Observations of radio pulses from CU virginis

The magnetic chemically peculiar star CU Virginis is a unique astrophysical laboratory for stellar magnetospheres and coherent emission processes. It is the only known main-sequence star to emit a radio pulse every rotation period. Here we report on new observations of the CU Virginis pulse profile in the 13- and 20-cm radio bands. The profile is known to be characterized by two peaks of 100 per cent circularly polarized emission that are thought to arise in an electron-cyclotron maser mechanism. We find that the trailing peak is stable at both 13 and 20 cm, whereas the leading peak is intermittent at 13 cm. Our measured pulse arrival times confirm the discrepancy previously reported between the putative stellar rotation rates measured with optical data and with radio observations. We suggest that this period discrepancy might be caused by an unknown companion or by instabilities in the emission region. Regular long-term pulse timing and simultaneous multiwavelength observations are essential to clarify the behaviour of this emerging class of transient radio source.