SNR 0104-72.3: A remnant of Type Ia Supernova in a Star-forming region?
  We report our 110 ks Chandra observations of the supernova remnant (SNR)
0104-72.3 in the Small Magellanic Cloud (SMC). The X-ray morphology shows two
prominent lobes along the northwest-southeast direction and a soft faint arc in
the east. Previous low resolution X-ray images attributed the unresolved
emission from the southeastern lobe to a Be/X-ray star. Our high resolution
Chandra data clearly shows that this emission is diffuse, shock-heated plasma,
with negligible X-ray emission from the Be star. The eastern arc is
positionally coincident with a filament seen in optical and infrared
observations. Its X-ray spectrum is well fit by plasma of normal SMC
abundances, suggesting that it is from shocked ambient gas. The X-ray spectra
of the lobes show overabundant Fe, which is interpreted as emission from the
reverse-shocked Fe-rich ejecta. The overall spectral characteristics of the
lobes and the arc are similar to those of Type Ia SNRs, and we propose that SNR
0104-72.3 is the first case for a robust candidate Type Ia SNR in the SMC. On
the other hand, the remnant appears to be interacting with dense clouds toward
the east and to be associated with a nearby star-forming region. These features
are unusual for a standard Type Ia SNR. Our results suggest an intriguing
possibility that the progenitor of SNR 0104-72.3 might have been a white dwarf
of a relatively young population.
