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TOPIC: Gamma-Ray Bursts


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Gamma-ray Burst Cosmology
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Title: Gamma-ray Burst Cosmology
Author: F. Y. Wang (NJU), Z. G. Dai (NJU), E. W. Liang (GXU)

Gamma-ray bursts (GRBs) are the most luminous electromagnetic explosions in the Universe, which emit up to 8.8 x 1054 erg isotropic equivalent energy in the hard X-ray band. The high luminosity makes them detectable out to the largest distances yet explored in the Universe. GRBs, as bright beacons in the deep Universe, would be the ideal tool to probe the properties of high-redshift universe: including the cosmic expansion and dark energy, star formation rate, the reionisation epoch and the metal enrichment history of the Universe. In this article, we review the luminosity correlations of GRBs, and implications for constraining the cosmological parameters and dark energy. Observations show that the progenitors of long GRBs are massive stars. So it is expected that long GRBs are tracers of star formation rate. We also review the high-redshift star formation rate derived from GRBs, and implications for the cosmic reionisation history. The afterglows of GRBs generally have broken power-law spectra, so it is possible to extract intergalactic medium (IGM) absorption features. We also present the capability of high-redshift GRBs to probe the pre-galactic metal enrichment and the first stars.

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RE: Gamma-Ray Bursts
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Title: A size-duration trend for gamma-ray burst progenitors
Author: Anna Barnacka, Abraham Loeb

Gamma-ray bursts (GRBs) show a bimodal distribution of durations, separated at a duration of ~2 s. Observations have confirmed the association of long GRBs with the collapse of massive stars. The origin of short GRBs is still being explored. We examine constraints on the emission region size in short and long GRBs detected by Fermi/GBM. We find that the emission region size during the prompt emission, R, and the burst duration, T90, are consistent with the relation R ~ c x T90, for both long and short GRBs. We find the characteristic size for the prompt emission region to be ~2 x 1010 cm, and ~4 x 1011 cm for short and long GRBs, respectively.

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Title: Can a Single High-energy Neutrino from Gamma-ray Bursts be a Discovery?
Author: Imre Bartos, Szabolcs Marka

Current emission models of GeV-PeV neutrinos from gamma-ray bursts (GRBs) predict a neutrino flux with << 1 detected neutrinos per GRB with kilometer-scale neutrino observatories. The detection of this flux will require the stacking of data from a large number of GRBs, leading to an increased background rate, decreasing the significance of a single neutrino detection. We show that utilizing the temporal correlation between the expected gamma-ray and neutrino fluxes, one can significantly improve the neutrino signal-to-noise ratio. We describe how this temporal correlation can be used. Using realistic GRB and atmospheric neutrino fluxes and incorporating temporal, spectral and directional information, we estimate the probability of a single detected GRB-neutrino being a 5-sigma discovery.

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Title: Novel distance indicator for gamma-ray bursts associated with supernovae
Authors: G. B. Pisani, L. Izzo, R. Ruffini, C. L. Bianco, M. Muccino, A. V. Penacchioni, J. A. Rueda, Y. Wang

Context. It has been proposed that the temporal coincidence of a gamma-ray burst (GRB) and a type Ib/c supernova (SN) can be explained with the concept of induced gravitational collapse (IGC), induced by the matter ejected from an SN Ib/c accreting onto a neutron star (NS). The NS is expected to reach the critical mass necessary for it to collapse to a black hole (BH) and emit a GRB. We found a standard luminosity light curve behaviour in the late-time X-ray emission of this subclass of GRBs.
Aims. We test if this standard behaviour in the luminosity found in this subclass of GRBs can become a redshift estimator of these sources.
Methods. We selected a sample of GRBs that belong to this subclass of IGC GRBs associated to an SN (IGC GRB-SN sources). These sources have an isotropic energy E_{iso} > 10^{52} erg and their cosmological redshifts are in the range of z = 0.49-1.261. We focused on the corresponding X-ray luminosity light curves.
Results. We find that all GRBs of the sample with measured redshift present a standard luminosity late-time light curve in the 0.3-10 keV rest-frame energy range. We used these results to estimate the GRB redshift of the sample without a measured redshift and found results consistent with other possible redshift indicators.
Conclusions. The standard late-time X-ray luminosity light curve of all GRBs of the sample shows a common physical mechanism in this particular phase of the X-ray emission, possibly related to the creation of the NS from the SN process. This scaling law moreover represents strong evidence of very low or even absent beaming in this late phase of the X-ray afterglow emission process. This could be a fundamental tool for estimating the redshift of GRBs that belong to this subclass of events. We are currently expanding this subclass of GRBs to further verify the universal validity of this new redshift estimation method.

