Deep-imaging observations of a candidate of an absorbed QSO at z=0.653, AXJ131831+3341

The results of deep-imaging observations of a candidate of an absorbed QSO at z = 0.653 AX J131831+3341, are presented. AX J131831+3341 was found duri ng the course of optical follow-up observations of the ASCA Large Sky Surve y, and has an X-ray luminosity of 10(45) erg s(-1) (2-10 keV), which corres ponds to those of QSOs. Its optical spectrum shows no significant broad H b eta emission line, suggesting that the object is an absorbed QSO. Deep R an d V band images reveal the presence of a point-like nucleus and an asymmetr ic extended component. The nuclear component has a blue color, and the opti cal magnitude is much fainter than that expected from the observed X-ray fl ux for typical type-1 AGNs. These photometric properties and the presence o f broad MgII 2800 Angstrom emission can be explained simultaneously if the observed nuclear light is dominated by scattered nuclear light, though ther e is a possibility that the nuclear component is a slightly absorbed nucleu s if its intrinsic X-ray to optical flux ratio is the largest among X-ray s elected AGNs. The size of the extended component, which is thought to be th e host galaxy of the QSO, is larger than those of normal disk galaxies at z = 0-0.75, and the absolute magnitude is similar to those of the brightest host galaxies of QSOs at redshifts smaller than 0.5. The Ir - R and R - I c olors of the component are consistent with a 1 Gyr-old stellar population m odel without absorption.