Using simultaneous observations from the Chandra X-Ray Observatory and the Rossi X-Ray Timing Explorer , we investigated the low-mass X-ray binary ( LMXB ) and “ clocked burster ” GS 1826–238 with the goal of studying its spectral and timing properties .
The uninterrupted Chandra observation captured 6 bursts ( RXTE saw 3 of the 6 ) , yielding a recurrence time of 3.54 \pm 0.03 hr .
Using the proportional counter array on board RXTE , we made a probable detection of 611 Hz burst oscillations in the decaying phases of the bursts with an average rms signal amplitude of 4.8 % .
The integrated persistent emission spectrum can be described as the dual Comptonization of \sim 0.3 keV soft photons by a plasma with kT _ { e } \sim 20 keV and \tau \sim 2.6 ( interpreted as emission from the accretion disk corona ) , plus the Comptonization of hotter \sim 0.8 keV seed photons by a \sim 6.8 keV plasma ( interpreted as emission from or near the boundary layer ) .
We discovered evidence for a neutral Fe K \alpha emission line , and we found interstellar Fe L II and Fe L III absorption features .
The burst spectrum can be fit by fixing the disk Comptonization parameters to the persistent emission best-fit values , and adding a blackbody .
The temperature of the boundary layer seed photons was tied to the blackbody temperature .
The blackbody/seed photon temperature at the peak of the burst is \sim 1.8 keV and returns to \sim 0.8 keV over 200 s. The blackbody radius is consistent with R _ { bb } \approx 10.3–11.7 km assuming a distance of 6 kpc , though this value can not be interpreted as the physical size of the neutron star due to partial covering of the stellar surface by the accretion disk .
By accounting for the fraction of the surface that is obscured by the disk as a function of binary inclination , we determined the source distance must actually be near 5 kpc in order for the stellar radius to lie within the commonly assumed range of 10–12 km .
The order of magnitude increase in flux at burst peak is seen to cause Compton cooling of the electron plasma surrounding the disk , as the plasma temperature decreases to \sim 3 keV at burst onset , and then slowly returns to the persistent emission value after about 150 s .