2014ApJ...780..118F

We present radio, optical/NIR, and X-ray observations of the afterglow of the short-duration Swift and Konus-Wind GRB 130603B, and uncover a break in the radio and optical bands at ~0.5 day after the burst, best explained as a jet break with an inferred jet opening angle of ~4°-8°. GRB 130603B is only the third short GRB with a radio afterglow detection to date, and represents the first time that a jet break has been evident in the radio band. We model the temporal evolution of the spectral energy distribution to determine the burst explosion properties and find an isotropic-equivalent kinetic energy of ~(0.6-1.7)x10⁵¹ erg and a circumburst density of ~5x10^–3-30/cm3. From the inferred opening angle of GRB 130603B, we calculate beaming-corrected energies of E_γ~ (0.5-2)x10⁴⁹ erg and E_K~ (0.1-1.6)x10⁴⁹ erg. Along with previous measurements and lower limits we find a median opening angle of ~10°. Using the all-sky observed rate of 10 G/pc3/yr, this implies a true short GRB rate of ~20/yr within 200 Mpc, the Advanced LIGO/VIRGO sensitivity range for neutron star binary mergers. Finally, we uncover evidence for significant excess emission in the X-ray afterglow of GRB 130603B at ≳ 1 day and conclude that the additional energy component could be due to fall-back accretion or spin-down energy from a magnetar formed following the merger.