Broadband spectrum of the total X-ray emission from the galaxy M31
Abstract
We present the results of measurements of the total X-ray flux from the Andromeda galaxy (M31) in the 3-100 keV band based on data from the RXTE/PCA, INTEGRAL/ISGRI, and SWIFT/BAT space experiments. We show that the total emission from the galaxy has a multicomponent spectrum whose main characteristics are specified by binaries emitting in the optically thick and optically thin regimes. The galaxy's luminosity at energies 20-100 keV gives about 6% of its total luminosity in the 3-100 keV band. The emissivity of the stellar population in M31 is L 2-20 keV ∼ 1.1 × 1029 erg s-1 M {⊙/-1} in the 2-20 keV band and L 20-100 keV ∼ 8 × 1027 erg s-1 M {⊙/-1} in the 20-100 keV band. Since low-mass X-ray binaries at high luminosities pass into a soft state with a small fraction of hard X-ray emission, the detection of individual hard X-ray sources in M31 requires a sensitivity that is tens of times better (up to 10-13 erg s-1 cm-2) than is needed to detect the total hard X-ray emission from the entire galaxy. Allowance for the contribution from the hard spectral component of the galaxy changes the galaxy's effective Compton temperature approximately by a factor of 2, from ∼1.1 to ∼2.1 keV.
- Publication:
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Astronomy Letters
- Pub Date:
- January 2014
- DOI:
- 10.1134/S1063773714010046
- Bibcode:
- 2014AstL...40...22R
- Keywords:
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- X-ray sources