Measurements of radio pulsar braking indices

¹ Department of Physics & Astronomy, University of Nigeria, Nsukka, Nigeria e-mail: aus_chukwude@yahoo.com
² Anambra State University, Uli, Anambra State, Nigeria

Received: 9 January 2009
Accepted: 5 February 2010

Abstract

A quantitative analysis of radio pulsar timing noise is presented. Our analysis employs the recently reported strong correlation (with correlation coefficient r = 0.95) between the observed second time derivative of the pulse rotation frequency (), obtained from fully phase-coherent timing analyses, and a timing noise statistic (), used to quantify the amount of pulsar rotational fluctuations absorbed by the coefficient of the cubic term, to isolate the presumed deterministic braking index from the effects attributable to pulsar timing activity. Application of this method to a sample of 27 radio pulsars, whose timing data span ~9–13 years, reveals that (i) for 22 pulsars, a sensible braking index measurement was impossible: with numerical values of the braking index either appreciably less than the corresponding uncertainty or anomalously large; (ii) save for the relatively large uncertainties, the braking index appears to be significantly measured in five pulsars. Current results are discussed in the context of the prevailing standard model for radio pulsar spin-down.