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Journal articles on the topic 'Gamma-ray blazars'

Author: Grafiati

Published: 4 June 2021

Last updated: 28 January 2023

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1

Salvati, M., M. Spada, and F. Pacini. "Rapid Variability of Gamma-Ray Blazars." Highlights of Astronomy 11, no. 2 (1998): 816–19. http://dx.doi.org/10.1017/s1539299600018864.

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This paper is devoted to a discussion of the rapid variability observed in γ-ray blazars. We do this in the framework of a widely accepted scenario, according to which the blazar emission arises from a jet, i.e. a continuous flow of relativistic fluid, with perturbations occasionally superimposed. The jet is assumed to have a bulk Lorentz factor Γ ≫ 1, and length z and radius r such that r ã z/Γ.

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Massaro, Francesco, R. D'Abrusco, M. Giroletti, A. Paggi, N. Masetti, and G. Tosti. "Unveiling the nature of the unidentified gamma-ray sources: blazar counterparts at low radio frequencies." Proceedings of the International Astronomical Union 9, S304 (2013): 95. http://dx.doi.org/10.1017/s1743921314003433.

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AbstractAbout one third of the gamma-ray sources detected by Fermi have still no firmly established counterpart at lower energies. Here we propose a new approach to find candidate counterparts for the unidentified gamma-ray sources (UGSs) based on the 325 MHz radio survey performed with Westerbork Synthesis Radio Telescope (WSRT) in the northern hemisphere. First we investigate the low-frequency radio properties of blazars, the largest known population of gamma-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern S

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Uwitonze, 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 (2019): 355–57. http://dx.doi.org/10.1017/s1743921320003336.

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AbstractBlazars are radio-loud Active Galactic Nuclei (AGN) with relativistic jets oriented towards the observer’s line-of-sight. Based on their optical spectra, blazars may be classified as flat-spectrum radio quasars (FSRQs) or BL Lacs. FSRQs are more luminous blazars with both narrow and broad emission and absorption lines, while BL Lacs are less luminous and featureless. Recent studies show that blazars dominate (˜93%) the already-identified EGRET sources (142), suggesting that among the unidentified sources (129) there could still be faint blazars. Due to the presence of a strong non-ther

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Langejahn, M., M. Kadler, J. Wilms, et al. "Hard X-ray properties of radio-selected blazars." Astronomy & Astrophysics 637 (May 2020): A55. http://dx.doi.org/10.1051/0004-6361/202037469.

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Context. Hard X-ray properties of beamed active galactic nuclei have been published in the 105-month Swift/BAT catalog, but there have not been any studies carried out so far on a well-defined, radio-selected sample of low-peaked blazars in the hard X-ray band. Aims. Using the statistically complete MOJAVE-1 sample, we aim to determine the hard X-ray properties of radio-selected blazars, including the enigmatic group of gamma-ray-faint blazars. Additionally, we aim to determine the contribution of radio-selected low-peaked blazars to the diffuse cosmic X-ray background (CXB). Methods. We deter

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Fukazawa, Yasushi, Hiroto Matake, Taishu Kayanoki, Yoshiyuki Inoue, and Justin Finke. "High-energy Emission Component, Population, and Contribution to the Extragalactic Gamma-Ray Background of Gamma-Ray-emitting Radio Galaxies." Astrophysical Journal 931, no. 2 (2022): 138. http://dx.doi.org/10.3847/1538-4357/ac6acb.

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Abstract In this study, we systematically studied the X-ray to GeV gamma-ray spectra of 61 Fermi Large Area Telescope detected radio galaxies. We found an anticorrelation between peak frequency and peak luminosity in the high-energy spectral component of radio galaxies, similar to blazars. With this sample, we also constructed a gamma-ray luminosity function (GLF) of gamma-ray-loud radio galaxies. We found that blazar-like GLF shapes can reproduce their redshift and luminosity distribution, but the log N–log S relation prefers models with more low-z radio galaxies. Utilizing our latest GLF, th

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Takahashi, 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.

