The Afterglow and Early-type Host Galaxy of the Short GRB 150101B at Z = 0.1343

Abstract

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 shortGRB 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 a NS-NS/NS-BH merger progenitor. From modeling the evolution of the broad-band 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 & 9 ◦. Using observations extending to ≈ 30 days, we place upper limits of . (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.