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 $\beta$-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 ${\Delta}m=$ 0.07$\pm$0.03 mag; i.e., the source galaxy is slightly magnified by the lens cluster A 3408.Comment: 13 pages, 6 figures, to appear in PASJ vol. 5

ASCA Observation of the Crab-Like Supernova Remnant 3C58

We present here the X-ray observation of a Crab-like supernova remnant (SNR) 3C58 with ASCA. We find that the integrated energy spectrum over the nebula is consistent with previous results, showing a power-law spectrum with the photon index $\gamma = 2.2-2.4$ modified by interstellar absorption of about $(3-4)\times 10^{21}{\rm cm^{-2}}$. Inclusion of a blackbody component which is attributable to the central compact source significantly improves the spectral fit. Stringent upper limits for any line emitting thin hot plasma are established. We find for the first time that the nebular spectrum is harder in the central part of the SNR, becoming softer toward the periphery, while the absorption column is uniform across the nebula. Correspondingly, the nebular size decreases with increasing photon energy which is a steeper function of radius than that of the Crab nebula. The results are compared with synchrotron energy loss models and the nature of the putative pulsar is discussed. Timing analysis was performed to search for pulsed X-ray emission from the central compact source. No significant pulsations are observed, and we present the upper limit for the pulsed fraction.Comment: 27 pages, 7 figures, to appear in PAS