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During the last years it has become evident that blazar class of AGN emit a lot of energy in the gamma-ray regime. It is generally thought that the non-thermal emission from blazars, observed from radio to GeV/TeV 7-rays, is radiation of very energetic particles via both synchrotron and Compton processes. This underlines the importance of high-energy emission for models of the blazar class of active galactic nuclei. Most of the gamma-bright AGN are variable, and flares with time scales as short as a day have been observed. This suggests that the site of gamma-ray emission is very compact and s

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Damascène Mbarubucyeye, Jean, Felicia Krauß, and Pheneas Nkundabakura. "Multiwavelength study of potential blazar candidates among Fermi-LAT unidentified gamma-ray sources." Proceedings of the International Astronomical Union 15, S356 (2019): 326–28. http://dx.doi.org/10.1017/s1743921320003245.

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AbstractStudying unidentified γ-ray sources is important as they may hide new discoveries. We conducted a multiwavelength analysis of 13 unidentified Fermi-LAT sources in the 3FGL catalogue that have no known counterparts (Unidentified Gamma-ray Sources, UnIDs). The sample was selected for sources that have a single radio and X-ray candidate counterpart in their uncertainty ellipses. The purpose of this study is to find a possible blazar signature and to model the Spectral Energy Distribution (SED) of the selected sources using an empirical log parabolic model. The results show that the synchr

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GIEBELS, BERRIE. "VERY HIGH ENERGY GAMMA-RAY MEASUREMENTS OF BLAZARS." International Journal of Modern Physics D 17, no. 09 (2008): 1431–41. http://dx.doi.org/10.1142/s0218271808013005.

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The origin of γ-rays emitted by blazars is widely attributed to radiative cooling of the most energetic particles in a relativistic flow, which itself is thought to originate from the surroundings of a supermassive black hole. The linkage between the accreting gas, the black hole, jet formation, and the observed radiation from the jet, are still very difficult to establish. The most energetic γ-rays are likely to be produced close to the comptonizing particles acceleration zone, and are therefore a unique probe of the underlying physical mechanisms at play. This report contains a review of the

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Canac, N. E., K. N. Abazajian, T. Tajima, T. Ebisuzaki, and S. Horiuchi. "Observational signatures of gamma-rays from bright blazars and wakefield theory." Monthly Notices of the Royal Astronomical Society 493, no. 2 (2020): 2229–37. http://dx.doi.org/10.1093/mnras/staa338.

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ABSTRACT Gamma-ray observations have revealed strong variability in blazar luminosities in the gamma-ray band over time-scales as short as minutes. We show, for the first time, that the correlation of the spectrum with intensity is consistent with the behaviour of the luminosity variation of blazar spectral energy distributions (SEDs) along a blazar sequence for low synchrotron peak blazars. We show that the observational signatures of variability with flux are consistent with wakefield acceleration of electrons initiated by instabilities in the blazar accretion disc. This mechanism reproduces

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10

Kreter, Michael. "Search for high-redshift blazars with Fermi-LAT." Proceedings of the International Astronomical Union 15, S356 (2019): 23. http://dx.doi.org/10.1017/s1743921320002501.

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AbstarctHigh-redshift blazars (z ⩾ 2.5) are one of the most powerful classes of gamma-ray sources in the Universe. These objects posses the highest jet powers and luminosities and have black-hole masses often in excess of 109 solar masses. In addition, high-redshift blazars are important cosmological probes and serve as test objects for blazar evolution models. Due to their large distance, their high-energy emission peak is downshifted to energies below the GeV range, which makes them difficult to study with Fermi/LAT and only the very brightest objects are detectable. Hence, only a small numb

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Paggi, Alessandro, R. D'Abrusco, F. Massaro, et al. "Multi-wavelength selection and identification of gamma-ray blazar candidates." Proceedings of the International Astronomical Union 10, S313 (2014): 58–63. http://dx.doi.org/10.1017/s1743921315001878.

