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

Patel, M ORCID: 0000-0001-9772-1071, Gompertz, BP ORCID: 0000-0002-5826-0548, O’Brien, PT, Lamb, GP ORCID: 0000-0001-5169-4143, Starling, RLC ORCID: 0000-0001-5803-2038, Evans, PA ORCID: 0000-0002-8465-3353, Amati, L, Levan, AJ, Nicholl, M ORCID: 0000-0002-2555-3192, Ackley, K, Dyer, MJ ORCID: 0000-0003-3665-5482, Lyman, J ORCID: 0000-0002-3464-0642, Ulaczyk, K, Steeghs, D ORCID: 0000-0003-0771-4746, Galloway, DK, Dhillon, VS ORCID: 0000-0003-4236-9642, Ramsay, G, Noysena, K, Kotak, R, Breton, RP ORCID: 0000-0001-8522-4983 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:	04 Jul 2025 18:15
DOI or ID number:	10.1093/mnras/stad1703
URI:	https://researchonline.ljmu.ac.uk/id/eprint/20003

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