0420087

The Clocked Burster GS 1826-24 is a key source for comparisons of thermonuclear (type-I) burst properties and theoretical predictions. It is the only source which consistently exhibits bright regular hydrogen-rich bursts and is thus also a laboratory for studies of rp-process burning. We propose to observe the source twice during AO-4 for 50 ks each to continue our monitoring of the burst behaviour which commenced in 1997. Measurements of the burst recurrence times burst profiles and energetics will be compared to the existing dataset and best theoretical predictions to provide an increasingly stringent test of numerical ignition models. With steadily increasing persistent flux (accretion rate) over time we expect this source to eventually transition to unsteady bursting providing the opportunity to observe and hence understand this phenomenon better than ever before. [truncated! Please see actual data for full text]