Abstract
Chandra observations of M31 allow the first spatially resolved X-ray image of a supernova remnant (SNR) in an external spiral galaxy. CXOM31 J004327.7+411829 is a slightly elongated ring-shaped object with a diameter of 11'' (42 pc). In addition, the X-ray image hints that the chemical composition of the SNR is spatially dependent. The age of the SNR is estimated to be 3210-22300 years and the number density of ambient gas is 0.003-0.3 cm-3. Ground-based narrow-band optical images of the SNR show a resolved object. In addition, we found two newly discovered X-ray emitting SNRs which are also nicely resolved in radio within 250 pc of the center of M31. This indicates that there might be active star formation in the bulge of M31. In one case, the SNR is spatially resolved in X-ray (Chandra), radio (VLA) and optical (HST) images. This is the first example of a resolved X-ray/radio/optical SNR in an external spiral galaxy. This research was supported by NASA LTSA grants, NAG5-10705 and NAG5-10889.