Extremely narrow spectrum of GRB110920A: Further evidence for localized, subphotospheric dissipation

S. Iyyani, F. Ryde, B. Ahlgren, J. M. Burgess, J. Larsson, A. Pe'er, C. Lundman, M. Axelsson, S. McGlynn

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


Much evidence points towards that the photosphere in the relativistic outflow in GRBs plays an important role in shaping the observed MeV spectrum. However, it is unclear whether the spectrum is fully produced by the photosphere or whether a substantial part of the spectrum is added by processes far above the photosphere. Here we make a detailed study of the γ - ray emission from single pulse GRB110920A which has a spectrum that becomes extremely narrow towards the end of the burst. We show that the emission can be interpreted as Comptonization of thermal photons by cold electrons in an unmagnetized outflow at an optical depth of τ ~ 20. The electrons receive their energy by a local dissipation occurring close to the saturation radius. The main spectral component of GRB110920A and its evolution is thus, in this interpretation, fully explained by the emission from the photosphere including localized dissipation at high optical depths.

Original languageEnglish
Pages (from-to)1651-1663
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - 10 Apr 2015
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


  • Gammaray burst: general
  • Radiation mechanisms: non-thermal
  • Radiation mechanisms: thermal


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