X - X-ray variability is known in both intensity and...

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X-ray variability is known in both intensity and spectral shape. There is evidence of changes in the soft X-ray cutoff produced by H photoelectric absorption (Barr et al 1977 MNRAS 181, 438), probably as clouds drift across the line of sight to the tiny central X-ray source; the variations observed would be Poisson fluctuations. There would be typically 100 clouds in front of the nucleus, with column densities typically 5 × 10 22 cm -2 and velocities 1000 km/s. This may be direct detection of BLR clouds. Strong, rapid, and continual X-ray variability has proven to be a hallmark of a subset of AGN with the slightly oxymoronic designation of narrow-line Seyfert 1 galaxies (NLSy1). Their optical spectra show all the usual high-density lines, but with widths of 1000 km/s or so instead of the 5000 which is more usual (I Zw 1 is a prime example). This may indicate that these objects have simultaneously lower central masses and higher accretion rates relative to the
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This note was uploaded on 11/10/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

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