TY  - JOUR
A1  - Hosseinzadeh, Griffin
A1  - Cowperthwaite, Philip S.
A1  - Gomez, Sebastian
A1  - Villar, Victoria Ashley
A1  - Nicholl, Matt
A1  - Margutti, Raffaella
A1  - Berger, Edo
A1  - Chornock, Ryan
A1  - Paterson, Kerry
A1  - Fong, Wen-fai
A1  - Savchenko, Volodymyr
A1  - Short, Phil
A1  - Alexander, Kate D.
A1  - Blanchard, Peter K.
A1  - Braga, Joao
A1  - Calkins, Michael L.
A1  - Cartier, Regis
A1  - Coppejans, Deanne L.
A1  - Eftekhari, Tarraneh
A1  - Laskar, Tanmoy
A1  - Ly, Chun
A1  - Patton, Locke
A1  - Pelisoli, Ingrid Domingos
A1  - Reichart, Daniel E.
A1  - Terreran, Giacomo
A1  - Williams, Peter K. G.
T1  - Follow-up of the Neutron Star Bearing Gravitational-wave Candidate Events S190425z and S190426c with MMT and SOAR
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters
N2  - 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 d(L) = 156 +/- 41 Mpc, while S190426c is possibly the first NS-black hole (BH) merger ever detected, at d(L) = 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 gamma-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 gamma-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 deg(2) are likely essential.
KW  - binaries: close
KW  - gravitational waves
KW  - methods: observational
KW  - stars: black holes
KW  - stars: neutron
Y1  - 2019
U6  - https://doi.org/10.3847/2041-8213/ab271c
SN  - 2041-8205
SN  - 2041-8213
VL  - 880
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -