Low-efficiency long gamma-ray bursts: a case study with AT2020blt
The Zwicky Transient Facility recently announced the detection of an optical transient AT2020blt at redshift z = 2.9, consistent with the afterglow of an on-axis gamma-ray burst. However, no prompt emission was observed. We analyse AT2020blt with detailed models, showing the data are best explained as the afterglow of an on-axis long gamma-ray burst, ruling out other hypotheses such as a cocoon and a low-Lorentz factor jet. We search Fermi data for prompt emission, setting deeper upper limits on the prompt emission than in the original detection paper. Together with KONUS-Wind observations, we show that the gamma-ray efficiency of AT2020blt is ≲0.3−4.5 percent. We speculate that AT2020blt and AT2021any belong to the low-efficiency tail of long gamma-ray burst distributions that are beginning to be readily observed due to the capabilities of new observatories like the Zwicky Transient Facility.
Australian Government Research Training Program (RTP) Scholarship
Australian Research Council Future Fellowship FT160100112 and CE170100004
ARC. Discovery Project DP180103155
CitationMonthly Notices of the Royal Astronomical Society, Volume 512, Issue 1, May 2022, Pages 1391–1399, https://doi.org/10.1093/mnras/stac601
Author affiliationDepartment of Physics and Astronomy
- AM (Accepted Manuscript)