Swift and NuSTAR observations of GW170817: Detection of a blue kilonova.
P A EvansS Bradley CenkoJ A KenneaS W K EmeryN P M KuinO KorobkinR T WollaegerChristopher L FryerK K MadsenF A HarrisonY XuE NakarK HotokezakaA LienS CampanaS R OatesEleonora TrojaAlice A BreeveldF E MarshallS D BarthelmyA P BeardmoreD N BurrowsG CusumanoA D'AìP D'AvanzoV D'EliaM de PasqualeW P EvenChristopher J FontesK ForsterJavier A GarciaPaolo GiommiB GrefenstetteC GronwallD H HartmannM HeidaA L HungerfordMansi M KasliwalH A KrimmA J LevanDaniele B MalesaniA MelandriH MiyasakaJ A NousekPaul O'BrienJ P OsborneC PaganiK L PageD M PalmerMatteo PerriS PikeJ L RacusinS RosswogM H SiegelT SakamotoBoris SbarufattiG TagliaferriNial R TanvirAaron TohuvavohuPublished in: Science (New York, N.Y.) (2017)
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 (Ye ≈ 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 γ-ray burst afterglow).