# Exploring the Relationship Between Swift Short Gamma-Ray Burst Afterglows and their Host Galaxy Properties

## TL;DR

This study analyzes how short gamma-ray burst afterglows across X-ray, optical, and radio bands relate to their host galaxy properties, revealing environmental influences on afterglow brightness and detectability, and supporting merger origin theories.

## Contribution

It provides a comprehensive, uniform analysis of 150 short GRB afterglows and their host galaxies, identifying key environmental factors affecting afterglow luminosities.

## Key findings

- X-ray afterglows are brighter in younger, lower-mass, actively star-forming galaxies.
- Optical afterglows are brighter in hosts with higher star formation rates.
- X-ray and radio afterglows are more luminous or detectable at low galactocentric offsets.

## Abstract

We present a comprehensive compilation of short-duration gamma-ray burst (GRB) afterglows in the X-ray, optical, and radio bands, comprising 150 events discovered primarily by the Neil Gehrels Swift Observatory over 2005-2023. We pair these observations with uniformly modeled host galaxies to understand how broadband afterglow luminosities are influenced by their environmental properties. We compare the X-ray and optical afterglow luminosities at 3 hr with projected physical and host-normalized galactocentric offsets, host stellar mass, star-formation rate (SFR), specific SFR, and stellar population age. In the radio band, we explore how these environmental properties may influence afterglow detectability. We find statistical support that X-ray afterglows are brighter in galaxies with younger ages, lower masses, and higher active star formation - trends that also scale with ISM density. While we also visualize these differences for optical afterglows, the only statistically significant trend is that they are brighter in hosts with higher SFR. We further find that X-ray (radio) afterglows are more luminous (more likely to be detected) at low projected offsets. Overall, this indicates that X-ray afterglow luminosity is the most predictable indicator of host environment among the three bands. We find the afterglow luminosities of three possible merger-driven long GRBs to be unremarkable compared to the traditional short GRB population, strengthening the case that these events arise from mergers. Finally we find that the estimated on-axis afterglow luminosity of GW170817 is in the faintest ~30%, aligning with its quiescent, old and massive host environment.