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Thermal Emissions Spanning the Prompt and the Afterglow Phases of the Ultra-long GRB 130925A

Basak, Rupal and Rao, A. R. (2015) Thermal Emissions Spanning the Prompt and the Afterglow Phases of the Ultra-long GRB 130925A. Astrophysical Journal, 807 (1). Art. No. 34. ISSN 0004-637X. doi:10.1088/0004-637X/807/1/34.

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GRB 130925A is an ultra-long gamma-ray burst (GRB), and it shows clear evidence for thermal emission in the soft X-ray data of the Swift/X-ray Telescope (XRT; ~0.5 keV), lasting until the X-ray afterglow phase. Due to the long duration of the GRB, the burst could be studied in hard X-rays with high-resolution focusing detectors (NuSTAR). The blackbody temperature, as measured by the Swift/XRT, shows a decreasing trend until the late phase (Piro et al.) whereas the high-energy data reveal a significant blackbody component during the late epochs at an order of magnitude higher temperature (~5 keV) compared to contemporaneous low energy data (Bellm et al.). We resolve this apparent contradiction by demonstrating that a model with two black bodies and a power law (2BBPL) is consistent with the data right from the late prompt emission to the afterglow phase. Both blackbodies show a similar cooling behavior up to late times. We invoke a structured jet, having a fast spine and a slower sheath layer, to identify the location of these blackbodies. Independent of the physical interpretation, we propose that the 2BBPL model is a generic feature of the prompt emission of all long GRBs, and the thermal emission found in the afterglow phase of different GRBs reflects the lingering thermal component of the prompt emission with different timescales. We strengthen this proposal by pointing out a close similarity between the spectral evolutions of this GRB and GRB 090618, a source with significant wide band data during the early afterglow phase.

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Additional Information:© 2015. The American Astronomical Society. Received 2014 September 17; accepted 2015 May 10; published 2015 June 26. This research has made use of data obtained through the HEASARC Online Service, provided by the NASA/GSFC, in support of NASA High Energy Astrophysics Programs. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. We thank the referee for valuable comments that made the presentation more rigorous.
Subject Keywords:gamma-ray burst: general; gamma-ray burst: individual (130925A) ; methods: data analysis; methods: observational; radiation mechanisms: thermal
Issue or Number:1
Record Number:CaltechAUTHORS:20160128-195055808
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Official Citation:Rupal Basak and A. R. Rao 2015 ApJ 807 34
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64072
Deposited By: Joy Painter
Deposited On:29 Jan 2016 17:07
Last Modified:10 Nov 2021 23:25

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