# Periodic Q-mode modulation in PSR J1825$-$0935 (PSR B1822$-$09)

## TL;DR

This study reveals that PSR J1825$-$0935 exhibits a periodic, longitude-stationary intensity modulation in both interpulse and main pulse, with a period of about 43 rotation periods, and shows phase-locked modulation patterns confirmed through high-sensitivity observations.

## Contribution

The paper demonstrates that the periodic Q-mode modulation in PSR J1825$-$0935 is a longitude-stationary intensity modulation, clarifying its nature and phase-locking, differing from earlier interpretations of drifting subpulses.

## Key findings

- Modulation period is about 43 P1.
- Interpulse and main pulse modulations are phase-locked.
- Polarization differs between strong and weak Q-mode states.

## Abstract

PSR J1825$-$0935 (PSR B1822$-$09) switches between radio-quiet (Q-mode) and radio-bright (B-mode) modes. The Q-mode is known to have a periodic fluctuation that modulates both the interpulse and the main pulse with the same period. Earlier investigators argued that the periodic Q-mode modulation is associated with drifting subpulses. We report on single-pulse observations of PSR J1825$-$0935 that were made using the Parkes 64-m radio telescope with a central frequency of 1369 MHz. The high-sensitivity observations revealed that the periodic Q-mode modulation is in fact a periodic longitude-stationary intensity modulation occurring in the interpulse and the main pulse. The fluctuation spectral analysis showed that the modulation period is about $43 P_1$, where $P_1$ is the rotation period of the pulsar. Furthermore, we confirm that the modulation patterns in the interpulse and the main pulse are phase-locked. Specifically, the intensities of the interpulse and the immediately following main pulse are more highly correlated than for the main pulse and interpulse at any other lag. Polarization properties of the strong and weak Q-mode states are different, even for the trailing part of the main pulse which does not show the periodic intensity modulation.