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

Cowperthwaite, P S and Berger, E and Villar, V A and Metzger, B D and Nicholl, M and Chornock, R and Blanchard, P K and Fong, W and Margutti, R and Soares-Santos, M and Alexander, K D and Allam, S and Annis, J and Brout, D and Brown, D A and Butler, R E and Chen, H Y and Diehl, H T and Doctor, Z and Drout, M R and Eftekhari, T and Farr, B and Finley, D A and Foley, R J and Frieman, J A and Fryer, C L and García-Bellido, J and Gill, M S S and Guillochon, J and Herner, K and Holz, D E and Kasen, D and Kessler, R and Marriner, J and Matheson, T and Neilsen, E H and Quataert, E and Palmese, A and Rest, A and Sako, M and Scolnic, D M and Smith, N and Tucker, D L and Williams, P K G and Balbinot, E and Carlin, J L and Cook, E R and Durret, F and Li, T S and Lopes, P A A and Lourenço, A C C and Marshall, J L and Medina, G E and Muir, J and Munoz, R R and Sauseda, M and Schlegel, D J and Secco, L F and Vivas, A K and Wester, W and Zenteno, A and Zhang, Y and Abbott, T M C and Banerji, M and Bechtol, K and Benoit-Lévy, A and Bertin, E and Buckley-Geer, E and Burke, D L and Capozzi, D and Carnero Rosell, A and Carrasco Kind, M and Castander, F J and Crocce, M and Cunha, C E and D’Andrea, C B and Costa, L N da and Davis, C and DePoy, D L and Desai, Shantanu and Dietrich, J P and Drlica-Wagner, A and Eifler, T F and Evrard, A E and Fernandez, E and Flaugher, B and Fosalba, P and Gaztanaga, E and Gerdes, D W and Giannantonio, T and Goldstein, D A and Gruen, D and Gruendl, R A and Gutierrez, G and Honscheid, K and Jain, B and James, D J and Jeltema, T and Johnson, M W G and Johnson, M D and Kent, S and Krause, E and Kron, R and Kuehn, K and Nuropatkin, N and Lahav, O and Lima, M and Lin, H and Maia, M A G and March, M and Martini, P and McMahon, R G and Menanteau, F and Miller, C J and Miquel, R and Mohr, J J and Neilsen, E and Nichol, R C and Ogando, R L C and Plazas, A A and Roe, N and Romer, A K and Roodman, A and Rykoff, E S and Sanchez, E and Scarpine, V and Schindler, R and Schubnell, M and Sevilla-Noarbe, I and Smith, M and Smith, R C and Sobreira, F and Suchyta, E and Swanson, M E C and Tarle, G and Thomas, D and Thomas, R C and Troxel, M A and Vikram, V and Walker, A R and Wechsler, R H and Weller, J and Yanny, B and Zuntz, J (2017) 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. The Astrophysical Journal, 848 (2). pp. 1-10. ISSN 2041-8213

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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 Hubble Space Telescope ( 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 × 10 14 cm (corresponding to an expansion velocity of v ≈ 0 . 3 c ), and a bolometric luminosity of L bol ≈ 5 × 10 41 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 56 Ni, 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 M blue ej ≈ 0 . 01 M and v blue ej ≈ 0 . 3c, and the “red” component has M red ej ≈ 0 . 04 M and v red ej ≈ 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.

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