We analyze 24 type I X-ray bursts from GS 1826 - 24 observed by the Rossi X-ray Timing Explorer between 1997 November and 2002 July .
The bursts observed between 1997–98 were consistent with a stable recurrence time of 5.74 \pm 0.13 hr .
The persistent intensity of GS 1826 - 24 increased by 36 % between 1997–2000 , by which time the burst interval had decreased to 4.10 \pm 0.08 hr .
In 2002 July the recurrence time was shorter again , at 3.56 \pm 0.03 hr .
The bursts within each epoch had remarkably identical lightcurves over the full \approx 150 s burst duration ; both the initial decay timescale from the peak , and the burst fluence , increased slightly with the rise in persistent flux .
The decrease in the burst recurrence time was proportional to \dot { M } ^ { -1.05 \pm 0.02 } ( assuming that \dot { M } is linearly proportional to the X-ray flux ) , so that the ratio \alpha between the integrated persistent and burst fluxes was inversely correlated with \dot { M } .
The average value of \alpha was 41.7 \pm 1.6 .
Both the \alpha value , and the long burst durations indicate that the hydrogen is burning during the burst via the rapid-proton ( rp ) process .
The variation in \alpha with \dot { M } implies that hydrogen is burning stably between bursts , requiring solar metallicity ( Z \sim 0.02 ) in the accreted layer .
We show that solar metallicity ignition models naturally reproduce the observed burst energies , but do not match the observed variations in recurrence time and burst fluence .
Low metallicity models ( Z \sim 0.001 ) reproduce the observed trends in recurrence time and fluence , but are ruled out by the variation in \alpha .
We discuss possible explanations , including extra heating between bursts , or that the fraction of the neutron star covered by the accreted fuel increases with \dot { M } .