Upper Limits on Periodic, Pulsed Radio Emission from the X-Ray Point Source in Cassiopeia A

The Chandra X-ray Observatory recently discovered an X-ray point source nearthe center of Cassiopeia A, the youngest known Galactic supernova remnant. Wehave conducted a sensitive search for radio pulsations from this source withthe Very Large Array, taking advantage of the high angular resolution of thearray to resolve out the emission from the remnant itself. No convincingsignatures of a dispersed, periodic source or of isolated dispersed pulses werefound, whether for an isolated or a binary source. We derive upper limits of 30and 1.3 mJy at 327 and 1435 MHz for the phase-averaged pulsed flux density fromthis source. The corresponding luminosity limits are lower than those for anypulsar with age less than 10^4 years. The sensitivities of our search to singlepulses were 25 and 1.0 Jy at 327 and 1435 MHz. For comparison, the Crab pulsaremits roughly 80 pulses per minute with flux densities greater than 100 Jy at327 MHz and 8 pulses per minute with flux densities greater than 50 Jy at 1435MHz. These limits are consistent with the suggestion that the X-ray pointsource in Cas A adds to the growing number of neutron stars which are not radiopulsars.Comment: accepted by ApJ Letter