A DECADE of SHORT-DURATION GAMMA-RAY BURST BROADBAND AFTERGLOWS: ENERGETICS, CIRCUMBURST DENSITIES, and JET OPENING ANGLES

We present a comprehensive catalog and analysis of broadband afterglow observations for 103 short-duration gamma-ray bursts (GRBs), comprised of all short GRBs from 2004 November to 2015 March with prompt follow-up observations in the X-ray, optical, near-infrared (NIR), 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 γ-ray and kinetic energies of E_γ,iso ≈ 2 × 10⁵¹ erg, and E_K,iso ≈ (1-3) × 10⁵¹ 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) × 10^-3 cm^-3, and that ≈80%-95% of bursts have densities of n ≲ 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 intergalactic medium-like environment. Using late-time afterglow data for 11 events, we find a median jet opening angle of θ_j = 16 ± 10°. We also calculate a median beaming factor of f_b ≈ 0.04, leading to a beaming-corrected total energy release of E_true ≈ 1.6 × 10⁵⁰ erg. Furthermore, we calculate a beaming-corrected event rate of Gpc^-3 yr^-1, or yr^-1 within a 200 Mpc volume, the Advanced LIGO/Virgo typical detection distance for NS-NS binaries.