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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.
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Submitted on : Tuesday, May 17, 2022 - 3:20:28 PM
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J. Rodi, E. Jourdain, J. P. Roques. Hard X-Ray Tail Discovered in the Clocked Burster GS 1826-238. The Astrophysical Journal, 2016, 817, ⟨10.3847/0004-637X/817/2/101⟩. ⟨insu-03670548⟩

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