X-ray emission and supernova remnants

X-ray emission from the Magellanic Clouds was first observed in a five-minute rocket flight from Johnston Atoll in the South Pacific on October 29, 1968. The LMC was detected as an ∼ 4 σ excess in two adjacent 5° bins, the flux was ∼ 1.5 × 10 −9 erg cm −2 s −1 and the spectrum was slightly softer than that of the diffuse background (Mark et al . 1969). Two years later two source regions in the LMC were identified by Price et al . (1971) and emission from the SMC was recorded. The same year Leong et al . (1971) showed that the LMC emission could be resolved by the collimated detector system of the Uhuru satellite into three steady and one possible highly variable source; they were designated LMC X-1, X-2, X-3, and X-4. There was also a possible diffuse emission extending over much of the Cloud. The SMC emission was located to a single, highly variable source, called SMC X-1, in the Wing region. It was the first stellar X-ray source to be confirmed in an external galaxy. Confirmation of the existence of LMC X-4 was presented in the second Uhuru catalogue (Giaconi et al . 1972). The LMC sources X-1, X-2, and X-3 were confirmed by Copernicus satellite observations (Rapley and Tuohy 1974) and given more accurate positions. Also Markert and Clark (1975), using the OSO 7 satellite confirmed these three sources, defined an upper limit for LMC X-4, and introduced a fifth source, LMCX-5.