Expected imprints of the carousel in multi-frequency pulsar observations and new evidence for multi-altitude emission

Abstract

Subpulse modulation has been regarded as one of the most insightful and intriguing aspects of pulsar radio emission. This phenomenon is generally explained by the presence of a carousel of sparks in the polar acceleration gap region that rotates around the magnetic axis due to the E$\times$B drift. While there have been extensive single pulse studies, geometric signatures of the underlying carousel, or lack thereof, in simultaneous multi-frequency observations have remained largely unexplored. This work presents a theoretical account of such expected signatures, particularly that of a geometry induced phase-offset in subpulse modulation, including various formulae that can be readily applied to observations. A notable result is a method to resolve aliasing in the measured subpulse modulation period without relying on knowledge of the viewing geometry parameters. It is also shown in detail that the geometry induced phase-offset enables critical tests of various observed phenomena as well as proposed hypotheses, e.g., multi-altitude emission, magnetic field twisting, pseudo-nulls, etc., in addition to that of the carousel model itself. Finally, a detailed analysis of a 327 MHz pulse-sequence of PSR B1237+25 is presented as a case study to test the single-frequency multi-altitude emission scenario. The analysis provides a firm evidence of inner and outer conal components of this pulsar to have originated from the same carousel of subbeams and emitted at different heights.

arXiv commentAccepted for publication in ApJ

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Cited by in corpus (5)

• Pulsars with NenuFAR: backend and pipelines
• Revisiting the sub-pulse drifting phenomenon in PSR J1822-2256: Drift Modes, Sparks, and Emission Heights
• Single pulse modeling and the bi-drifting subpulses of radio pulsar B1839-04
• Circular polarization in radio pulsar PSR B1451-68: coherent mode transitions and intrabeam interference
• Testing the circularity of PSR B0818-41's carousel