(ISS-TAO and TAP Science Teams)
The recent detection by LIGO-Virgo of the gravitational wave (GW) event GW170817, and the associated electromagnetic (EM) follow-up by a large community of astronomers, has stimulated great interest in future GW counterpart searches. In this talk we present two GW counterpart missions now under study by NASA: ISS-TAO (Transient Astrophysics Observer on the ISS), and TAP (Transient Astrophysics Probe). ISS-TAO, a $70M Mission of Opportunity recently awarded a Phase A study, is a wide-field X-ray transient detector proposed to be deployed on the International Space Station in 2022. Through its unique Lobster imaging X-ray optics that allow 400 deg2 FoV, 1 arc min position resolution and good sensitivity, ISS-TAO will observe X-ray counterparts of LIGO gravitational wave detections involving neutron stars and black holes. TAP, selected by NASA for a funded Probe Concept Study, is a $1B wide-field high-energy transient satellite proposed for flight starting in the late 2020s. TAP’s instruments include Lobster X-ray optics; a high sensitivity, 1 deg2 FoV soft X-ray telescope based on single crystal silicon optics; a passively cooled, 1 deg2 FoV Infrared telescope with bandpass 0.3-2.5 micron; and a set of 8 small NaI gamma-ray detectors. TAP will observe X-ray and IR counterparts of GWs involving neutron stars and stellar mass black holes detected by LIGO, and possibly X-ray counterparts of GWs from supermassive black holes, detected by LISA and Pulsar Timing Arrays. Both missions will also perform time-domain astrophysics, observing many events per year of X-ray transients related to compact objects, including tidal disruptions of stars, supernova shock breakouts, novae and neutron star bursts, and high redshift Gamma-Ray Bursts.