Susmita Chakravorty, Ranjeev Misra, Martin Elvis, Ajit K. Kembhavi, Gary Ferland
The radiation from the central regions of active galactic nuclei, including
that from the accretion disk surrounding the black hole, is likely to peak in
the extreme ultraviolet $\sim 13 -100 \ev$. However, due to Galactic
absorption, we are limited to constraining the physical properties - black hole
mass and accretion rate - from what observations we have below $\sim 10 \ev$ or
above $\sim 100 \ev$. In this paper we predict the thermal and ionization
states of warm absorbers as a function of the shape of the unobservable
continuum. In particular we model an accretion disk at $kT_{in} \sim 10 \ev$
and a {\it soft excess} at $kT_{se} \sim 150 \ev$. The warm absorber, which is
the highly ionized gas along the line of sight to the continuum, shows
signatures in the $\sim 0.3 - 2 \kev$ energy range consisting of numerous
absorption lines and edges of various ions, some of the prominent ones being H-
and He-like oxygen, neon, magnesium and silicon. We find that the properties of
the warm absorber are significantly influenced by the changes in the
temperature of the accretion disk, as well as by the strength of the {\it soft
excess}, as they affect the optical depth particularly for iron and oxygen.
These trends may help develop a method of characterising the shape of the
unobservable continuum and the occurrence of warm absorbers.
View original:
http://arxiv.org/abs/1201.5435
No comments:
Post a Comment