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Статті в журналах з теми "Active Galactic Nuclei – Blazars – Gamma-ray blazars"
TAVECCHIO, F. "GAMMA-RAY EMISSION FROM AGNS (SPECIAL FOCUS ON BL LAC OBJECTS)." International Journal of Modern Physics D 19, no. 06 (June 2010): 841–48. http://dx.doi.org/10.1142/s0218271810017081.
Повний текст джерелаUwitonze, Emmanuel, Pheneas Nkundabakura, and Tom Mutabazi. "Determination of K4000 of potential blazar candidates among EGRET unidentified gamma-ray sources." Proceedings of the International Astronomical Union 15, S356 (October 2019): 355–57. http://dx.doi.org/10.1017/s1743921320003336.
Повний текст джерелаTakahashi, T., H. Kubo, and G. Madejski. "ASCA Observations of Blazars." Highlights of Astronomy 11, no. 2 (1998): 812–15. http://dx.doi.org/10.1017/s1539299600018852.
Повний текст джерелаLangejahn, M., M. Kadler, J. Wilms, E. Litzinger, M. Kreter, N. Gehrels, W. H. Baumgartner, C. B. Markwardt, and J. Tueller. "Hard X-ray properties of radio-selected blazars." Astronomy & Astrophysics 637 (May 2020): A55. http://dx.doi.org/10.1051/0004-6361/202037469.
Повний текст джерелаPaggi, Alessandro, R. D'Abrusco, F. Massaro, M. Landoni, D. Milisavljevic, N. Masetti, F. Ricci, et al. "Multi-wavelength selection and identification of gamma-ray blazar candidates." Proceedings of the International Astronomical Union 10, S313 (September 2014): 58–63. http://dx.doi.org/10.1017/s1743921315001878.
Повний текст джерелаBhatta, Gopal. "Blazar Jets as Possible Sources of Ultra-High Energy Photons: A Short Review." Universe 8, no. 10 (October 1, 2022): 513. http://dx.doi.org/10.3390/universe8100513.
Повний текст джерелаPaggi, A., M. Bonato, C. M. Raiteri, M. Villata, G. De Zotti, and M. I. Carnerero. "A new multiwavelength census of blazars." Astronomy & Astrophysics 641 (September 2020): A62. http://dx.doi.org/10.1051/0004-6361/202038430.
Повний текст джерелаXiao, Hubing, Junhui Fan, Zhihao Ouyang, Liangjun Hu, Guohai Chen, Liping Fu, and Shaohua Zhang. "An Extensive Study of Blazar Broad Emission Line: Changing-look Blazars and the Baldwin Effect." Astrophysical Journal 936, no. 2 (September 1, 2022): 146. http://dx.doi.org/10.3847/1538-4357/ac887f.
Повний текст джерелаLott, B., E. Cavazzuti, S. Ciprini, S. Cutini, and D. Gasparrini. "Gamma-ray blazars and active galactic nuclei seen by the Fermi-LAT." Proceedings of the International Astronomical Union 10, S313 (September 2014): 12–16. http://dx.doi.org/10.1017/s1743921315001787.
Повний текст джерелаSikora, Marek. "High-Energy Radiation From Active Galactic Nuclei." International Astronomical Union Colloquium 142 (1994): 923–28. http://dx.doi.org/10.1017/s0252921100078325.
Повний текст джерелаДисертації з теми "Active Galactic Nuclei – Blazars – Gamma-ray blazars"
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.
Повний текст джерелаDickinson, Mark R. "Very high energy gamma ray observations of southern hemisphere blazars." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/4705/.
Повний текст джерелаRoustazadeh, Sheikhyousefi Parisa. "Pair Cascades in Blazars and Radio Galaxies." Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1327333900.
Повний текст джерелаArrieta, Lobo Maialen. "A study of the emission processes of two different types of gamma-emitting Active Galactic Nuclei." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLE0010/document.
Повний текст джерелаThis thesis manuscript presents the study of the emission processes of two types of gamma-emitting active galactic nuclei: TeV-detected blazars and GeV-detected Narrow Line Seyfert 1s (NLS1s).The Spectral Energy Distribution (SED) of TeV blazars can in general be well described by simple one-zone synchrotron self-Compton models. Such model has been applied to the blazar 1ES2322-409 that was first detected at TeV by the HESS collaboration.Additional external photon fields such as the obscuring torus, the accretion disc, the X-ray corona or the broad line region are necessary to describe the observed radiation and broad-band SED of gamma-emitting NLS1s. A numerical model that takes into account emission from these external fields has been developed. The model explains the observed emission and the transition from quiescent to gamma-ray flaring states of three gamma-emitting NLS1s: 1H0323+342, B20954+25A and PMN J0948+0022
Beckmann, Volker. "Unification of Active Galactic Nuclei at X-rays and soft gamma-rays." Habilitation à diriger des recherches, Université Paris-Diderot - Paris VII, 2010. http://tel.archives-ouvertes.fr/tel-00601042.
