Polarization observations of 20 millisecond pulsars

Abstract

Polarization profiles are presented for 20 millisecond pulsars that are being observed as part of the Parkes Pulsar Timing Array project. The observations used the Parkes multibeam receiver with a central frequency of 1369 MHz and the Parkes digital filterbank pulsar signal-processing system PDFB2. Because of the large total observing time, the summed polarization profiles have very high signal/noise ratios and show many previously undetected profile features. Thirteen of the 20 pulsars show emission over more than half of the pulse period. Polarization variations across the profiles are complex and the observed position angle variations are generally not in accord with the rotating-vector model for pulsar polarization. Never-the-less, the polarization properties are broadly similar to those of normal (non-millisecond) pulsars, suggesting that the basic radio emission mechanism is the same in both classes of pulsar. The results support the idea that radio emission from millisecond pulsars originates high in the pulsar magnetosphere, probably close to the emission regions for high-energy X-ray and gamma-ray emission. Rotation measures were obtained for all 20 pulsars, eight of which had no previously published measurements.Comment: 15pages, 21 figures, 3 tables, accepted for publication in MNRA

Rotation measure variations for 20 millisecond pulsars

“…To measure the long-term changes in mean PA, we took the weighted average of the differences between the PAs across an individual observation profile and the PAs across the grand-average profile from Yan et al (2011). This gives a relative PA shift for that observation and its estimated uncertainty.…”

“…Polarization parameters are in accordance with the astronomical conventions described by van Straten et al (2010); in particular, PAs are absolute and referred to celestial north, increasing toward east. Table 1 lists the basic parameters for the 20 PPTA MSPs with RM values derived from PDFB2 observations following Yan et al (2011).…”

“…The PPTA sample is unusual if not unique in having a large number of observations over a long data span with high signal/noise ratio and accurately calibrated polarization data for a significant number of pulsars. Mean pulse total intensity and polarization profiles have been published for the 20 PPTA pulsars by Yan et al (2011) showing that the pulsed emission extends over more than half of the pulse period for most of the sample and that the polarization variations across the profile are generally complex.…”

The mode switching of PSR B2020+28

“…The averaged pulses were obtained by de-dispersing the data at a dispersion measure (DM) of 24.6 pc cm −3 . Four Stokes parameters were recorded and have been corrected for dispersion, interstellar Faraday rotation and various instrumental polarization effects following the method described by Yan et al (2011). The data are analysed offline using the PSRCHIVE package (Hotan et al 2004) and corrected for parallactic angle and the orientation of the feed.…”

“…The observed PA swings are various. Yan et al (2011) presented polarization profiles of 20 pulsars with smooth, continuous and discontinuous PA variation. Discontinuities of approximately 90 • are often observed (Manchester et al 1975;Backer & Rankin 1980;Stinebring et al 1984;Han et al 2009), and these are interpreted as resulting from overlapping emission from orthogonally polarized emission modes (McKinnon & Stinebring 1998;Gangadhara 1997).…”