POLARIZED QUASIPERIODIC STRUCTURES IN PULSAR RADIO EMISSION REFLECT TEMPORAL MODULATIONS OF NON-STATIONARY PLASMA FLOW

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 s resolution polarimetric observations of 11 P-band and 32 L-band pulsars with period...

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Bibliographic Details
Published in:The Astrophysical journal 2015-06, Vol.806 (2), p.1-25
Main Authors: Mitra, Dipanjan, Arjunwadkar, Mihir, Rankin, Joanna M.
Format: Article
Language:English
Subjects:
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
COHERENT RADIATION
EMISSION
Fluctuation
FLUCTUATIONS
INDIUM FLUORIDES
MAGNETOHYDRODYNAMICS
magnetohydrodynamics (MHD)
Microstructure
Modulation
PERIODICITY
PLASMA
plasmas
PULSARS
pulsars: general
radiation mechanism: non-thermal
Radio emission
STOKES PARAMETERS
Temporal logic
Time
TIME RESOLUTION
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Summary: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 s resolution polarimetric observations of 11 P-band and 32 L-band pulsars with periods ranging from 150 ms to 3.7 s. These higher-frequency observations form the most reliable basis for detailed microstructure studies. Close inspection of individual pulses reveals that most pulses exhibit quasi-periodicities with a well-defined periodicity timescale ( P ). While we find some pulses with deeply modulating microstructure, most pulses show low-amplitude modulations on top of broad smooth subpulse 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 P via autocorrelation analysis. We find that the microstructure timescale P 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 P 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, P reflects the temporal modulation of non-stationary plasma flow.
ISSN:0004-637X
1538-4357
1538-4357
DOI:10.1088/0004-637X/806/2/236