scholarly journals Gamma-Ray Emission from Extragalactic Radio Sources: EGRET Observations of Active Galactic Nuclei

1996 ◽  
Vol 175 ◽  
pp. 277-280
Author(s):  
Peter F. Michelson
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Radio Spectrum ◽  
Active Galaxies ◽  
Emission Characteristics ◽  
Radio Sources ◽  
Emission Models ◽  
Gamma Ray Emission

The Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory is an imaging high-energy telescope with sensitivity from approximately 20 MeV to 30 GeV. EGRET has observed more than 129 sources during more than 4 years of operation. Among these sources, 51 have been identified with active galaxies. A common characteristic of the AGN sources is that they are all radio-loud, flat radio spectrum sources. Many of them are seen as superluminal radio sources as well. The gamma-ray emission characteristics of these sources are reviewed and some of the proposed emission models are discussed.

Relativistic astrophysics and cosmology

2019 ◽  
pp. 244-291
Author(s):  
Malcolm S. Longair
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
High Energy ◽  
Active Galaxies ◽  
Relativistic Astrophysics ◽  
Radio Sources ◽  
X Ray ◽  
Binary Black Hole ◽  
Wide Range ◽  
New Challenges

Although relativistic astrophysics began in the 1930s with study of supernovae and neutron stars, it was only three decades later that the discovery of extragalactic radio sources, quasars and pulsars marked the emergence of special and general relativity as essential tools of the high energy astrophysicist. X-ray and γ-ray astronomy provided many new insights, culminating in the discovery of γ-ray bursts at cosmological distances in 1997. Supermassive black holes in active galactic nuclei provided major new challenges for theorists and observers alike, revealing many remarkable relativistic phenomena, such as superluminal motions observed in some of the most active galaxies. Einstein’s prediction of gravitational waves of 1916 was substantiated exactly 100 years later with their discovery in coalescing binary black hole systems by the LIGO project. These remarkable discoveries, mostly in the non-optical wavebands, brought a wide range of physicists into the astronomical and cosmological communities.

scholarly journals Gamma-Ray and Neutrino Signals from Accretion Disk Coronae of Active Galactic Nuclei

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 36
Author(s):  
Yoshiyuki Inoue ◽  
Dmitry Khangulyan ◽  
Akihiro Doi
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Thermal Activity ◽  
X Ray ◽  
Cascade Models ◽  
Coronal Activity ◽  
Ngc 1068 ◽  
High Energy Particles

To explain the X-ray spectra of active galactic nuclei (AGN), non-thermal activity in AGN coronae such as pair cascade models has been extensively discussed in the past literature. Although X-ray and gamma-ray observations in the 1990s disfavored such pair cascade models, recent millimeter-wave observations of nearby Seyferts have established the existence of weak non-thermal coronal activity. In addition, the IceCube collaboration reported NGC 1068, a nearby Seyfert, as the hottest spot in their 10 yr survey. These pieces of evidence are enough to investigate the non-thermal perspective of AGN coronae in depth again. This article summarizes our current observational understanding of AGN coronae and describes how AGN coronae generate high-energy particles. We also provide ways to test the AGN corona model with radio, X-ray, MeV gamma ray, and high-energy neutrino observations.

scholarly journals The connection between the 15 GHz radio and gamma-ray emission in blazars

2014 ◽  
Vol 10 (S313) ◽  
pp. 17-20
Author(s):  
W. Max-Moerbeck ◽  
J. L. Richards ◽  
T. Hovatta ◽  
V. Pavlidou ◽  
T. J. Pearson ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Statistical Tests ◽  
High Energy ◽  
Light Curves ◽  
Owens Valley ◽  
Noise Characteristics ◽  
Power Spectral ◽  
Emission Models ◽  
Gamma Ray Emission ◽  
Many Sources

AbstractSince mid-2007 we have carried out a dedicated long-term monitoring programme at 15 GHz using the Owens Valley Radio Observatory 40 meter telescope (OVRO 40m). One of the main goals of this programme is to study the relation between the radio and gamma-ray emission in blazars and to use it as a tool to locate the site of high energy emission. Using this large sample of objects we are able to characterize the radio variability, and study the significance of correlations between the radio and gamma-ray bands. We find that the radio variability of many sources can be described using a simple power law power spectral density, and that when taking into account the red-noise characteristics of the light curves, cases with significant correlation are rare. We note that while significant correlations are found in few individual objects, radio variations are most often delayed with respect to the gamma-ray variations. This suggests that the gamma-ray emission originates upstream of the radio emission. Because strong flares in most known gamma-ray-loud blazars are infrequent, longer light curves are required to settle the issue of the strength of radio-gamma cross-correlations and establish confidently possible delays between the two. For this reason continuous multiwavelength monitoring over a longer time period is essential for statistical tests of jet emission models.

