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Savitribai Phule Pune University All Models Are False, Some Are Useful

Technical Report CMS-TR-20150223


Title Polarized quasiperiodic structures in pulsar radio emission reflect temporal modulations of non-stationary plasma flow
Author/s Dipanjan Mitra
National Centre for Radio Astrophysics, Pune 411 007, India


Mihir Arjunwadkar
Centre for Modeling and Simulation, Savitribai Phule Pune University, Pune 411 007, India


Joanna Rankin
Department of Physics, University of Vermont, Burlington, VT 05405 USA
Abstract Bright single pulses of many radio pulsars show rapid intensity fluctuations (called microstructure) when observed with time resolutions of tens of microseconds. Here, we report an analysis of Arecibo 59.5 μsec-resolution polarimetric observations of 11 P-band and 32 L-band pulsars with periods ranging from 150 msec to 3.7 sec. These higher frequency observations forms the most reliable basis for detailed microstructure studies. Close inspection of individual pulses reveals that most pulses exhibit quasiperiodicities with a well-defined periodicity timescale (Pμ). While we find some pulses with deeply modulating microstructure, most pulses show low-amplitude modulations on top of broad smooth subpulses features, thereby making it difficult to infer periodicities. We have developed a method for such low-amplitude fluctuations wherein a smooth subpulse envelope is subtracted from each de-noised subpulse; the fluctuating portion of each subpulse is then used to estimate Pμ via autocorrelation analysis. We find that the microstructure timescale Pμ is common across all Stokes parameters of polarized pulsar signals. Moreover, no clear signature of curvature radiation in vacuum in highly resolved microstructures was found. Our analysis further shows strong correlation between Pμ and the pulsar period P. We discuss implications of this result in terms of a coherent radiation model wherein radio emission arises due to formation and acceleration of electron-positron pairs in an inner vacuum gap over magnetic polar cap, and a subpulse corresponds to a series of non-stationary sparking discharges. We argue that in this model, Pμ reflects the temporal modulation of non-stationary plasma flow.
Keywords magnetohydrodynamics (MHD); plasmas; pulsars: general; radiation mechanism: non-thermal
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Citing This Document Dipanjan Mitra, Mihir Arjunwadkar, and Joanna Rankin , Polarized quasiperiodic structures in pulsar radio emission reflect temporal modulations of non-stationary plasma flow . Technical Report CMS-TR-20150223 of the Centre for Modeling and Simulation, Savitribai Phule Pune University, Pune 411007, India (2015); available at http://cms.unipune.ac.in/reports/.
Notes, Published Reference, Etc. Published as The Astrophysical Journal 806(2), 236 (2015)
Contact dmitra AT ncra.tifr.res.in, mihir AT cms.unipune.ac.in, Joanna.Rankin AT uvm.edu
Supplementary Material Please click on the links below to download pulsarwise
average profiles (4.1M), and
microstructure timescale analysis results (510M)
for pulsars in this study. A description of this supplementary information (which is part of the main paper) can be found here (1.9M). Additional profile-specific information can be found in the README file inside the first tarball above.


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