scholarly journals γ-Ray Flux and Spectral Variability of Blazar Ton 599 during Its 2021 Flare

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 118
Author(s):  
Bhoomika Rajput ◽  
Ashwani Pandey
Keyword(s):  
Gamma Ray ◽  
Thermal Emission ◽  
Electromagnetic Spectrum ◽  
Spectral Variability ◽  
Line Region ◽  
Wide Range ◽  
Γ Rays ◽  
Γ Ray ◽  
One Year ◽  
Variability Study

Blazars are known to emit exceptionally variable non-thermal emission over the wide range (from radio to γ-rays) of electromagnetic spectrum. We present here the results of our γ-ray flux and spectral variability study of the blazar Ton 599, which has been recently observed in the γ-ray flaring state. Using 0.1−300 GeV γ-ray data from the Fermi Gamma-ray Space Telescope (hereinafter Fermi), we generated one-day binned light curve of Ton 599 for a period of about one-year from MJD 59,093 to MJD 59,457. During this one year period, the maximum γ-ray flux detected was 2.24 ± 0.25 ×10−6 ph cm−2 s−1 at MJD 59,399.50. We identified three different flux states, namely, epoch A (quiescent), epoch B (pre-flare) and epoch C (main-flare). For each epoch, we calculated the γ-ray flux variability amplitude (Fvar) and found that the source showed largest flux variations in epoch C with Fvar∼ 35%. We modelled the γ-ray spectra for each epoch and found that the Log-parabola model adequately describes the γ-ray spectra for all the three epochs. We estimated the size of the γ-ray emitting region as 1.03 ×1018 cm and determined that the origin of γ-ray radiation, during the main-flare, could be outside of the broad line region.

scholarly journals 20 Years of Indian Gamma Ray Astronomy Using Imaging Cherenkov Telescopes and Road Ahead

Universe ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 96
Author(s):  
Krishna Kumar Singh ◽  
Kuldeep Kumar Yadav
Keyword(s):  
Gamma Ray ◽  
Thermal Emission ◽  
Galactic Nuclei ◽  
Indirect Detection ◽  
Special Focus ◽  
Cherenkov Telescopes ◽  
Γ Rays ◽  
Γ Ray ◽  
The Universe ◽  
Future Plans

The field of ground-based γ-ray astronomy has made very significant advances over the last three decades with the extremely successful operations of several atmospheric Cherenkov telescopes worldwide. The advent of the imaging Cherenkov technique for indirect detection of cosmic γ rays has immensely contributed to this field with the discovery of more than 220 γ-ray sources in the Universe. This has greatly improved our understanding of the various astrophysical processes involved in the non-thermal emission at energies above 100 GeV. In this paper, we summarize the important results achieved by the Indian γ-ray astronomers from the GeV-TeV observations using imaging Cherenkov telescopes over the last two decades. We mainly emphasize the results obtained from the observations of active galactic nuclei with the TACTIC (TeV Atmospheric Cherenkov Telescope with Imaging Camera) telescope, which has been operational since 1997 at Mount Abu, India. We also discuss the future plans of the Indian γ-ray astronomy program with special focus on the scientific objectives of the recently installed 21 m diameter MACE (Major Atmospheric Cherenkov Experiment) telescope at Hanle, India.

scholarly journals Molecular Clouds Observed by the EGRET Gamma-Ray Telescope

1997 ◽  
Vol 170 ◽  
pp. 22-24 ◽  
Author(s):  
Seth. W. Digel ◽  
Stanley D. Hunter ◽  
Reshmi Mukherjee ◽  
Eugéne J. de Geus ◽  
Isabelle A. Grenier ◽  
...  
Keyword(s):  
Molecular Mass ◽  
Molecular Clouds ◽  
Gamma Ray ◽  
Angular Resolution ◽  
Cosmic Ray ◽  
High Energy ◽  
Background Rejection ◽  
Γ Rays ◽  
Γ Ray ◽  
Production Mechanisms

