Magnetospheric Switching in PSR B1828-11
I. H. Stairs, A. G. Lyne, M. Kramer, B. W. Stappers, J. van Leeuwen, A. Tung, R. N Manchester, G. B. Hobbs, D. R. Lorimer, A. Melatos
PPulsar Astrophysics - The Next 50 YearsProceedings IAU Symposium No. 337, 2017P. Weltevrede, B.B.P. Perera, L. Levin Preston & S. Sanidas, eds. c (cid:13) Magnetospheric Switching in PSR B1828 − I. H. Stairs, A. G. Lyne, M. Kramer, , B. W. Stappers, J. van Leeuwen, , A. Tung, , R. N. Manchester, , G. B. Hobbs, D. R. Lorimer, , A. Melatos Dept. of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road,Vancouver, B.C., V6T 1Z1, Canadaemail: [email protected] Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University ofManchester, Manchester, M13 9PL, UK Max-Planck-Institut f¨ur Radioastronomie, Auf dem H¨ugel 69, D-53121 Bonn, Germany ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA, Dwingeloo,The Netherlands Anton Pannekoek Institute for Astronomy, Univ. of Amsterdam, Science Park 904, 1098 XHAmsterdam, The Netherlands Teacher Education Office, University of British Columbia, 2125 Main Mall, Vancouver, BCV6T 1Z4, Canada CSIRO Astronomy and Space Science, Marsfield NSW 2122, Australia Department of Physics and Astronomy, West Virginia University, PO Box 6315, Morgantown,WV 26506, USA Center for Gravitational Waves and Cosmology, Chestnut Ridge Research Building,Morgantown, WV 26505, USA School of Physics, University of Melbourne, Parkville VIC 3010, Australia
Abstract.
PSR B1828 −
11 is a young pulsar once thought to be undergoing free precessionand recently found instead to be switching magnetospheric states in tandem with spin-downchanges. Here we show the two extreme states of the mode-changing found for this pulsar andcomment briefly on its interpretation.
Keywords. pulsars: individual (PSR B1828 −
1. Introduction
PSR B1828 −
11 is young pulsar with a spin period of 0.405 s and DM of about 160 pc cm − (Clifton et al. 1992). Years of routine observations with the Jodrell Bank Observatoryshowed that its period derivative varied with an approximately dual-sinusoidal patternwith periods of about 500 and 250 days. At the same time, the profile was seen to varybetween “wide” and “narrow” states, with the average profile shape following the samepattern as ˙ P . These phenomena were initially interpreted as evidence for free precession(Stairs, Lyne & Shemar 2000) and an abundant literature sprang up (e.g., Link 2006)attempting to understand such precession given the standard picture of the superfluidneutron-star interior with vortices pinned to the crust (e.g., Sedrakian, Wasserman &Cordes 1999).The recognition of a difference of 50% in spin-down rate in PSR B1931+24 when thatintermittent pulsar was in one of its weeks-long off states (Kramer et al. 2006) led toa new interpretation for these and other pulsars: namely that the changes in ˙ P wererelated to abrupt switches in the profile state, a phenomenon labeled “magnetosphericswitching” (Lyne et al. 2010). PSR B1828 −
11 was also noted to show evidence of rapid1 a r X i v : . [ a s t r o - ph . H E ] M a r I. H. Stairs et al.
Figure 1.
Narrow (1) and wide (0) states identified for the long data sets at differentobserving epochs. The last 4 epochs were observed with the GBT; the rest with Parkes. profile changes, as in mode-changing pulsars. Meanwhile, other authors continued todevelop alternative models for the effects seen in PSR B1828 −
11, including free precessioncombined with magnetospheric switching (Jones 2012) and non-radial oscillations (Rosen,McLaughlin & Thompson 2011). Seymour & Lorimer (2013) found evidence that the ˙ P variations are consistent with behaviour seen in low-dimensional chaotic systems. Theiranalysis suggests that the variations could be produced by a coupled system of threedifferential equations with ˙ P as one of the governing variables controlling the changes inthe pulsar. SR B1828 − Figure 2.
Cumulative narrow (solid) and wide (dashed) profiles for data taken with Parkes onMJD 52466.
2. Data and Results
We obtained long (generally multi-hour) 1400-MHz observations of PSR B1828 − P variations as determined by Lyneet al. (2010). On 16 occasions we used the Parkes telescope, employing the 2 × × µ s sampling. Each observation was folded with 10-second sub-integrations using dspsr (van Straten & Bailes 2011) and wide and narrowprofiles were identified by eye using viewing programs from the PSRCHIVE distribution(van Straten, Demorest & Os(cid:32)lowski 2012).Full details of the data acquistion, reduction, analysis and interpretation will be shortlybe presented elsewhere (Stairs et al., in prep.). Here we present a subset of the results.Mode-changing is seen in many of the long observations, while other days show onlynarrow or only wide profiles. Fig. 1 summarizes the states seen on each day. It is clearthat the transition rate of the mode changes varies as well as the average profile shape. I. H. Stairs et al.Fig. 2 show the profiles observed with Parkes on MJD 52466. These were obtainedby summing, respectively, all the 10-s sub-integrations labeled “narrow” or “wide” onthat day. The flux density is uncalibrated. The cumulative profile for each Parkes epochis well-described as a linear combination of these two extreme profiles; the GBT dataare similarly well-described using one day’s extrema. This agreement with two extremeprofiles argues strongly against the precession model, in which one would expect smoothchanges.The mode-changing transition rate has a relationship to the ˙ P cycle which may indicatethat this quantity forms the second governing variable in the chaos model; see Stairs etal. (in prep.) for a complete discussion. We advocate that other pulsars with known ˙ P quasi-periodicities be carefully examined for evidence of variable rates of mode-changing. Acknowledgements
IHS is supported by an NSERC Discovery Grant and by the Canadian Institute forAdvanced Research. JvL received funding for this research from the Netherlands Or-ganisation for Scientific Research (NWO) under project ”CleanMachine” (614.001.301).The Green Bank Observatory is a facility of the National Science Foundation operatedunder cooperative agreement by Associated Universities, Inc. The Parkes radio telescopeis part of the Australia Telescope National Facility which is funded by the AustralianGovernment for operation as a National Facility managed by CSIRO. We thank RyanHyslop, Jennifer Riley, Raymond Lum and Cindy Tam for their work on earlier versionsof the profile analysis.