On the origin of the bi-drifting subpulse phenomenon in pulsars

Abstract

The unique and highly unusual drift feature reported for PSR J0815+0939, wherein one component's subpulses drift in the direction opposite of the general trend, is a veritable challenge to pulsar theory. In this paper, we observationally quantify the drift direction throughout its profile, and find that the second component is the only one that exhibits "bi-drifting", meaning that only second component moves in the direction opposite of the others. We here present a model that shows that the observed bi-drifting phenomenon follows from the insight that the discharging regions, i.e. sparks, do not rotate around the magnetic axis per se, but rather around the point of electric potential extremum at the polar cap: minimum in the pulsar case ($\mathbf{\Omega }\cdot \mathbf{B}<0$) and maximum in the antipulsar case ($\mathbf{\Omega }\cdot \mathbf{B}>0$). We show that a purely dipolar surface magnetic field cannot exhibit bi-drifting behaviour, though certain non-dipolar configurations can. We can distinguish two types of solutions, with relatively low ($\sim 10^{12}\mathrm{G}$) and high ($\sim 10^{14}\mathrm{G}$) surface magnetic fields. Depending on the strength of the surface magnetic field, the radius of the curvature of magnetic field lines ranges from $10^5\mathrm{cm}$ to $10^7\mathrm{cm}$. Pulsar \J~allows us to gain an understanding of the polar-cap conditions essential for plasma generation processes in the inner acceleration region, by linking the observed subpulse shift to the underlying spark motion.

14 pages, 21 figures, published in ApJ, editorial and erratum corrections added

References in corpus (5)

• The subpulse modulation properties of pulsars at 92 cm and the frequency dependence of subpulse modulation
• Investigation of the bi-drifting subpulses of radio pulsar B1839-04 utilising the open-source data-analysis project PSRSALSA
• Deep Analyses of Nulling in Arecibo Pulsars Reveal Further Periodic Behavior
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Cited by in corpus (19)

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• The Period-Width relationship for radio pulsars revisited
• The Thousand-Pulsar-Array programme on MeerKAT -- VIII. The subpulse modulation of 1198 pulsars
• Mode switching and oscillations in PSR B1828-11
• Subpulse Drifting, Nulling and Mode changing in PSR J2006$-$0807 with Core emission
• A Mechanism of Spark Motion in Inner Acceleration Region to Investigate Subpulse Drifting in Pulsars
• Characterising the nature of Subpulse Drifting in Pulsars
• Single pulse modeling and the bi-drifting subpulses of radio pulsar B1839-04
• B0943+10: low-frequency study of subpulse periodicity in the Bright mode with LOFAR
• MeerKAT observations of the reversing drifting subpulses in PSR J1750-3503
• Two Dimensional Configuration and Temporal Evolution of Sparking discharges in Pulsars
• Estimating the evolution of Sparks in Partially Screened Gap of Pulsars from Subpulse Drifting
• Quasi-regular variations of subpulse drifting for PSR J1857+0057
• Expected imprints of the carousel in multi-frequency pulsar observations and new evidence for multi-altitude emission
• Individual pulse emission from the diffuse drifter PSR J1401$-$6357 using the ultrawideband receiver on the Parkes radio telescope
• New upper limits on low-frequency radio emission from isolated neutron stars with LOFAR
• Properties of the emission region in pulsars with opposite subpulse drift directions in different profile components