2016ApJ...833..151F

We present the discovery of the X-ray and optical afterglows of the short-duration GRB 150101B, pinpointing the event to an early-type host galaxy at z = 0.1343 ± 0.0030. This makes GRB 150101B the most nearby short gamma-ray burst (GRB) with an early-type host galaxy discovered to date. Fitting the spectral energy distribution of the host galaxy results in an inferred stellar mass of ~7×10¹⁰ M_☉, stellar population age of ≃2-2.5 Gyr, and star formation rate of <=0.4 M_☉ yr^–1. The host of GRB 150101B is one of the largest and most luminous short GRB host galaxies, with a B-band luminosity of ~4.3L^* and half-light radius of ≃8 kpc. GRB 150101B is located at a projected distance of 7.35 ± 0.07 kpc from its host center and lies on a faint region of its host rest-frame optical light. Its location, combined with the lack of associated supernova, is consistent with an NS-NS/NS-BH merger progenitor. From modeling the evolution of the broadband afterglow, we calculate isotropic-equivalent gamma-ray and kinetic energies of ~1.3×10⁴⁹ erg and ~(6–14)×10⁵¹ erg, respectively, a circumburst density of ~(0.8–4)×10^–5 cm^–3, and a jet opening angle of >=9deg. Using observations extending to ≃30 days, we place upper limits of \lesssim(2–4)×10⁴¹ erg s^–1 on associated kilonova emission. We compare searches following previous short GRBs to existing kilonova models and demonstrate the difficulty of performing effective kilonova searches from cosmological short GRBs using current ground-based facilities. We show that at the Advanced LIGO/VIRGO horizon distance of 200 Mpc, searches reaching depths of ≃23-24 AB mag are necessary to probe a meaningful range of kilonova models.