EGRET, the high-energy γ-ray telescope on the Compton Gamma-Ray Observatory, has the sensitivity, angular resolution, and background rejection necessary to study diffuse γ-ray emission from the interstellar medium (ISM). High-energy γ rays produced in cosmic-ray (CR) interactions in the ISM can be used to determine the CR density and calibrate the CO line as a tracer of molecular mass. Dominant production mechanisms for γ rays of energies ∼30 MeV–30 GeV are the decay of pions produced in collisions of CR protons with ambient matter and Bremsstrahlung scattering of CR electrons.

scholarly journals Review of observational results on γ-ray background: (Invited discourse)

1970 ◽  
Vol 37 ◽  
pp. 269-279 ◽  
Author(s):  
G. W. Clark ◽  
G. P. Garmire ◽  
W. L. Kraushaar
Keyword(s):  
Power Law ◽  
Strong Evidence ◽  
Galactic Plane ◽  
High Energy ◽  
Electromagnetic Spectrum ◽  
Γ Rays ◽  
Γ Ray ◽  
Region 10

Recent observations in the X- and γ-Ray region of the electromagnetic spectrum have given strong evidence for the existence of an extragalactic intensity with a slowly steepening power law spectrum in the region 103 to 108 eV. Further data from the OSO-III high energy γ-Ray detector are in agreement with earlier published reports, and suggest that the γ-Rays from high galactic latitudes have a softer spectrum than those from the galactic plane.

scholarly journals Gamma-Ray Bursts and Binary Neutron Star Mergers

1996 ◽  
Vol 165 ◽  
pp. 489-502
Author(s):  
Tsvi Piran
Keyword(s):  
Neutron Star ◽  
Gravitational Radiation ◽  
Gamma Ray ◽  
Indirect Evidence ◽  
Gamma Ray Bursts ◽  
Binary Neutron Star ◽  
Merger Event ◽  
Γ Rays ◽  
Γ Ray ◽  
The One

Neutron star binaries, such as the one observed in the famous binary pulsar PSR 1913+16, end their life in a catastrophic merger event (denoted here NS2M). The merger releases ∼5 1053 ergs, mostly as neutrinos and gravitational radiation. A small fraction of this energy suffices to power γ-ray bursts (GRBs) at cosmological distances. Cosmological GRBs must pass, however, an optically thick fireball phase and the observed γ rays emerge only at the end of this phase. Hence, it is difficult to determine the nature of the source from present observations (the agreement between the rates of GRBs and NS2Ms providing only indirect evidence for this model). In the future a coinciding detection of a GRB and a gravitational-radiation signal could confirm this model.

scholarly journals A Possible Discovery of a Flaring 1012 eV Gamma-Ray Source near the Red Dwarf EV Lac

1995 ◽  
Vol 151 ◽  
pp. 78-79
Author(s):  
I.Yu. Alekseev ◽  
N.N. Chalenko ◽  
V.P. Fomin ◽  
R.E. Gershberg ◽  
O.R. Kalekin ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Electronic Device ◽  
Angular Size ◽  
High Energy ◽  
Optical Systems ◽  
Relativistic Electrons ◽  
Large Area ◽  
Γ Rays ◽  
Γ Ray ◽  
Ev Lac

During the 1994 coordinated observations of the red dwarf flare star EV Lac, the star was monitored in the very high energy (VHE) γ-ray range around 1012 eV with the Crimean ground-based γ-ray telescope GT-48. This telescope consists of two identical optical systems (Vladimirsky et al. 1994) which were directed in parallel on EV Lac.The detection principle of the VHE γ-rays is based on the Čerenkov radiation emitted by relativistic electrons and positrons. The latter are generated in the interaction of the γ-rays with nuclei in the Earth’s atmosphere that leads to an appearance of a shower of charged particles and γ-quanta. The duration of the Cherenkov radiation flash is very short, just about a few nanoseconds. The angular size of the shower is ∼ 1°. To detect such flashes we use an optical system with large area mirrors and a set of 37 photomultipliers (PMs) in the focal plane. Using the information from these PMs which are spaced hexagonally and correspond to a field of view of 2°.6 on the sky, we can obtain the image of an optical flash. The electronic device permits us to detect nanosecond flashes (40 ns exposure time and 12 μs readout dead-time).

