The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. II. UV, Optical, and Near-infrared Light Curves and Comparison to Kilonova Models

摘要

We present UV, optical, and NIR photometry of the first electromagnetic counterpart to a gravitational wave source fromudAdvanced LIGO/Virgo, the binary neutron star merger GW170817. Our data set extends from the discovery of the opticaludcounterpart at 0ud.ud47 days to 18ud.ud5 days post-merger, and includes observations with the Dark Energy Camera (DECam), Gemini-udSouth/FLAMINGOS-2 (GS/F2), and theudHubble Space Telescopeud(udHSTud). The spectral energy distribution (SED) inferred fromudthis photometry at 0ud.ud6 days is well described by a blackbody model withudTud≈ud8300 K, a radius ofudRud≈ud4ud.ud5ud×ud10ud14udcm (correspondingudto an expansion velocity ofudvud≈ud0ud.ud3udcud), and a bolometric luminosity ofudLudbolud≈ud5ud×ud10ud41uderg sud−ud1ud. At 1ud.ud5 days we find a multi-udcomponent SED across the optical and NIR, and subsequently we observe rapid fading in the UV and blue optical bands andudsignificant reddening of the optical/NIR colors. Modeling the entire data set we find that models with heating from radioactiveuddecay ofud56udNi, or those with only a single component of opacity fromudrud-process elements, fail to capture the rapid optical declineudand red optical/NIR colors. Instead, models with two components consistent with lanthanide-poor and lanthanide-rich ejectaudprovide a good fit to the data; the resulting “blue” component hasudMudblueudejud≈ud0ud.ud01 Mudandudvudblueudejud≈ud0ud.ud3c, and the “red” componentudhasudMudredudejud≈ud0ud.ud04 Mudandudvudredudejud≈ud0ud.ud1c. These ejecta masses are broadly consistent with the estimatedudrud-process production rateudrequired to explain the Milky Wayudrud-process abundances, providing the first evidence that BNS mergers can be a dominant siteudofudrud-process enrichment.