The hidden population of long gamma-ray bursts from compact object mergers

Maccary, R ORCID: 0000-0002-8799-2510, Guidorzi, C ORCID: 0000-0001-6869-0835, Amati, L ORCID: 0000-0001-5355-7388, Bulla, M ORCID: 0000-0002-8255-5127, Kobayashi, S ORCID: 0000-0001-7946-4200, Maistrello, M ORCID: 0009-0000-4422-4151, Rossi, A ORCID: 0000-0002-8860-6538, Stratta, G ORCID: 0000-0003-1055-7980 and Tsvetkova, A ORCID: 0000-0003-0292-6221 (2026) The hidden population of long gamma-ray bursts from compact object mergers. Astronomy & Astrophysics, 708. ISSN 0004-6361

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Abstract

Context. The prompt-emission time profiles of GRB 230307A and other long-duration compact object merger (COM) candidates exhibit a unique set of temporal properties, characterised by a deterministic evolution of waiting times and pulse widths.

Aims. We searched the Fermi/GBM catalogue for other unidentified long COM candidates exhibiting temporal properties similar to those observed in GRB 230307A.

Methods. We examined the temporal and spectral prompt-emission properties of GRBs featuring at least eight light-curve peaks. For candidates, all with unknown redshifts, that exhibited properties similar to GRB 230307A, we analysed their trajectories in the Ep, i − Eiso plane as a function of redshift. We then evaluated the joint likelihood of their compatibility with the Ep, i − Eiso relation satisfied by the bulk of long GRBs. Furthermore, we calculated their minimum variability timescales (MVTs) for comparison against known COM and collapsar populations.

Results. We identified nine COM candidates with unknown redshifts and demonstrated that there are at least two outliers of the Ep, i − Eiso relation with 3.1σ (Gaussian) confidence level. Furthermore, their MVTs are more consistent with those of COM than with collapsar GRBs.

Conclusions. These results indicate that this specific set of temporal properties can serve as a diagnostic tool to distinguish long-duration COMs from the broader collapsar population. Furthermore, our findings suggest that the fraction of unidentified COMs among long GRBs might be larger than previously assumed.

Item Type:	Article
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	EDP Sciences
Date of acceptance:	16 March 2026
Date of first compliant Open Access:	7 May 2026
Date Deposited:	07 May 2026 08:12
Last Modified:	07 May 2026 08:12
DOI or ID number:	10.1051/0004-6361/202659083
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28528

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