The integrated X-ray spectrum of galactic populations of luminous supersoft X-ray sources

Abstract

We compute the composite X-ray spectrum of a population of unresolved SSSs in a spiral galaxy such as our own or M31. The sources are meant to represent the total underlying population corresponding to all sources which have bolometric luminosities in the range of 10³⁷–10³⁸ ergs s⁻¹ and kT on the order of tens of eV. These include close-binary supersoft sources, symbiotic novae, and planetary nebulae, for example. In order to determine whether the associated X-ray signal would be detectable, we also “seed” the galaxy with other types of X-ray sources, specifically low-mass X-ray binaries (LMXBs) and high-mass X-ray binaries (HMXBs). We find that the total spectrum due to SSSs, LMXBs, and HMXBs exhibits a soft peak which owes its presence to the SSS population. Preliminary indications are that this soft peak may be observable.