Soft X-Rays from the Large Magellanic Cloud and the Galaxy: Implications on the Origin of the Diffuse X-Ray Background

Observations of Southern Hemisphere X-ray sources are reported, obtained on two attitude-controlled sounding rocket experiments launched from Woomera, Australia on 1 and 8 November 1973. The X-ray luminosity of the Large Magellanic Cloud was observed to be 1038 ergs s -1 between 0.4 and 1.5 keV. An upper limit on the extragalactic diffuse X-ray flux of 250 photons (cm2 s keV sr)-l at 0.215 keV was derived, based on the lack of modulation of soft X-rays by neutral interstellar matter in the direction of the Large Magellanic Cloud. Spectra of three extended soft X-ray regions are reported. Two of the regions, in Eridanus and in Gemini-Monoceros, are of Galactic origin. The third lies in a direction of very low neutral hydrogen column density and hence its spatial origin cannot be unambiguously established. The volume emissivity required in Galactic enhanced regions, which are interpreted as plasmas with temperatures of several million degrees, does not differ greatly from what is required to generate the soft X-ray background. An anomalously high X-ray flux between 0.4 and 1.5 keV was observed in the direction of Cen X-3 in the 5° x 10° detector on both flights 1 and 2. However, this emission does not originate from Cen X-3 as reported by Bleeker et al. (1973) or from n Car as suggested by Hill et al. (1972). A possible energy dependence in the pulsed flux fraction from Cen X-3 is discussed.