The newly discovered 11 Hz accreting pulsar, IGR J17480-2446, located in the
globular cluster Terzan 5, has shown several bursts with a recurrence time as
short as few minutes. The source shows the shortest recurrence time ever
observed from a neutron star. Here we present a study of the morphological,
spectral and temporal properties of 107 of the bursts observed by the Rossi
X-ray Timing Explorer. The recurrence time and the fluence of the bursts
clearly anticorrelate with the increase of the persistent X-ray flux. The ratio
between the energy generated by the accretion of mass and that liberated during
bursts indicate that Helium is ignited in a Hydrogen rich layer. Therefore we
conclude that all the bursts shown by IGR J17480-2446 are Type-I X-Ray bursts.
Pulsations could be detected in all the brightest bursts and no drifts of the
frequency are observed within 0.25 Hz of the spin frequency of the neutron
star. These are also phase locked with respect to the pulsations observed
during the persistent emission and no rise of the rms associated to the pulse
frequency is observed during the burst. This behavior would favor a scenario
where the flash is ignited within a region which is consistent to be as large
as the neutron star surface.Comment: 11 pages, 7 figures and 2 tables. Accepted by MNRAS 2011 February 06.
Received 2011 January 07 ; in original form 2010 November 2