  Type I X-ray bursts from low-mass X-ray binaries result from a thermonuclear
runaway in the material accreted onto the neutron star. Although typical
recurrence times are a few hours, consistent with theoretical ignition model
predictions, there are also observations of bursts occurring as promptly as ten
minutes or less after the previous event. We present a comprehensive assessment
of this phenomenon using a catalog of 3387 bursts observed with the
BeppoSAX/WFCs and RXTE/PCA X-ray instruments. This catalog contains 136 bursts
with recurrence times of less than one hour, that come in multiples of up to
four events, from 15 sources. Short recurrence times are not observed from
so-called ultra-compact binaries, indicating that hydrogen burning processes
play a crucial role. As far as the neutron star spin frequency is known, these
sources all spin fast at over 500 Hz; the rotationally induced mixing may
explain burst recurrence times of the order of 10 min. Short recurrence time
bursts generally occur at all mass accretion rates where normal bursts are
observed, but for individual sources the short recurrence times may be
restricted to a smaller interval of accretion rate. The fraction of such bursts
is roughly 30%. We also report the shortest known recurrence time of 3.8
minutes.

High Energy Astrophysical Phenomena