The clumpy torus around type II AGN as revealed by X-ray fluorescent
  lines
  The reflection spectrum of the torus around AGN is characterized by X-ray
fluorescent lines, which are most prominent for type II AGN. A clumpy torus
allows photons reflected from the back-side of the torus to leak through the
front free-of-obscuration regions. Therefore, the observed X-ray fluorescent
lines are sensitive to the clumpiness of the torus. We analyse a sample of type
II AGN observed with Chandra HETGS, and measure the fluxes for the Si Ka and Fe
Ka lines. The measured Fe Ka/Si Ka ratios, spanning a range between $5-60$, are
far smaller than the ratios predicted from simulations of smooth tori,
indicating that the tori of the studied sources have clumpy distributions
rather than smooth ones. Compared with simulation results of clumpy tori with a
half-opening angle of 60$^{\circ}$, the Circinus galaxy has a Fe Ka/Si Ka ratio
of $\sim60$, which is close to the simulation results for $N=5$, where $N$ is
the average number of clumps along the line of sight. The Fe Ka/Si Ka ratios of
the other sources are all below the simulation results for $N=2$. Overall, it
shows that the non-Fe fluorescent lines in the soft X-ray band are a
potentially powerful probe of the clumpiness of the torus around AGN.
