X-Ray Variability from the Compact Source in the Supernova Remnant RCW 103

A new ASCA observation of 1E 161348-5055, the central compact X-ray source in the supernova remnant RCW 103, reveals an order-of-magnitude decrease in its 3-10 keV flux since the previous ASCA measurement 4 yr earlier. This result is difficult to reconcile with suggestions that the bulk of the emission is simple quasi-blackbody, cooling radiation from an isolated neutron star. Furthermore, archived Einstein and ROSAT data sets spanning 18 yr confirm that this source manifests long-term variability, to a lesser degree. This provides a natural explanation for difficulties encountered in reproducing the original Einstein detection of 1E 161348-5055. Spectra from the new data are consistent with no significant spectral change despite the decline in luminosity. We find no evidence for a pulsed component in any of the data sets, with a best upper limit on the pulsed modulation of 13%. We discuss the phenomenology of this remarkable source.