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Title: INTEGRAL Results on Gamma-Ray Bursts
Authors: Diego Gotz

Despite being a general observatory, and not a Gamma-Ray Bursts (GRBs) oriented mission, INTEGRAL has contributed to several important discoveries in the GRB field. This has been obtained thanks to its unprecedented localisation capabilities, and sensitivity in the soft gamma-ray domain. In this paper I will review the main results obtained during the last 10 years with, and thanks to, INTEGRAL GRBs, including the discovery of one of the few GRBs spectroscopically associated with a Supernova, the first measurement of variable polarisation in the GRB prompt emission, the indication of the existence of a low-luminosity population of GRBs, as well as the recent application of GRBs as probes for the fundamental physics. I will mention the main global characteristics of the INTEGRAL sample, and make the point on the lessons learnt from INTEGRAL in the perspective of designing future GRB dedicated missions.

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Title: Hints for a possible distance indicators from GRB-SN association
Authors: L. Izzo, G.B. Pisani, M. Muccino, J.A. Rueda, Y. Wang, C.L. Bianco, A.V. Penacchioni, R. Ruffini

The possibility to divide GRBs in different subclasses allow to understand better the physics underlying their emission mechanisms and progenitors. The induced gravitational collapse (IGC) scenario proposes a binary progenitor to explain the time-sequence of the GRB-SN events. We show the existence of a common behaviour of the late decay of the X-ray afterglow emission of this subclass of GRBs, pointing to a common physical mechanism of this late GRB emission, consistent with the IGC picture.

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Title: The most powerful explosions in the Universe: genesis and evolution of Supernova and Gamma-Ray Burst Italian programs at ESO
Authors: Elena Pian (1,2,3) ((1) INAF-OATrieste, Italy (2) Scuola Normale Superiore, Pisa, Italy (3) INFN-Pisa, Italy)

The Italian communities engaged in Gamma-Ray Burst (GRB) and supernova research have been using actively the ESO telescopes and have contributed to improve and refine the observing techniques and even to guide the characteristics and performances of the instruments that were developed. Members of these two communities have recently found ground for a close collaboration on the powerful supernovae that underlie some GRBs. I will review the programs that have led to some important discoveries and milestones on thermonuclear and core-collapse supernovae and on GRBs.

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Title: A method for determination of gamma-ray direction in space
Authors: S. Akkoyun

Gamma-ray bursts (GRBs) are short and most intense bursts of gamma-rays that come from random direction in space. Their origin are still unknown and they originate likely from cosmological distances, probably after birth of a new black hole or death of a giant star. In this work, Geant simulations of a detector array whose aim is to identify gamma-ray directions in space were performed and a method for this identification was developed. The array consists of three quadratic NaI(Tl) scintillators which are facing different directions and the method is based on the difference of the counts registered in these three detectors. By using the method the gamma-ray directions are obtained with 10° accuracy. This form of the array which can scan three dimensions in space is crucial to pinpoint origin of the GRBs. The array would also be applicable in various fields where identifications of the gamma-ray directions are necessary.

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Ed ~ Ultrahigh energy gamma rays are not scrambled by magnetic fields and travel in straight lines, unlike cosmic rays which are deflected. however, Ultra high energy gamma rays interact with magnetic fields to produce electron-positron pairs.



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Title: Gamma Ray Bursts
Authors: Peter Mészáros

Gamma-ray bursts have been detected at photon energies up to tens of GeV. We review some recent developments in the X-ray to GeV photon phenomenology in the light of swift and fermi observations, and some of the theoretical models developed to explain them, with a view towards implications for C.T.A.

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Real-time gamma ray bursts

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