Mode changing and giant pulses in the millisecond pulsar PSR B1957+20

TL;DR

This study reveals that the millisecond pulsar PSR B1957+20 exhibits rapid mode switching between two emission states, with correlated changes in giant pulse properties, providing new insights into pulsar emission mechanisms.

Contribution

First observation of mode changing in a millisecond pulsar, showing rapid switching and correlation with giant pulse characteristics, expanding understanding of pulsar emission behavior.

Findings

Mode switching occurs every 1.7 seconds, the shortest observed so far.

Giant pulse rate and phase depend on the emission mode.

Energy distribution of giant pulses varies with mode.

Abstract

Many radio pulsars have stable pulse profiles, but some exhibit mode changing where the profile switches between two or more quasi-stable modes of emission. So far, these effects had only been seen in relatively slow pulsars, but we show here that the pulse profile of PSR B1957+20, a millisecond pulsar, switches between two modes, with a typical time between mode changes of only $1.7$ s (or $\sim\!1000$ rotations), the shortest observed so far. The two modes differ in both intensity and polarization, with relatively large differences in the interpulse and much more modest ones in the main pulse. We find that the changes in the interpulse precede those in the main pulse by $\sim\!25$ ms, placing an empirical constraint on the timescale over which mode changes occurs. We also find that the properties of the giant pulses emitted by PSR B1957+20 are correlated with the mode of the regular emission: their rate and the rotational phase at which they are emitted both depend on mode. Furthermore, the energy distribution of the giant pulses emitted near the main pulse depends on mode as well. We discuss the ramifications for our understanding of the radio emission mechanisms as well as for pulsar timing experiments.