Prompt gamma-ray burst emission from internal shocks - new insights

S. K.Minhajur Rahaman, Jonathan Granot, Paz Beniamini

Research output: Contribution to journalArticlepeer-review

Abstract

Internal shocks are a leading candidate for the dissipation mechanism that powers the prompt γ-ray emission in gamma-ray bursts (GRBs). In this scenario a compact central source produces an ultra-relativistic outflow with varying speeds, causing faster parts or shells to collide with slower ones. Each collision produces a pair of shocks - a forward shock (FS) propagating into the slower leading shell and a reverse shock (RS) propagating into the faster trailing shell. The RS's lab-frame speed is always smaller, while the RS is typically stronger than the FS, leading to different conditions in the two shocked regions that both contribute to the observed emission. We show that optically thin synchrotron emission from both (weaker FS + stronger RS) can naturally explain key features of prompt GRB emission such as the pulse shapes, time evolution of the νFν peak flux and photon energy, and the spectrum. Particularly, it can account for two features commonly observed in GRB spectra: (i) a sub-dominant low-energy spectral component (often interpreted as 'photospheric'-like), or (ii) a doubly broken power-law spectrum with the low-energy spectral slope approaching the slow-cooling limit. Both features can be obtained while maintaining high-overall radiative efficiency without any fine tuning of the physical conditions.

Original languageEnglish
Pages (from-to)L45-L51
JournalMonthly Notices of the Royal Astronomical Society: Letters
Volume528
Issue number1
DOIs
StatePublished - 1 Feb 2024

Bibliographical note

Publisher Copyright:
© 2023 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.

Keywords

  • (transients:) gamma-ray bursts
  • hydrodynamics
  • relativistic processes
  • shock waves

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