@article{6dd7be530ada483b89cf8884e4dad646,
title = "Follow-up of the Neutron Star Bearing Gravitational-wave Candidate Events S190425z and S190426c with MMT and SOAR",
abstract = "On 2019 April 25.346 and 26.640 UT the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo gravitational-wave (GW) observatory announced the detection of the first candidate events in Observing Run 3 that contained at least one neutron star (NS). S190425z is a likely binary neutron star (BNS) merger at dL = 156 ± 41 Mpc, while S190426c is possibly the first NS-black hole (BH) merger ever detected, at dL = 377 ± 100 Mpc, although with marginal statistical significance. Here we report our optical follow-up observations for both events using the MMT 6.5 m telescope, as well as our spectroscopic follow-up of candidate counterparts (which turned out to be unrelated) with the 4.1 m SOAR telescope. We compare to publicly reported searches, explore the overall areal coverage and depth, and evaluate those in relation to the optical/near-infrared (NIR) kilonova emission from the BNS merger GW170817, to theoretical kilonova models, and to short gamma-ray burst (SGRB) afterglows. We find that for a GW170817-like kilonova, the partial volume covered spans up to about 40% for S190425z and 60% for S190426c. For an on-axis jet typical of SGRBs, the search effective volume is larger, but such a configuration is expected in at most a few percent of mergers. We further find that wide-field γ-ray and X-ray limits rule out luminous on-axis SGRBs, for a large fraction of the localization regions, although these searches are not sufficiently deep in the context of the γ-ray emission from GW170817 or off-axis SGRB afterglows. The results indicate that some optical follow-up searches are sufficiently deep for counterpart identification to about 300 Mpc, but that localizations better than 1000 deg2 are likely essential.",
keywords = "binaries: close, gravitational waves, methods: observational, stars: black holes, stars: neutron",
author = "G. Hosseinzadeh and Cowperthwaite, {P. S.} and S. Gomez and Villar, {V. A.} and M. Nicholl and R. Margutti and E. Berger and R. Chornock and K. Paterson and W. Fong and V. Savchenko and P. Short and Alexander, {K. D.} and Blanchard, {P. K.} and J. Braga and Calkins, {M. L.} and R. Cartier and Coppejans, {D. L.} and T. Eftekhari and T. Laskar and C. Ly and L. Patton and I. Pelisoli and Reichart, {D. E.} and G. Terreran and Williams, {P. K.G.}",
note = "Funding Information: The Berger Time-Domain Group is supported in part by NSF grant AST-1714498 and NASA grant NNX15AE50G. G.H. thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining Grant #1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. P.S.C. is grateful for support provided by NASA through the NASA Hubble Fellowship grant #HST-HF2-51404.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. M.N. is supported by a Royal Astronomical Society Research Fellowship. W.F. and K.P. acknowledge support by the National Science Foundation under award No. AST-1814782. I.P. acknowledges funding by the Deutsche Forschungsgemeinschaft under grant GE2506/ 12-1. R.M. acknowledges support for this work provided by the National Aeronautics and Space Administration through Chandra award No. DD8-19101A and DDT-18096A issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. K.D.A. is grateful for support provided by NASA through the NASA Hubble Fellowship grant #HSTHF2- 51403.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. Development of the Boxfit code was supported in part by NASA through grant NNX10AF62G issued through the Astrophysics Theory Program and by the NSF through grant AST-1009863. Funding Information: 2019-07-20 2019-07-18 08:37:43 cgi/release: Article released bin/incoming: New from .zip National Science Foundation AST-1714498 AST-1814782 National Aeronautics and Space Administration HST-HF-51404.001-A HST-HF2-51403.001-A Deutsche Forschungsgemeinschaft GE2506/12-1 yes Publisher Copyright: {\textcopyright} 2019. The American Astronomical Society. All rights reserved.",
year = "2019",
month = jul,
day = "20",
doi = "10.3847/2041-8213/ab271c",
language = "English (US)",
volume = "880",
journal = "Astrophysical Journal Letters",
issn = "2041-8205",
publisher = "IOP Publishing Ltd.",
number = "1",
}