The large-scale magnetic field of our Galaxy can be probed in three dimensions using Faraday rotation of pulsar signals. We report on the determination of 223 rotation measures from polarization observations of relatively distant southern pulsars made using the Parkes radio telescope. Combined with previously published observations these data give clear evidence for large-scale counterclockwise fields (viewed from the north Galactic pole) in the spiral arms interior to the Sun and weaker evidence for a counterclockwise field in the Perseus arm. However, in interarm regions, including the Solar neighbourhood, we present evidence that suggests that large-scale fields are clockwise. We propose that the large-scale Galactic magnetic field has a bisymmetric structure with reversals on the boundaries of the spiral arms. Streaming motions associated with spiral density waves can directly generate such a structure from an initial inwardly directed radial field. Large-scale fields increase toward the Galactic Center, with a mean value of about 2 µG in the Solar neighbourhood and 4 µG at a Galactocentric radius of 3 kpc. Frick et al. 2001). Faraday rotation gives a measure of the line-of-sight component of the magnetic field. Extragalactic sources have the advantage of large numbers but pulsars have the advantage of being spread through the Galaxy at approximately known distances, allowing direct three-dimensional mapping of the field. Pulsars also give a direct estimate of the strength of the field through normalisation by the dispersion measure (DM). The rotation measure (RM) is defined by φ = RM λ 2where φ is the position angle in radians of linearly polarised radiation relative to its infinite-frequency (λ = 0) value and λ is its wavelength (in m). For a pulsar at distance D (in pc), the RM (in rad m −2 ) is given by RM = 0.810

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We have obtained 63 rotation measures (RMs) from polarization observations of southern pulsars, of which 54 are new measurements and 3 are varied from previous values. The new pulsar RM data at high Galactic latitudes are mostly consistent with the antisymmetric RM distribution found previously. For the Galactic disc, evidence for a field reversal near the Perseus arm, and possibly another beyond it, is presented. Inside the Solar Circle, in addition to the two known field reversals in or near the Carina-Sagittartus arm and the Crux-Scutum arm, a further reversal in the Norma arm is tentatively identified. These reversals, together with the pitch angle derived from pulsar RM and stellar polarization distributions, are consistent with bisymmetric spiral (BSS) models for the large-scale magnetic field structure in the disc of our Galaxy. However, discrimination between models is complicated by the presence of smaller-scale irregularities in the magnetic field, as well as uncertainties in the theoretical modelling.Comment: 10pages; 8 figures; Accepted by MNRA

Timing observations from the Parkes 64-m radio telescope for 165 pulsars between 1990 and 2011 have been searched for period glitches. Data spans for each pulsar ranged between 5.3 years and 20.8 years. From the total of 1911 years of pulsar rotational history, 107 glitches were identified in 36 pulsars. Out of these glitches, 61 have previously been reported whereas 46 are new discoveries. Glitch parameters, both for the previously known and the new glitch detections, were measured by fitting the timing residual data. Observed relative glitch sizes ∆ν g /ν range between 10 −10 and 10 −5 , where ν = 1/P is the pulse frequency. We confirm that the distribution of ∆ν g /ν is bimodal with peaks at approximately 10 −9 and 10 −6 . Glitches are mostly observed in pulsars with characteristic ages between 10 3 and 10 5 years, with large glitches mostly occurring in the younger pulsars. Exponential post-glitch recoveries were observed for 27 large glitches in 18 pulsars. The fraction Q of the glitch that recovers exponentially also has a bimodal distribution. Large glitches generally have low Q, typically just a few per cent, but large Q values are observed in both large and small glitches. Observed time constants for exponential recoveries ranged between 10 and 300 days with some tendency for longer timescales in older pulsars. Shorter timescale recoveries may exist but were not revealed by our data which typically have observation intervals of 2 -4 weeks. For most of the 36 pulsars with observed glitches, there is a persistent linear increase inν (i.e., decrease in the slow-down rate |ν|) in the inter-glitch interval. Where an exponential recovery is also observed, the effects of this are superimposed on the linear increase inν. In some but not all cases, the slope of the linear recovery changes at the time of a glitch. Theν values characterising the linear changes inν are almost always positive and, after subtracting the magnetospheric component of the braking, are approximately proportional to the ratio of |ν| and the inter-glitch interval, as predicted by vortex-creep models.

Pulsar braking torques due to magnetodipole radiation and to unipolar generator are considered, which results in braking index being less than 3 and could be employed to test the emission models. Improved equations to obtain pulsar braking index and magnetic field are presented if we deem that the rotation energy loss rate equals to the sum of the dipole radiation energy loss rate and that of relativistic particles powered by unipolar generator. The magnetic field calculated by conventional way could be good enough but only modified by a factor of ∼ 0.6 at most. Both inner and outer gaps may coexist in the magnetosphere of the Vela pulsar.