Broad-band X-ray measurements of GS 1826-238

TL;DR

This study presents broad-band X-ray spectral measurements of the LMXB GS 1826-238, revealing a Comptonized thermal spectrum, and analyzes its burst energetics and stability over time.

Contribution

First detailed broad-band X-ray spectrum of GS 1826-238, confirming its spectral shape and stability, and providing constraints on its distance and luminosity.

Findings

Spectrum consistent with thermal Comptonization at 20 keV

Distance upper limit of 8 kpc, lower limit of 4 kpc

Persistent luminosity between 3.5 x 10^36 and 1.4 x 10^37 erg/s

Abstract

The broad band X-ray spectrum of the low-mass X-ray binary (LMXB) GS1826-238 was measured with the narrow-field instruments on BeppoSAX on April 6 and 7, 1997. The spectrum is consistent with the Comptonization of a 0.6 keV thermal spectrum by a hot cloud of temperature equivalent kT=20 keV. During the observation two type I X-ray bursts were detected. From the bursts an upper limit to the distance could be derived of 8 kpc. Combined with an elsewhere determined lower limit of 4 kpc this implies a persistent X-ray luminosity between 3.5 X 10^36 and 1.4 X 10^37 erg/s which is fairly typical for a LMXB X-ray burster. The accurate determination of the energetics of the two bursts and the persistent emission confirm results with the Wide Field Cameras on BeppoSAX in a narrower bandpass (Ubertini et al. 1999). Comparison with independent X-ray measurements taken at other times indicates that GS 1826-238 since its turn-on in 1988 is a rather stable accretor, which is in line with the strong regularity of type I X-ray bursts.