Characterization of low-significance gravitational-wave compact binary sources

LIGO and Virgo will start their third observing run in early 2019. Given our current rate estimates, we expect the detection of a binary black hole signal every week. The majority of these sources will be far away, and thus have low signal-to-noise ratios (SNRs). In this talk, we show if and to which extent the physical parameters of neutron stars and black holes in binaries can be measured at low SNRs. We find that subthreshold binary neutron stars, with SNRs below 12 (10), yield uncertainties in their sky position larger than 400 (700) deg² (90% credible interval), allowing electromagnetic follow-ups by wide-field/all-sky survey instruments. The luminosity distance, which could be used to measure the Hubble constant with standard sirens, has relative uncertainties larger than 40% for binary neutron stars and neutron star black hole mergers. We will also show that we may be able to recover some information for intrinsic parameters, masses and spins, at SNRs as low as 6, but multimodality is not uncommon and can significantly broaden the posteriors. For spins, in particular, the uncertainty is higher for systems with comparable component masses or lack of spin precession.