Other
Scientific paper
May 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aas...186.5803r&link_type=abstract
American Astronomical Society Meeting, 186, #58.03
Other
Scientific paper
We present and analyze ROSAT-PSPC observations of eight Seyfert 2 galaxies, two Seyfert 1/QSOs, and one IR-luminous non-Seyfert. These targets were selected from the Extended 12-Micron Galaxy Sample and, therefore, have different multiwavelength properties from most (optically or X-ray selected) Seyferts previously observed in the soft X-rays. The targets were also selected as having atypical X-ray fluxes among their respective classes, e.g. relatively X-ray strong Seyfert 2s and X-ray weak Seyfert 1/QSOs. Comparing our observations with those from the ROSAT All-Sky Survey, we find variability (in flux and spectral shape) in both of the Seyfert 1/QSOs, but in none of the Seyfert 2s. Both variable objects have steeper photon indices in the more luminous state, with the softest ($<$1.0 keV) varying the most. Fitting the spectra to an absorbed power-law model, we find that both the Seyfert 2s and the Seyfert 1/QSOs are best fit with a photon index of 3.1--3.2. This is in agreement with the average photon index of a sample of Markarian Seyfert 2s observed by Turner, Urry, & Mushotzky (1993, ApJ 418, 653), indicating that most Seyfert 2s, even those displaying a wide variety of characteristics, as well as some Seyfert 1/QSOs, have a photon index much steeper than the canonical (Seyfert 1) value of ~1.7. One possible explanation is that these objects have a flatter continuum plus an ultra-soft ($<1.0$ keV) excess in the form of high-EW iron and/or oxygen fluorescence lines, a black-body or even a thermal plasma. Alternatively, the underlying continuum may indeed be steep, powered by a different physical mechanism than that which produced the flat continua in other Seyfert 1s/QSOs. We imaged one Seyfert 2 (NGC 5005) with the ROSAT HRI, finding about 12% of the soft X-rays to come from an extended source. This object also has the most evidence from spectral fitting for an extra contribution to the soft-X-ray flux in addition to a power-law component, indicating that different components to the soft X-ray spectrum of this object (and likely of other X-ray-weak Seyferts) may come from spatially distinct regions.
Malkan Matthew A.
Rush Brian
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