A Decade of Short-Duration Gamma-Ray Burst Broadband Afterglows: Energetics, Circumburst Densities, and Jet Opening Angles

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 wellsampled 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 × 10 51 erg, and E K,iso ≈ (1 − 3) × 10 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) × 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 IGM-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 × 10 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.

Radio Counterparts of Compact Binary Mergers Detectable in Gravitational Waves: A Simulation for an Optimized Survey

“…sGRB afterglows. sGRB afterglow observations allow for circum-merger density constraints (e.g., Fong et al 2015). However, good constraints are necessary from detections of sGRB afterglows because there exists a degeneracy between the density and  B .…”

“…In addition, the sGRB jet produces a radio afterglow with a timescale of a few weeks, which can be seen provided that the viewing angle is not too large. In fact, radio afterglows have been already detected for four sGRBs(e.g., Fong et al 2015) and they will be detectable counterparts of GW merger events (Feng et al 2014). Recent observations suggest that the radio transient sky is far quieter compared to the optical one, so we expect far fewer false positives by a factor of a hundred or more depending on the sky location than in the optical-IR (e.g., Frail et al 2012;Mooley et al 2013Mooley et al , 2016.…”

Radio Constraints on Long-Lived Magnetar Remnants in Short Gamma-Ray Bursts

“…In each panel, the curves represent upper limits on the parameter space, where the region below each curve is allowed and the region above is ruled out. Light gray regions represent 1σ ranges of allowed circumburst densities independently determined from afterglow observations for ò B =0.1 (Fong et al 2015); there is not enough information to constrain the circumburst density of GRB 090515. The average maximum value of the rotational energy constrained by the observations, E max , at ò B =0.1 is denoted by a gray triangle, corresponding to the values in Table 2.…”

“…Short GRBs explode in low-density environments, with a median circumburst density of ≈4×10 −3 cm −3 (Fong et al 2015); thus we consider a range of circumburst densities over 10 −4 -1 cm −3 . We fix the value of the power-law index p to the median of the short GRB population, p = 2.4 (Fong et al 2015), ò e =ò B =0.1, and ν obs =6.0 GHz. The resulting light curves are shown in Figure 1.…”

“…We collect the inferred circumburst densities for eight bursts from Fong et al (2015); there is not enough information to constrain the circumburst density of GRB 090515. These values are listed in Table 2 and shown in Figures 2-3, where the ranges shown for each region denote the 1σ uncertainty.…”