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 } { 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 .