External irradiation of a neutron star (NS) accretion disc induces
Poynting-Robertson (PR) drag, removing angular momentum and increasing the mass
accretion rate. Recent simulations show PR drag significantly enhancing the
mass accretion rate during Type I X-ray bursts, which could explain X-ray
spectral features such as an increase in the persistent emission and a soft
excess. However, prograde spin of the NS is expected to weaken PR drag,
challenging its importance during bursts. Here, we study the effect of spin on
PR drag during X-ray bursts. We run four simulations, with two assuming a
non-spinning NS and two using a spin parameter of aββ=0.2, corresponding to a
rotation frequency of 500 Hz. For each scenario, we simulate the disc evolution
subject to an X-ray burst and compare it to the evolution found with no burst.
PR drag drains the inner disc region during a burst, moving the inner disc
radius outward by β1.6 km in the aββ=0 and by β2.2 km in the
aββ=0.2 simulation. The burst enhances the mass accretion rate across the
innermost stable circular orbit β7.9 times when the NS is not spinning
and β11.2 times when it is spinning. The explanation for this seemingly
contradictory result is that the disc is closer to the NS when aββ=0.2, and
the resulting stronger irradiating flux offsets the weakening effect of spin on
the PR drag. Hence, PR drag remains a viable explanation for the increased
persistent emission and soft excess observed during X-ray bursts in spinning NS
systems.Comment: 9 pages, 8 figures, accepted for publication in MNRA