scholarly journals Searching for Optical Counterparts to High-Energy Neutrino Sources with the Zwicky Transient Facility

2019 ◽  
Vol 207 ◽  
pp. 03001 ◽  
Author(s):  
Ludwig Rauch
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Correlation Study ◽  
High Energy Neutrino ◽  
Energy Neutrino ◽  
Ice Cube ◽  
Sky Survey ◽  
High Cadence

The IceCube neutrino observatory has discovered a flux of extragalactic neutrinos. However, the origin of these neutrinos is still unknown. Among the possible candidates are Gamma-Ray Bursts (GRBs), Core-Collapse Supernovae (SNe), Active Galactic Nuclei (AGN) and Tidal Disruption Events (TDEs) - all are accompanied by a characteristic optical counterpart. The goal of this study is thus to identify the neutrino sources by detecting their optical counterparts with the Zwicky Transient Facility (ZTF). ZTF features a high cadence northern-sky survey enabling realtime correlation of optical transients with high-energy neutrino candidates. In this talk I will highlight the multimessenger potential of ZTF for an online neutrino correlation study with Ice- Cube.

Upper Limits on TeV Gamma-Ray Emission from Active Galactic Nuclei

1995 ◽  
Vol 452 ◽  
pp. 588 ◽  
Author(s):  
A. D. Kerrick ◽  
C. W. Akerlof ◽  
S. Biller ◽  
J. Buckley ◽  
D. A. Carter-Lewis ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Upper Limits ◽  
Gamma Ray Emission

scholarly journals HIGH-ENERGY EMISSION FROM JET–CLOUD INTERACTIONS IN AGNs

2010 ◽  
Vol 19 (06) ◽  
pp. 931-936 ◽  
Author(s):  
ANABELLA T. ARAUDO ◽  
VALENTÍ BOSCH-RAMON ◽  
GUSTAVO E. ROMERO
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Line Emission ◽  
Galactic Nuclei ◽  
Small Region ◽  
High Energy ◽  
Energy Emission ◽  
Central Regions ◽  
High Energy Emission

Active galactic nuclei present continuum and line emission. The emission lines are originated by gas located close to the central supermassive black hole. Some of these lines are broad, and would be produced in a small region called broad-line region. This region could be formed by clouds surrounding the central black hole. In this work, we study the interaction of such clouds with the base of the jets in active galactic nuclei, and we compute the produced high-energy emission. We focus on sources with low luminosities in the inner jet regions, to avoid strong gamma-ray absorption. We find that the resulting high-energy radiation may be significant in Centaurus A. Also, this phenomenon might be behind the variable gamma-ray emission detected in M87, if very large dark clouds are present. The detection of jet–cloud interactions in active galactic nuclei would give information on the properties of the jet base and the very central regions.

scholarly journals Soft gamma rays from low accreting supermassive black holes and connection to energetic neutrinos

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shigeo S. Kimura ◽  
Kohta Murase ◽  
Péter Mészáros
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
High Energy ◽  
Hadronic Interactions ◽  
Neutrino Detectors ◽  
Accretion Flows ◽  
Diffuse Background ◽  
The Universe

AbstractThe Universe is filled with a diffuse background of MeV gamma-rays and PeV neutrinos, whose origins are unknown. Here, we propose a scenario that can account for both backgrounds simultaneously. Low-luminosity active galactic nuclei have hot accretion flows where thermal electrons naturally emit soft gamma rays via Comptonization of their synchrotron photons. Protons there can be accelerated via turbulence or reconnection, producing high-energy neutrinos via hadronic interactions. We demonstrate that our model can reproduce the gamma-ray and neutrino data. Combined with a contribution by hot coronae in luminous active galactic nuclei, these accretion flows can explain the keV – MeV photon and TeV – PeV neutrino backgrounds. This scenario can account for the MeV background without non-thermal electrons, suggesting a higher transition energy from the thermal to nonthermal Universe than expected. Our model is consistent with X-ray data of nearby objects, and testable by future MeV gamma-ray and high-energy neutrino detectors.

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