On the emitting region of X-ray fluorescent lines around Compton-thick AGN

X-ray fluorescent lines are unique features of the reflection spectrum of the torus when irradiated by the central active galactic nuclei (AGN). Their intrinsic line width can be used to probe the line-emitting region. Previous studies have focused on the Fe K alpha line at 6.4 keV, which is the most prominent fluorescent line. These studies, however, are limited by the spectral resolution of currently available instruments, the best of which is similar to 1860 km s(-1) afforded by the Chandra High-Energy Grating (HEG). The HEG spectral resolution is improved by a factor of 4 at 1.74 keV, where the Si K alpha line is located. We measured the full width at half-maximum of the Si K alpha line for Circinus, Mrk 3, and NGC 1068, which are 570 +/- 240, 730 +/- 320, and 320 +/- 280 km s(-1), respectively. They are 3-5 times smaller than those measured with the Fe Ka line previously. It shows that the intrinsic widths of the Fe K alpha line are most likely to be overestimated. The measured widths of the Si K alpha line put the line-emitting region outside the dust sublimation radius in these galaxies. It indicates that for Compton-thick AGN, the X-ray fluorescence material are likely to be the same as the dusty torus emitting in the infrared band.