X-ray flares in GRBs: General considerations and photospheric origin

Paz Beniamini, Pawan Kumar

Research output: Contribution to journalArticlepeer-review


Observations of X-ray flares from Gamma Ray Bursts imply strong constraints on possible physical models.We provide a general discussion of these. In particular, we show that in order to account for the relatively flat and weak optical flux during the X-ray flares, the size of the emitting region should be ≳3 × 1014cm. The bolometric luminosity of flares also strongly constrain the energy budget, and are inconsistent with late time activity of a central engine powered by the spin-down of a magnetar. We provide a simple toy model according to which flares are produced by an outflow of modest Lorentz factor (a few tens instead of hundreds) that is launched more or less simultaneously with the highly relativistic jet which produced the prompt gamma-ray emission. The 'slower moving outflow produces the flare as it reaches its photosphere. If the X-ray flare jets are structured, the existence of such a component may naturally resolve the observational challenges imposed by flares, outlined in this work.

Original languageEnglish
Pages (from-to)L108-L112
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
StatePublished - 7 Jan 2016
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2016 The Authors.


  • Gamma-ray burst: general


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