GRB 120422A: A low-luminosity gamma-ray burst driven by a central engine

Bin Bin Zhang, Yi Zhong Fan, Rong Feng Shen, Dong Xu, Fu Wen Zhang, Da Ming Wei, David N. Burrows, Bing Zhang, Neil Gehrels

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Abstract

GRB 120422A is a low-luminosity gamma-ray burst (GRB) associated with a bright supernova, which distinguishes itself by its relatively short T 90 (∼5 s) and an energetic and steep-decaying X-ray tail. We analyze the Swift Burst Alert Telescope and X-ray Telescope data and discuss the physical implications. We show that the steep decline early in the X-ray light curve can be interpreted as the curvature tail of a late emission episode around 58-86s, with a curved instantaneous spectrum at the end of the emission episode. Together with the main activity in the first ∼20 s and the weak emission from 40s to 60s, the prompt emission is variable, which points to a central engine origin in contrast to a shock-breakout origin, which is used to interpret some other nearby low-luminosity supernova GRBs. Both the curvature effect model and interpreting the early shallow decay as the coasting external forward shock emission in a wind medium provide a constraint on the bulk Lorentz factor Γ to be around several. Comparing the properties of GRB 120422A and other supernova GRBs, we find that the main criterion to distinguish engine-driven GRBs from shock-breakout GRBs is the time-averaged γ-ray luminosity. Engine-driven GRBs likely have a luminosity above ∼10 48 erg s-1.

Original languageEnglish (US)
Article number190
JournalAstrophysical Journal
Volume756
Issue number2
DOIs
StatePublished - Sep 10 2012

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Zhang, B. B., Fan, Y. Z., Shen, R. F., Xu, D., Zhang, F. W., Wei, D. M., Burrows, D. N., Zhang, B., & Gehrels, N. (2012). GRB 120422A: A low-luminosity gamma-ray burst driven by a central engine. Astrophysical Journal, 756(2), [190]. https://doi.org/10.1088/0004-637X/756/2/190