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Perley, DA, Ho, AYQ, Fausnaugh, M, Lamb, GP, Kasliwal, MM, Ahumada, T, Anand, S, Andreoni, I, Bellm, E, Bhalerao, V, Bolin, B, Brink, TG, Burns, E, Cenko, SB, Corsi, A, Filippenko, AV, Frederiks, D, Goldstein, A, Hamburg, R, Jayaraman, R , Jonker, PG, Kool, EC, Kulkarni, SR, Kumar, H, Laher, R, Levan, A, Lysenko, A, Perley, RA, Ricker, GR, Riddle, R, Ridnaia, A, Rusholme, B, Smith, R, Svinkin, D, Ulanov, M, Vanderspek, R, Waratkar, G and Yao, Y (2025) The luminous, slow-rising orphan afterglow AT2019pim as a candidate moderately relativistic outflow. Monthly Notices of the Royal Astronomical Society, 537 (3). pp. 1-18. ISSN 0035-8711
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The luminous, slow-rising orphan afterglow AT2019pim as a candidate.pdf - Published Version Available under License Creative Commons Attribution. Download (2MB) | Preview |
Abstract
Classical gamma-ray bursts (GRBs) have two distinct emission episodes: prompt emission from ultrarelativistic ejecta and afterglow from shocked circumstellar material. While both components are extremely luminous in known GRBs, a variety of scenarios predict the existence of luminous afterglow emission with little or no associated high-energy prompt emission. We present AT 2019pim, the first spectroscopically confirmed afterglow with no observed high-energy emission to be identified. Serendipitously discovered during follow-up observations of a gravitational-wave trigger and located in a contemporaneous TESS sector, it is hallmarked by a fast-rising ( h), luminous ( mag) optical transient with accompanying luminous X-ray and radio emission. No gamma-ray emission consistent with the time and location of the transient was detected by Fermi-GBM or by Konus, placing constraining limits on an accompanying GRB. We investigate several independent observational aspects of the afterglow in the context of constraints on relativistic motion and find all of them are consistent with an initial Lorentz factor of 10-30 for the on-axis material, significantly lower than in any well-observed GRB and consistent with the theoretically predicted 'dirty fireball' scenario in which the high-energy prompt emission is stifled by pair production. However, we cannot rule out a structured jet model in which only the line-of-sight material was ejected at low-, off-axis from a classical high- jet core, and an on-axis GRB with below-average gamma-ray efficiency also remains a possibility. This event represents a milestone in orphan afterglow searches, demonstrating that luminous optical afterglows lacking detected GRB counterparts can be identified and spectroscopically confirmed in real time.
| Item Type: | Article |
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| Uncontrolled Keywords: | astro-ph.HE; astro-ph.HE; 5101 Astronomical Sciences; 51 Physical Sciences; 7 Affordable and Clean Energy; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences |
| Subjects: | Q Science > QB Astronomy Q Science > QC Physics |
| Divisions: | Astrophysics Research Institute |
| Publisher: | Oxford University Press (OUP) |
| SWORD Depositor: | A Symplectic |
| Date Deposited: | 14 Mar 2025 15:44 |
| Last Modified: | 14 Mar 2025 15:44 |
| DOI or ID number: | 10.1093/mnras/staf125 |
| URI: | https://researchonline.ljmu.ac.uk/id/eprint/25898 |
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