Abstract for Proposal 084390
Testing the Lense-Thirring precession model with a slow spinning pulsar
The 11 Hz pulsar IGR J17480-2446 has previously displayed X-ray
quasi-periodic oscillations (QPOs) with frequencies too high to result
from Lense-Thirring (LT) precession for such a slowly spinning neutron
star (NS). Since these QPOs are similar to those from other NSs and
even black holes (BHs), this challenges the popular LT precession QPO
model. In contrast, the recent discovery of a QPO phase dependence of the
iron emission line energy in a BH X-ray binary provides strong evidence
that BH QPOs result from precession. We propose a 130ks observation of IGR
J17480-2446, or a new slowly spinning NS displaying QPOs, in order to test
for precession using phase-resolved spectroscopy of the iron line. Such
sources are rare transients, thus the triggering probability is <~10%.
Details on Observing Strategy and Trigger Criteria
Trigger on a new outburst of the source IGR J17480-2446 or of any new
source discovered to be a neutron star with spin frequency <~50 Hz that
also displays quasi-periodic oscillations (QPOs).
We propose one long look exposure of a full orbit of XMM-Newton (~130
ks) to occur during the outburst rise, whilst the source is displaying
a QPO, and before the source becomes too bright to observe without
pileup. We will use all sky monitors (MAXI & Swift/BAT) to track the
flux and Swift/XRT to check for the presence of a QPO. For the only
previous outburst of IGR J17480-2446, the time period between
discovery and the flux becoming too high was ~5 days.