Query : 2011A&A...529A.155C

2011A&A...529A.155C - Astronomy and Astrophysics, volume 529A, 155-155 (2011/5-1)

BeppoSAX view of the NS-LMXB GS 1826-238.


Abstract (from CDS):

The spectroscopic characteristics of GS 1826-238, a neutron star in a low-mass X-ray binary system, have already been studied by sensitive, wide band X-ray telescopes (e.g. BeppoSAX, RXTE, INTEGRAL). Up to now, the source has always been observed in a low-hard spectral state, with two spectral components typically detected. The persistent high-energy (>10 keV) emission is effectively explained by thermal Comptonisation by a hot electron cloud (kTe∼20keV); a further low energy component, modelled either by pure blackbody emission or by Compton-modified blackbody radiation by a few keV electron plasma, is generally needed to yield acceptable fits in the soft X-ray band. The aim of the present work is to investigate the origin and the nature of the low energy emission of GS 1826-238 further, along with its contribution to the bolometric output of the source, dominated by the high-temperature thermally Comptonised radiation. This kind of investigation needs sensitive data in the widest available energy band. Simultaneous covering of both the soft X-rays (below 1keV) and the hard X-rays (up to hundreds of keV) is crucial for an unbiased characterisation of the two spectral components, so we searched the whole BeppoSAX-NFI archive for all the available GS 1826-238observations. We analysed a total of six data sets, collected from 1997 to 2000; data analysis of two of them was still unpublished. In this study we applied both a well-established (comptt) and a more recent, updated Comptonisation model (comptb), in order to get the widest quantitative information about the physical parameters at work. Our results confirm that the 0.1-200keV emission of GS 1826-238 needs two components to be explained. In particular, two populations of soft seed photons, with different colour temperatures, are observed. One population is Comptonised to high energies by a hot electron cloud (temperatures in the range 19-24 keV, anticorrelated with the source luminosity), while the other is directly observed and can be modelled by a pure blackbody. We also propose an alternative model in which both the seed photon populations are Compton-modified by the electron plasma. This model explains the observed emission of GS 1826-238 as accurately as the traditional one and, moreover, fits well in a wider evolutionary scenario able to describe the state transitions observed in neutron-star low-mass X-ray binaries. The use of comptb also indicates that, in the case of GS 1826-238, the seed photons populations are not distributed as a pure blackbody.

Abstract Copyright:

Journal keyword(s): X-rays: general - X-rays: binaries - X-rays: individual: GS 1826-238 - radiation mechanisms: thermal

Simbad objects: 2

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Number of rows : 2
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 NAME Slow Burster LXB 17 31 57.73 -33 50 02.5     15.50     ~ 803 1
2 V* V4634 Sgr LXB 18 29 28.2 -23 47 49 18.90 19.40 19     ~ 326 0

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