We report the optical identification of the hardest X-ray source ( AX J131501+3141 ) detected in an unbiased wide-area survey in the 0.5–10 keV band , the ASCA Large Sky Survey ( LSS ) .
The X-ray spectrum of the source is very hard and is well reproduced by a power law component ( \Gamma = 1.5 ^ { +0.7 } _ { -0.6 } ) with N _ { H } = 6 ^ { +4 } _ { -2 } \times 10 ^ { 22 } cm ^ { -2 } ( [ Sakano et al .
1998 ] ) .
We have found a galaxy with R = 15.62 mag near the center of the error circle for the X-ray source .
The optical spectrum of the galaxy shows only narrow emission lines whose ratios correspond to those of a type 2 Seyfert galaxy at z = 0.072 , implying an absorption-corrected X-ray luminosity of 2 \times 10 ^ { 43 } erg sec ^ { -1 } ( 2–10 keV ) and M _ { B } = -20.93 mag .
A radio point source is also associated with the center of the galaxy .
We thus identify the X-ray source with this galaxy as an obscured AGN .
The hidden nature of the nucleus of the galaxy in the optical band is consistent with the X-ray spectrum .
These results support the idea that the obscured AGNs/QSOs contribute significantly to the cosmic X-ray background in the hard band at the faint flux level .