Cake Talk by Matteo Ferro

The knowledge of short gamma-ray bursts (SGRBs) has experienced an impressive boost over the past two decades. Following recent major breakthroughs, we now have direct evidence for the Neutron Star-Neutron Star (NS-NS) / SGRB association, the existence of Neutron Star-Black Hole (NS-BH) systems, SGRB outflows shaped as structured jets, off-axis afterglow emission, the existence of r-process kilonovae, and their association with SGRBs. Most studies on SGRB properties reported in the literature are based on the sample of events with measured redshift (z). Although this approach has the advantage of describing the intrinsic properties of SGRBs, it can be affected by biases, given that a significant fraction of SGRBs lack a measured z. To overcome this issue, in 2014, a sub-sample of Swift SGRBs with favorable observing conditions for z determination and brightness in the 15–150 keV Swift-BAT energy band was presented. Although relatively small (16 events up to June 2013), this sample (S-BAT4) is complete in flux with a high completeness in z (70%), providing a useful benchmark to study SGRB properties. The sample has recently been extended, now more than tripled in size (51 events up to December 2022), with considerable completeness in z (78%), thanks to recent and dedicated studies on SGRB host galaxies. In this talk, I will review the current understanding and perspectives of SGRBs and will discuss how the S-BAT4 sample can represent a robust base for SGRB studies, regarding prompt energetics and afterglow properties. Next, I will present the analysis of the environmental properties of S-BAT4 events, including host galaxy features, offsets, and neutral hydrogen column densities (NH) derived from Swift/XRT spectra. Host galaxy properties and magnitudes have been analyzed in comparison to carefully selected samples of field galaxies, as well as typical galaxies of long GRBs (LGRBs), to investigate how the environment plays a role in the GRB progenitor systems.