scholarly journals Determination of K4000 of potential blazar candidates among EGRET unidentified gamma-ray sources

2019 ◽  
Vol 15 (S356) ◽  
pp. 355-357
Author(s):  
Emmanuel Uwitonze ◽  
Pheneas Nkundabakura ◽  
Tom Mutabazi
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Line Of Sight ◽  
Relativistic Jets ◽  
Thermal Component ◽  
Broad Emission ◽  
Spectrum Radio ◽  
Bl Lacs

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-thermal component inside their jets, blazars are found to display a weaker depression at ˜4000 Å (K 4000 ≤ 0.4). In this study, we aimed at determining the K 4000 break for a selected sample among the potential blazar candidates from unidentified EGRET sources to confirm their blazar nature. We used two blazar candidates, 3EG J1800-0146 and 3EG J1709-0817 associated with radio counterparts, J1802-0207 and J1713-0817, respectively. Their optical counterparts were obtained through spectroscopic observations using Robert Stobie spectrograph (RSS) at the Southern African Large Telescope (SALT) in South Africa. The observed Ca II H & K lines depression at ˜4000 Å in spectra of these sources show a shallow depression, K 4000 = 0.35 ± 0.02 and 0.24 ± 0.01, respectively, suggesting that these sources are blazar candidates. Moreover, the redshifts z = 0.165 and 0.26 measured in their spectra confirm the extragalactic nature of these sources.

scholarly journals Polarimetric Properties of Blazars Caught by the WEBT

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 42
Author(s):  
Claudia M. Raiteri ◽  
Massimo Villata
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Plasma Jets ◽  
Line Of Sight ◽  
Optical Behaviour ◽  
Relativistic Jets ◽  
Comprehensive Picture ◽  
Multi Wavelength ◽  
Extreme Variability ◽  
Continuous Range

Active galactic nuclei come in many varieties. A minority of them are radio-loud, and exhibit two opposite prominent plasma jets extending from the proximity of the supermassive black hole up to megaparsec distances. When one of the relativistic jets is oriented closely to the line of sight, its emission is Doppler beamed and these objects show extreme variability properties at all wavelengths. These are called “blazars”. The unpredictable blazar variability, occurring on a continuous range of time-scales, from minutes to years, is most effectively investigated in a multi-wavelength context. Ground-based and space observations together contribute to give us a comprehensive picture of the blazar emission properties from the radio to the γ-ray band. Moreover, in recent years, a lot of effort has been devoted to the observation and analysis of the blazar polarimetric radio and optical behaviour, showing strong variability of both the polarisation degree and angle. The Whole Earth Blazar Telescope (WEBT) Collaboration, involving many tens of astronomers all around the globe, has been monitoring several blazars since 1997. The results of the corresponding data analysis have contributed to the understanding of the blazar phenomenon, particularly stressing the viability of a geometrical interpretation of the blazar variability. We review here the most significant polarimetric results achieved in the WEBT studies.

scholarly journals Similarity and diversity of black holes - view from the Very High Energies

2016 ◽  
Vol 12 (S324) ◽  
pp. 11-18
Author(s):  
Elina Lindfors
Keyword(s):  
Black Holes ◽  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Mass Scale ◽  
Relativistic Jets ◽  
Very High Energy ◽  
Energy Gamma ◽  
Very High

AbstractActive galactic nuclei, hosting supermassive black holes and launching relativistic jets, are the most numerous objects on the gamma-ray sky. At the other end of the mass scale, phenomena related to stellar mass black holes, in particular gamma-ray bursts and microquasars, are also seen on the gamma-ray sky. While all of them are thought to launch relativistic jets, the diversity even within each of these classes is enormous. In this review, I will discuss recent very high energy gamma-ray results that underline both the similarity of the black hole systems, as well as their diversity.

scholarly journals Radio Galaxies at TeV Energies: Preface

Galaxies ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 18
Author(s):  
Dorit Glawion
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Plasma Jets ◽  
Line Of Sight ◽  
Spectral Features ◽  
Viewing Angle ◽  
Special Issue ◽  
Key Aspects

