scholarly journals Multi-TeV flaring in nearby high-energy blazars: A photohadronic scenario

2019 ◽  
Vol 65 (4 Jul-Aug) ◽  
pp. 307 ◽  
Author(s):  
Sarira Sahu
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Temporal Correlation ◽  
High Energy ◽  
Spectral Shape ◽  
Extragalactic Background Light ◽  
X Ray ◽  
Major Activity ◽  
Electron Positron ◽  
Energy Gamma

Blazars are a subclass of AGN and flaring in multi-TeV gamma-ray seems to be the major activity in high energy blazars a subgroup of blazars. Flaring is also unpredictable and switches between quiescent and active states involving different time scales and fluxes. While in some high energy blazars a strong temporal correlation between X-ray and multi-TeV gamma-ray has been observed, outbursts in some other have no low energy counterparts and explanation of such extreme activity needs to be addressed through different mechanisms as it is not understood well. The extragalactic background light (EBL) plays an important role in the observation of these high energy gamma-rays as it attenuates through pair production of electron-positron and also changes the spectral shape of the high energy photons. In the context of photohadronic model and taking EBL correction into account, flaring can be explained very well. Here in this review, photohadronic model is discussed and applied to explain the multi-TeV flaring from nearby high energy blazars:Markarian 421, Markarian 501 and 1ES1959+650.

scholarly journals VERY HIGH ENERGY GAMMA RAYS FROM e± PAIR HALOS

2009 ◽  
Vol 18 (06) ◽  
pp. 911-927 ◽  
Author(s):  
A. EUNGWANICHAYAPANT ◽  
F. AHARONIAN
Keyword(s):  
Energy Spectrum ◽  
Gamma Rays ◽  
High Energy ◽  
Angular Distributions ◽  
Extragalactic Background Light ◽  
Electron Positron ◽  
Very High Energy ◽  
Energy Gamma ◽  
Electron Positron Pair ◽  
Very High

In this paper we study the formation of giant electron–positron pair halos around the powerful high energy extragalactic sources. We investigate the dependence of radiation of pair halos, in particular the spectral and angular distributions on the energy spectrum of the primary gamma rays, the redshift of the source, and the flux of the extragalactic background light.

scholarly journals High-energy gamma- and cosmic-ray observations with future space-based GAMMA-400 gamma-ray telescope

2019 ◽  
Vol 208 ◽  
pp. 14004 ◽  
Author(s):  
N.P. Topchiev ◽  
A.M. Galper ◽  
I.V. Arkhangelskaja ◽  
A.I. Arkhangelskiy ◽  
A.V. Bakaldin ◽  
...  
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
High Energy ◽  
Electron Positron ◽  
Future Space ◽  
Long Time ◽  
Energy Gamma ◽  
Celestial Sphere ◽  
Better Than

The future space-based GAMMA-400 gamma-ray telescope will be installed on the Navigator platform of the Russian Astrophysical Observatory. A highly elliptical orbit will provide observations for 7-10 years of many regions of the celestial sphere continuously for a long time (~ 100 days). GAMMA-400 will measure gamma-ray fluxes in the energy range from ~ 20 MeV to several TeV and electron + positron fluxes up to ~ 20 TeV. GAMMA-400 will have an excellent separation of gamma rays from the background of cosmic rays and electrons + positrons from protons and an unprecedented angular (~ 0.01° at Eγ = 100 GeV) and energy (~ 1% at Eγ = 100 GeV) resolutions better than for Fermi-LAT, as well as ground-based facilities, by a factor of 5-10. Observations of GAMMA-400 will provide new fundamental data on discrete sources and spectra of gamma-ray emission and electrons + positrons, as well as the nature of dark matter.

scholarly journals Techniques for Gamma Rays

1971 ◽  
Vol 41 ◽  
pp. 14-36 ◽  
Author(s):  
Carl E. Fichtel
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Scintillation Counter ◽  
High Energy ◽  
Detector System ◽  
Detector Arrays ◽  
High Particle ◽  
Electron Positron ◽  
Energy Gamma ◽  
Counter Telescope

The detecting systems used in high energy astrophysics are generally more similar to particle detectors than to optical devices. The basic design of the gamma ray instrument depends on whether the energy range is below about 10 MeV and therefore in the region where the Compton effect predominates in the absorption of the gamma-rays, or above that energy where electron-positron pair production is most important. The most usual approach to the detector system in the lower of the two energy intervals is to use a scintillation counter in the center of the detector system to absorb the photons and permit a measure of their energy, and to surround it by another detector which is employed as an active anticoincidence shield to discriminate against charged particles. In the gamma-ray interval above about 10 MeV, the very low flux of gamma rays and the high particle background has directed the development of high energy gamma-ray telescopes towards complicated techniques and large detector arrays. As a result, several investigators have now turned to the spark chamber as the heart of a detector system. Generally, it is surrounded by an anticoincidence system and is triggered by a counter telescope.

scholarly journals Possible X-Ray Counterparts to Gamma-Ray Bursts, GRB930131 and GRB940217

1998 ◽  
Vol 188 ◽  
pp. 459-460
Author(s):  
R. Shibata ◽  
T. Murakami ◽  
Y. Ueda ◽  
A. Yoshida ◽  
F. Tokanai ◽  
...  
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
High Energy ◽  
Small Error ◽  
Gamma Ray Bursts ◽  
X Ray ◽  
High Energy Gamma ◽  
Energy Gamma

We made a search of quiescent X-ray counterparts of two Gamma-Ray Bursts (GRBs), GRB930131 and GRB940217. These GRBs were detected with BATSE, EGRET, COMPTEL on board CGRO together with the GRB detector on Ulysses spacecraft, then they were localized in small error regions. These observations showed that the bursts were remarkably bright accompanying delayed high energy gamma-rays. ASCA observations have found a single X-ray source for each GRB on the possible location determined with the above instruments.

