Gravitational wave searches for postmerger remnants of GW170817 and GW190425

We present the results of two searches for gravitational waves from the postmerger remnants of the binary neutron star coalescence events GW170817 and GW190425. The searches are fully coherent over 1800 s of data from the second (for GW170817) and third (for GW190425) observing runs of the LIGO and Virgo observatories. The searches compute the matched filter $\mathcal{F}$-statistic, and use a piecewise model of the rapidly changing frequency evolution appropriate for young neutron stars. No detection is claimed. The peak root-sum-squared strain upper limit at 50% detection probability (${h}_{\mathrm{rss}}^{50%}$) of both searches occurs at 1700 Hz and is estimated at $1.64\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}\text{ }\text{ }{\mathrm{Hz}}^{\ensuremath{-}1/2}$ for GW170817, and $1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}\text{ }\text{ }{\mathrm{Hz}}^{\ensuremath{-}1/2}$ for GW190425. This is the first gravitational wave search for a neutron star remnant of GW190425.