Hard X-Ray Tail Discovered in the Clocked Burster GS 1826-238
Abstract
The low-mass X-ray binary (LMXB) neutron star (NS) GS 1826-238 was discovered by Ginga in 1988 September. Due to the presence of quasi-periodicity in the type I X-ray burst rate, the source has been a frequent target of X-ray observations for almost 30 years. Though the bursts were too soft to be detected by INTEGRAL/SPI, the persistent emission from GS 1826-238 was detected over 150 keV during the ∼10 years of observations. Spectral analysis found a significant high-energy excess above a Comptonization model that is well fit by a power law, indicating an additional spectral component. Most previously reported spectra with hard tails in LMXB NS have had an electron temperature of a few keV and a hard tail dominating above ∼50 keV with an index of Γ ∼ 2-3. GS 1826-238 was found to have a markedly different spectrum with kTe ∼ 20 keV and a hard tail dominating above ∼150 keV with an index of Γ ∼ 1.8, more similar to black hole X-ray binaries. We report on our search for long-term spectral variability over the 25-370 keV energy range and on a comparison of the GS 1826-238 average spectrum to the spectra of other LMXB NSs with hard tails.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2016
- DOI:
- 10.3847/0004-637X/817/2/101
- arXiv:
- arXiv:1512.05514
- Bibcode:
- 2016ApJ...817..101R
- Keywords:
-
- X-rays: binaries;
- X-rays: general;
- stars: individual: GS 1826–238;
- stars: neutron;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- doi:10.3847/0004-637X/817/2/101