Abeysekara, A. U. 2011 HAWC可观测伽马暴

主要内容:
将在2014年完工。

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The High Altitude Water Cherenkov (HAWC) observatory is a very high-energy (VHE) gamma-ray detector currently under construction near the peak of Volc´an Sierra Negra, Mexico.

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Title:		On the sensitivity of the HAWC observatory to gamma-ray bursts
Authors:		HAWC collaboration; Abeysekara, A. U.;
Publication:		eprint arXiv:1108.6034
Publication Date:		08/2011
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Bibliographic Code:		2011arXiv1108.6034H

Abstract

We present the sensitivity of HAWC to Gamma Ray Bursts (GRBs). HAWC is a very high-energy gamma-ray observatory currently under construction in Mexico at an altitude of 4100 m. It will observe atmospheric air showers via the water Cherenkov method. HAWC will consist of 300 large water tanks instrumented with 4 photomultipliers each. HAWC has two data acquisition (DAQ) systems. The main DAQ system reads out coincident signals in the tanks and reconstructs the direction and energy of individual atmospheric showers. The scaler DAQ counts the hits in each photomultiplier tube (PMT) in the detector and searches for a statistical excess over the noise of all PMTs. We show that HAWC has a realistic opportunity to observe the high-energy power law components of GRBs that extend at least up to 30 GeV, as it has been observed by Fermi LAT. The two DAQ systems have an energy threshold that is low enough to observe events similar to GRB 090510 and GRB 090902b with the characteristics observed by Fermi LAT. HAWC will provide information about the high-energy spectra of GRBs which in turn could help to understanding about e-pair attenuation in GRB jets, extragalactic background light absorption, as well as establishing the highest energy to which GRBs accelerate particles.

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Acciari, V. A. 2011 VERITAS的甚高能观测

主要内容:
主要能段是260GeV，但没看到任何东西。

Very Energetic Radiation Imaging Telescope Array System (VERITAS)，
VERITAS, MAGIC, HESS它们是一类的

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Title:		VERITAS Observations of Gamma-Ray Bursts Detected by Swift
Authors:		Acciari, V. A.;...

Publication:		The Astrophysical Journal, Volume 743, Issue 1, article id. 62 (2011). (ApJ Homepage)
Publication Date:		12/2011
Origin:		IOP
Astronomy Keywords:		astroparticle physics, gamma-ray burst: general
DOI:		10.1088/0004-637X/743/1/62
Bibliographic Code:		2011ApJ...743...62A

Abstract

We present the results of 16 Swift-triggered Gamma-ray burst (GRB) follow-up observations taken with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) telescope array from 2007 January to 2009 June. The median energy threshold and response time of these observations were 260 GeV and 320 s, respectively. Observations had an average duration of 90 minutes. Each burst is analyzed independently in two modes: over the whole duration of the observations and again over a shorter timescale determined by the maximum VERITAS sensitivity to a burst with a t ^-1.5 time profile. This temporal model is characteristic of GRB afterglows with high-energy, long-lived emission that have been detected by the Large Area Telescope on board the Fermi satellite. No significant very high energy (VHE) gamma-ray emission was detected and upper limits above the VERITAS threshold energy are calculated. The VERITAS upper limits are corrected for gamma-ray extinction by the extragalactic background light and interpreted in the context of the keV emission detected by Swift. For some bursts the VHE emission must have less power than the keV emission, placing constraints on inverse Compton models of VHE emission.

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Kakuwa, Jun 2012 Cherenkov望远镜阵列的特点

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Title:		Prospects for Detecting Gamma-Ray Bursts at Very High Energies with the Cherenkov Telescope Array
Authors:		Kakuwa, Jun; Murase, Kohta; Toma, Kenji; Inoue, Susumu; Yamazaki, Ryo; Ioka, Kunihito
Publication:		eprint arXiv:1112.5940
Publication Date:		12/2011
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		14 pages, 8 figures, submitted to MNRAS
Bibliographic Code:		2011arXiv1112.5940K

Abstract

We discuss the prospects for the detection of gamma-ray bursts (GRBs) by the Cherenkov Telescope Array (CTA), the next generation, ground-based facility of Imaging Atmospheric Cherenkov Telescopes (IACTs) operating above a few tens of GeV. By virtue of its fast slewing capabilities, the lower energy threshold compared to current IACTs, and the much larger effective area compared to satellite instruments, CTA can measure the spectra and variability of GRBs with excellent photon statistics at multi-GeV energies, which would revolutionize our understanding of the physics of GRBs, test their validity as the origin of ultra-high-energy cosmic rays, and provide powerful probes of the extragalactic background light as well as Lorentz-invariance violation. Employing a model of the GRB population whose properties are broadly consistent with observations by Swift as well as the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) onboard Fermi, we simulate follow-up observations of GRBs with the Large Size Telescopes (LSTs), the component of CTA with the fastest slew speed and the best sensitivity at energies below a few hundred GeV. For our fiducial assumptions, we foresee that the LSTs can detect ~0.1--0.2 GRBs per year during the prompt phase and ~1 per year in the afterglow phase, considering only one array site and both GBM and the Space-based multi-band astronomical Variable Object Monitor (SVOM) as the alert instruments. The expected distribution of redshift and photon counts are presented, showing that despite the modest event rate, hundreds or more multi-GeV photons can be anticipated from a single burst once they are detected. We also study how the detection rate depends on the intrinsic GRB properties and the delay time between the burst trigger and the follow-up observation.

