TORQUE ENHANCEMENT, SPIN EQUILIBRIUM, AND JET POWER FROM DISK-INDUCED OPENING OF PULSAR MAGNETIC FIELDS

Journal Article · Sun May 01 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/822/1/33· OSTI ID:22862979

Parfrey, Kyle; Spitkovsky, Anatoly ^[1]

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1. Department of Astrophysical Sciences, Princeton University, Peyton Hall, Princeton, NJ 08544 (United States)

The interaction of a rotating star’s magnetic field with a surrounding plasma disk lies at the heart of many questions posed by neutron stars in X-ray binaries. We consider the opening of stellar magnetic flux due to differential rotation along field lines coupling the star and disk, using a simple model for the disk-opened flux, the torques exerted on the star by the magnetosphere, and the power extracted by the electromagnetic wind. We examine the conditions under which the system enters an equilibrium spin state, in which the accretion torque is instantaneously balanced by the pulsar wind torque alone. For magnetic moments, spin frequencies, and accretion rates relevant to accreting millisecond pulsars, the spin-down torque from this enhanced pulsar wind can be substantially larger than that predicted by existing models of the disk–magnetosphere interaction, and is in principle capable of maintaining spin equilibrium at frequencies less than 1 kHz. We speculate that this mechanism may account for the non-detection of frequency increases during outbursts of SAX J1808.4-3658 and XTE J1814-338, and may be generally responsible for preventing spin-up to sub-millisecond periods. If the pulsar wind is collimated by the surrounding environment, the resulting jet can satisfy the power requirements of the highly relativistic outflows from Cir X-1 and Sco X-1. In this framework, the jet power scales relatively weakly with accretion rate, L{sub j}∝ M-dot {sup 4/7}, and would be suppressed at high accretion rates only if the stellar magnetic moment is sufficiently low.

• OSTI ID: 22862979
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 822; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
DETECTION
MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETIC MOMENTS
NEUTRON STARS
PLASMA
PULSARS
RELATIVISTIC RANGE
SMALL ANGLE SCATTERING
STELLAR WINDS
X RADIATION
X-RAY DIFFRACTION