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AbstractA significant fraction (~ 30%) of the gamma-ray sources detected by the Fermi Gamma-ray Space Telescope is still of unknown origin, being not yet associated with counterparts at lower energies. Many unidentified gamma-ray sources (UGSs) could be blazars, the largest identified population of extragalactic gamma-ray sources and the rarest class of active galactic nuclei. In particular, it has been found that blazars occupy a defined region in WISE three dimensional color space, well separated from that occupied by other sources in which thermal emission prevails. For farther sources with

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Fan, J. H. "Gamma-ray emission of blazars." Astrophysics and Space Science 246, no. 1 (1997): 119–28. http://dx.doi.org/10.1007/bf00637403.

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Ciprini, Stefano. "Gamma-Ray Waveband and Multi-Waveband Variability of Blazars." Proceedings of the International Astronomical Union 7, S285 (2011): 121–24. http://dx.doi.org/10.1017/s1743921312000415.

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AbstractThe Fermi Gamma-ray Space Telescope, as an all-sky survey and monitoring mission, is producing well-sampled gamma-ray light curves for dozens of blazars and other high-energy sources. We report highlights of gamma-ray variability properties, and outline multi-frequency observing campaigns that are targeted to new or known blazars which emit gamma rays.

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Bower, Geoffrey C. "Millimeter VLBI Observations of the Gamma-Ray Blazar NRAO 530." International Astronomical Union Colloquium 164 (1998): 41–42. http://dx.doi.org/10.1017/s0252921100044432.

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AbstractWe present here 3 epochs of 3 and 7 millimeter wavelength VLBI observations and 2 epochs of lower frequency VLBA imaging of the gamma-ray blazar NRAO 530. These observations document the evolution of the parsec scale jet in this source during the brightest flare in 3 decades. New jet components were created during the flare and are probably related to an increase in gamma-ray activity. The components travel at superluminal velocities, further confirming the connection between superluminal sources and gamma-ray blazars. The rapid evolution of the source makes tracking of components diff

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Pichel, Ana, Laura G. Donoso, Laura D. Baravalle, et al. "High-energy gamma-ray sources in the VVV survey – I. The blazars." Monthly Notices of the Royal Astronomical Society 491, no. 3 (2019): 3448–60. http://dx.doi.org/10.1093/mnras/stz3239.

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ABSTRACT There is a lack of blazar detections in the galactic plane area, even in the most recent blazar catalogues, mainly due to incompleteness resulting from interstellar dust and stellar contamination of our Galaxy. The VISTA Variables in the Vía Láctea survey (VVV) aims to map variable sources towards the galactic plane in the near-infrared (IR). There are three catalogued and one candidate blazars in the VVV area, which are also detected by Fermi-LAT in the gamma-ray band and by the Wide-field Infrared Survey Explorer (WISE) at mid-IR wavelengths. We study the physical properties of thes

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TAVECCHIO, F. "GAMMA-RAY EMISSION FROM AGNS (SPECIAL FOCUS ON BL LAC OBJECTS)." International Journal of Modern Physics D 19, no. 06 (2010): 841–48. http://dx.doi.org/10.1142/s0218271810017081.

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Blazars, radio-loud active galactic nuclei with the relativistic jet closely aligned with the line of sight, dominate the extragalactic sky observed at gamma-ray energies, above 100 MeV. We discuss some of the emission properties of these sources, focusing in particular on the "blazar sequence" and the interpretative models of the high-energy emission of BL Lac objects.

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17

Xiong, Zhang, Zhao Gang, Xie Guang-zhong, Zheng Guang-sheng, and Zhang Li. "Gamma-ray and x-ray emission from gamma-ray-loud blazars." Chinese Physics 10, no. 6 (2001): 568–74. http://dx.doi.org/10.1088/1009-1963/10/6/320.