Повний текст джерелаThe study of the evolutionary behaviour of X-ray selected blazars (Beckmann & Wolter 2001; Beckmann et al. 2002, 2003b; Beckmann 2003) shows that their evolution is not as strongly negative as indicated by previous studies. The overall luminosity function is consistent with no evolution in the 0.1−2.4 keV band as seen by ROSAT/PSPC. There is still a difference compared to the luminosity function of FSRQ and LBL, which seem to show a positive evolution, indicating that they have been more luminous and/or numerous at cosmological distances. We indicated a scenario in order to explain this discrepancy, in which the high luminous FSRQ develop into the fainter LBL and finally into the BL Lac objects with high frequency peaks in their spectral energy distribution but overall low bolometric luminosity.
Studying the variability pattern of hard X-ray selected Seyfert galaxies, we actually found differences between type 1 and type 2 objects, in the sense that type 2 seemed to be more variable (Beckmann et al. 2007a). This breaking of the unified model is caused by the different average luminosity of the absorbed and unabsorbed sources, as discussed in Sect. 4.7.3. This can be explained by a larger inner disk radius when the AGN core is most active (the so-called receding disc model).
The work on the sample characteristics of hard X-ray detected AGN also led to the proof that the average intrinsic spectra of type 1 and type 2 objects are the same when reflection processes are taken into account (Beckmann et al. 2009d). This also explains why in the past Seyfert 2 objects were seen to have harder X-ray spectra than Seyfert 1, as the stronger reflection hump in the type 2 objects makes the spectra appear to be flatter, although the underlying continuum is the same.
Further strong evidence for the unification scheme comes from the observation of a fundamental plane which connects type 1 and type 2 objects smoothly (Beckmann et al. 2009d). In addition, in the case of the Seyfert 1.9 galaxy MCG-05-23-016 I showed that the spectral energy distribution of this source and its accretion rate is similar to that of a Galactic binary (Beckmann et al. 2008a).
Throughout the studies I have shown that the intrinsic spectral shape appears to be very stable on weeks to year time scale (Beckmann et al. 2004d, 2005b, 2007b, 2008a). This implies that the overall geometry of the AGN over these time scales did not change dramatically. The variations in intensity can then be explained in two ways: either the amount of material emitting the hard X-rays varies, or the amount of plasma visible to the observer varied, e.g. through different orientation of the disk with respect to the observer. In an upcoming paper we will show though, that NGC 4151 indeed also shows different spectral states, similar to the low-hard versus high-soft spectra in Galactic black hole binaries (Lubinski et al. 2010). A similar result seems to emerge from our INTEGRAL studies on NGC 2110 (Beckmann & Do Cao 2011). For INTEGRAL's AO-8 I have submitted a proposal in order to study spectral states in the Seyfert 2 galaxy NGC 2992, which seems to show a state change over the past 5 years as seen in Swift/BAT longterm monitoring.
The work on the luminosity function of AGN at hardest X-rays (Beckmann et al. 2006d) had a large impact on our understanding of the cosmic X-ray background. As this was the first study of its kind, it showed for the first time that indeed the fraction of highly obscured Compton thick AGN is much lower than expected before the launch of INTEGRAL and Swift. The X-ray luminosity function we revealed is indeed not consistent with the source population seen by INTEGRAL (Beckmann et al. 2006a, 2009d; Sazonov et al. 2007) and Swift (Tueller et al. 2008) being the only contributors to the cosmic hard X-ray background. Thus other sources outside the parameter space observable by these missions have to contribute significantly to the cosmic X-ray background. Our work on the luminosity function triggered several other studies on this issue. The subsequent derived luminosity functions by other groups (Sazonov et al. 2007; Tueller et al. 2008; Paltani et al. 2008) are consistent with our findings.
This also gave rise to an increased interest in the exact shape of the Cosmic X-ray background around its peak at 30 keV, triggering several attempts to a new measurement. Background studies were presented based on a Earth-occultation observation by INTEGRAL (Churazov et al. 2007, 2008; Türler et al. 2010) and by Swift (Ajello et al. 2008).
