A Decade of Short-duration Gamma-ray Burst Broad-band Afterglows: Energetics, Circumburst Densities, and Jet Opening Angles

TL;DR

This study compiles and analyzes 103 short gamma-ray burst afterglows, revealing their energetics, low-density environments, jet angles, and implications for gravitational wave detection rates.

Contribution

It provides the first comprehensive catalog and detailed analysis of short GRB afterglows, including energetics, circumburst densities, and jet properties, based on a decade of observations.

Findings

Median isotropic gamma-ray energy ~2x10^51 erg

Median circumburst density ~(3-15)x10^-3 cm^-3

Median jet opening angle ~16 degrees

Abstract

We present a comprehensive catalog and analysis of broad-band afterglow observations for 103 short-duration gamma-ray bursts (GRBs), comprised of all short GRBs from November 2004 to March 2015 with prompt follow-up observations in the X-ray, optical, near-infrared and/or radio bands. These afterglow observations have uncovered 71 X-ray detections, 30 optical/NIR detections, and 4 radio detections. Employing the standard afterglow synchrotron model, we perform joint probability analyses for a subset of 38 short GRBs with well-sampled light curves to infer the burst isotropic-equivalent energies and circumburst densities. For this subset, we find median isotropic-equivalent gamma-ray and kinetic energies of E_gamma,iso~2x10^51 erg, and E_K,iso~(1-3)x10^51 erg, respectively, depending on the values of the model input parameters. We further find that short GRBs occur in low-density environments, with a median density of n~(3-15)x10^-3 cm^-3, and that ~80-95% of bursts have densities of less than 1 cm^-3. We investigate trends between the circumburst densities and host galaxy properties, and find that events located at large projected offsets of >10 effective radii from their hosts exhibit particularly low densities of n<10^-4 cm^-3, consistent with an IGM-like environment. Using late-time afterglow data for 11 events, we find a median jet opening angle of theta_jet=16+/-10 deg. We also calculate a median beaming factor of f_b~0.04, leading to a beaming-corrected total energy release of E_true~1.6x10^50 erg. Furthermore, we calculate a beaming-corrected event rate of R_true=270 (+1580,-180) Gpc^-3 yr^-1, or ~8 (+47,-5) yr^-1 within a 200 Mpc volume, the Advanced LIGO/Virgo typical detection distance for NS-NS binaries.