Investigation of Emission States of PSR J1722-3207

We have conducted a detailed study of single-pulse emission from PSR J1722-3207, which was observed at 1369 MHz using the Parkes 64 m radio telescope. PSR J1722-3207 has an asymmetric two-component mean pulse profile. We find that the brighter leading component exhibits a periodic phase-stationary nondrift amplitude modulation while the trailing component remains unchanged. As a result of this, this pulsar switches between a strong state and a weak emission state periodically. Spectral analysis of the fluctuations showed that the modulation period is very short (similar to 2.0 s or 20P), where P is the rotation period of the pulsar. The polarization properties of the strong and weak states were investigated. The swings in the position angle of the two states are similar, suggesting that their basic emission geometry is the same. At present, it is difficult to explain the periodic mode-changing phenomenon observed in this pulsar with existing subpulse drifting models.