scholarly journals On the origin of the TeV gamma-ray emission from Cygnus X-3

2019 ◽  
Vol 208 ◽  
pp. 14008
Author(s):  
V.G. Sinitsyna ◽  
V.Y. Sinitsyna
Keyword(s):  
Energy Range ◽  
Particle Production ◽  
Cosmic Ray ◽  
High Energy ◽  
Wide Energy Range ◽  
Electromagnetic Spectrum ◽  
Essential Information ◽  
Wide Range ◽  
Γ Ray ◽  
Very High

Cygnus X-3 binary system is a famous object studied over the wide range of electromagnetic spectrum. Early detections of ultra-high energy gamma-rays from Cygnus X-3 by Kiel, Havera Park and then by Akeno triggered the construction of several large air shower detectors. Also, Cygnus X-3 has been proposed to be one of the most powerful sources of charged cosmic ray particles in the Galaxy. The results of twenty-year observations of the Cyg X-3 binary at energies 800 GeV - 85 TeV are presented with images, spectra during periods of flaring activity and at low flux periods. The correlation of TeV flux increases with flaring activity at the lower energy range of X-ray and radio emission from the relativistic jets of Cygnus X-3 is found as well as 4.8-hour orbital modulation of TeV γ-ray intensity. Detected modulation of TeV γ-ray emission with orbit and important characteristics of Cyg X-3 such as the high luminosity of the companion star and the close orbit leads to an efficient generation of γ-ray emission through inverse Compton scattering in this object. The different type variability of very high-energy γ-emission and correlation of radiation activity in the wide energy range can provide essential information on the mechanism of particle production up to very high energies.

scholarly journals Gamma-ray-emitting narrow-line Seyfert 1 galaxies: the Swift view

2020 ◽  
Vol 496 (2) ◽  
pp. 2213-2229 ◽  
Author(s):  
F D’Ammando
Keyword(s):  
Gamma Ray ◽  
Thermal Emission ◽  
Optical Emission ◽  
X Rays ◽  
Narrow Line ◽  
X Ray ◽  
Relativistic Jet ◽  
Photon Index ◽  
Γ Ray ◽  
Lower Variability

ABSTRACT We report the analysis of all Swift observations available up to 2019 April of γ-ray-emitting narrow-line Seyfert 1 galaxies (NLSy1). The distribution of X-ray luminosities (and fluxes) indicates that the jet radiation significantly contributes to their X-ray emission, with Doppler boosting making values higher than other radio-loud NLSy1. The 0.3–10 keV photon indices are on average harder with respect to radio-quiet and radio-loud NLSy1, confirming a dominant jet contribution in X-rays. However, the lower variability amplitude with respect to blazars and the softening of the spectrum in some periods suggests that also the corona radiation contributes to the X-ray emission. In optical and ultraviolet (UV) significant flux changes have been observed on daily, weekly, and monthly time-scale, providing a clear indication of the significant contribution of the jet radiation in this part of spectrum. A strong correlation between X-ray, UV, and optical emission and simultaneous flux variations have been observed in 1H 0323+342, SBS 0846+513, PMN J0948+0022 as expected in case the jet radiation is the dominant mechanism. Correlated multiband variability favours the jet-dominated scenario also in FBQS J1644+2619 and PKS 2004−447. The summed X-ray Telescope spectra of 1H 0323+342, SBS 0846+513, PMN J0948+0022, and FBQS J1644+2619 are well fitted by a broken power law with a break around 2 keV. The spectrum above 2 keV is dominated by the non-thermal emission from a beamed relativistic jet, as suggested by the hard photon index. A Seyfert-like feature like the soft X-ray excess has been observed below 2 keV, making these γ-ray-emitting NLSy1 different from typical blazars.

scholarly journals Massive stars at (very) high energies: γ-ray binaries

2010 ◽  
Vol 6 (S272) ◽  
pp. 581-586
Author(s):  
Guillaume Dubus ◽  
Benoît Cerutti
Keyword(s):  
High Energy Physics ◽  
Thermal Emission ◽  
Compact Object ◽  
High Energy ◽  
Be Stars ◽  
Radiative Power ◽  
Very High Energy ◽  
Γ Rays ◽  
Γ Ray ◽  
Very High