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Piner, B. G., P. G. Edwards, S. Fodor, and T. A. Rector. "The Parsec-scale Jets of Extragalactic TeV Gamma-ray Sources." Publications of the Astronomical Society of Australia 19, no. 1 (2002): 114–16. http://dx.doi.org/10.1071/as01114.

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AbstractWe present results of VLBI monitoring observations of the blazars detected by ground-based TeV gamma-ray telescopes. Preliminary results have shown that the apparent speeds of the parsec-scale jet features in these sources are predominantly subluminal, and significantly slower than those in the GeV-peaked (EGRET) gamma-ray blazars. Here we add results from additional sources and additional epochs that increase the statistical significance of this comparison. These slower speeds may indicate rapid deceleration of the jets in TeV blazars between the TeV gamma-ray emitting scales and VLBI

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Simpemba, Prospery. "Spectral energy distribution of blazars." Proceedings of the International Astronomical Union 15, S356 (2019): 374. http://dx.doi.org/10.1017/s1743921320003464.

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AbstractThis study focuses on spectral energy distributions and light-curves of blazars and radio galaxies, and the testing of the existing models with a view to appropriately predict a new model that will nearly accurately present the nature of the energy outflows of these super-massive bodies. Understanding blazar emission is very important as it relates more directly to the physics of the AGN’s central black hole. X-ray, radio and gamma-ray wavelength range data on blazars and radio galaxies from archived data has been collected and a detailed investigation of the spectral energy distributi

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Protheroe, R. J. "High Energy Neutrinos from Blazars." International Astronomical Union Colloquium 163 (1997): 585–88. http://dx.doi.org/10.1017/s0252921100043244.

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AbstractI describe a model of energetic gamma ray and neutrino emission in blazars which is consistent with most of the gamma-ray observations, and use this model to estimate the diffuse intensity of high energy neutrinos from blazars.

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GHISELLINI, GABRIELE. "EXTRAGALACTIC GAMMA-RAYS: GAMMA RAY BURSTS AND BLAZARS." International Journal of Modern Physics A 20, no. 29 (2005): 6991–7000. http://dx.doi.org/10.1142/s0217751x05030673.

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The extragalactic gamma-ray sky is dominated by two classes of sources: Gamma-Ray Bursts (GRBs) and radio loud active galactic nuclei whose jets are pointing at us (blazars). We believe that the radiation we receive from them originates from the transformation of bulk relativistic energy into random energy. Although the mechanisms to produce, collimate and accelerate the jets in these sources are uncertain, it is fruitful to compare the characteristics of both classes of sources in search of enlightening similarities. I will review some general characteristics of radio loud AGNs and GRBs and I

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Sobacchi, Emanuele, Joonas Nättilä, and Lorenzo Sironi. "A fully kinetic model for orphan gamma-ray flares in blazars." Monthly Notices of the Royal Astronomical Society 503, no. 1 (2021): 688–93. http://dx.doi.org/10.1093/mnras/stab562.

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ABSTRACT Blazars emit a highly variable non-thermal spectrum. It is usually assumed that the same non-thermal electrons are responsible for the IR-optical-UV emission (via synchrotron) and the gamma-ray emission (via inverse Compton). Hence, the light curves in the two bands should be correlated. Orphan gamma-ray flares (i.e. lacking a luminous low-frequency counterpart) challenge our theoretical understanding of blazars. By means of large-scale two-dimensional radiative particle-in-cell simulations, we show that orphan gamma-ray flares may be a self-consistent by-product of particle energizat

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Böttcher, Markus. "Progress in Multi-Wavelength and Multi-Messenger Observations of Blazars and Theoretical Challenges." Galaxies 7, no. 1 (2019): 20. http://dx.doi.org/10.3390/galaxies7010020.

