Poynting-flux-dominated jets challenged by their photospheric emission

D. Bégué, A. Pe'er

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One of the key open question in the study of jets, in general, and jets in gamma-ray bursts (GRBs), in particular, is the magnetization of the outflow. Here we consider the photospheric emission of Poynting-flux-dominated outflows, when the dynamics is mediated by magnetic reconnection. We show that thermal three-particle processes, responsible for the thermalization of the plasma, become inefficient at a radius of rsup ∼ 109.5 cm, far below the photosphere, at ∼1011.5 cm. Conservation of the total photon number above rsup combined with Compton scattering below the photosphere enforces kinetic equilibrium between electrons and photons. This, in turn, leads to an increase in the observed photon temperature, which reaches ≳8 MeV (observed energy) when decoupling the plasma at the photosphere. This result is weakly dependent on the free model parameters. We show that in this case, the expected thermal luminosity is a few percent of the total luminosity, and could therefore be detected. The predicted peak energy is more than an order of magnitude higher than the observed peak energy of most GRBs, which puts strong constraints on the magnetization of these outflows.

Original languageEnglish
Article number134
JournalAstrophysical Journal
Issue number2
StatePublished - 1 Apr 2015
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2015. The American Astronomical Society. All rights reserved.


  • Gamma-ray burst: general
  • Magnetic reconnection
  • Plasmas
  • Radiation mechanisms: thermal


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