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Abstract: The low-mass X-ray binary GS 1826-238 is presently unique for itsconsistently regular bursting behavior. In previous Rossi X-Ray Timing ExplorerRXTE measurements between 1997 November and 2002 July, this source exhibitednearly limit-cycle bursts with recurrence times that decreasedproportionately as the persistent flux increased. Here we report additionalmeasurements of the burst recurrence time by RXTE, Chandra, and XMM-Newton, aswell as observations of optical bursts. On a few occasions we measured burstrecurrence times which deviated significantly from the earlier flux-recurrencetime relationship, and most of these bursts occurred earlier than would bepredicted based on the X-ray flux level. The epochs with early bursts were alsoaccompanied by unusual broadband timing signatures, with the entire powerspectrum shifting to higher frequencies. Concurrent XMM-Newton observationsduring one of these occasions, in 2003 April, indicate that an additional softcomponent may be present in the spectrum containing enough flux 30% of thetotal to account for the burst recurrence time discrepancy. A self-consistentinterpretation for the increase in soft flux and accompanying timing changesduring 2003 April is that accretion disk extends down to smaller radialdistances from the source than during the other observing epochs. The RXTEobservations since 2003 April show that the spectral and timing properties havenearly returned to the previously established level.



Author: Thomas W. J. Thompson, Duncan K. Galloway, Richard E. Rothschild, Lee Homer

Source: https://arxiv.org/







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