Multi-frequency study of the peculiar pulsars PSR B0919+06 and PSR B1859+07

TL;DR

This study investigates the frequency-dependent emission properties of pulsars PSR B0919+06 and PSR B1859+07, revealing new emission modes, chromatic effects, and supporting a common underlying emission mechanism.

Contribution

It provides the first detailed multi-frequency analysis of swooshes and discovers a new emission mode in PSR B1859+07, supporting a unified emission model.

Findings

Emission during swooshes is not absent at low frequencies.

Pulses during swooshes show frequency-dependent offsets.

A new quasi-periodic emission mode was discovered in PSR B1859+07.

Abstract

Since their discovery more than 50 years ago, broadband radio studies of pulsars have generated a wealth of information about the underlying physics of radio emission. In order to gain some further insights into this elusive emission mechanism, we performed a multi-frequency study of two very well-known pulsars, PSR~B0919+06 and PSR~B1859+07. These pulsars show peculiar radio emission properties whereby the emission shifts to an earlier rotation phase before returning to the nominal emission phase in a few tens of pulsar rotations (also known as `swooshes'). We confirm the previous claim that the emission during the swoosh is not necessarily absent at low frequencies and the single pulses during a swoosh show varied behaviour at 220~MHz. We also confirm that in PSR~B0919+06, the pulses during the swoosh show a chromatic dependence of the maximum offset from the normal emission phase with the offset following a consistent relationship with observing frequency. We also observe that the flux density spectrum of the radio profile during the swoosh is inverted compared to the normal emission. For PSR~B1859+07, we have discovered a new mode of emission in the pulsar that is potentially quasi-periodic with a different periodicity than is seen in its swooshes. We invoke an emission model previously proposed in the literature and show that this simple model can explain the macroscopic observed characteristics in both pulsars. We also argue that pulsars that exhibit similar variability on short timescales may have the same underlying emission mechanism.