Deep search of the full O3 LIGO data for continuous gravitational waves from the Cassiopeia A central compact object

We present the deepest search to date for continuous gravitational waves from the neutron star in the Cassiopeia A (Cas A) supernova remnant, using the full LIGO dataset from the LIGO-Virgo-KAGRA (LVK) third observing run (O3). We use the weave semicoherent method with a first-stage coherence time of 30 days while restricting the search band to 20--200 Hz for assumed source ages greater than 300 years, substantially improving upon the sensitivity of a previous weave-based search for this source. No gravitational wave signal is detected. Estimates from simulated continuous wave signals indicate we achieve the most sensitive results to date across the explored parameter space volume, probing to a median strain magnitude as low as 4×10^-26 for frequencies near 200 Hz at 95% confidence level. The method presented here provides a template for future searches for Cas A and other central compact objects of interest using data from the ongoing fourth LVK run (O4).