A1 Refereed original research article in a scientific journal
A Systematic Study of Millihertz Quasiperiodic Oscillations in GS 1826−238
Authors: Xiao, Hua; Ji, Long; Tsygankov, Sergey; Chen, Yupeng; Zhang, Shu; Li, Zhaosheng
Publisher: American Astronomical Society
Publishing place: BRISTOL
Publication year: 2025
Journal: Astrophysical Journal
Journal name in source: The Astrophysical Journal
Journal acronym: ASTROPHYS J
Article number: 180
Volume: 982
Issue: 2
Number of pages: 9
ISSN: 0004-637X
eISSN: 1538-4357
DOI: https://doi.org/10.3847/1538-4357/adbcaa
Web address : https://doi.org/10.3847/1538-4357/adbcaa
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/491709290
We performed a systematic investigation of millihertz quasiperiodic oscillations (mHz QPOs) in the low-mass X-ray binary GS 1826-238 observed with NICER and Insight-HXMT. We discovered 37 time intervals exhibiting mHz QPOs out of 106 Good Time Interval (GTI) samples in the frequency range of 3-17 mHz at a significance level of >99.99%. The source remains in a soft state in our study. No significant differences are found between the samples with and without mHz QPOs according to positions in the color-color and hardness-intensity diagrams. These QPOs were discovered at an accretion rate of similar to 0.1M(Edd)(center dot), similar to other sources. The broadband spectrum of GS 1826-238 can be modeled as a combination of a multicolor blackbody from the accretion disk and a Comptonization with seed photons emitted from the neutron star (NS) surface. The flux modulations of mHz QPOs are related to variations of the temperature of Comptonization seed photons, consistent with the marginally stable burning theory.
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Funding information in the publication:
This work is supported by the National Natural Science Foundation of China under grant Nos. 12173103 and 12261141691. This work made use of data from the High Energy Astrophysics Science Archive Research Center (HEASARC), provided by NASA's Goddard Space Flight Center, and from the Insight-HXMT mission, a project funded by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS).
