1995A&A...301...25P

Significant variability in the quasar 4C 38.41 is found at 92cm with the Westerbork Synthesis Radio Telescope (WSRT). In this paper, calibration techniques and the detection method for flux density variability are briefly described. A fractional variability of 13.1% was estimated during a 36-day period of observation, and the maximum percentage change in flux density over this period was about 18%. The computed brightness temperature T_B is ∼7.5x10¹⁸K in the co-moving frame, which significantly exceeds the inverse Compton limit. A Doppler factor of D∼195 would be required in terms of relativistic bulk motion. In addition, preliminary results from the analysis of another 14 short observations at 92cm with the WSRT fully confirm the detection of the rapid variability in 4C 38.41. The light curves of the quasars DA406 and 3C345, recorded in the same mosaic field, are also presented.