Astronomy and Astrophysics – Astrophysics
Scientific paper
1998-04-29
Astronomy and Astrophysics
Astrophysics
Accepted for publication in ApJ Letters. 6 pages formatted with aas2pp4 and one embedded figure (consisting of two postscript
Scientific paper
10.1086/311444
As a class, LINERs and Low-Luminosity AGN tend to show little or no significant short-term variability (i.e., with time-scales less than a day). This is a marked break for the trend of increased variability in Seyfert 1 galaxies with decreased luminosity. We propose that this difference is due to the lower accretion rate in LINERs and LLAGN which is probably causing the accretion flow to be advection-dominated. This results in a larger characteristic size for the X-ray producing region than is the case in ``normal'' AGN. Short-term variability may be caused by a localized instability or occultation events, but we note that such events would likely be accompanied by broad-band spectral changes. Since the ADAF is more compact in a Kerr metric, it is possible that the X-ray emission from ADAFs around rotating blackholes would be more variable than X-ray emission from ADAFs in a Schwarzchild metric. Similar variability arguments also apply to other wavelengths, and accordingly multiwavelength monitoring of LLAGN could serve to ``map'' the ADAF regions.
Griffiths Richard
Mushotzky Richard
Ptak Andrew
Serlemitsos Peter
Yaqoob Tahir
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