Improved upper limits on gravitational wave emission from NS 1987A

We report on a new search for continuous gravitational waves from NS 1987A, the neutron star born in SN 1987A, using open data from Advanced LIGO and Virgo’s third observing run (O3). The search covered frequencies from 35 to 1050 Hz, more than five times the band of the only previous gravitational wave search to constrain NS 1987A. It used an improved code and coherently integrated from 5.10 days to 14.85 days depending on frequency. No astrophysical signals were detected. By expanding the frequency range and using O3 data, this search improved on strain upper limits from the previous search and was sensitive at the highest frequencies to ellipticities of 1.6 × 10⁻⁵ and r-mode amplitudes of 4.4 × 10⁻⁴, both an order of magnitude improvement over the previous search and both well within the range of theoretical predictions.