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 near the center of Cassiopeia A, the youngest known Galactic supernova remnant. We have conducted a sensitive search for radio pulsations from this source with the Very Large Array, taking advantage of the high angular resolution of the array to resolve out the emission from the remnant itself. No convincing signatures of a dispersed, periodic source or of isolated dispersed pulses were found, whether for an isolated or a binary source. We derive upper limits of 30 and 1.3 mJy at 327 and 1435 MHz for its phase-averaged pulsed flux density. The corresponding luminosity limits are lower than those for any known radio pulsar with an age less than 10(4) yr. Our search sensitivities to single pulses were 25 and 1.0 Jy at 327 and 1435 MHz. For comparison, the Crab pulsar emits roughly 80 pulses per minute with flux densities greater than 100 Jy at 327 MHz and eight pulses per minute with flux densities greater than 50 Jy at 1435 MHz. These limits suggest that Cas A belongs to the growing population of young neutron stars that are radio-quiet.