X-RAY REPROCESSING BY A MOLECULAR TORUS IN THE SEYFERT-1.9 GALAXY NGC-2992

We present new X-ray spectral data for the Seyfert 1.9 galaxy NGC 2992 obtained with the Advanced Satellite for Cosmology and Astrophysics ( ASCA). These data are combined with archival and published data to out line a 16 year history of flux variability in the X-ray band. We find that, while the 2-10 keV flux has decreased by a factor of similar to 20 in 16 yr, the flux of the Fe K alpha fluorescence line has decrease d by only a factor of 2-3, and the inferred amount of Compton reflecti on is 5 times stronger compared to the continuum than 16 yr ago. From the delay in the response of the Fe K line and inferred Compton reflec tion to decreases in the continuum flux, we estimate that the reproces sed flux lags the continuum flux by similar to 10 yr, giving a distanc e of similar to 3.2 pc to the reprocessor. The observed time delay, al ong with the fact that the Fe K line is narrow (< 6600 km s(-1) FWHM), essentially rules out reprocessing in an accretion disk. This implies the existence of dense, neutral gas with N-H - 10(23)-10(25) Cm-2 wit hin the central regions of the galaxy in addition to a disk, as might be expected for a molecular torus. We find that the flux in the simila r to 0.1-4 keV soft X-ray band has decreased by a factor of similar to 15 in 14 yr, similar to the flux in the 2-10 keV band. In addition, t he ASCA data, when combined with prior spectral results, imply the pre sence of a soft excess that is well modeled with partial covering of t he nuclear continuum source. We have searched for and found no signifi cant evidence for extended X-ray emission in the ROSAT HRI image of NG C 2992. This lack of extent, coupled with the observed long-term varia bility of the soft X-ray flux and spectral results for the soft excess , imply that the soft X-ray emission from NGC 2992 is nuclear in origi n and is not due to scattering.