Faint galactic X-ray binaries

Abstract

We present a short overview of the properties of faint Galactic X‐ray binaries. We place emphasis on current classification scenarios. One of the important parameters for the faint sources is their intrinsic luminosity. In the case of low‐mass X‐ray binaries it has recently been realised that besides a phase of radius expansion, the duration of type I X‐ray bursts can be used as a primer for the source luminosity in some cases. Further, we show that a very low equivalent width of hydrogen and helium emission lines in the optical spectrum alone is not a tell‐tale sign for an ultra‐compact system. Finally, we list and discuss some unusual sources that could be X‐ray binaries