Constraints on the circumburst environments of short gamma-ray bursts

Brendan O’Connor, Paz Beniamini, Chryssa Kouveliotou

Research output: Contribution to journalArticlepeer-review

Abstract

Observational follow up of well localized short gamma-ray bursts (SGRBs) has left 20–30 per cent of the population without a coincident host galaxy association to deep optical and NIR limits (≳26 mag). These SGRBs have been classified as observationally hostless due to their lack of strong host associations. It has been argued that these hostless SGRBs could be an indication of the large distances traversed by the binary neutron star system (due to natal kicks) between its formation and its merger (leading to an SGRB). The distances of GRBs from their host galaxies can be indirectly probed by the surrounding circumburst densities. We show that a lower limit on those densities can be obtained from early afterglow light curves. We find that ≲16 per cent of short GRBs in our sample took place at densities ≲10−4 cm−3. These densities represent the expected range of values at distances greater than the host galaxy’s virial radii. We find that out of the five SGRBs in our sample that have been found to be observationally hostless, none are consistent with having occurred beyond the virial radius of their birth galaxies. This implies one of two scenarios. Either these observationally hostless SGRBs occurred outside of the half-light radius of their host galaxy, but well within the galactic halo, or in host galaxies at moderate to high redshifts (z ≳ 2) that were missed by follow-up observations.

Original languageEnglish
Pages (from-to)4782-4799
Number of pages18
JournalMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume495
Issue number4
DOIs
StatePublished - 2020
Externally publishedYes

Keywords

  • Gamma-ray bursts
  • Neutron star mergers
  • Stars: jet

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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