SPECTRAL VARIABILITY OF THE X-RAY-BRIGHT BL-LACERTAE OBJECT PKS-2005-489

Two deep ROSAT PSPC observations of the X-ray-bright BL Lac object PKS 2005-489 have yielded high signal-to-noise spectra with a total of 18,900 and 31,000 counts. The 0.2 - 2.0 keV spectrum is rather steep, with a photon index around 3.0 at both epochs. The X-ray flux decreased by a factor of approximate to 2 in 6 months, accompanied by a steepening of the spectrum. Analysis of the broadband energy distribution shows that the continuum emission of PKS 2005 - 489 peaks at approximate to 1016 Hz and that spectral variability is greater above the peak. The application of synchrotron self-Compton models indicates that large magnetic energy densities dominate the emission region in PKS 2005-489 and that the observed variability may be the result of a variable electron energy and density. The models predict the largest variability in the gamma-ray band, where the source was recently detected by the Gamma Ray Observatory (GRO).