2004IAUC.8403....1C

G. Cimo, S. Ellingsen, S. Carter, and P. McCulloch, University of Tasmania; and D. Jauncey and J. Lovell, Australia Telescope National Facility, CSIRO, write: "We have observed a new episode of rapid variability in the flux density of the quasar PKS 0405-385 on hourly time scales. VLBI observations with the Australian Long Baseline Array at 2.2 GHz in Apr. 2004 revealed variations at a level of 10 percent with a period of 2 hr superimposed on a mean flux density of about 1.6 Jy. Observations at 6.7 GHz with the University of Tasmania Ceduna 30-m radio telescope over 10 days in August show that this variability currently continues. Since its discovery in 1996 (IAUC 6418), PKS 0405-385 has shown episodic periods of extremely fast (intra-hour) variability at centimeter radio wavelengths due to interstellar scintillation. The source has alternated between long periods (years) of quiescence and short (a few months) periods of intense activity. The reasons for the sudden change in behavior are not understood, and observations at radio and other wavelengths during the current active phase are encouraged."