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Date and Time of the Query: 2019-06-17 T15:03:37 PDT
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For refcode 1999ApJ...527..125I:
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1999ApJ...527..125I Using the Bulge of M31 as a Template for the Integrated X-Ray Emission from Low-Mass X-Ray Binaries Jimmy A. Irwin and Joel N. Bregman Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1090; jirwin@astro.lsa.umich.edu, jbregman@umich.edu Received 1999 May 3; accepted 1999 July 23 ABSTRACT We have performed joint ASCA + ROSAT PSPC spectral fitting on the inner 5' of the bulge of M31. We find that single-component spectral models provide an inadequate fit to the spectrum, in contrast to previous studies by Einstein and Ginga. Although the 2-10 keV spectrum can be fitted adequately with a bremsstrahlung model with kT = 7.4 +/- 0.3 keV, an additional soft component with kT = 0.38 +/- 0.03 keV is required to fit the spectrum below 2 keV. This soft component comprises 38% +/- 6% of the total emission in the 0.1-2.0 keV band, and possibly more depending on the absorption value used in the fit. Since previous spatial studies of the bulge of M31 indicate that less than 25% of the X-ray emission from the bulge in this band is from a diffuse gaseous component, this implies that stellar sources, namely, low-mass X-ray binaries (LMXBs), are responsible for some if not all of the soft component. The spectral properties of M31 are very similar to those of the X-ray-faint early-type galaxy NGC 4382. This supports the claim that the unexplained soft X-ray emission seen previously in these galaxies also emanates from LMXBs. Subject headings: binaries: close-galaxies: elliptical and lenticular, cD- galaxies: individual (M31)-galaxies: ISM -X-rays: galaxies-X-rays: stars
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