Abstractγ-ray binaries are systems that emit most of their radiative power above 1 MeV. They are associated with O or Be stars in orbit with a compact object, possibly a young pulsar. Much like colliding wind binaries, the pulsar generates a relativistic wind that interacts with the stellar wind. The result is non-thermal emission from radio to very high energy γ-rays. The wind, radiation and magnetic field of the massive star play a major role in the dynamics and radiative output of the system. They are particularly important to understand the high energy physics at work. Inversely, γ-ray binaries offer novel probes of stellar winds and insights into the fate of O/B binaries.

scholarly journals Radiocarbon Production by the Gamma-Ray Component of Supernova Explosions

Radiocarbon ◽  
1995 ◽  
Vol 37 (2) ◽  
pp. 599-604 ◽  
Author(s):  
Paul E. Damon ◽  
Dai Kaimei ◽  
Grant E. Kocharov ◽  
Irina B. Mikheeva ◽  
Alexei N. Peristykh
Keyword(s):  
Cross Section ◽  
Tree Rings ◽  
Confidence Level ◽  
Gamma Ray ◽  
Visual Observation ◽  
Total Production ◽  
Average Increase ◽  
Supernova Explosions ◽  
Γ Rays ◽  
Γ Ray

We selected SN1006, the brightest and closest to Earth of all supernovas historically observed, for a study of 14C production by e−,e+-bremsstrahlung cascades initiated by hard γ rays (>10 MeV) from that event. During the cascade, bremsstrahlung energies eventually fall within a giant (n,γ), (n,2γ) cross-section, peaking at 23 MeV and approaching effectively zero below 10 MeV and above 40 MeV. The neutrons are absorbed primarily in the reaction 14N(n,p)14C. Cellulose from single-year tree rings from ad 1003 to ad 1020 was measured to determine ∆14C. Three years after the first visual observation of SN1006, ∆14C rose and remained above pre-ad 1009 values until ad 1018. Comparison of the 7 years before ad 1009 with the 9 years following show an average increase of 6.1 ± 1.6 (s.d.)‰ (significant at the 99.6% confidence level). Such a pulse of 14C requires a total production of neutrons of 17.1 × 107n cm−2e, implying an input of 11.3 × 104 ergs cm−2e γ-ray energy. This requires the total supernova γ-ray energy (>10 MeV) to have been 1 × 1050 ergs.

Study of Template Measurement of Plutonium Pit Based on Gamma-Ray Detection

2010 ◽  
Author(s):  
Changfan Zhang ◽  
Jian Gong ◽  
Junrui Teng ◽  
Suping Liu
Keyword(s):  
Spontaneous Fission ◽  
Counting Rate ◽  
Gamma Ray ◽  
Unique Property ◽  
Nuclear Disarmament ◽  
Neutron Counting ◽  
Neutron Counting Rate ◽  
Γ Rays ◽  
Γ Ray ◽  
Nuclear Warhead

Template measurement is an important method in deep nuclear disarmament. The gamma-ray spectrum of Plutonium pit shows unique property due to age, abundance, amounts and thickness of the Plutonium pit; that is, same designed pits yield similar gamma-ray spectra while different design give distinct spectra. Useful information is extracted from gamma-ray spectrum generated by the reliable Plutonium pit radiation as ‘template’. Comparison of the data from inspected objects with the template can give conclusion whether they are of the same type. This paper studies how to choose template data from gamma-ray spectrum and discusses the limits of the gamma-ray measurement. Because of the strong self-absorption of Plutonium, some characteristics of Plutonium pit can’t be identified only by gamma spectrum. MCNP simulation was employed to prove that in some cases, template depending on gamma-ray spectrum from the reliable Plutonium pit alone can’t effectively distinguish the spurious objects. And a further approach indicates that enhancing neutron counting rate of spontaneous fission of Plutonium can improve the problem. Neutron counting rate can be indirectly acquired by spontaneous fissile neutrons bombarding a 10B target. 478 keV γ rays are concomitant with the nuclear reaction 10B(n,α)7Li* from 7Li* nuclei’s deexcitation. Neutron information is gathered by detecting 478 keV γ photons. Using HPGe γ detector can both detect γ-ray spectrum and acquire neutron counting rate. This method efficiently increases confidence of template measurement and also ensures the dismantling process without revealing sensitive nuclear warhead design information.

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