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This review provides an overview of recent advances in multi-wavelength and multi-messenger observations of blazars, the current status of theoretical models for blazar emission, and prospects for future facilities. The discussion of observational results will focus on advances made possible through the Fermi Gamma-Ray Space Telescope and ground-based gamma-ray observatories (H.E.S.S., MAGIC, VERITAS), as well as the recent first evidence for a blazar being a source of IceCube neutrinos. The main focus of this review will be the discussion of our current theoretical understanding of blazar mul

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Kovačević, M., G. Chiaro, S. Cutini, and G. Tosti. "Optimizing neural network techniques in classifying Fermi-LAT gamma-ray sources." Monthly Notices of the Royal Astronomical Society 490, no. 4 (2019): 4770–77. http://dx.doi.org/10.1093/mnras/stz2920.

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ABSTRACT Machine learning is an automatic technique that is revolutionizing scientific research, with innovative applications and wide use in astrophysics. The aim of this study was to develop an optimized version of an Artificial Neural Network machine learning method for classifying blazar candidates of uncertain type detected by the Fermi Large Area Telescope γ-ray instrument. The final result of this study increased the classification performance by about 80 ${{\ \rm per\ cent}}$ with respect to previous method, leaving only 15 unclassified blazars out of 573 blazar candidates of uncertain

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Dondi, Laura, and Gabriele Ghisellini. "Gamma-ray-loud blazars and beaming." Monthly Notices of the Royal Astronomical Society 273, no. 3 (1995): 583–95. http://dx.doi.org/10.1093/mnras/273.3.583.

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Halpern, J. P., M. Eracleous, and J. R. Mattox. "Redshifts of Candidate Gamma-Ray Blazars." Astronomical Journal 125, no. 2 (2003): 572–79. http://dx.doi.org/10.1086/345796.

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Blinov, Dmitry, and Vasiliki Pavlidou. "The RoboPol Program: Optical Polarimetric Monitoring of Blazars." Galaxies 7, no. 2 (2019): 46. http://dx.doi.org/10.3390/galaxies7020046.

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After three years of polarimetric monitoring of blazars, the RoboPol project has uncovered several key characteristics of polarimetric rotations in the optical for these most variable sources. The most important of these is that polarization properties of the synchrotron emission in the optical appear to be directly linked with gamma-ray activity. In this paper, we discuss the evidence for this connection, as well as the broader features of polarimetric behavior in blazars that are key in making progress with theoretical modeling of blazar emission.

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Blinov, Dmitry, E. Angelakis, M. Balokovic, et al. "Optical polarization of gamma-ray bright blazars." Proceedings of the International Astronomical Union 9, S304 (2013): 227. http://dx.doi.org/10.1017/s1743921314003846.

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AbstractWe report about first results of the RoboPol project. RoboPol is a large-sample, high-cadence, polarimetric monitoring program of blazars in optical wavelengths, using a camera specifically constructed for this project, mounted at the University of Crete's Skinakas Observatory 1.3 m telescope. The analysis of RoboPol data is conducted in conjunction with Fermi LAT gamma-ray data, and multifrequency radio data from the OVRO (Caltech), F-GAMMA (MPIfR), and Torun (NCU) monitoring programs. Using carefully selected samples of gamma-ray bright and weak blazars we investigate a connection be

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LOTT, BENOIT. "NEW INSIGHT INTO GAMMA-RAY BLAZARS FROM THE FERMI-LAT." International Journal of Modern Physics D 19, no. 06 (2010): 831–39. http://dx.doi.org/10.1142/s021827181001707x.

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The first three months of sky-survey operation with the Large Area Telescope (LAT) on board the Fermi satellite revealed 132 bright sources at |b| > 10° with test statistic greater than 100 (corresponding to about 10σ). Two methods, based on the CGRaBS, CRATES and BZCat catalogs, indicated high-confidence associations of 106 of these sources with known AGNs. This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and four blazars w

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Ghisellini, Gabriele. "X-Ray and Gamma–Ray Emission in Blazars." Symposium - International Astronomical Union 175 (1996): 413–16. http://dx.doi.org/10.1017/s0074180900081286.

