Why the braking indices of young pulsars are less than 3?

Free access article

Issue		A&A Volume 450, Number 1, April IV 2006


Page(s)		L1 - L4
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:200600019

A&A 450, L1-L4 (2006)
DOI: 10.1051/0004-6361:200600019

Letter

Why the braking indices of young pulsars are less than 3?

W. C. Chen and X. D. Li

Department of Astronomy, Nanjing University, Nanjing 210093, PR China
e-mail: [chenwc;lixd]@nju.edu.cn

(Received 11 October 2005 / Accepted 24 February 2006)

Abstract
In this letter we discuss two possible reasons which cause the observed braking indices n of young radio pulsars to be smaller than 3: (a) the evolving spin-down model of the magnetic field component $B_{\perp}$ increases with time; (b) the extrinsic braking torque model in which the tidal torques exerted on the pulsar by the fallback disk, and carries away the spin angular momentum from the pulsar. Based on some simple assumptions, we derive the expression of the braking indices, and calculate the spin-down evolutionary tracks of pulsars for different input parameters.

Key words: pulsars: general -- stars: magnetic fields -- stars: rotation

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