We report on the first focused NuSTAR observations of the neutron star low mass X-ray binary GS 1826-238, the “Clocked Burster,” since the extended soft state began in 2014. Throughout this day-long observation, we see spectral variability that is consistent with the “banana” branch of atoll LMXBs. The NuSTAR hard X-ray spectrum is consistent with that seen during the initial soft-state excursion in 2014 and is modeled as a double Comptonized plasma: one with low temperature and high optical depth, the other with high temperature and low optical depth. The spectral variations that we see in this source are mostly consistent with variations in the optical depth of the hot component, though the total flux from the source remains nearly constant. A single Type I X-ray burst is seen during this observation, which has a short main peak (timescales of seconds) followed by an extended tail of emission. The shape of this burst is not consistent with a PRE and provide diagnostic information on the regions of the NS surface supplying the fuel for the thermonuclear reaction.
NuSTAR Observations of GS 1826-238 in the Extended Soft State
Abstract
Copyright and License
© 2025. The Author(s). Published by the American Astronomical Society.
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Acknowledgement
B.G. would like the thank the anonymous referee for productive comments and Dr. Ed Nathan and Dr. Malu Sudha for useful discussions on the timing analysis sections. This work was supported by the National Aeronautics and Space Administration (NASA) under grant No. 80NSSC22K1812 issued through the NuSTAR Guest Observer program. This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC.
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Additional details
- National Aeronautics and Space Administration
- 80NSSC22K1812
- Accepted
-
2025-05-31
- Available
-
2025-07-08Published
- Caltech groups
- Division of Physics, Mathematics and Astronomy (PMA), NuSTAR, Space Radiation Laboratory
- Publication Status
- Published