The majority of the known extragalactic sky from TeV gamma-ray energies consists of blazars having plasma jets pointing in the direction of the line-of-sight, which results in a large Doppler boosting of their emission. Up to now, only six galaxies with a larger viewing angle have been detected in the TeV range. These objects also show fascinating properties, such as fast variability or spectral features and are called “radio galaxies”. The TeV radio galaxies provide a unique laboratory for studying key aspects of active galactic nuclei. This Special Issue of Galaxies targets these exciting objects.

scholarly journals Radio and Gamma-ray emission in nearby BL Lacs

2013 ◽  
Vol 9 (S304) ◽  
pp. 200-203 ◽  
Author(s):  
G. Giovannini ◽  
E. Liuzzo ◽  
B. Boccardi ◽  
M. Giroletti
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Scale Structure ◽  
Bl Lac Objects ◽  
Long Baseline ◽  
Γ Ray ◽  
Gamma Ray Emission ◽  
Very Long Baseline Array ◽  
Bl Lacs

AbstractThe advent of Fermi is changing our understanding on the radio and γ-ray emission in active galactic nuclei. Unlike pre-Fermi ideas, BL Lac objects are found to be the most abundant emitters in the γ-ray band. However, since they are relatively weak radio sources, most of their parsec-scale structure and their multifrequency properties are poorly understood and/or have not been investigated in a systematic fashion. Here we are analyzing the radio and γ-ray emission properties of a sample of 42 BL Lacs selected with no constraint on their radio and γ-ray emission. Thanks to new Very Long Baseline Array observations at 8 and 15 GHz for the whole sample, we discuss their parsec-scale structure. Parsec-scale radio emission is observed in the majority of the sources at both frequencies. The comparison between our results in radio and gamma-ray bands points out the presence of a large number of faint BL Lacs showing “non-classical” properties such as low source compactness, low core dominance, no gamma-ray emission.

scholarly journals Doppler Boosting Effect on the Jet Radiation of Gamma-Ray Bursts and Active Galactic Nuclei

2016 ◽  
Vol 12 (S324) ◽  
pp. 82-84
Author(s):  
Xiao-Li Huang ◽  
Hai-Ming Zhang ◽  
Shu-Qing Zhong ◽  
En-Wei Liang
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
High Energy ◽  
Mass Scale ◽  
Gamma Ray Bursts ◽  
Radiation Physics ◽  
Physical Laws ◽  
Bl Lacs

AbstractHigh energy photon radiations of gamma-ray bursts (GRBs) and active galactic nuclei (AGNs) are dominated by their jet radiations. It was suggested that relativistic jets powered by different mass-scale black holes may share the same physical laws. A tight relation among the peak luminosity, the peak photon energy in the νfν spectrum, and the initial Lorentz factor is found for GRBs. With samples of GeV-TeV BL Lacs, FSRQs, and NLS1 galaxies, we show that these sources do not follow this relation. This may be attributed to the jet geometry and continuous/episodic jet as well as radiation physics for different kinds of sources.

scholarly journals Particle-in-Cell Simulations of Astrophysical Relativistic Jets

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 450
Author(s):  
Athina Meli ◽  
Ken-ichi Nishikawa
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Relativistic Jets ◽  
High Energy Astrophysics ◽  
Jet Interaction ◽  
Particle In Cell ◽  
Electron Positron ◽  
Kinetic Instabilities

Astrophysical relativistic jets in active galactic nuclei, gamma-ray bursts, and pulsars is the main key subject of study in the field of high-energy astrophysics, especially regarding the jet interaction with the interstellar or intergalactic environment. In this work, we review studies of particle-in-cell simulations of relativistic electron–proton (e−−p+) and electron–positron (e±) jets, and we compare simulations that we have conducted with the relativistic 3D TRISTAN-MPI code for unmagnetized and magnetized jets. We focus on how the magnetic fields affect the evolution of relativistic jets of different compositions, how the jets interact with the ambient media, how the kinetic instabilities such as the Weibel instability, the kinetic Kelvin–Helmholtz instability and the mushroom instability develop, and we discuss possible particle acceleration mechanisms at reconnection sites.

scholarly journals A New Sample of Gamma-Ray Emitting Jetted Active Galactic Nuclei—Preliminary Results

