A deep Chandra observation of oxygen-rich supernova remnant B0049-73.6 in the Small Magellanic cloud

We report on the initial results from our deep Chandra observation (450 ks) of O-rich supernova remnant (SNR) B0049-73.6 in the Small Magellanic Cloud. We detect small metal-rich ejecta features extending out to the outermost boundary of B0049-73.6, which were not seen in the previous data with a shorter exposure. The central nebula is dominated by emission from reverse-shocked ejecta material enriched in O, Ne, Mg, and Si. O-rich ejecta distribution is relatively smooth throughout the central nebula. In contrast, the Si-rich material is highly structured. These results suggest that B0049-73.6 was produced by an asymmetric core-collapse explosion of a massive star. The estimated abundance ratios among these ejecta elements are in plausible agreement with the nucleosynthesis products from the explosion of a 13-15 M _⊙ progenitor. The central ring-like (in projection) ejecta nebula extends to ∼9 pc from the SNR center. This suggests that the contact discontinuity may be located at a further distance from the SNR center than the previous estimate. We estimate the Sedov age of ∼17,000 yr and an explosion energy of E ₀ ∼1.7 × 10⁵¹ erg for B0049-73.6. We place a stringent upper limit on the 2-7 keV band luminosity of L_X ∼ 8.5 × 10³¹ erg s^-1 for the embedded compact stellar remnant at the center of B0049-73.6.