With the first direct detection of merging black holes in 2015, the era of gravitational wave (GW) astrophysics began. A complete picture of compact object mergers, however, requires the detection of an electromagnetic (EM) counterpart. We report ultraviolet (UV) and x-ray observations by Swift and the Nuclear Spectroscopic Telescope Array of the EM counterpart of the binary neutron star merger GW170817. The bright, rapidly fading UV emission indicates a high mass (0.03 solar masses) wind-driven outflow with moderate electron fraction ( Y e 0.27). Combined with the x-ray limits, we favor an observer viewing angle of 30° away from the orbital rotation axis, which avoids both obscuration from the heaviest elements in the orbital plane and a direct view of any ultrarelativistic, highly collimated ejecta (a -ray burst afterglow).
Chemistry and Pharmacology
Natural Sciences in General