An observed correlation between thermal and non-thermal emission in gamma-ray bursts

J. Michael Burgess, Robert D. Preece, Felix Ryde, Peter Veres, Peter Mészáros, Valerie Connaughton, Michael Briggs, Asaf Pe'Er, Shabnam Iyyani, Adam Goldstein, Magnus Axelsson, Matthew G. Baring, P. N. Bhat, David Byrne, Gerard Fitzpatrick, Suzanne Foley, Daniel Kocevski, Nicola Omodei, William S. Paciesas, Veronique PelassaChryssa Kouveliotou, Shaolin Xiong, Hoi Fung Yu, Binbin Zhang, Sylvia Zhu

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Abstract

Recent observations by the Fermi Gamma-ray Space Telescope have confirmed the existence of thermal and non-thermal components in the prompt photon spectra of some gamma-ray bursts (GRBs). Through an analysis of six bright Fermi GRBs, we have discovered a correlation between the observed photospheric and non-thermal γ-ray emission components of several GRBs using a physical model that has previously been shown to be a good fit to the Fermi data. From the spectral parameters of these fits we find that the characteristic energies, Ep and kT, of these two components are correlated via the relation Ep∝T α which varies from GRB to GRB. We present an interpretation in which the value of the index α indicates whether the jet is dominated by kinetic or magnetic energy. To date, this jet composition parameter has been assumed in the modeling of GRB outflows rather than derived from the data.

Original languageEnglish (US)
Article numberL43
JournalAstrophysical Journal Letters
Volume784
Issue number2
DOIs
StatePublished - Apr 1 2014

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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