Vol 21, No 9 (2021) / Han

Frequency dependence in the emission from subpulse drifting pulsars

Xiao-Hong Han, Rai Yuen

Abstract

We investigate relations in the emission properties as revealed by drifting subpulses detected at different observing frequencies based on the method that incorporates the rotating carousels in pulsar magnetospheres of multiple emission states. An emission state is associated with particular emission properties as determined by the drifting subpulses at a particular frequency, and different emission states obtained at different frequencies reveal the variation of emission properties across the emission region. The method allows the determination of the essential radio emission properties such as the relative emission height, subpulse number, charge density and the plasma flow relative to corotation in an emission region for a particular frequency. We apply the method to seven pulsars that exhibit subpulse drifting along single drift-band at 326 MHz and 1429 MHz. Our results show that drifting subpulses observed at different frequencies correspond to particular emission states suggesting that the pulsar emission properties are frequency dependent. We show that emission follows the frequency-to-radius mapping for pulsars with obliquity angle \(\geq30^{\circ}\) regardless of the sign and magnitude of the drift-rate. For pulsars with long rotation periods in our sample, the circulation time for the plasma to revolve once around the magnetosphere relative to corotation increases as the rotation period increases at both frequencies, but exhibits irregularity for pulsars with short rotation periods. Our results suggest that evolution of the obliquity angles in subpulse drifting pulsars is from large to small, and the emission region tends to be ‘thicker’ in younger pulsars.

Keywords


radiation mechanisms: non-thermal — pulsar: general

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DOI: https://doi.org/10.1088/1674-4527/21/9/228

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