On the Integrated Spectrum of the X-ray Binaries and the Origin of Soft X-ray Emission from the Bulge of M31

Abstract

Using ROSAT PSPC data, we have performed several tests aimed at understanding the origin of the soft X-ray spectral component detected from the bulge of M31. We find that a significant soft component in the spectrum of the bulge is spatially correlated with the unresolved X-ray emission near the core of M31, which is probably a hot interstellar medium or perhaps a population of multiple faint sources. For the first time, we extracted the spectrum of this unresolved emission, by removing point sources dominating the integral spectrum of the bulge, and found it to be responsible for the most of soft excess. A soft spectral component is not at all needed to fit the point source spectrum that remains after subtracting the unresolved emission. The integral spectra of bright point sources, both inside and outside of the M31 bulge, can be fitted with a single power-law in the ROSAT band. Our analysis rules out the previous suggestion that all bulge emission in M31 may be generated by low mass X-ray binaries (Irwin & Bregman, 1999).

11 pages incl. 2 figures, 2 tables, accepted to ApJL

References in corpus (2)

• Using the Bulge of M31 as a Template for the Integrated X-ray Emission from LMXBs
• The X-ray Faint Early-Type Galaxy NGC4697

Cited by in corpus (8)

• Chandra X-ray Observations of the X-ray Faint Elliptical Galaxy NGC 4697
• The second ROSAT PSPC survey of M31 and the complete ROSAT PSPC source list
• The central region of M31 observed with XMM-Newton. II. Variability of the individual sources
• Unresolved emission and ionized gas in the bulge of M31
• XMM-Newton and Chandra Observations of the Central Region of M31
• Constraints on a Local Group X-ray Halo
• Long term X-ray spectral variability of the nucleus of M81
• ASCA Observations of the Central Regions of M31