2017/10/16 by P. S. Cowperthwaite, E. Berger, V. A. Villar +141 · 2 citations
Physics and Astronomy · #astro-ph.HE
paper · pdf · doi:10.3847/2041-8213/aa8fc7
13 Pages, 3 Figures, 2 Tables. ApJL, In Press. Keywords: GW170817, LVC
arxiv created 2017/10/16 · arxiv updated 2017/10/17
We present UV, optical, and NIR photometry of the first electromagnetic counterpart to a gravitational wave source from Advanced LIGO/Virgo, the binary neutron star merger GW170817. Our data set extends from the discovery of the optical counterpart at 0.47 days to 18.5 days post-merger, and includes observations with the Dark Energy Camera (DECam), Gemini-South/FLAMINGOS-2 (GS/F2), and the \it Hubble Space Telescope (\it HST). The spectral energy distribution (SED) inferred from this photometry at 0.6 days is well described by a blackbody model with T≈ 8300 K, a radius of R≈ 4.5× 1014 cm (corresponding to an expansion velocity of v≈ 0.3c), and a bolometric luminosity of L\rm bol≈ 5×1041 erg s-1. At 1.5 days we find a multi-component SED across the optical and NIR, and subsequently we observe rapid fading in the UV and blue optical bands and significant reddening of the optical/NIR colors. Modeling the entire data set we find that models with heating from radioactive decay of 56Ni, or those with only a single component of opacity from r-process elements, fail to capture the rapid optical decline and red optical/NIR colors. Instead, models with two components consistent with lanthanide-poor and lanthanide-rich ejecta provide a good fit to the data, the resulting "blue" component has Mejblue≈ 0.01 M_\odot and vejblue≈ 0.3c, and the "red" component has Mejred≈ 0.04 M_\odot and vejred≈ 0.1c. These ejecta masses are broadly consistent with the estimated r-process production rate required to explain the Milky Way r-process abundances, providing the first evidence that BNS mergers can be a dominant site of r-process enrichment.