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

Patel, M, Gompertz, BP, O’Brien, PT, Lamb, GP, Starling, RLC, Evans, PA, Amati, L, Levan, AJ, Nicholl, M, Ackley, K, Dyer, MJ, Lyman, J, Ulaczyk, K, Steeghs, D, Galloway, DK, Dhillon, VS, Ramsay, G, Noysena, K, Kotak, R, Breton, RP et al (2023) GRB 201015A and the nature of low-luminosity soft gamma-ray bursts. Monthly Notices of the Royal Astronomical Society, 523. pp. 4923-4937. ISSN 0035-8711

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Abstract

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 % of photons from the GRB), and an associated supernova (likely to be type Ic or Ic-BL). GRB 201015A has an isotropic energy $E_{\gamma , \rm iso}$$= 1.75 ^{+0.60} _{-0.53} \times 10^{50}$ erg, and photon index $\Gamma = 3.00 ^{+0.50} _{-0.42}$ (15–150 keV). It follows the Amati relation, a correlation between $E_{\gamma , \rm iso}$ 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 $t = 1.67 ^{+1.14} _{-0.65} \times 10^6$ 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.

Item Type:	Article
Uncontrolled Keywords:	0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press (OUP)
Date of acceptance:	7 June 2023
Date of first compliant Open Access:	22 June 2023
Date Deposited:	22 Jun 2023 09:55
Last Modified:	20 May 2025 14:00
DOI or ID number:	10.1093/mnras/stad1703
URI:	https://researchonline.ljmu.ac.uk/id/eprint/20003

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