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ASCA Observation of the Nearest Gravitational Lensing Cluster Candidate -- A 3408

We observed the nearest gravitational lensing cluster candidate, A 3408 (${\it z}=0.042$), with ASCA. The projected mass profile of A 3408 was determined from the ICM temperature and the $β$-model parameters obtained with ASCA, assuming that the hot gas is spherically symmetric and in hydrostatic equilibrium. The projected mass within an arc radius, $r_{\rm arc}$, of 110 kpc is $M(r_{\rm arc})=1.2^{+0.8}_{-0.4} \times10^{13} \MO$. This is 18 -- 45% of the mass previously derived from a lensing analysis by Campusano et al. (1998, AAA 069.160.189) without any X-ray information. The primary cause of this discrepancy is in their assumption that the center of the cluster potential coincides with the position of the brightest cluster galaxy (BCG), while we reveal the BCG position to be 60$''$ outside of the X-ray center. We further calculated a model for the source galaxy position and the gravitational potential that can reproduce both the X-ray data and the arc image. In this model, the magnification factor of the lens for the source galaxy was evaluated to be $Δm=$ 0.07$\pm$0.03 mag; i.e., the source galaxy is slightly magnified by the lens cluster A 3408.