Order in the Chaos: Spin-up and Spin-down during the 2002 Outburst of SAX J1808.4-3658

Abstract

We present a timing analysis of the 2002 outburst of the accreting millisecond pulsar SAX J1808.4-3658. A study of the phase delays of the entire pulse profile shows a behavior that is surprising and difficult to interpret: superposed to a general trend, a big jump by about 0.2 in phase is visible, starting at day 14 after the beginning of the outburst. An analysis of the pulse profile indicates the presence of a significant first harmonic. Studying the fundamental and the first harmonic separately, we find that the phase delays of the first harmonic are more regular, with no sign of the jump observed in the fundamental. The fitting of the phase delays of the first harmonic with a model which takes into account the observed exponential decay of the X-ray flux (and therefore of the mass accretion rate onto the neutron star) gives important information on the torque acting on the neutron star during the outburst. We find that the source shows spin-up in the first part of the outburst, while a spin-down dominates at the end. From these results we derive an estimate of the neutron star magnetic field strength.

arXiv comment6 pages, including 3 figures. ApJ Letters, in press

References in corpus (11)

• Nuclear-Powered Millisecond Pulsars and the Maximum Spin Frequency of Neutron Stars
• In-flight Performance of the High Energy X-ray Timing Experiment on the Rossi X-ray Timing Explorer
• The two-hour orbit of a binary millisecond X-ray pulsar
• Discovery of a High-Latitude Accreting Millisecond Pulsar in an Ultracompact Binary
• The Disk-Magnetosphere Interaction in the Accretion-Powered Millisecond Pulsar SAX J1808.4-3658
• Accretion Onto Fast X-Ray Pulsars
• Helium-rich thermonuclear bursts and the distance to the accretion-powered millisecond pulsar SAX J1808.4-3658
• Constraints on the Neutron Star Magnetic Field of the two X-ray Transients SAX J1808.4-3658 and Aql X-1
• The optical counterpart of SAX J1808.4-3658, the transient bursting millisecond X-ray pulsar
• Revised orbital parameters of the accreting millisecond pulsar SAX J1808.4-3658
• Observations of millisecond X-ray pulsars

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