  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 four years earlier. This
result is hard 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 datasets spanning 18 years 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 percent. We discuss the
phenomenology of this remarkable source.
