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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

Published version
Peer-reviewed

Type

Article

Change log

Abstract

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 Lbol≈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 and vejblue≈0.3c, and the "red" component has Mejred≈0.04 M 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.

Description

Keywords

binaries: close, catalogs, gravitational waves, stars: neutron, surveys

Journal Title

Astrophysical Journal Letters

Conference Name

Journal ISSN

2041-8205
2041-8213

Volume Title

848

Publisher

American Astronomical Society
Sponsorship
Science and Technology Facilities Council (ST/N000927/1)