Periodicities in rotation and DM of PSR B1557–50

Abstract

Abstract.We have analysed the pulse arrival time data of the pulsar B1557−50 collected over a period of nearly 13 years, from 1986 July to 1999 May, in order to investigate the long-term spin behaviour. The results reveal sustained cyclic variations in both the timing residuals and dispersion measure (DM) of this object. Both the timing and DM sequences are well described by two harmonically-related periodicities of ∼1600 and 800 days. The variations in spin-down rate and DM are significantly anticorrelated in the sense that maximumν corresponds to minimum DM. Interpretation of the data in terms of free precession of an isolated radio pulsar suggests a wobble angle θ ≈ 0.01• . The data are consistent with at least 6.5% of the stellar moment of inertia being coupled to the crust.

Mimicking neutron star precession by polar cap current-pattern drifting

“…The good agreement with Ω p and N s deduced by Deshpande & Rankin (1999) for PSR B0943+10 is comforting but far from compelling and very different kinds of models have also been proposed for such drifting subpulse observations in which outer-magnetosphere plasma plays an important role (cf. Wright 2003).…”

“…3, models for a family of related "drifting spark" models which give the very different magnitudes of Table 1. Deshpande & Rankin (1999) have made the most detailed observations and analysis of narrow subpulses moving through pulse envelopes in radiopulsars. Particularly striking is their deduction of the arrangement and motion relative to the NS of very many narrow radioemission beams in a single pulsar.…”

10.1007/s11444-008-1007-0

“…A spectral analysis of the pulse variations for PSR B1642-03 indicates the presence of ∼5000-, 2500-, 1250-, and 667-day periodicities [8], which could be due to free precession of the pulsar spin axis with a wobble angle of θ ∼ 0.3 • -0.5 • [7]. PSR B1557-50 is a relatively young neutron star (∼0.60 × 10 6 yrs) with a period of 192 ms and a surface magnetic field of 10 12 G. Analysis of a 13-yr series of observational data revealed variations of the PAT with periods of 800 and 1600 days, interpreted as free precession of an isolated neutron star with a wobble angle of θ ∼ 0.01 • [12].…”

“…Pulsar emission is characterized by high stability of the pulse arrival time (PAT), and analyses of fluctuations in the PATs enable detailed investigation of the dynamics of neutron stars. Periodic variations of the PATs are observed for many pulsars with periods of 25 to 5000 days, such as PSR B1620-26 [3], PSR 1828-11 [4,5], PSR B1642-03 [6][7][8], PSR 0531+21 [9,10], PSR B0329+54 [11], PSR B1557-50 [12], PSR B0833-45 [13], and Her X-1 [14] (Table 1). …”

Oscillations in the angular velocity of pulsars

“…After the largest-ever glitch in the angular velocity of a pulsar, DW/W=20.5·10 -6 , was observed in the pulsar PSR B2334+61, oscillations with a period of 364 days were observed [3]. Oscillations with periods of 800 and 1600 days have been observed in the pulsar PSR B1557-50 [4]. Periodic oscillations with a period of 200 days have been observed in the pulsar PSR B0531+21 in the Crab nebula [5].…”