Universe ◽  
2021 ◽  
Vol 7 (10) ◽  
pp. 372
Author(s):  
Luigi Foschini ◽  
Matthew L. Lister ◽  
Sonia Antón ◽  
Marco Berton ◽  
Stefano Ciroi ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Point Sources ◽  
Large Area ◽  
Bl Lac Objects ◽  
Preliminary Results ◽  
Spectrum Radio ◽  
Many Sources

We are compiling a new list of gamma-ray jetted active galactic nuclei (AGN), starting from the fourth catalog of point sources of the Fermi Large Area Telescope (LAT). Our aim is to prepare a list of jetted AGN with known redshifts and classifications to be used to calibrate jet power. We searched in the available literature for all the published optical spectra and multiwavelength studies useful to characterize the sources. We found new, missed, or even forgotten information leading to a substantial change in the redshift values and classification of many sources. We present here the preliminary results of this analysis and some statistics based on the gamma-ray sources with right ascension within the interval 0h--12h (J2000). Although flat-spectrum radio quasars and BL Lac objects are still the dominant populations, there is a significant increase in the number of other objects, such as misaligned AGN, narrow-line Seyfert 1 galaxies, and Seyfert galaxies. We also introduced two new classes of objects: changing-look AGN and ambiguous sources. About one third of the sources remain unclassified.

scholarly journals PHYSICS INSIGHTS FROM RECENT MAGIC AGN OBSERVATIONS

2009 ◽  
Vol 18 (10) ◽  
pp. 1489-1492
Author(s):  
◽  
ROBERT WAGNER
Keyword(s):  
Energy Spectrum ◽  
Active Galactic Nuclei ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Radio Galaxy ◽  
Galactic Nuclei ◽  
New Physics ◽  
Spectrum Radio ◽  
Tev Gamma Rays ◽  
Radio Quasar

The total set of the 14 active galactic nuclei detected by MAGIC so far includes well-studied bright blazars like Mkn 501, the giant radio galaxy M 87, but also the distant flat-spectrum radio quasar 3C 279, and an intriguing gamma-ray source in the 3C 66A/B region, whose energy spectrum is not compatible with the expectations from 3C 66A. Besides scheduled observations, so far MAGIC succeeded in discovering TeV gamma rays from three blazars following triggers from high optical states. I report selected highlights from recent MAGIC observations of extragalactic TeV gamma-ray sources, emphasizing and discussing the new physics insights the MAGIC observations were able to contribute.

scholarly journals Determining Quasar Orientation

2019 ◽  
Author(s):  
Suk Yee Yong ◽  
Rachel L Webster ◽  
Anthea L King ◽  
Nicholas F Bate ◽  
Kathleen Labrie ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Viewing Angle ◽  
Wind Model ◽  
Disk Wind ◽  
Broad Emission ◽  
Line Region ◽  
Improved Accuracy ◽  
Other Orientation

Abstract Since the discovery of active galactic nuclei (AGN) and their subclasses, a unification scheme of AGN has been long sought. Orientation-based unified models predict that some of the diversity within AGN subclasses can be explained by the different viewing angles of the observer. Several orientation categorisations have been suggested, but a widely applicable measure has yet to be found. Using the properties of the ultraviolet and optical broad emission lines of quasars, in particular the velocity offsets and line widths of high-ionisation C iv and low-ionisation Mg ii lines, a correlation has been measured. It is postulated that this correlation is due to the viewing angle of the observer. Comparison with other orientation tracers shows consistency with this interpretation. Using a simulation of a wide angle disk-wind model for the broad emission line region, we successfully replicate the observed correlation with inclination. Future more detailed modelling will not only enable improved accuracy in the determination of the viewing angle to individual AGN, but will also substantially increase our understanding of the emitting regions of AGN.

scholarly journals GAMMA-RAY EMISSION FROM AGNS (SPECIAL FOCUS ON BL LAC OBJECTS)

2010 ◽  
Vol 19 (06) ◽  
pp. 841-848
Author(s):  
F. TAVECCHIO
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Line Of Sight ◽  
Special Focus ◽  
Bl Lac Objects ◽  
Relativistic Jet ◽  
Bl Lac ◽  
High Energy Emission

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.

Sign in / Sign up

Export Citation Format

Share Document