UNIQUE TeV FLARES OF PKS 2155-304 IN JULY 2006

2008 ◽  
Vol 17 (09) ◽  
pp. 1443-1448
Author(s):  
◽  
ROLF BÜHLER
Keyword(s):  
Southern Hemisphere ◽  
Time Scales ◽  
High Frequency ◽  
Gamma Ray ◽  
High Energy ◽  
High State ◽  
Spectral Variability ◽  
Bl Lac ◽  
First Results ◽  
Stereoscopic System

The high-frequency-peaked BL Lac PKS 2155-304 is one of the brightest and best-studied VHE gamma-ray sources in the southern hemisphere. Since 2002, the High Energy Stereoscopic System (H.E.S.S.) has monitored this source and found it to be in an unusually high state in July 2006. On the nights of 28 and 30 July, two major outbursts occurred, with peak fluxes ~ 80 times the usual values and well-resolved structures varying on time scales of ~ 200 s. Here, we report on spectral variability studies of VHE data of the first flare and show first results of the H.E.S.S. observations during the second flare night.

scholarly journals VLBI Observations of Southern EGRET Identifications

1996 ◽  
Vol 175 ◽  
pp. 19-20
Author(s):  
J.E.J. Lovell ◽  
S.J. Tingay ◽  
P.G. Edwards ◽  
D.L. Jauncey ◽  
R.A. Preston
Keyword(s):  
High Resolution ◽  
Southern Hemisphere ◽  
Gamma Ray ◽  
Radio Sources ◽  
Vlbi Observations ◽  
First Results

We present high resolution VLBI images of three southern radio sources: PKS 0208–512, PKS 0521–365 and PKS 0537–441. These sources have been identified as > 100 MeV gamma-ray sources with the Energetic Gamma-Ray Telescope (EGRET) on board the Compton Gamma-Ray Observatory (Thompson et al. 1995). These are the first results in a continuing program of VLBI observations of southern EGRET identifications with the Southern Hemisphere VLBI Experiment (SHEVE) array of telescopes (Jauncey et al., 1994).

scholarly journals Gamma-ray counterparts of 2WHSP high-synchrotron-peaked BL Lac objects as possible signatures of ultra-high-energy cosmic ray emission

2020 ◽  
Vol 497 (2) ◽  
pp. 2455-2468
Author(s):  
Michael W Toomey ◽  
Foteini Oikonomou ◽  
Kohta Murase
Keyword(s):  
Energy Range ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
High Energy ◽  
Potential Candidate ◽  
Ultra High Energy ◽  
Bl Lac Objects ◽  
Cherenkov Telescopes ◽  
Bl Lac ◽  
Γ Ray

ABSTRACT We present a search for high-energy γ-ray emission from 566 Active Galactic Nuclei at redshift z > 0.2, from the 2WHSP catalogue of high-synchrotron peaked BL Lac objects with 8 yr of Fermi-LAT data. We focus on a redshift range where electromagnetic cascade emission induced by ultra-high-energy cosmic rays can be distinguished from leptonic emission based on the spectral properties of the sources. Our analysis leads to the detection of 160 sources above ≈5σ (TS ≥25) in the 1–300 GeV energy range. By discriminating significant sources based on their γ-ray fluxes, variability properties, and photon index in the Fermi-LAT energy range, and modelling the expected hadronic signal in the TeV regime, we select a list of promising sources as potential candidate ultra-high-energy cosmic ray emitters for follow-up observations by Imaging Atmospheric Cherenkov Telescopes.

scholarly journals High-energy emission from transients

2013 ◽  
Vol 371 (1992) ◽  
pp. 20120279 ◽  
Author(s):  
J. A. Hinton ◽  
R. L. C. Starling
Keyword(s):  
Particle Acceleration ◽  
Time Scales ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Experimental Situation ◽  
High Energy ◽  
Galactic Cosmic Rays ◽  
Time Variable ◽  
Wide Range ◽  
Cosmic Explosions

Cosmic explosions dissipate energy into their surroundings on a very wide range of time scales: producing shock waves and associated particle acceleration. The historical culprits for the acceleration of the bulk of Galactic cosmic rays are supernova remnants: explosions on approximately 10 4 year time scales. Increasingly, however, time-variable emission points to rapid and efficient particle acceleration in a range of different astrophysical systems. Gamma-ray bursts have the shortest time scales, with inferred bulk Lorentz factors of approximately 1000 and photons emitted beyond 100 GeV, but active galaxies, pulsar wind nebulae and colliding stellar winds are all now associated with time-variable emission at approximately teraelectron volt energies. Cosmic photons and neutrinos at these energies offer a powerful probe of the underlying physical mechanisms of cosmic explosions, and a tool for exploring fundamental physics with these systems. Here, we discuss the motivations for high-energy observations of transients, the current experimental situation, and the prospects for the next decade, with particular reference to the major next-generation high-energy observatory, the Cherenkov Telescope Array.

