Implications of the search for optical counterparts during the first six months of the Advanced LIGO’s and Advanced Virgo’s third observing run: possible limits on the ejecta mass and binary properties

Abstract

GW170817 showed that neutron star mergers not only emit gravitational waves but also can release electromagnetic signatures in multiple wavelengths. Within the first half of the third observing run of the Advanced LIGO and Virgo detectors, there have been a number of gravitational wave candidates of compact binary systems for which at least one component is potentially a neutron star. In this article, we look at the candidates S190425z, S190426c, S190510g, S190901ap, and S190910h, predicted to have potentially a non-zero remnant mass, in more detail. All these triggers have been followed up with extensive campaigns by the astronomical community doing electromagnetic searches for their optical counterparts; however, according to the released classification, there is a high probability that some of these events might not be of extraterrestrial origin. Assuming that the triggers are caused by a compact binary coalescence and that the individual source locations have been covered during the EM follow-up campaigns, we employ three different kilonova models and apply them to derive possible constraints on the matter ejection consistent with the publicly available gravitational-wave trigger information and the lack of a kilonova detection. These upper bounds on the ejecta mass can be related to limits on the maximum mass of the binary neutron star candidate S190425z and to constraints on the mass-ratio, spin, and NS compactness for the potential black hole-neutron star candidate S190426c. Our results show that deeper electromagnetic observations for future gravitational wave events near the horizon limit of the advanced detectors are essential.

Measuring the Hubble constant with a sample of kilonovae

“…Given the potential of multiple components and the change in color depending on the lanthanide fraction, it is useful to use kilonova models to perform the standardization. While it may be possible to standardize the kilonova luminosities based on measured properties, as is done for SN Ia cosmology measurements, in this analysis, we assume that we can use quantities inferred from the light-curve models 31 ; this assumption will be testable when a sufficiently large sample of high-quality kilonovae observations are available. In this analysis, we use models from Kasen et al 24 and Bulla 25 .…”

Optical follow-up of the neutron star–black hole mergers S200105ae and S200115j

“…Using semi-analytical formulae calibrated to the results of numerical simulations, we can estimate M ej,dyn and M ej,pm as functions of the mass ratio of the binary (Q = M BH /M NS ), the component of the dimensionless black hole spin aligned with the orbital angular momentum (χ), and the neutron star compactness (C NS = GM NS R NS c 2 ) (see also Refs. 3,18,[107][108][109][110] ). We compute M ej,pm using Ref.…”

Implications of the search for optical counterparts during the second part of the Advanced LIGO’s and Advanced Virgo’s third observing run: lessons learned for future follow-up observations

“…The LIGO Scientific and Virgo collaborations used the same near-time alert system during O3b as during O3a, releasing alerts within 2-6 min in general (with an important exception, S200105ae, discussed below). For a summary of the second observing run, please see Abbott et al (2019d), and for the first six months of the third observing run, see Coughlin et al (2019c) and references therein. In addition to the classifications for the event in categories BNS, BHNS, 'MassGap,' or terrestrial noise (Kapadia et al 2020) and an indicator to estimate the probability of producing an EM signature assuming the candidate is of astrophysical origin, p(HasRemnant) (Chatterjee et al 2020), skymaps using BAYESTAR (Singer et al 2014) are also released.…”

“…In this article, we build on our summary of the O3a observations (Coughlin et al 2019c) to explore constraints on potential counterparts based on the wide field-of-view telescope observations during O3b, and provide analyses summarizing how we may improve existing strategies with respect to the fourth observational run of advanced LIGO and advanced Virgo (O4). In Section 2, we review the optical follow-up campaigns for these sources.…”