Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aas...189.3603f&link_type=abstract
American Astronomical Society, 189th AAS Meeting, #36.03; Bulletin of the American Astronomical Society, Vol. 28, p.1316
Astronomy and Astrophysics
Astronomy
Scientific paper
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 Kalpha 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 +/- 0.3) absorbed by material with a covering factor of 0.95 and a large column density, N_H = (3.1 +/- 0.8) x 10(23) cm(-2) . The Fe Kalpha 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 Kalpha 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 ~ 0.6 keV). The drop in continuum flux and accompanying fall in Fe Kalpha line intensity over a period of ~ 2 years indicates that the material responsible for the fluorescent emission lies within ~ 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.
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