The Derived Population of Luminous Supersoft X-Ray Sources
Abstract
The existence of a new class of astrophysical object, luminous supersoft X-ray sources, has been established through ROSAT satellite observations and analysis during the past ~3 yr. Because most of the radiation emitted by supersoft sources spans a range of wavelengths readily absorbed by interstellar gas, a substantial fraction of these sources may not be detectable with present satellite instrumentation. It is therefore important to derive a reliable estimate of the underlying population, based on the ~30 sources that have been observed to date. The work reported here combines the observational results with a theoretical analysis, to obtain an estimate of the total number of sources likely to be present in M 31, the Magellanic Clouds, and in our own Galaxy. We find that in M31, where ~15 supersoft sources have been identified and roughly an equal number of sources are being investigated as supersoft candidates, there are likely to be ~2500 active supersoft sources at the present time. In our own Galaxy, where about four supersoft sources have been detected in the Galactic plane, there are likely to be ~1000 active sources. Similarly, with about six and about four (nonforeground) sources observed in the Large and Small Magellanic Clouds, respectively, there should be ~30 supersoft sources in the LMC, and ~20 in the SMC. The likely uncertainties in the numbers quoted above, and the properties of observable sources relative to those of the total underlying population, are also derived in detail. These results can be scaled to estimate the numbers of supersoft sources likely to be present in other galaxies. The results reported here on the underlying population of supersoft X-ray sources are in good agreement with the results of a prior population synthesis study of the white dwarf accretor model for luminous supersoft X-ray sources (Rappaport, Di Stefano, & Smith 1994a). It should be emphasized, however, that the questions asked in these two investigations are distinct, that the approaches taken to answer these questions are largely independent, and that the findings of these two studies could in principle have been quite different.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 1994
- DOI:
- 10.1086/175035
- Bibcode:
- 1994ApJ...437..733D
- Keywords:
-
- Astronomical Models;
- Cataclysmic Variables;
- Cosmic X Rays;
- Interstellar Gas;
- Supernovae;
- X Ray Sources;
- Luminosity;
- Magellanic Clouds;
- Milky Way Galaxy;
- Rosat Mission;
- White Dwarf Stars;
- Astronomy;
- STARS: BINARIES: GENERAL;
- STARS: WHITE DWARFS;
- STARS: NOVAE;
- CATACLYSMIC VARIABLES;
- STARS: SUPERNOVAE: GENERAL;
- X-RAYS: GENERAL