2025ApJ...986..202M

We conduct two searches for continuous, nearly monochromatic gravitational waves originating from the central compact objects in the supernova remnants Cassiopeia A (Cas A) and Vela Jr. using public LIGO data. The search for Cas A targets signal frequencies between 20 Hz and 400 Hz, and the Vela Jr. search covers between 400 and 1700 Hz. They both investigate the broadest set of waveforms ever considered with highly sensitive deterministic search methods. Above 1500 Hz, the Vela Jr. search is the most sensitive carried out thus far, improving on previous results by over 300%. Above 976 Hz these results improve on existing ones by 50%. In all, we investigate over 10¹⁸ waveforms, leveraging the computational power donated by thousands of Einstein@Home volunteers. We perform a four-stage follow-up on more than 6 million waveforms. None of the considered waveforms survives the follow-up scrutiny, indicating no significant detection candidate. Our null results constrain the maximum amplitude of continuous signals as a function of signal frequency from the targets. The most stringent 90% confidence upper limit for Cas A is ${h}_{0}^{90 \% }\approx 7.3\times 1{0}^{-26}$ near 200 Hz, and for Vela Jr. it is ${h}_{0}^{90 \% }\approx 8.9\times 1{0}^{-26}$ near 400 Hz. Translated into upper limits on the ellipticity and r-mode amplitude, our results probe physically interesting regions: for example, the ellipticity of Vela Jr. is constrained to be smaller than 10^–7 across the frequency band, with a tighter constraint of less than 2 × 10^–8 at the highest frequencies.