Previous
abstract 
Next
abstract
Session 36 - Extragalactic X-Ray Sources.
Display session, Tuesday, January 14
Metropolitan Ballroom,
The X-ray properties of the type 2 Seyfert galaxy NGC 4388 have been investigated using simultaneous observations by ROSAT and ASCA in 1993 and an ASCA observation in 1995. It was found that the hard X-ray flux had dropped by a factor of two between these observations and that the profile and strength of the Fe K\alpha emission line had also changed.
The overall X-ray spectrum of NGC 4388 between 0.5 and 10.0 keV is well described by a flat power law (\Gamma = 1.5 \pm 0.3) absorbed by material with a covering factor of 0.95 and a large column density, N_H = (3.1 \pm 0.8) \times 10^23 cm^-2. The Fe K\alpha emission line feature in the 1993 ASCA spectra can be modeled with a complex of broad and narrow components at energies consistent with highly ionized Iron. However, the Fe K\alpha emission line in the 1995 spectra has only a single, narrow component and is consistent with emission due to neutral Iron.
The soft X-ray flux of the July 1993 ASCA observation is consistent with the flux observed during a June - July 1993 ROSAT PSPC observation. When the spectra from both satellites are modeled simultaneously, the greater soft X-ray sensitivity of the ROSAT PSPC indicated that an additional thermal component to the X-ray emission is present (kT \sim 0.6 keV).
The drop in continuum flux and accompanying fall in Fe K\alpha line intensity over a period of \sim 2 years indicates that the material responsible for the fluorescent emission lies within \sim 0.6 pc of the continuum source.
These hard X-ray spectral properties are similar to those seen for the prototype obscured Seyfert 1 galaxies NGC 1068 and Mkn 3. There is also evidence for further emission features in the ASCA spectra reminiscent of the reflection dominated hard X-ray spectra of NGC 6552 and the Circinus galaxy. Such low significance spectral features have also been seen in the ASCA spectra of NGC 1068 and Mkn 3.
The author(s) of this abstract have provided an email address for comments about the abstract: karlfor@mikado.phys.columbia.edu
