Abstract
Abstract The neutron star low-mass X-ray binary GS 1826−238 was observed with Suzaku on 2009 October 21, for a total exposure of 1030 ks. Except for the type I bursts, the source intensity was constant within ∼10%. Combining the Suzaku XIS, HXD-PIN, and HXD-GSO data, burst-removed persistent emission was detected over the 0.8–100 keV range, at an unabsorbed flux of 2.6 × 10−9 erg s−1 cm−2. Although the implied 0.8–100 keV luminosity, 1.5 × 1037 erg s−1 (assuming a distance of 7 kpc), is relatively high, the observed hard spectrum confirms that the source was in the hard state. The spectrum was successfully explained by an emission from a soft standard accretion disk partially Comptonized by a hot electron cloud, and a blackbody emission Comptonized by another hotter electron cloud. These results are compared with those from previous studies, including those on the same source by Thompson et al. (2005, ApJ, 634, 1261) and Cocchi, Farinelli, and Paizis (2011, A&A, 529, A155), as well as that of Aql X-1 in the hard state obtained with Suzaku (Sakurai et al. 2014, PASJ, 66, 10).
Highlights
A neutron-star (NS) Low Mass X-ray binary (LMXB) is one of the most typical Xray sources involving NS
The soft-state spectra have long been understood to consist of a multi-color disk blackbody (MCD) emission from a standard accretion disk, and a blackbody radiation from the NS surface (Mitsuda et al 1984)
7 Suzaku data sets of the transient LMXB Aquila X-1, obtained during its outburst in 2007. They successfully explained the broad-band spectra of this source in the hard state considering that the Compton seed photons are provided by the blackbody emission from the NS surface, and that the soft excess is produced by the MCD emission from an accretion disk which is truncated at a radius of ∼ 20 km, larger than that of the NS
Summary
A neutron-star (NS) Low Mass X-ray binary (LMXB) is one of the most typical Xray sources involving NS. Sakurai et al (2012) and Sakurai et al (2014) addressed the above questions by analyzing They successfully explained the broad-band spectra of this source in the hard state considering that the Compton seed photons are provided by the blackbody emission from the NS surface, and that the soft excess is produced by the MCD emission from an accretion disk which is truncated at a radius of ∼ 20 km, larger than that of the NS. At this radius, the accreting matter is considered to turn into an optically-thin hot flow, i.e. a corona, and plunges onto the NS surface to be thermalized therein.
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