Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998larm.confe..37a&link_type=abstract
"IX Latin American Regional IAU Meeting, "Focal Points in Latin American Astronomy", held in Tonantzintla, Mexico, Nov 9-13, 199
Astronomy and Astrophysics
Astronomy
Scientific paper
Several years of observations of young pulsars made possible to measure their observational braking indices n_obs (for 4 pulsars) and jerk parameters m_obs (2 pulsars). One striking feature from the data is that all estimates disagree from the rotating magnetic dipole model expected values. Besides, the Crab pulsar has suffered permanent changes in its angular velocity derivative dOmega/dt at every glitch registered. After each event, the angular velocity Omega becomes smaller (pulsar rotates faster) than before. These facts tells us that the decelerating external torque acting on the neutron star may be changing in time-scales <10^4 years. Thanks to this, the characteristic age tau=P/(2dP/dt) turns to be a bad age estimator for young pulsars. Three simple hypothesis will be adressed in the present work. They are 1) the growth of the angle between magnetic moment and rotation axis, 2) an increase of magnetic field intensity (on surface) and 3) the decrease of moment of inertia. A general model, based on the growth of "torque function" K=-(dOmega/dt)/Omega^n, is proposed. We show that choosing constant observational braking index, for which there are evidences, model equations are simplified, and initial values for several physical quantities can be evaluated. The results supports a higher degree of similarity between pulsars at birth. One problem arises from here: evolution of pulsars with n_obs<3 in the P-Pdot diagram cannot lead to the observed main locus of pulsars. Another model must be proposed, one which makes n_obs>3 from age ~10^5 years up. We will discuss briefly on this "reversion mechanism".
Allen Michael P.
Horvath Jorge Ernesto
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