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 nea r the center of Cassiopeia A, the youngest known Galactic supernova remnant . We have conducted a sensitive search for radio pulsations from this sourc e with the Very Large Array, taking advantage of the high angular resolutio n of the array to resolve out the emission from the remnant itself. No conv incing signatures of a dispersed, periodic source or of isolated dispersed pulses were found, whether for an isolated or a binary source. We derive up per limits of 30 and 1.3 mJy at 327 and 1435 MHz for its phase-averaged pul sed 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 sensi tivities to single pulses were 25 and 1.0 Jy at 327 and 1435 MHz. For compa rison, the Crab pulsar emits roughly 80 pulses per minute with flux densiti es greater than 100 Jy at 327 MHz and eight pulses per minute with flux den sities greater than 50 Jy at 1435 MHz. These limits suggest that Cas A belo ngs to the growing population of young neutron stars that are radio-quiet.