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

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

1 IAP - Institut d'Astrophysique de Paris

We present UV, optical, and near-infrared (NIR) photometry of the first electromagnetic counterpart to a gravitational wave source from Advanced Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo, the binary neutron star merger GW170817. Our data set extends from the discovery of the optical counterpart at 0.47–18.5 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 $T\approx 8300$ K, a radius of $R\approx 4.5\times {10}^{14}$ cm (corresponding to an expansion velocity of $v\approx 0.3c$), and a bolometric luminosity of ${L}_{\mathrm{bol}}\approx 5\times {10}^{41}$ 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 ${M}_{\mathrm{ej}}^{\mathrm{blue}}\approx 0.01\,{M}_{\odot }$ and ${v}_{\mathrm{ej}}^{\mathrm{blue}}\approx 0.3\,{\rm{c}}$, and the “red” component has ${M}_{\mathrm{ej}}^{\mathrm{red}}\approx 0.04\,{M}_{\odot }$ and ${v}_{\mathrm{ej}}^{\mathrm{red}}\approx 0.1\,{\rm{c}}$. 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 binary neutron star (BNS) mergers can be a dominant site of r-process enrichment.

Mots clés: binaries: close; catalogs; gravitational waves; stars: neutron; surveys; neutron star: binary; velocity: expansion; optical; LIGO; gravitational radiation; electromagnetic; color; VIRGO; radioactivity; dark energy; black body; satellite; bolometer; ultraviolet; infrared; galaxy; spectral; opacity; capture; star; site

Domaines: Astrophysique [astro-ph]

P.S. Cowperthwaite, E. Berger, V.A. Villar, B.D. Metzger, M. Nicholl, et al.. 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. Astrophys.J.Lett., 2017, 848 (2), pp.L17. ⟨10.3847/2041-8213/aa8fc7⟩. ⟨hal-01669860⟩