skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Revised Pulsar Spindown

Abstract

We address the issue of electromagnetic pulsar spindown by combining our experience from the two limiting idealized cases which have been studied in great extent in the past: that of an aligned rotator where ideal MHD conditions apply, and that of a misaligned rotator in vacuum. We construct a spindown formula that takes into account the misalignment of the magnetic and rotation axes, and the magnetospheric particle acceleration gaps. We show that near the death line aligned rotators spin down much slower than orthogonal ones. In order to test this approach, we use a simple Monte Carlo method to simulate the evolution of pulsars and find a good fit to the observed pulsar distribution in the P-{dot P} diagram without invoking magnetic field decay. Our model may also account for individual pulsars spinning down with braking index n < 3, by allowing the corotating part of the magnetosphere to end inside the light cylinder. We discuss the role of magnetic reconnection in determining the pulsar braking index. We show, however, that n {approx} 3 remains a good approximation for the pulsar population as a whole. Moreover, we predict that pulsars near the death line have braking index values n >more » 3, and that the older pulsar population has preferentially smaller magnetic inclination angles. We discuss possible signatures of such alignment in the existing pulsar data.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
877495
Report Number(s):
SLAC-PUB-11551
Journal ID: ISSN 0004-637X; ASJOAB; astro-ph/0512002; TRN: US200608%%182
DOE Contract Number:
AC02-76SF00515
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ACCELERATION; ALIGNMENT; DECAY; DISTRIBUTION; INCLINATION; MAGNETIC FIELDS; MAGNETIC RECONNECTION; MONTE CARLO METHOD; PULSARS; ROTATION; SPIN; Astrophysics,ASTRO

Citation Formats

Contopoulos, Ioannis, /Athens Academy, Spitkovsky, Anatoly, and /KIPAC, Menlo Park. Revised Pulsar Spindown. United States: N. p., 2005. Web.
Contopoulos, Ioannis, /Athens Academy, Spitkovsky, Anatoly, & /KIPAC, Menlo Park. Revised Pulsar Spindown. United States.
Contopoulos, Ioannis, /Athens Academy, Spitkovsky, Anatoly, and /KIPAC, Menlo Park. Wed . "Revised Pulsar Spindown". United States. doi:. https://www.osti.gov/servlets/purl/877495.
@article{osti_877495,
title = {Revised Pulsar Spindown},
author = {Contopoulos, Ioannis and /Athens Academy and Spitkovsky, Anatoly and /KIPAC, Menlo Park},
abstractNote = {We address the issue of electromagnetic pulsar spindown by combining our experience from the two limiting idealized cases which have been studied in great extent in the past: that of an aligned rotator where ideal MHD conditions apply, and that of a misaligned rotator in vacuum. We construct a spindown formula that takes into account the misalignment of the magnetic and rotation axes, and the magnetospheric particle acceleration gaps. We show that near the death line aligned rotators spin down much slower than orthogonal ones. In order to test this approach, we use a simple Monte Carlo method to simulate the evolution of pulsars and find a good fit to the observed pulsar distribution in the P-{dot P} diagram without invoking magnetic field decay. Our model may also account for individual pulsars spinning down with braking index n < 3, by allowing the corotating part of the magnetosphere to end inside the light cylinder. We discuss the role of magnetic reconnection in determining the pulsar braking index. We show, however, that n {approx} 3 remains a good approximation for the pulsar population as a whole. Moreover, we predict that pulsars near the death line have braking index values n > 3, and that the older pulsar population has preferentially smaller magnetic inclination angles. We discuss possible signatures of such alignment in the existing pulsar data.},
doi = {},
journal = {Astrophysical Journal},
number = ,
volume = ,
place = {United States},
year = {Wed Dec 14 00:00:00 EST 2005},
month = {Wed Dec 14 00:00:00 EST 2005}
}
  • The measured spindown rates in quiescence of the transient accreting millisecond pulsars IGR J00291+5934, XTE J1751–305, SAX J1808.4–3658, and Swift J1756.9–2508 have been used to estimate the magnetic moments of these objects assuming standard magnetic dipole braking. It is shown that this approach leads to an overestimate if the amount of residual accretion is enough to distort the magnetosphere away from a force-free configuration through magnetospheric mass loading or crushing, so that the lever arm of the braking torque migrates inside the light cylinder. We derive an alternative spindown formula and calculate the residual accretion rates where the formula ismore » applicable. As a demonstration we apply the alternative spindown formula to produce updated magnetic moment estimates for the four objects above. We note that based on current uncertain observations of quiescent accretion rates, magnetospheric mass loading and crushing are neither firmly indicated nor ruled out in these four objects. Because quiescent accretion rates are not measured directly (only upper limits are placed), without more data it is impossible to be confident about whether the thresholds for magnetospheric mass loading or crushing are reached or not.« less
  • The hydromagnetic spinup or spindown of an incompressible, rotating, electrically conducting fluid over an infinite insulated disk with an applied magnetic field is studied when the impulsive motion is imparted either to the fluid or to the disk. The nonlinear partial differential equations governing the flow are solved numerically using an implicit finite-difference scheme. It is found that the spinup (or spindown) time due to impulsive motion of the disk is much shorter than the spinup (or spindown) time due to the impulsive motion of the distant fluid. The spinup (or spindown) time for the hydromagnetic case is comparatively smallermore » than the corresponding nonmagnetic case. Spindown is not merely a mirror reflection of spinup.« less
  • We study the spindown of isolated neutron stars from initially rapid rotation rates, driven by two factors: (1) gravitational wave emission due to r-modes and (2) magnetic braking. In the context of isolated neutron stars, we present the first study including self-consistently the magnetic damping of r-modes in the spin evolution. We track the spin evolution employing the RNS code, which accounts for the rotating structure of neutron stars for various equations of state. We find that, despite the strong damping due to the magnetic field, r-modes alter the braking rate from pure magnetic braking for B {<=} 10{sup 13}more » G. For realistic values of the saturation amplitude {alpha}{sub sat}, the r-mode can also decrease the time to reach the threshold central density for quark deconfinement. Within a phenomenological model, we assess the gravitational waveform that would result from r-mode-driven spindown of a magnetized neutron star. To contrast with the persistent signal during the spindown phase, we also present a preliminary estimate of the transient gravitational wave signal from an explosive quark-hadron phase transition, which can be a signal for the deconfinement of quarks inside neutron stars.« less