Through the lens of Sgr A*: identifying strongly lensed Continuous Gravitational Waves beyond the Einstein radius

Abstract

Once detected, lensed gravitational waves will afford new means to probe thematter distribution in the universe, complementary to electromagnetic signals.Sources of continuous gravitational waves (CWs) are long-lived and stable,making their lensing signatures synergic to short mergers of compact binaries.CWs emitted by isolated neutron stars and lensed by Sgr A$^*$, thesuper-massive black hole at the center of our galaxy, might be observable bythe next generation of gravitational wave detectors. However, it is unknownunder which circumstances these sources can be identified as lensed. Here weshow that future detectors can distinguish lensed CWs and measure allparameters with precision $\sim 1-10\%$ for sources within $2-4$ Einstein radiiof Sgr A$^*$, depending on the source's distance. Such a detection, whichrelies on the relative motion of the observer-lens-source system, can beobserved for transverse velocities above 3 km/s. Therefore, the chances ofobserving strongly lensed neutron stars increase by one order of magnitude withrespect to previous estimates. Observing strongly lensed CWs will enable novelprobes of the galactic center and fundamental physics.<br