Leo Singer
Our understanding of gamma-ray bursts (GRBs) has been propelled by our ability to localize these rare and energetic events precisely. Although the Fermi Gamma-Ray Space Telescope has provided unique insights into the GRB phenomenon, the coarse localizations of tens to a hundred square degrees provided by the Fermi Gamma-ray Burst Monitor (GBM) have posed formidable obstacles to pinpointing and following up the afterglows. We are using the Palomar Transient Factory to perform targeted searches for Fermi afterglows. In the first year of this program, we have discovered eight afterglows, including the first optical afterglow ever found based solely on a Fermi GBM localization. Two of the bursts (GRBs 130702A and 140606B) were at low redshift (z = 0.145 and 0.384 respectively) and had spectroscopically confirmed broad-line type Ic supernovae. We find that these two bursts are energetically consistent with the picture of a mildly relativistic shock breaking out from the progenitor star, rather than the ultra-relativistic internal shock mechanism that is thought to power "standard" cosmological bursts. In the context of the Zwicky Transient Facility, I will describe how we plan to use our experiences with Palomar Transient Factory to bootstrap the search for optical counterparts of binary neutron star mergers that may soon be detected by Advanced LIGO and Virgo, which will shortly begin gravitational-wave observations with record sensitivity.