Possible origin of AT2021any: A failed gamma-ray burst from a structured jet
Abstract
Afterglows not associated with any gamma-ray bursts (GRBs) are called orphan afterglows. The detection of such afterglows is an important goal in many sky survey programs. Recently, a promising orphan afterglow candidate, AT2021any, was found by the Zwicky Transient Facility. In this work, we performed multi-wavelength fittings of AT2021any with two different outflow models, namely, the top-hat jet model and the structured Gaussian jet model. Although both models can fit the observed light curves well, we found that the structured Gaussian jet model presents a better result and is thus preferred by observations. In this framework, the best-fit Lorentz factor is about 68, which indicates that AT2021any should be a failed GRB. The half-opening angle of the jet and the viewing angle were found to be 0.1 and 0.02, respectively, which means that the jet is essentially observed on-axis. We inferred the trigger time of the GRB to be about 1000 s before the first detection of the orphan afterglow, and we derived an upper limit of 21.5% for the radiative efficiency, which is typical for GRBs.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 2023
- DOI:
- arXiv:
- arXiv:2304.09051
- Bibcode:
- 2023A&A...679A.103X
- Keywords:
-
- gamma-ray burst: general;
- gamma-ray burst: individual: AT2021any;
- methods: numerical;
- radiation mechanisms: non-thermal;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 22 pages, 6 figures, 4 tables, revised according to referee's suggestions, main conclusion unchanged