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arXiv · 1206.0298

GRB 120422A: A Low-luminosity Gamma-ray Burst Driven by 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 T90 ~ 5 s and an energetic X-ray tail. We analyze the Swift BAT and XRT data and discuss the physical implications. We show that the early steep decline in the X-ray light curve can be interpreted as the curvature tail of a late emission episode around 58-86 s, 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 40 s to 60 s, the prompt emission is variable, which points towards a central engine origin, in contrast to the shock breakout origin as invoked to interpret some other nearby low-luminosity supernova GRBs. The curvature effect interpretation and interpreting the early shallow decay as the coasting external forward shock emission in a wind medium both give a constraint on the bulk Lorentz factor \Gamma to be around several. Comparing the properties of GRB 120422A and other supernova GRBs, we found that the main criterion to distinguish engine-driven GRBs from the shock breakout GRBs is the time-averaged luminosity, with a separation line of about ~ 10^48 erg s^-1.

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Bin-Bin Zhang, Yi-Zhong Fan, Rong-Feng Shen, Dong Xu, Fu-Wen Zhang, Da-Ming Wei, David N. Burrows, Bing Zhang, Neil Gehrels. 2012-06-01. GRB 120422A: A Low-luminosity Gamma-ray Burst Driven by Central Engine. https://doi.org/10.1088/0004-637x/756/2/190

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