scholarly journals GRAVITATIONAL SHOCKS AS A KEY INGREDIENT OF GAMMA-RAY BURSTS

2012 ◽  
Vol 27 (20) ◽  
pp. 1250110
Author(s):  
ANASTASIOS AVGOUSTIDIS ◽  
RAUL JIMENEZ ◽  
LUIS ÁLVAREZ-GAUMÉ ◽  
MIGUEL A. VÁZQUEZ-MOZO
Keyword(s):  
Numerical Simulations ◽  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Initial Conditions ◽  
Strong Field ◽  
Galactic Nuclei ◽  
Relevant Parameter ◽  
Supernova Explosions ◽  
Γ Ray ◽  
Neutron Core

We identify a novel physical mechanism that may be responsible for energy release in γ-ray bursts. Radial perturbations in the neutron core, induced by its collision with collapsing outer layers during the early stages of supernova explosions, can trigger a gravitational shock, which can readily eject a small but significant fraction of the collapsing material at ultra-relativistic speeds. The development of such shocks is a strong-field effect arising in near-critical collapse in general relativity and has been observed in numerical simulations in various contexts, including, in particular, radially perturbed neutron star collapse, albeit for a tiny range of initial conditions. Therefore, this effect can be easily missed in numerical simulations if the relevant parameter space is not exhaustively investigated. In the proposed picture, the observed rarity of γ-ray bursts would be explained if the relevant conditions for this mechanism appear in only about one in every 104–105 core collapse supernovae. We also mention the possibility that near-critical collapse could play a role in powering the central engines of active galactic nuclei.

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 Radio Galaxies at VHE Energies

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 116 ◽  
Author(s):  
Frank Rieger ◽  
Amir Levinson
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Concise Overview ◽  
Recent Developments ◽  
Γ Ray ◽  
Very High

Radio Galaxies have by now emerged as a new γ-ray emitting source class on the extragalactic sky. Given their remarkable observed characteristics, such as unusual gamma-ray spectra or ultrafast VHE variability, they represent unique examples to probe the nature and physics of active galactic nuclei (AGN) in general. This review provides a compact summary of their observed characteristics at very high γ-ray energies (VHE; greater than 100 GeV) along with a discussion of their possible physics implications. A particular focus is given to a concise overview of fundamental concepts concerning the origin of variable VHE emission, including recent developments in black hole gap physics.

scholarly journals Gamma-ray observations of low-luminosity active galactic nuclei

2020 ◽  
Vol 492 (3) ◽  
pp. 4120-4130 ◽  
Author(s):  
Raniere de Menezes ◽  
Rodrigo Nemmen ◽  
Justin D Finke ◽  
Ivan Almeida ◽  
Bindu Rani
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Detailed Comparison ◽  
Spectral Energy ◽  
X Rays ◽  
Large Area ◽  
Accretion Flow ◽  
Γ Rays ◽  
Γ Ray

ABSTRACT The majority of the activity around nearby (z ≈ 0) supermassive black holes is found in low-luminosity active galactic nuclei (LLAGN), the most of them being classified as low-ionization nuclear emission regions. Although these sources are well studied from radio up to X-rays, they are poorly understood in γ-rays. In this work, we take advantage of the all sky-surveying capabilities of the Large Area Telescope on board Fermi Gamma-ray Space Telescope to study the whole Palomar sample of LLAGN in γ-rays. Precisely, the four radio-brightest LLAGN in the sample are identified as significant γ-ray emitters, all of which are recognized as powerful Fanaroff–Riley I galaxies. These results suggest that the presence of powerful radio jets is of substantial importance for observing a significant γ-ray counterpart even if these jets are misaligned with respect to the line of sight. We also find that most of the X-ray-brightest LLAGN do not have a significant γ-ray and strong radio emission, suggesting that the X-rays come mainly from the accretion flow in these cases. A detailed analysis of the spectral energy distributions (SEDs) of NGC 315 and NGC 4261, both detected in γ-rays, is provided where we make a detailed comparison between the predicted hadronic γ-ray emission from a radiatively inefficient accretion flow (RIAF) and the γ-ray emission from a leptonic jet-dominated synchrotron self-Compton (SSC) model. Both SEDs are better described by the SSC model, while the RIAF fails to explain the γ-ray observations.