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Gilmore, Rudy C. 2012 Cherenkov望远镜观测高能伽马暴光子

主要内容:
结论是upcoming Cherenkov Telescope Array (CTA)可能在二三十个月里看到一个事例。

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Title:		IACT observations of gamma-ray bursts: prospects for the Cherenkov Telescope Array
Authors:		Gilmore, Rudy C.; Bouvier, Aurelien; Connaughton, Valerie; Goldstein, Adam; Otte, Nepomuk; Primack, Joel R.; Williams, David A.
Publication:		eprint arXiv:1201.0010
Publication Date:		12/2011
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		28 pages, 27 figures, 5 tables, submitted to MNRAS on 12/26/11
Bibliographic Code:		2012arXiv1201.0010G

Abstract

Gamma rays at rest frame energies as high as 90 GeV have been reported from gamma-ray bursts (GRBs) by the Fermi Large Area Telescope (LAT). There is considerable hope that a confirmed GRB detection will be possible with the upcoming Cherenkov Telescope Array (CTA), which will have a larger effective area and better low-energy sensitivity than current imaging atmospheric Cherenkov telescopes (IACTs) such at VERITAS, MAGIC, and H.E.S.S. To estimate the likelihood of such a detection, we develop a phenomenological model for GRB emission between 1 GeV and 1 TeV. Motivated by the GRBs detected with Fermi-LAT, we consider two possible ways to extrapolate the statistics of GRBs seen by lower energy instruments. The performance characteristics of CTA are not firmly determined at this time, but we have considered two approximations for the effective area functions of the large- and medium-sized telescope arrays: first a conservative best estimate of the telescope properties, and the other intended to represent the largest effective area and lowest energy threshold that could reasonably be expected. We show a number of statistics for detected GRBs, and describe how our results could vary based on a number of parameters, such as the typical observation delay between the burst onset and the start of ground observations. We also consider the possibility of using GBM on Fermi as a finder of GRBs for rapid ground follow-up, and discuss strategies for dealing with the problematic uncertainty in GBM localization. Overall, our results indicate that CTA should be able to detect one GRB every 20 to 30 months with our baseline instrument model, assuming consistently rapid pursuit of GRB alerts, and provided that spectral breaks below about 100 GeV are not a common feature of the bright GRB population. With the more optimistic instrument model, the detection rate can be 1 to 2 GRBs per year.

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伽马暴作为高能辐射的来源

记得Tsvi他们曾经做过超新星作为超高能辐射的来源的，它们只能来自于银河系，或者较近的其它星系。但是为什么不能是伽马暴呢？

不过很可能不行，不然他们更自然地应该认为是伽马暴而不是超新星。（可能是爆发率的问题，银河系一百万年才有一次伽马暴，而超新星的频率更高。）

Domainko 2011 球状星团Terzan 5中的VHE可能是伽马暴遗迹

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Title:		Finding short GRB remnants in globular clusters: the VHE gamma-ray source in Terzan 5
Authors:		Domainko, Wilfried F.
Publication:		eprint arXiv:1106.4397
Publication Date:		06/2011
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		4 pages, submitted, comments welcome
Bibliographic Code:		2011arXiv1106.4397D

Abstract

Globular cluster are believed to boost the rate of compact binary mergers which may launch a certain type of cosmological gamma-ray bursts (GRBs). Therefore globular clusters appear to be potential sites to search for remnants of such GRBs. The very-high-energy (VHE) gamma-ray source HESS J1747-248 recently discovered in the direction of the Galactic globular cluster Terzan 5 is investigated for being a GRB remnant. Signatures created by the ultra-relativistic outflow, the sub-relativistic ejecta and the ionizing radiation of a short GRB are estimated for an expected age of such a remnant of t > 10^4 years. The kinetic energy of a short GRB could roughly be adequate to power the VHE source in a hadronic scenario. The age of the proposed remnant estimated from its extension possibly agrees with the occurrence of such events in the Galaxy. Sub-relativistic merger ejecta could shock-heat the ambient medium. Further VHE observations can probe the presence of a break towards lower energies expected for particle acceleration in ultra-relativistic shocks. Deep X-ray observations would have the potential to examine the presence of thermal plasma heated by the sub-relativistic ejecta. The identification of a GRB remnant in our own Galaxy may also help to explore the effect of such a highly energetic event on the Earth.

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