Pulse Variations in XTE J1814-338 and Comparisons to a Precession Model

Details Pulse Variations in XTE J1814-338 and Comparisons to a Precession Model Pulse Variations in XTE J1814-338 and Comparisons to a Precession Model

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008head...10.0605c&link_type=abstract

American Astronomical Society, HEAD meeting #10, #6.05

Astronomy and Astrophysics

Astronomy

Scientific paper

Accreting millisecond pulsars have been predicted to precess with periods of order hours to days, resulting in characteristic variations in their pulse properties.
We compute theoretically the periodic modulation of the mean flux, phase residuals and fractional amplitude of a pulsar with assumed surface intensity patterns featuring one and two hotspots. Using observations taken by the Rossi X-ray Timing Explorer, we then search for these signatures from the accreting millisecond pulsar XTE J1814-338 (pulse frequency 314.4 Hz), which has previously shown long-term, approximately periodic variations in the pulse arrival times. We measure the period of these variations at 12.2 days, and also detect variations at a consistent period in the pulse amplitude and mean (pulse-averaged) X-ray intensity. These variations are consistent with a freely precessing neutron star only if the inclination angle is < 0.1°, an a priori unlikely configuration. Our study suggests that:
1) if the observed flux variations are not due to precession, we place an upper limit on the product ɛ Cos θ ≤ 10-9 for XTE J1814-338, where ɛ is the ellipticity and θ is the tilt angle of the pulsar.
2) if the observed flux variations are due to precession, our model insufficiently describes the pulsar's surface intensity map. We can place an upper limit of ɛ ≤ 3.0 × 10-9 and estimate 5° ≤ θ ≤ 10°. This translates to a gravitational wave strain of ≤ 10-27 and Advanced LIGO signal-to-noise ratio of ≤ 10-2 (for a 120 day integration time).

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