A Unique X-Ray Unabsorbed Seyfert 2 Galaxy: IRAS F01475-0740

Abstract

X-ray unabsorbed Seyfert 2 galaxies appear to have X-ray absorption column densities that are too low (N _H < 10²² cm^-2) to explain the absence of broad emission lines in their optical spectra, challenging the standard active galactic nucleus (AGN) unification model. In this Letter, we report Suzaku exposure on the X-ray unabsorbed Seyfert 2 galaxy IRAS F01475-0740, in which a hidden broad-line region was detected through spectropolarimetric observation. The X-ray data show rapid and significant variations on timescales down to 5 ks, indicating that we are viewing its central engine directly. A newly obtained optical spectrum and previous optical/X-ray data suggest that state transition is unlikely in this source. These make IRAS F01475-0740 a very peculiar X-ray unabsorbed Seyfert 2 galaxy which can only be explained by absorption from materials with abnormally high dust-to-gas ratio (by a factor of >4 larger than Galactic). This is in contrast to most AGNs, which typically show dust-to-gas ratios 3-100 times lower than the Galactic.