A near-infrared and X-ray study of W49B: A wind cavity explosion

Abstract

We present near-infrared narrowband images of the supernova remnant W49 B, taken with the WIRC instrument on the Hale 200 inch (5 m) telescope on Mount Palomar. The 1.64 μm [Fe II] image reveals a barrel-shaped structure with coaxial rings, which is suggestive of bipolar wind structures surrounding massive stars. The 2.12 μm 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 jetlike structure along the axis of the [Fe II] barrel, 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 W49 B originated inside a wind-blown bubble (R ∼ 5 pc) inside a dense molecular cloud. This suggests that W49 B'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, 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.