http://arxiv.org/abs/2002.09395
GW190425 is the newly discovered compact object binary coalescence consistent with a neutron star-neutron star merger, with a chirp mass of $1.44\pm0.02M_\odot$. No electromagnetic counterpart is firmly associated with this event, due to the poorly informative sky localisation and larger distance, compared to GW/GRB170817. The detection of the gravitational wave signal alone can not rule out the presence of a black hole in the binary. In this case, the system would host a neutron star and a very light stellar black hole, with a mass close to the maximum value for neutron stars. We show that the possible presence of such a black hole in GW190425 would produce a brighter kilonova emission with respect to the double neutron star case. Therefore in GW190425-like events more precisely localised, the identification of a kilonova could help distinguishing the nature of the merging system. The chirp mass is a key parameter when joint gravitational and electromagnetic observations are possible. The knowledge of its value could help conducting strategic electromagnetic follow-up campaigns that would enhance the probability to identify the nature of the binary and the host galaxy. For GW190425-like events, we construct kilonova light curve models, for both double neutron star and black hole-neutron star binaries, considering two equations of state both consistent with the observations of GW170817 and GW190425, and including black hole spin effects. We show that among the candidate counterparts of GW190425, all classified as supernovae, our models would exclude two events through their early $r$-band flux evolution. This illustrates that combining the chirp mass and luminosity distance information (provided by the GW signal) with a library of kilonovae light curves can help the electromagnetic follow up campaign, particularly for events with a poor sky localization.
C. Barbieri, O. Salafia, M. Colpi, et. al.
Mon, 24 Feb 20
45/49
Comments: 7 pages, 5 figures, submitted to A&A
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