Observations of the Binary X-ray Source SMC X-1 from OSO-7

WE report here the results of 40 days of coverage, April 15,1972, to May 25, 1972, of the binary X-ray source SMC X-1 with the UCSD OSO-7 X-ray telescope¹. These observations above 7 keV complement the 2-6 keV Uhuru satellite results reported by Schreier et al.² and permit an extension of the spectrum to at least 35 keV. Combined with other observations, they could help determine long term periodic variations, if any exist. Further information about this source is of particular interest because of its high intrinsic luminosity and its recent identification with SK 160 (ref. 3).