Expected imprints of the carousel in multi-frequency pulsar observations and new evidence for multi-altitude emission. (arXiv:1812.01010v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Maan_Y/0/1/0/all/0/1">Yogesh Maan</a>
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.
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.
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