A Near-Infrared and X-ray Study of W49B: A Wind Cavity Explosion
  We present near-infrared narrow-band images of the supernova remnant W49B, taken with the WIRC instrument on the Hale 200 inch telescope on Mt. Palomar. The 1.64 micron [Fe II] image reveals a barrel-shaped structure with coaxial rings, which is suggestive of bipolar wind structures surrounding massive stars. The 2.12 micron shocked molecular hydrogen image extends 1.9 pc outside of the [Fe II] emission to the southeast. We also present archival Chandra data, which show an X-ray jet-like structure along the axis of the [Fe II] barrel, and flaring at each end. Fitting single temperature X-ray emission models reveals: an enhancement of heavy elements, with particularly high abundances of hot Fe and Ni, and relatively metal-rich core and jet regions. We interpret these findings as evidence that W49B originated inside a wind-blown bubble (R ~ 5 pc) interior to a dense molecular cloud. This suggests that W49B's progenitor was a supermassive star, that could significantly shape its surrounding environment. We also suggest two interpretations for the jet morphology, abundance variations and molecular hydrogen emission: (1) the explosion may have been jet-driven and interacting with the molecular cavity (i.e. a Gamma-ray burst); or (2) the explosion could have been a traditional supernova, with the jet structure being the result of interactions between the shock and an enriched interstellar cloud. 
Jonathan W. Keohane, William T. Reach, Jeonghee Rho and Thomas H.   Jarrett