Bibcode
Altamirano, D.; Watts, A.; Linares, M.; Markwardt, C. B.; Strohmayer, T.; Patruno, A.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 409, Issue 3, pp. 1136-1145.
Advertised on:
12
2010
Citations
37
Refereed citations
31
Description
We report the discovery of burst oscillations at the spin frequency in
ten thermonuclear bursts from the accreting millisecond X-ray pulsar
(AMXP) IGR J17511-3057. The burst oscillation properties are, like those
from the persistent AMXPs SAX J1808.4-3658 and XTE J1814-338, anomalous
compared to burst oscillations from intermittent pulsars or non-pulsing
low-mass X-ray binaries. Like SAX J1808.4-3658 they show frequency
drifts in the rising phase rather than the tail. There is also evidence
for harmonic content. Where IGR J17511-3057 is unusual compared to the
other two persistent pulsars is that oscillations are not detected
throughout all bursts. As accretion rate drops the bursts get brighter
and their rise/decay time-scales become shorter, while the oscillation
amplitude falls below the detection threshold: first in the burst peak
and then also in the rise. None of the bursts from IGR J17511-3057 shows
evidence for photospheric radius expansion (which might be expected to
suppress oscillation amplitude) which allow us to set an upper limit to
the distance of 6.9 kpc. We discuss the implications of our results for
models of the burst oscillation mechanism.