BLR eindeutig nachgewiesen. Durch moderne Gammastrahlen-Detektoren, wie das Fermi Large Area Telescope oder den Major Atmospheric Gamma-ray Imaging Cherenkov Teleskopen, wurden neben der Kurzzeit-Variabilität auch spektrale Merkmale gefunden, die nicht durch konventionelle Modelle, die die zweihöckrigen spektralen Energieverteilungen wiedergeben können, erklärt werden können. Zwei solcher besonderen spektralen Merkmale werden in dieser Arbeit diskutiert. Für den Blasar Markarian 501 wurden bei einer im Juli 2014 durchgeführten Multiwellenlängenkampagne Hinweise auf einen schmalen Buckel bei 3 TeV gefunden, während für 3C 279 in Daten von 2018 eine Mulde im Spektrum gefunden wurde, die mit oft verwendeten Fit-Funktionen nur schlecht beschrieben werden kann. In dieser Arbeit wird untersucht, ob diese spektralen Besonderheiten der Blasar-Jet-Emission erklärt werden können, wenn die vollständige Reprozessierung der Strahlung durch eine inverse Compton-Paar-Kaskade berücksichtigt wird. Eine solche Kaskade ist die mehrfache Aneinanderreihung von inverser Compton-Streuung und Paarproduktion. Bei den in dieser Arbeit allgemein betrachteten Kaskaden werden relativistische Elektronen und hochenergetische Photonen in eine Region mit niederenergetischen Photonen konstanter Dichte injiziert. Auf der Grundlage von Vorarbeiten wird eine mathematische Beschreibung für lineare inverse Compton-Paar-Kaskaden mit Entweichtermen ausgearbeitet. Es werden die zeit-unabhängigen kinetischen Gleichungen für Elektronen und Photonen hergeleitet, wobei auf eine vollständige Formulierung und auf die Begründung der korrekten Integrationsgrenzen aller Integrale durch die kinematischen Vorgaben geachtet wird. Bei der Bestimmung des potentiell beobachtbaren Gammastrahlenflusses werden sowohl der teilweise absorbierte, injizierte Fluss als auch der Fluss, der sich als Effekt der inversen Compton-Streuung, der Paar-Absorption und des Entweichens ergibt, einbezogen, was den entstehenden Spektren charakteristische Formen aufprägt. Die kinetische Gleichung der Elektronen wird durch iterative Vorgehensweisen numerisch gelöst. Es wird erklärt, warum eine punktweise Iteration von höheren zu niedrigeren Lorentz-Faktoren effizienter ist als die Iteration des gesamten Satzes von Stützstellen. Der Algorithmus wird an zwei Stellen parallelisiert. Erstens können mehrere Prozessor-Kerne gleichzeitig punktweise Iterationen durchführen. Zweitens wird das rechenintensivste Integral in mehrere Teilintegrale zerlegt, die von mehreren Kernen berechnet werden können. Durch diese Maßnahmen kann der Python-Code zur Simulation von zeitunabhängigen inversen Compton-Paar-Kaskaden eingesetzt werden. Im Fall von Markarian 501 wird folgendes Modell bemüht. Der aktive Galaxienkern hat einen advektionsdominierten Akkretionsfluss mit einer normalisierten Akkretionsrate von mehreren \(10^{-4}\) und einer Elektronentemperatur um \(10^{10}\) K. Einerseits bestrahlt der Akkretionsfluss die wenigen umgebenden Gaswolken mit ungefährem Radius von \(10^{11}\) m, die einen Faktor 0,01 der Leuchtkraft in Form von Wasserstoff- und Helium-Emissionslinien wieder abstrahlen. Andererseits erzeugen die vom Akkretionsfluss stammenden Gammaphotonen in einer zeitweise aktiven Vakuum-Lücke in der Magnetosphäre des Schwarzen Lochs Elektronen und Positronen. In der geöffneten Lücke wird dem rotierenden Schwarzen Loch durch einen Potentialunterschied von mehreren \(10^{18}\) V eine Leistung von etwa 0,001 der Blandford-Znajek-Leistung entzogen, wodurch ultra-relativistische Elektronen erzeugt werden, die anschließend durch Wechselwirkung mit den Photonen des Akkretionsflusses um einen Faktor von etwa \(10^6\) multipliziert werden. Dieser Elektronenstrahl verlässt die Magnetosphäre und trifft auf das Photonenfeld einer vorbeiziehenden ionisierten Wolke. Die daraus resultierende inverse Compton-Paar-Kaskade wird simuliert und das sich ergebende Gammastrahlenspektrum wird berechnet. Unmittelbar oberhalb der durch die Wasserstofflinien verursachten Absorptionströge erscheint bei rund 3 TeV ein schmaler Höcker. Wenn die Strahlung der Kaskade der aus größerer Entfernung stammenden Strahlung überlagert wird, wird die gesamte spektrale Energieverteilung einschließlich des scharfen Buckels bei 3 TeV reproduziert. Das bedeutet, dass schmale spektrale Merkmale für die Relevanz von Strahlungsprozessen sprechen, die über konventionelle Modelle hinausgehen. Der Trog im Spektrum von 3C 279 wird mit einem ähnlichen Kaskadenmodell untersucht. Es werden drei Fälle der Injektion betrachtet, die sich im Verhältnis der Photonen-Anzahl zur Elektronen-Anzahl und im spektralen Verlauf unterscheiden. Es wird angenommen, dass die Kaskade entweder im dichten Photonenfeld der BLR mit einer Leuchtkraft von mehreren \(10^{37}\) W und einer radialen Ausdehnung von einigen \(10^{14}\) m oder im ausgedünnten Photonenfeld außerhalb der BLR stattfindet. Das letztgenannte Szenario muss jedoch verworfen werden, da die spektrale Steigung bei einigen 100 MeV und der Absorptionstrog bei einigen 10 GeV innerhalb dieses Modells nicht miteinander in Einklang gebracht werden können. Die innerhalb der BLR kaskadierte Strahlung kann die Beobachtungsdaten unabhängig von der angenommenen Injektionsrate erklären. Daraus folgt, dass die Gammastrahlung während dieses Emissionsereignisses am Rande der BLR von 3C 279 produziert wird. Beide Untersuchungen zeigen, dass inverse Compton-Paar-Kaskaden Feinstrukturen in der spektralen Energieverteilung von Blasaren erklären können. Es reicht nicht aus, den Strahlungstransport auf reine exponentielle Absorption eines Injektionsterms zu beschränken. Paarbildung und inverse Compton-Streuung im optisch dicken Bereich und über alle Generationen von Photonen und Elektronen hinweg prägen die entstehenden Spektren entscheidend. Da künftige, verbesserte Detektoren detailliertere Spektren liefern werden, darf man weitere Berichte über schmale spektrale Merkmale erwarten. Es erscheint daher empfehlenswert, die Kaskadierung in konventionelle Modelle der Strahlungsproduktion mit einzubeziehen oder das in dieser Arbeit entwickelte Modell um Synchrotronstrahlung zu erweitern.

No description available.