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GRB 201015A and the nature of low-luminosity soft gamma-ray bursts

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posted on 2023-08-09, 09:56 authored by M Patel, BP Gompertz, PT O'Brien, GP Lamb, RLC Starling, PA Evans, L Amati, AJ Levan, M Nicholl, K Ackley, MJ Dyer, J Lyman, K Ulaczyk, D Steeghs, DK Galloway, VS Dhillon, G Ramsay, K Noysena, R Kotak, RP Breton, LK Nuttall, E Pallé, D Pollacco

GRB 201015A is a peculiarly low luminosity, spectrally soft gamma-ray burst (GRB), with T90 = 9.8 ± 3.5 s (time interval of detection of 90  per cent of photons from the GRB), and an associated supernova (likely to be type Ic or Ic-BL). GRB 201015A has an isotropic energy Eγ,iso

=1.75+0.60−0.53×1050

 erg, and photon index Γ=3.00+0.50−0.42

 (15–150 keV). It follows the Amati relation, a correlation between Eγ,iso

 and spectral peak energy Ep followed by long GRBs. It appears exceptionally soft based on Γ, the hardness ratio of HR  = 0.47 ± 0.24, and low-Ep, so we have compared it to other GRBs sharing these properties. These events can be explained by shock breakout, poorly collimated jets, and off-axis viewing. Follow-up observations of the afterglow taken in the X-ray, optical, and radio reveal a surprisingly late flattening in the X-ray from t = (2.61 ± 1.27) × 104 s to t=1.67+1.14−0.65×106

 s. We fit the data to closure relations describing the synchrotron emission, finding the electron spectral index to be p=2.42+0.44−0.30

 and evidence of late-time energy injection with coefficient q=0.24+0.24−0.18

⁠. The jet half opening angle lower limit (θj ≥ 16°) is inferred from the non-detection of a jet break. The launch of SVOM and Einstein Probe in 2023 should enable detection of more low-luminosity events like this, providing a fuller picture of the variety of GRBs.

History

Author affiliation

School of Physics & Astronomy, University of Leicester

Version

  • VoR (Version of Record)

Published in

Monthly Notices of the Royal Astronomical Society

Volume

523

Issue

4

Pagination

4923 - 4937

Publisher

Oxford University Press (OUP)

issn

0035-8711

eissn

1365-2966

Copyright date

2023

Available date

2023-08-09

Language

en

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