The unusual supernova remnant surrounding the ultraluminous X-ray source IC 342 X-1.

We report the results of an observation of a large-diameter (110 pc) supernova remnant (SNR) found to encircle the position of the ultraluminous X-ray source (ULX) IC 342 X-1. The inferred initial energy input to the SNR is at least 2-3 times greater than the canonical energy for an `ordinary' SNR. Two regions on the inside of the shell are bright in [O III]λ5007 emission, possibly as the result of X-ray photoionization by the ULX. If this is the case, then the morphology of this nebulosity implies that the X-ray emission from the ULX is anisotropic. The presence of the ULX, most probably a black hole X-ray binary, within an unusually energetic SNR suggests that we may be observing the aftermath of a gamma-ray burst, although other origins for the energetic nebula are discussed