Time-Resolved Spectroscopy of the 3 Brightest and Hardest Short Gamma-Ray Bursts Observed with the FGST Gamma-Ray Burst Monitor - Astrophysics > High Energy Astrophysical PhenomenaReport as inadecuate




Time-Resolved Spectroscopy of the 3 Brightest and Hardest Short Gamma-Ray Bursts Observed with the FGST Gamma-Ray Burst Monitor - Astrophysics > High Energy Astrophysical Phenomena - Download this document for free, or read online. Document in PDF available to download.

Abstract: From July 2008 to October 2009, the Gamma-ray Burst Monitor GBM on boardthe Fermi Gamma-ray Space Telescope FGST has detected 320 Gamma-Ray BurstsGRBs. About 20% of these events are classified as short based on their T90duration below 2 s. We present here for the first time time-resolvedspectroscopy at timescales as short as 2 ms for the three brightest short GRBsobserved with GBM. The time-integrated spectra of the events deviate from theBand function, indicating the existence of an additional spectral component,which can be fit by a power-law with index ~-1.5. The time-integrated Epeakvalues exceed 2 MeV for two of the bursts, and are well above the valuesobserved in the brightest long GRBs. Their Epeak values and their low-energypower-law indices {\alpha} confirm that short GRBs are harder than long ones.We find that short GRBs are very similar to long ones, but with light curvescontracted in time and with harder spectra stretched towards higher energies.In our time-resolved spectroscopy analysis, we find that the Epeak values rangefrom a few tens of keV up to more than 6 MeV. In general, the hardnessevolutions during the bursts follows their flux-intensity variations, similarto long bursts. However, we do not always see the Epeak leading the light-curverises, and we confirm the zero-short average light-curve spectral lag below 1MeV, already established for short GRBs. We also find that the time-resolvedlow-energy power-law indices of the Band function mostly violate the limitsimposed by the synchrotron models for both slow and fast electron cooling andmay require additional emission processes to explain the data. Finally, weinterpreted these observations in the context of the current existing modelsand emission mechanisms for the prompt emission of GRBs.



Author: Sylvain Guiriec, Michael S. Briggs, Valerie Connaugthon, Erin Kara, Frederic Daigne, Chryssa Kouveliotou, Alexander J. van der Ho

Source: https://arxiv.org/







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