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More than 50 sources have been detected by EGRET in 4 years of operations (e.g. von Montigny et al. 1995). Almost all of them show the violent characteristics typical of blazars, such as superluminal motions, strong radio emission mainly produced in a flat spectrum core and large amplitude variability at all frequencies. Interestingly, optical polarization does not seem to be required, since more than 1/3 of the detected sources are less than 3% polarized.

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Marscher, Alan P., and Svetlana G. Jorstad. "Frequency and Time Dependence of Linear Polarization in Turbulent Jets of Blazars." Galaxies 9, no. 2 (2021): 27. http://dx.doi.org/10.3390/galaxies9020027.

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Time-variable polarization is an extremely valuable observational tool to probe the dynamical physical conditions of blazar jets. Since 2008, we have been monitoring the flux and linear polarization of a sample of gamma-ray bright blazars at optical frequencies. Some of the observations were performed on nightly or intra-night time-scales in four optical bands, providing information on the frequency and time dependence of the polarization. The observed behavior is similar to that found in simulations of turbulent plasma in a relativistic jet that contains a standing shock and/or a helical back

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Pei, Z. Y., J. H. Fan, Y. Liu, H. J. Xie, Y. Gao, and C. Lin. "The core dominance parameter for gamma-ray loud blazars." Proceedings of the International Astronomical Union 10, S313 (2014): 83–84. http://dx.doi.org/10.1017/s1743921315001933.

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AbstractIn this work, we compiled 604 blazars with available core-dominance parameter, out of which 149 blazars are known to have γ-ray emissions. We compared the logR between the 149 Fermi-detected blazars (FDB) and the rest non-Fermi-detected blazars (non-FDB), and found that the average values are < logR > = 1.12 ± 0.88 for FDBs and < logR > = 0.05 ± 0.94 for non-FDBs. A K-S test shows that the probability for the distributions of FDB and non-FDB to come from the same parent distribution is P = 2.38 × 10−7. We also investigated the correlation between the core-dominance paramete

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Xie, G. Z., X. Zhang, J. M. Bai, and Z. H. Xie. "Gamma‐Ray and Near‐Infrared Emission from Gamma‐Ray–loud Blazars." Astrophysical Journal 508, no. 1 (1998): 180–85. http://dx.doi.org/10.1086/306378.

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Dermer, Charles D. "Blazar jet physics in the age of Fermi." Proceedings of the International Astronomical Union 6, S275 (2010): 111–21. http://dx.doi.org/10.1017/s1743921310015772.

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AbstractThe impact of the Fermi Gamma-ray Space Telescope on blazar research is reviewed. This includes a brief description of the Fermi Large Area Telescope, a summary of the various classes of extragalactic sources found in the First Large Area Telescope AGN Catalog, and more detailed discussion of the flat spectrum radio quasar 3C454.3 and the BL Lac object PKS 2155-304. Some theoretical studies related to ongoing blazar research with Fermi are mentioned, including implications of γ-ray observations of radio galaxies on blazar unification scenarios, variability in colliding shells, and whet

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Raab, Christoph, and Juan Antonio Aguilar Sánchez. "Searches for IceCube neutrinos from blazar flares using correlations with gamma-ray lightcurves." EPJ Web of Conferences 207 (2019): 02007. http://dx.doi.org/10.1051/epjconf/201920702007.

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Blazars have long been considered as accelerator candidates for cosmic rays. In such a scenario, hadronic interactions in the jet would produce neutrinos and gamma rays. Correlating the astrophysical neutrinos detected by IceCube with the gamma-ray emission from blazars could therefore help elucidate the origin of cosmic rays. In our method we focus on periods where blazars show an enhanced gamma-ray flux, as measured by Fermi-LAT, thereby reducing the background of the search. We present results for TXS 0506+056, using nearly 10 years of IceCube data and discuss them in the context of other r

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Kerby, Stephen, Amanpreet Kaur, Abraham D. Falcone, et al. "Multiwavelength Spectral Analysis and Neural Network Classification of Counterparts to 4FGL Unassociated Sources." Astrophysical Journal 923, no. 1 (2021): 75. http://dx.doi.org/10.3847/1538-4357/ac2e91.