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 DIFFUSE γ-RAY EMISSION FROM MISALIGNED ACTIVE GALACTIC NUCLEI

2013 ◽  
Vol 780 (2) ◽  
pp. 161 ◽  
Author(s):  
M. Di Mauro ◽  
F. Calore ◽  
F. Donato ◽  
M. Ajello ◽  
L. Latronico
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Γ Ray

scholarly journals A Test of External Compton Models for Gamma‐Ray Active Galactic Nuclei

2006 ◽  
Vol 646 (1) ◽  
pp. 8-15 ◽  
Author(s):  
Zhonghui Fan ◽  
Xinwu Cao ◽  
Minfeng Gu
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei

The photometric system of the Nanshan One-meter Wide field Telescope

2013 ◽  
Vol 9 (S298) ◽  
pp. 427-427
Author(s):  
Jinzhong Liu ◽  
Yu Zhang ◽  
Guojie Feng ◽  
Chunhai Bai
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Variable Stars ◽  
Optical Quality ◽  
Gamma Ray Bursts ◽  
Wide Field ◽  
Photometric System ◽  
Tracking Accuracy ◽  
Pointing Accuracy

AbstractA one-meter wide field astronomical telescope with Alt-Az mount, putting in work at prime focus with field corrector, is located at the Nanshan site of Xinjiang Astronomical Observatory. The Nanshan One meter Wide-field Telescope (hereafter NOWT) provides excellent optical quality, pointing accuracy and tracking accuracy. The main scientific goals of NOWT are supernovae, gamma-ray bursts, novae, variable stars, and active galactic nuclei. It is worthwhile to point out that the sky background at the Nanshan is a classic optical site.

scholarly journals Looking for the possible gluon condensation signature in sub-TeV gamma-ray spectra: from active galactic nuclei to gamma ray bursts

2021 ◽  
Vol 2021 (01) ◽  
pp. 038-038
Author(s):  
Wei Zhu ◽  
Zechun Zheng ◽  
Peng Liu ◽  
Lihong Wan ◽  
Jianhong Ruan ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Gamma Ray Bursts

scholarly journals Numerical Studies of Astrophysical Objects at Fesenkov Astrophysical Institute (FAI)

2018 ◽  
Vol 2 (1) ◽  
pp. 124-134
Author(s):  
Assylkhan Bibossinov ◽  
◽  
Denis Yurin ◽  
Chingis Omarov ◽  
◽  
...  
Keyword(s):  
Black Hole ◽  
Numerical Simulations ◽  
Active Galactic Nuclei ◽  
Accretion Disk ◽  
Large Scale ◽  
International Workshop ◽  
Star Clusters ◽  
Galactic Nuclei ◽  
Numerical Studies ◽  
Astrophysical Objects

Numerical studies of astrophysical objects are a relatively new direction in Fesenkov Astrophysical Institute (FAI) and is mainly represented by the Laboratory of Cosmology, Stellar Dynamics and Computational Astrophysics. The lab seeks to understand the evolution of gravitating systems at various scales – from star clusters to galaxies to large-scale structure of the universe as a whole, and tackles these problems both through analytical methods and through numerical simulations. The particular focus is on numerical simulations of star clusters, especially those found in active galactic nuclei – this is a topic of oldestablished collaboration with colleagues from Astronomisches Rechen-Institut (Heidelberg) and National Astronomical Observatories of China (Beijing). The prominent example is STARDISK project dedicated to the numerical research of active galactic nuclei as multicomponent systems composed of compact stellar cluster, gaseous accretion disk and a supermassive black hole. It is demonstrated that an accretion disk can noticeably decelerate stars and thus enhance the accretion rate onto the black hole. In 2013 FAI hosted the MODEST-13 International Workshop dedicated to modeling of star clusters. Recently a new project has been approved aimed at construction of triaxial equilibrium N-body systems that can be of great help in various numerical experiments with disk galaxies. There are also long standing plans to perform cosmological simulations of large scale structures to test a new approach to dark matter and energy actively developed at FAI. For numerical calculations, FAI has a small, but growing computer cluster consisting of several high-performance computing servers equipped with computational GPU cards.

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