[AGN, Quasars, Black Holes -- Oral ]
New Perspectives on Compton-thick AGN
Tahir Yaqoob, Johns Hopkins University
Kendrah Murphy (MIT, Kavli Institute)
Obscured AGN are now recognized as playing a major role in the
population of accreting supermassive black holes. We present new results
from theoretical calculations that reveal some rather surprising characteristics
of Compton-thick AGN. Our findings have a direct impact on the interpretation
of existing data, as well as data from the upcoming missions NuSTAR and
Astro-H. We show calculations of the dependence of the Fe K line EW,
flux, and observed to intrinsic continuum luminosity ratios on the
reprocessor column density, geometry, and orientation. We find that,
whilst a large EW Fe K emission line is traditionally thought to be a
hallmark for identifying Compton-thick AGN, there is a large part of
parameter space in which the Fe K line may not even be detectable due to
a small EW. We also show that the soft and hard reprocessed X-ray
continua differ significantly from those based on models that are
currently used to deduce column density distributions of AGN found in
surveys, such as those with Chandra, XMM, and the Swift-BAT. The origin
of the differences can be attributed to the inclusion of more realistic
assumptions in our models compared to those currently in use. These
results also impact synthesis models of the CXRB since our model can be
used to derive more realistic column density distributions for AGN. The
intrinsic continuum luminosity in Compton-thick AGN is a critical
quantity that cannot be directly measured and there is no proxy for
estimating it in a trivial manner. However, we show how a robust lower
limit on the intrinsic luminosity may be inferred. When applied to
Swift-BAT AGN, our calculations show that the BAT survey is actually
more biased towards Compton-thick type 1 AGN than Compton-thin type 2 OR
type 1 AGN.