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Abstract The Fermi-LAT unassociated sources represent some of the most enigmatic gamma-ray sources in the sky. Observations with the Swift-XRT and -UVOT telescopes have identified hundreds of likely X-ray and UV/optical counterparts in the uncertainty ellipses of the unassociated sources. In this work we present spectral fitting results for 205 possible X-ray/UV/optical counterparts to 4FGL unassociated targets. Assuming that the unassociated sources contain mostly pulsars and blazars, we develop a neural network classifier approach that applies gamma-ray, X-ray, and UV/optical spectral parame

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Dermer, Charles D., and Reinhard Schlickeiser. "On The Location of the Acceleration and Emission Sites in Gamma-Ray Blazars." International Astronomical Union Colloquium 142 (1994): 945–48. http://dx.doi.org/10.1017/s0252921100078350.

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AbstractCompton scattering of external radiation by nonthermal particles in outflowing blazar jets is dominated by accretion-disk photons rather than scattered radiation to distances ~ 0.01-0.1 pc from the central engine for standard parameters, thus clarifying the limits of validity of the model by the present authors and the model of Sikora, Begelman, & Rees. On the basis of contemporaneous Ginga X-ray and EGRET gamma-ray observations, we estimate the radius of 3C 279’s gamma-ray photosphere to be smaller than estimated by Blandford. There is thus no need to require that the acceleration

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Berton, M., V. Braito, S. Mathur, et al. "Broadband X-ray observations of four gamma-ray narrow-line Seyfert 1 galaxies." Astronomy & Astrophysics 632 (December 2019): A120. http://dx.doi.org/10.1051/0004-6361/201935929.

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Narrow-line Seyfert 1 galaxies (NLS1s) is one of the few classes of active galactic nuclei harboring powerful relativistic jets and detected in γ-rays. NLS1s are well-known X-ray sources. While in non-jetted sources the origin of this X-ray emission may be a hot corona surrounding the accretion disk, in jetted objects, especially beamed ones, the contribution of corona and relativistic jet is difficult to disentangle without a proper sampling of the hard X-ray emission. For this reason, we observed with NuSTAR the first four NLS1s detected at high energy γ-rays. These data, along with XMM-Newt

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d’Antonio, D., M. Giroletti, G. Giovannini, and A. Maini. "Radio spectral properties of cores and extended regions in blazars in the MHz regime." Monthly Notices of the Royal Astronomical Society 490, no. 4 (2019): 5798–806. http://dx.doi.org/10.1093/mnras/stz2967.

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ABSTRACT Low-frequency radio surveys allow in-depth studies and new analyses of classes of sources that were previously known and characterized only in other bands. In recent years, low radio frequency observations of blazars have become available as a result of new surveys, such as the GaLactic and Extragalactic All-sky Murchison Widefield Array (MWA) survey (GLEAM). We search for gamma-ray blazars in a low-frequency (ν &lt; 240 MHz) survey, to characterize the spectral properties of the spatial components. We cross-correlate GLEAM with the fourth catalogue of active galactic nuclei (4LAC

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Marcotulli, L., M. Di Mauro, and M. Ajello. "Source-count Distribution of Gamma-Ray Blazars." Astrophysical Journal 896, no. 1 (2020): 6. http://dx.doi.org/10.3847/1538-4357/ab8cbd.

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Impey, Chris. "Quasars, Blazars, and the Gamma-Ray Sky." Astronomical Journal 112 (December 1996): 2667. http://dx.doi.org/10.1086/118211.

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Nalewajko, Krzysztof. "The brightest gamma-ray flares of blazars." Monthly Notices of the Royal Astronomical Society 430, no. 2 (2013): 1324–33. http://dx.doi.org/10.1093/mnras/sts711.

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Tammi, Joni. "Bottom-up modelling of gamma-ray blazars." Journal of Physics: Conference Series 355 (March 26, 2012): 012014. http://dx.doi.org/10.1088/1742-6596/355/1/012014.

