Populations of Transient Galactic Bulge X-Ray Sources

TL;DR

This paper reports on RXTE observations of about 50 X-ray binary sources in the Galactic bulge, highlighting their accretion rate variability, discovery of new sources, and comparison with evolutionary models.

Contribution

It provides new observational data on transient X-ray sources, including 18 newly discovered by RXTE and BeppoSAX, and analyzes their accretion behaviors and evolutionary implications.

Findings

Observed accretion rates ranged from near Eddington to very low levels.

Identified neutron star binaries with short outburst cycles.

Compared low accretion rate binaries with evolutionary predictions.

Abstract

Starting in 1999, the Rossi X-ray Timing Explorer (RXTE) has monitored the central bulge region of the Galaxy with the Proportional Counter Array (PCA), resolving about 50 binary X-ray sources, including 18 sources discovered by RXTE and BeppoSAX. The accretion rates that RXTE observed from these sources ranged from highs approaching Eddington limits to lows that may correspond to mass exchange for a binary period near the minimum of 80 minutes. Several neutron star binaries with low peak luminosity have outburst or cycle time-scales which are shorter than those of brighter and better known counterparts. We compare the characteristics of the binaries with low rates of mass exchange to predictions of their evolution.