The understanding of the emission processes in AGN requires knowledge over a wide range of the spectral energy distribution (SED). In studies using CGRO/EGRET and Fermi/LAT data I derived the SED for blazars and non-blazars towards the gamma-ray range (Beckmann 2003; Beckmann et al. 2004b, 2010b). The work on the LAT data not only presented the gamma-ray detection of five gamma-ray blazars (QSO B0836+710, RX J1111.5+3452, H 1426+428, RX J1924.8-2914, and PKS 2149-306) for the first time, but also showed the potential in the combination of INTEGRAL and Fermi data. In the case of Cen A I derived the total energy output of the inverse Compton component based on the combined LAT, ISGRI, and JEM-X data, showing evidence for a spectral break at several hundred keV (Beckmann et al. 2010b).
In addition I successfully showed that gamma-ray blazars can be predicted through the study of their synchrotron branch at energies below 2 keV (Beckmann 2003 and this work).
Contributions of mine to research in fields other than AGN include the study of INTEGRAL detected gamma-ray bursts (e.g. Beckmann et al. 2003a, 2004a, 2008b, 2009a). Here and in collaboration with other colleagues I showed the potential of INTEGRAL data on GRB research. In the field of Galactic X-ray binaries I published one of the first Swift results on a newly discovered highly absorbed HMXB, IGR J16283-4838 (Beckmann et al. 2005a, 2006b). I also contributed significantly to analysis of many other Galactic sources, as shown in Section 4.6.1.
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.
Повний текст джерелаMany 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
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.
Повний текст джерелаNeutrinos 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
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.
Повний текст джерелаEscande, 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.
Повний текст джерелаThe 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
O'Rourke, Brogan Roisín. "AGN Candidates for High Energy Neutrino Emission in IceCube." Thesis, Uppsala universitet, Högenergifysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-409739.
Повний текст джерелаКниги з теми "Active Galactic Nuclei – Blazars – Gamma-ray blazars"
Urry, Claudia Megan. X-ray temporal and spectral studies of blazars with the Ginga satellite: Final report for NASA grant, NAG8-697. Baltimore, MD: Space Telescope Science Institute, 1994.
Знайти повний текст джерелаUnited States. National Aeronautics and Space Administration., ed. X-ray temporal and spectral studies of blazars with the Ginga satellite: Final report for NASA grant, NAG8-697. Baltimore, MD: Space Telescope Science Institute, 1994.
Знайти повний текст джерелаUnited States. National Aeronautics and Space Administration., ed. X-ray temporal and spectral studies of blazars with the Ginga satellite: Final report for NASA grant, NAG8-697. Baltimore, MD: Space Telescope Science Institute, 1994.
Знайти повний текст джерелаЧастини книг з теми "Active Galactic Nuclei – Blazars – Gamma-ray blazars"
Romero, Gustavo E., M. Boettcher, S. Markoff, and F. Tavecchio. "Relativistic Jets in Active Galactic Nuclei and Microquasars." In Jets and Winds in Pulsar Wind Nebulae, Gamma-Ray Bursts and Blazars, 5–61. Dordrecht: Springer Netherlands, 2017. http://dx.doi.org/10.1007/978-94-024-1292-5_2.
Повний текст джерелаTreves, A., G. Ghisellini, L. Maraschi, and E. G. Tanzi. "Spectral Properties of Blazars Observed at Ultraviolet and X-Ray Frequencies." In Structure and Evolution of Active Galactic Nuclei, 63–80. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-009-4562-3_5.
Повний текст джерелаMaraschi, Laura, Gabriele Ghisellini, and Alfredo Boccasile. "Gamma-Rays from Blazars: a Comparison of 3C 279, PKS 0537-441 and Mrk 421." In The Nature of Compact Objects in Active Galactic Nuclei, 381–84. Cambridge University Press, 1994. http://dx.doi.org/10.1017/cbo9780511564765.090.
Повний текст джерелаТези доповідей конференцій з теми "Active Galactic Nuclei – Blazars – Gamma-ray blazars"
Lott, Benoit. "Gamma-ray blazars and Active Galactic Nuclei seen by the Fermi-LAT." In 11th European VLBI Network Symposium & Users Meeting. Trieste, Italy: Sissa Medialab, 2016. http://dx.doi.org/10.22323/1.178.0018.
Повний текст джерела