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Raiteri, C. M., G. Ghisellini, M. Villata, et al. "Optical Monitoring of Gamma-Ray Loud Blazars." Symposium - International Astronomical Union 175 (1996): 287–88. http://dx.doi.org/10.1017/s0074180900080840.

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The observations by the Compton Gamma Ray Observatory (CGRO) have shown that highly variable and radio-loud quasars emit a significant fraction of their energy in the γ band. According to the Inverse Compton model, the γ-ray emission is due to upscattering of soft (IR-optical-UV) photons by high energy particles. Optical monitoring is thus of great value in providing information on the mechanisms that rule the production of the seed photons for the γ-ray radiation and on the γ-ray emission itself. In particular, detection of variability correlations between optical and γ-ray emissions would be

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D’Ammando, F., A. Bulgarelli, A. W. Chen, et al. "Gamma-ray blazars: The view from AGILE." Advances in Space Research 48, no. 1 (2011): 76–87. http://dx.doi.org/10.1016/j.asr.2011.02.011.

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Levinson, Amir, and Roger Blandford. "PAIR CASCADE MODELS OF GAMMA-RAY BLAZARS." Annals of the New York Academy of Sciences 759, no. 1 (1995): 534–37. http://dx.doi.org/10.1111/j.1749-6632.1995.tb17602.x.

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Urry, Meg. "Gamma-Ray and Multiwavelength Emission from Blazars." Journal of Astrophysics and Astronomy 32, no. 1-2 (2011): 139–45. http://dx.doi.org/10.1007/s12036-011-9072-x.

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Rosales de León, Alberto, Anthony M. Brown, and Paula M. Chadwick. "Photohadronic modelling of the 2010 gamma-ray flare from Mrk 421." Monthly Notices of the Royal Astronomical Society 501, no. 2 (2020): 2198–208. http://dx.doi.org/10.1093/mnras/staa3839.

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ABSTRACT Blazars are a subclass of active galactic nuclei (AGNs) that have a relativistic jet with a small viewing angle towards the observer. Recent results based on hadronic scenarios have motivated an ongoing discussion of how a blazar can produce high energy neutrinos during a flaring state and which scenario can successfully describe the observed gamma-ray behaviour. Markarian 421 is one of the closest and brightest objects in the extragalactic gamma-ray sky and showed flaring activity over a 14-days period in 2010 March. In this work, we describe the performed analysis of Fermi-LAT data

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Das, Saikat, Soebur Razzaque, and Nayantara Gupta. "Cosmogenic gamma-ray and neutrino fluxes from blazars associated with IceCube events." Astronomy & Astrophysics 658 (February 2022): L6. http://dx.doi.org/10.1051/0004-6361/202142123.

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Context. Blazars constitute the vast majority of extragalactic γ-ray sources. They can also contribute a sizable fraction of the diffuse astrophysical neutrinos detected by IceCube. In the past few years, the real-time alert system of IceCube has led to the multiwavelength follow-up of very high-energy neutrino events of plausible astrophysical origin. Spatial and temporal coincidences of a number of these neutrino events with γ-ray blazars provide a unique opportunity to decipher cosmic-ray interactions in the relativistic jets. Aims. The aim of this work is to test if the γ-ray blazars assoc

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Prandini, Elisa, and Gabriele Ghisellini. "The Blazar Sequence and Its Physical Understanding." Galaxies 10, no. 1 (2022): 35. http://dx.doi.org/10.3390/galaxies10010035.

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Introduced in 1998 to attempt a first unified view of the broad-band emission properties of blazars, the blazar sequence has been extensively used in the past 25 years to guide observations as well as the physical interpretation of the overall emission from these galaxies. In this review, we describe the evolution of the sequence along with the tremendous advances in the observational field, in particular in the gamma-ray band. A new version of the sequence built on TeV-detected objects is also presented. Two extreme classes of objects (MeV and hard-TeV blazars) are included in the discussion,

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