W49B

W49B (also known as SNR G043.3-00.2 or 3C 398) is a nebula in Westerhout 49 (W49). The nebula is a supernova remnant, probably from a type Ib or Ic supernova that occurred around 1,000 years ago. It may have produced a gamma-ray burst and is thought to have left a black hole remnant.

W49B is a supernova remnant (SNR) located roughly 33,000 light-years from Earth, Radio wavelengths show a shell four arc minutes across. There are infrared "rings" (about 25 light-years in diameter) forming a "barrel", and intense X-ray radiation coming from forbidden emission of nickel and iron in a bar along its axis. W49B is also one of the most luminous SNRs in the galaxy at gamma-ray wavelengths. It is invisible at optical wavelengths.

W49B has a number of other unusual properties. It shows x-ray emission from chromium and manganese, something seen in only one other SNR. The iron in the nebula is seen only in the western half of the nebula, while other elements are distributed throughout the nebula.

The outer shell is interpreted as a wind-blown bubble of molecular hydrogen within the interstellar medium, commonly seen around hot luminous stars. Away from the galactic plane, there is little gas and it is very faint optically. The shell is around 10 parsecs across and 1.9 parsecs thick. Inside the shell are the x-ray jets. Where the southeastern jet reaches the shell there is a bow-shock.