Simultaneous multi-frequency imaging of the nucleus of NGC 1275

Extract

An unusual counterjet feature was discovered in 3C 84, the compact radio nucleus of NGC 1275, in the “First Science” observations on the VLBA at 8.4 GHz (Walker et al., 1994), and simultaneously in Global VLBI observations at 22 GHz (Vermeulen et al., 1994). Comparison of these images indicated a strongly inverted spectrum in this feature, but the interpretation was clouded by the two-year difference between the epochs of observation. To resolve this ambiguity, and to study the spectrum of the counterjet, we exploited the capabilities of the VLBA to make nearly simultaneous observations of 3C 84 at 2.3, 5.0, 8.4, 15.4, 22, and 43 GHz, in four apparitions over a 16-day period in January 1995. These observations also served to continue structural monitoring programs at 15 and 22 GHz. This paper presents preliminary images from those observations. A companion contribution by Walker et al. (1995) discusses the interpretation of the images.