Magnetic AB stars are known to produce periodic radio pulses by the electron cyclotron maser emission (ECME) mechanism. Only 19 such stars, known as ‘Main-sequence Radio Pulse emitters’ (MRPs) are currently known. The majority of MRPs have been discovered through targeted observation campaigns that involve carefully selecting a sample of stars that are likely to produce ECME. The alternative is to use all-sky surveys. Until now, MRP candidates obtained from surveys were identified based on their high circular polarisation (>30%).

Das et al. introduce a complementary strategy, which does not require polarisation information. Using multi-epoch data from the Australian SKA Pathfinder (ASKAP) telescope, they identify four MRP candidates based on the variability in the total intensity light curves. Follow-up observations with the ATCA confirm three of them to be MRPs, thereby demonstrating the effectiveness of the strategy.

The figure above shows the ATCA dynamic spectra of one candidate MRP, HD 149764, in Stokes I (total intensity) and Stokes V (circular polarisation) over 1–3 GHz, averaged with 5 minute time resolution and 32 MHz frequency resolution.  The curve patterns in the top panel (Stokes I) are due to contamination from other sources in the field (rather than emission from our target). Since these emissions are not circularly polarized, the bottom panel (Stokes V) remains free of contamination, clearly highlighting pulses from HD 149764.  The star exhibits two pulses both of which are left circularly polarised, which confirms that the star is an MRP. The pulses sweep in opposite directions on the frequency-time plane, which is expected to arise from geometric effects.