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

## TL;DR

This paper explores the geometric signatures of pulsar carousel models in multi-frequency observations, introduces a method to resolve aliasing in subpulse periods, and provides evidence for multi-altitude emission in PSR B1237+25.

## Contribution

It offers a theoretical framework for detecting carousel signatures in multi-frequency pulsar data and presents a case study confirming multi-altitude emission in a specific pulsar.

## Key findings

- Identified geometry-induced phase-offset as a key signature of the carousel model.
- Developed a method to resolve aliasing without prior knowledge of viewing geometry.
- Provided evidence that different emission heights originate from the same carousel in PSR B1237+25.

## 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.