A Decade Of Timing An Accretion-Powered Millisecond Pulsar: The Continuing Spin Down And Orbital Evolution Of Sax J1808.4–3658
Morgan, Edward H.
Hartman, Jacob M.
Markwardt, Craig B.
van der Klis, Michiel
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AbstractThe Rossi X-ray Timing Explorer has observed five outbursts from the transient 2.5 ms accretion-powered pulsar SAX J1808.4–3658 during 1998-2008. We present a pulse timing study of the most recent outburst and compare it with the previous timing solutions. The spin frequency of the source continues to decrease at a rate of (–5.5 ± 1.2) × 10[superscript –18] Hz s[superscript –1], which is consistent with the previously determined spin derivative. The spin down occurs mostly during quiescence, and is most likely due to the magnetic dipole torque from a B = 1.5 × 10[superscript 8] G dipolar field at the neutron star surface. We also find that the 2 hr binary orbital period is increasing at a rate of (3.80 ± 0.06) × 10[superscript –12] s s[superscript –1], also consistent with previous measurements. It remains uncertain whether this orbital change reflects secular evolution or short-term variability.
United States. National Aeronautics and Space Administration (Grant NNX07AP93G)
United States. National Aeronautics and Space Administration (Grant NNX08AJ43G)
Hartman, Jacob M. et al. “A Decade Of Timing An Accretion-Powered Millisecond Pulsar: The Continuing Spin Down And Orbital Evolution Of Sax J1808.4–3658.” The Astrophysical Journal 702.2 (2009): 1673–1678. Web. 8 Jan. 2013.