scholarly journals Markarian 421: Te V Gamma-ray Flares and VLBI Structure

1998 ◽  
Vol 164 ◽  
pp. 45-46 ◽  
Author(s):  
P.G. Edwards ◽  
G.A. Moellenbrock ◽  
S.C. Unwin ◽  
A.E. Wehrle ◽  
T.C. Weekes
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Markarian 421 ◽  
Bl Lac

AbstractPhotons spanning over 17 decades in energy have been detected from Markarian 421. The discovery of >100 MeV photons by the EGRET instrument on board the Compton Gamma Ray Observatory led to the discovery of >300 GeV photons by the Whipple group using the air Čerenkov method. In May 1996 the source underwent an unprecedented outburst at these energies, inspiring observations with the VLBA to determine whether such high energy flares are associated with changes in the milliarcsecond structure of this BL Lac object.

The search for high energy muon neutrinos from southern hemisphere gamma-ray bursts with BUST

2015 ◽  
Vol 46 (2) ◽  
pp. 201-204 ◽  
Author(s):  
V. B. Petkov ◽  
M. M. Boliev ◽  
I. A. Alikhanov ◽  
A. V. Butkevich ◽  
I. M. Dzaparova ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Gamma Ray ◽  
High Energy ◽  
Gamma Ray Bursts ◽  
Muon Neutrinos ◽  
High Energy Muon

Space VLBI observations of southern hemisphere gamma-ray and non-gamma-ray AGN: First results for PKS 0637-752

2000 ◽  
Vol 26 (4) ◽  
pp. 677-680 ◽  
Author(s):  
S.J. Tingay ◽  
D.L. Jauncey ◽  
J.E. Reynolds ◽  
A.K. Tzioumis ◽  
E.A. King ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Gamma Ray ◽  
Vlbi Observations ◽  
First Results

scholarly journals Revealing x-ray and gamma ray temporal and spectral similarities in the GRB 190829A afterglow

Science ◽  
2021 ◽  
Vol 372 (6546) ◽  
pp. 1081-1085
Author(s):  
◽  
H. Abdalla ◽  
F. Aharonian ◽  
F. Ait Benkhali ◽  
E. O. Angüner ◽  
...  
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
High Energy ◽  
X Ray ◽  
Photon Index ◽  
Very High Energy ◽  
Stereoscopic System ◽  
Very High ◽  
Intrinsic Energy

Gamma-ray bursts (GRBs), which are bright flashes of gamma rays from extragalactic sources followed by fading afterglow emission, are associated with stellar core collapse events. We report the detection of very-high-energy (VHE) gamma rays from the afterglow of GRB 190829A, between 4 and 56 hours after the trigger, using the High Energy Stereoscopic System (H.E.S.S.). The low luminosity and redshift of GRB 190829A reduce both internal and external absorption, allowing determination of its intrinsic energy spectrum. Between energies of 0.18 and 3.3 tera–electron volts, this spectrum is described by a power law with photon index of 2.07 ± 0.09, similar to the x-ray spectrum. The x-ray and VHE gamma-ray light curves also show similar decay profiles. These similar characteristics in the x-ray and gamma-ray bands challenge GRB afterglow emission scenarios.

scholarly journals Locating the gamma-ray emission region in the brightest Fermi-LAT flat-spectrum radio quasars

2020 ◽  
Vol 500 (4) ◽  
pp. 5297-5321
Author(s):  
Atreya Acharyya ◽  
Paula M Chadwick ◽  
Anthony M Brown
Keyword(s):  
Time Scales ◽  
Gamma Ray ◽  
High Energy ◽  
Emission Region ◽  
Large Area ◽  
Line Region ◽  
Spectrum Radio ◽  
Show Evidence ◽  
Very High Energy ◽  
Gamma Ray Emission

ABSTRACT We present a temporal and spectral analysis of the gamma-ray flux from nine of the brightest flat-spectrum radio quasars (FSRQs) detected with the Fermi Large Area Telescope during its first 8 yr of operation, with the aim of constraining the location of the emission region. Using the increased photon statistics obtained from the two brightest flares of each source, we find evidence of sub-hour variability from B2 1520+31, PKS 1502+106, and PKS 1424−41, with the remaining sources showing variability on time-scales of a few hours. These indicate gamma-ray emission from extremely compact regions in the jet, potentially compatible with emission from within the broad-line region (BLR). The flare spectra show evidence of a spectral cut-off in 7 of the 18 flares studied, further supporting the argument for BLR emission in these sources. An investigation into the energy dependence of cooling time-scales finds evidence for both BLR origin and emission from within the molecular torus (MT). However, Monte Carlo simulations show that the very high energy (Eγ ≥ 20 GeV) emission from all sources except 3C 279, 3C 454.3, and 4C 21.35 is incompatible with a BLR origin. The combined findings of all the approaches used suggest that the gamma-ray emission in the brightest FSRQs originates in multiple compact emission regions throughout the jet, within both the BLR and the MT.

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