Very high energy gamma rays from x-ray binary pulsars

1990 ◽  
Vol 16 (12) ◽  
pp. 1773-1803 ◽  
Author(s):  
P M Chadwick ◽  
T J L McComb ◽  
K E Turver
Keyword(s):  
Gamma Rays ◽  
High Energy ◽  
X Ray ◽  
Binary Pulsars ◽  
High Energy Gamma ◽  
Very High Energy ◽  
Energy Gamma ◽  
Very High

scholarly journals G279.0+1.1: a new extended source of high-energy gamma-rays

2020 ◽  
Vol 492 (4) ◽  
pp. 5980-5986
Author(s):  
M Araya
Keyword(s):  
Spectral Index ◽  
Gamma Rays ◽  
Gamma Ray ◽  
High Energy ◽  
Particle Spectrum ◽  
Large Area ◽  
Extended Source ◽  
The North ◽  
Energy Gamma ◽  
High Energy Emission

ABSTRACT G279.0+1.1 is a supernova remnant (SNR) with poorly known parameters, first detected as a dim radio source and classified as an evolved system. An analysis of data from the Fermi-Large Area Telescope (LAT) revealing for the first time an extended source of gamma-rays in the region is presented. The diameter of the GeV region found is ${\sim} 2{^{\circ}_{.}}8$, larger than the latest estimate of the SNR size from radio data. The gamma-ray emission covers most of the known shell and extends further to the north and east of the bulk of the radio emission. The photon spectrum in the 0.5–500 GeV range can be described by a simple power law, $\frac{\mathrm{ d}N}{\mathrm{ d}E} \propto E^{-\Gamma }$, with a spectral index of Γ = 1.86 ± 0.03stat ± 0.06sys. In the leptonic scenario, a steep particle spectrum is required and a distance lower than the previously estimated value of 3 kpc is favoured. The possibility that the high-energy emission results from electrons that already escaped the SNR is also investigated. A hadronic scenario for the gamma-rays yields a particle spectral index of ∼2.0 and no significant constraints on the distance. The production of gamma-rays in old SNRs is discussed. More observations of this source are encouraged to probe the true extent of the shell and its age.

scholarly journals Very High Energy Gamma Rays from Plerions: CANGAROO Results

1998 ◽  
Vol 188 ◽  
pp. 125-128
Author(s):  
T. Kifune
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
High Energy ◽  
Current Status ◽  
Emission Region ◽  
Thermal Processes ◽  
High Energy Gamma ◽  
Very High Energy ◽  
Energy Gamma ◽  
Very High

The current status of very high energy gamma ray astronomy (in ~ 1 TeV region) is described by using as example results of CANGAROO (Collaboration of Australia and Nippon for a GAmma Ray Observatory in the Outback). Gamma rays at TeV energies, emitted through inverse Compton effect of electrons or π0 decay from proton interaction, provide direct evidence on “hot” non-thermal processes of the Universe, as well as environmental features, such as the strength of magnetic field in the emission region, for the non-thermal processes.

scholarly journals Physical Constraints on Models of Gamma-Ray Bursters

1986 ◽  
Vol 89 ◽  
pp. 305-321
Author(s):  
Richard I. Epstein
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
High Energy ◽  
X Rays ◽  
Burst Source ◽  
Gamma Ray Burst ◽  
Physical Constraints ◽  
Low Energies ◽  
Energy Gamma ◽  
Photon Interactions

AbstractThe power per logarithmic bandwidth in gamma-ray burst spectra generally increases rapidly with energy through the x-ray range and does not cut off sharply above a few MeV. This spectral form indicates that a very small fraction of the energy from a gamma-ray burst source is emitted at low energies or is reprocessed into x-rays and that the high-energy gamma rays are not destroyed by photon-photon interactions. The implications are that the emission mechanism for the gamma-ray bursts is not synchrotron radiation from electrons that lose most of their energy before being re-accelerated and that either the regions from which the gamma rays are emitted are large compared to the size of a neutron star or the emission is collimated and beamed away from the stellar surface.

scholarly journals Imaging in Hard X-ray Astronomy

2003 ◽  
Vol 214 ◽  
pp. 70-83 ◽  
Author(s):  
T. P. Li
Keyword(s):  
Gamma Ray ◽  
Signal To Noise Ratio ◽  
High Energy ◽  
High Signal ◽  
Wide Field ◽  
X Rays ◽  
X Ray ◽  
Energy Gamma ◽  
High Resolution Images ◽  
Energy Processes

The energy range of hard X-rays is a key waveband to the study of high energy processes in celestial objects, but still remains poorly explored. In contrast to direct imaging methods used in the low energy X-ray and high energy gamma-ray bands, currently imaging in the hard X-ray band is mainly achieved through various modulation techniques. A new inversion technique, the direct demodulation method, has been developed since early 90s. with this technique, wide field and high resolution images can be derived from scanning data of a simple collimated detector. The feasibility of this technique has been confirmed by experiment, balloon-borne observation and analyzing simulated and real astronomical data. Based the development of methodology and instrumentation, a high energy astrophysics mission – Hard X-ray Modulation Telescope (HXMT) has been proposed and selected in China for a four-year Phase-A study. The main scientific objectives are a full-sky hard X-ray (20–200 keV) imaging survey and high signal-to-noise ratio timing studies of high energy sources.

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