RX J050736-6847.8: A large supernova remnant around an X-ray binary in theLarge Magellanic Cloud

RX J050736-6847.8 in the Large Magellanic Cloud (LMC) is an intriguing X-ra y source consisting of a large ring (diameter similar to 150 pc) of diffuse emission and a central compact source. It is projected in the vicinity of the superbubble N103 around the star cluster NGC 1850. RX J050736-6847.8's ring of diffuse X-ray emission, offset from the superbubble N103, is not bo unded by any optical shell structure, while RX J050736-6847.8's central com pact X-ray source is projected within the cluster HS122. We have analyzed a rchival ROSAT observations of RX J050736-6847.8 to determine the physical p roperties of its X-ray-emitting gas. The X-ray luminosity of the diffuse X- ray emission is 5-6 x 10(35) ergs s(-1) in the 0.1-2.4 keV band, within the range for supernova remnants (SNRs). Assuming a shell geometry with a frac tional shell thickness (Delta R/R) of 0.05-0.2, we find the density of the hot gas to be 0.05-0.09 cm(-3) and a hot gas mass of similar to 820 M.. The physical properties of this shell of hot gas are consistent cm with Sedov' s solution for a similar to 5 x 10(4) yr old SNR in a low-density (similar to 0.015 cm(-3)) medium formed by a supernova of an explosion energy of 3 x 10(51) ergs. The density is so low that no detectable optical emission is expected. Therefore, we suggest that this ring of X-ray emission originates in a SNR, the largest known in the LMC. The large size, low density, and t he regular X-ray morphology suggest that this SNR is located in the halo of the LMC; the small absorption column density further suggests that this SN R is on the near side of the LMC halo. The central compact source of RX J05 0736-6847.8 is probably an X-ray binary in the cluster HS122. The relations hip between the compact source and the diffuse ring is unknown.