Evidence of Extended Emission in GRB 181123B and Other High-redshift Short GRBs

Abstract

We study the high-energy properties of GRB 181123B, a short gamma-ray burst (sGRB) at redshift z ≈ 1.75. We show that, despite its nominal short duration with T 90 < 2 s, this burst displays evidence of a temporally extended emission (EE) at high energies and that the same trend is observed in the majority of sGRBs at z  1. We discuss the impact of instrumental selection effects on the GRB classification, stressing that the measured T 90 is not an unambiguous indicator of the burst physical origin. By examining their environment (e.g., stellar mass, star formation, offset distribution), we find that these high-z sGRBs share many properties of long GRBs at a similar distance and are consistent with a short-lived progenitor system. If produced by compact binary mergers, these sGRBs with EE may be easier to localize at large distances and herald a larger population of sGRBs in the early universe.Unified Astronomy Thesaurus concepts: Gamma-ray bursts (629); Neutron stars (1108); Nucleosynthesis (1131); Chemical abundances (224); Gravitational waves (678)

GRB 160410A: the first Chemical Study of the Interstellar Medium of a Short GRB

“…A more recent and complete study on one SGRB with EE, GRB 050709, shows a low-luminosity host, a subsolar metallicity and a low SFR (Nicuesa Guelbenzu et al 2021), which would be all in line with what we see for GRB 160410A. A more recent case is GRB 181123B, a SGRB with EE and an associated star-forming and massive host at 𝑧 = 1.754 (see Paterson et al 2020b;Dichiara et al 2021) its association with the galaxy is still under debate (Rowlinson et al 2021).…”

“…Another classification distinction is the hardness ratio (HR), which is the ratio of the fluence in the 50-100 keV band over the 25-50 keV band. Dichiara et al (2021) obtained a HR = 2.3 ± 0.5 for the main spike and claim GRB 160410A is a short GRB with extended emission. Kann et al (2011) compare the afterglows of SGRBs to a large sample of those of long GRBs.…”

“…GRB 181123B was a high-redshift short GRB at 𝑧 = 1.754 with a bright host galaxy and a faint afterglow detection (Paterson et al 2020a). It shows extended emission (Dichiara et al 2021) and was rapidly observed in the radio bands (Rowlinson et al 2021;Anderson et al 2021). As there is only a single 𝑖 detection, we have no information on colour or potential line-of-sight extinction.…”

Constraints on the electromagnetic counterpart of the Neutron Star Black Hole merger GW200115

“…Troja, Rosswog, & Gehrels 2010), b) a main peak of short duration and hard spectrum and c) a temporally extended emission with soft spectrum (Norris & Bonnell 2006). The latter component is visible in <20% of the events, although might be present in a larger fraction of events and be undetected due to instrumental effects (Dichiara et al 2021).…”

“…Abbott et al 2017). However, the presence of a primary BH with a significantly higher mass and a definite event horizon, rather than a NS, unavoidably changes the merger dynamics and is likely to leave distinguishable imprints in the EM radiation, such as the color and luminosity of the kilonova or a long-lasting hard X-ray emission (Norris & Bonnell 2006;Troja et al 2008;Barbieri et al 2020;Dichiara et al 2021). An outstanding issue is whether in a NSBH event the dynamics will allow for full disruption of the NS and the formation of an accretion disk that will both release gravitational binding energy into a relativistic outflow to power the GRB and eject neutron-rich matter leading to a kilonova, or if the NS will be accreted whole leading to little or no counterpart EM emission.…”