A Decade Of Timing An Accretion-Powered Millisecond Pulsar: The Continuing Spin Down And Orbital Evolution Of Sax J1808.4–3658
Author(s)Chakrabarty, Deepto; Patruno, Alessandro; Markwardt, Craig B.; van der Klis, Michiel; Wijnands, Rudy; Morgan, Edward H; Hartman, Jacob M., Ph. D. Massachusetts Institute of Technology; ... Show more Show less
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The 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.
DepartmentMassachusetts Institute of Technology. Department of Physics; MIT Kavli Institute for Astrophysics and Space Research
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.
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