X-ray bursts from the Terzan 5 transient IGR J17480-2446: nuclear rather
  than gravitational
  The 2010 outburst of the transient neutron star low-mass X-ray binary IGR
J17480-2446 has exhibited a series of unique X-ray bursts, as well as
millihertz (mHz) quasi-periodic oscillations (QPOs) related to these bursts. It
has been recently proposed that these are type-II bursts, powered by the
gravitational energy. This implies that the current nuclear-burning based model
of mHz QPOs is not correct, and this timing feature cannot be used as a tool to
measure the neutron star parameters. We report the analysis of the Rossi X-ray
Timing Explorer data of IGR J17480-2446 to show that the burst properties of
this source are quite different from the properties of the type-II bursts
observed from the rapid burster and GRO J1744-28. For example, the inferred
ratio (~ 50-90) of the non-burst fluence to burst fluence is consistent with
the thermonuclear origin of IGR J17480-2446 bursts, and is significantly
different from this ratio (< 4) for type-II bursts. Our results suggest that
the bursts and the mHz QPOs from IGR J17480-2446 are powered by the nuclear
energy.
