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Paper: Are All Narrow-Line Seyfert 1s Ultrasoft and X-ray Bright?
Volume: 311, AGN Physics with the Sloan Digital Sky Survey
Page: 261
Authors: Williams, R.J.; Mathur, S.; Pogge, R.W.
Abstract: Many consider ultrasoft X-ray emission to be a defining characteristic of narrow-line Seyfert 1 galaxies (NLS1s); indeed, many known NLS1s have been selected on this basis. In our sample of 150 optically-selected NLS1s from the Sloan Digital Sky Survey Early Data Release, 52 were associated with X-ray sources detected in the ROSAT All-Sky Survey. Most of the objects not detected by ROSAT are optically faint, but a subset of them exhibit optical characteristics similar to the X-ray detected NLS1s, and so should have been detected themselves. We have observed eleven of these ROSAT-undetected NLS1s with Chandra ACIS-S for 2 ksec each. Eight of these objects appear to exhibit normal NLS1 X-ray properties, but three are uncharacteristically faint and may have very flat X-ray spectra. While the bright objects in our Chandra sample may be highly variable and thus were in a low-luminosity state when observed with ROSAT, the other three cannot be easily explained without invoking high intrinsic neutral column densities or other phenomena previously unobserved in NLS1s.
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