Multifrequency radio observations of 3C 31: a large radio galaxy with jets and peculiar spectra

Abstract

The radio source 3C 31 has recently been mapped with the Cambridge One-Mile Telescope at 0.4 and 1.4 GHz and with the 5-km Telescope at 2.7, 5.0 and 15 GHz. Jets have been found extending from opposite sides of an unresolved central source which is coincident with the galaxy NGC 383. The jets merge into complex outer regions of low surface brightness and total angular extent about 30 arcmin, much larger than shown by previous observations. Between 0.4 and 1.4 GHz, the spectra of the outer regions steepen with distance from the central source and the change in spectral index is ∼ 1.0. Results at 10 GHz from the 25-m Chilbolton telescope suggest that the spectra do not steepen further at higher frequencies, implying that the steepening cannot be attributed simply to energy losses in the radiating electrons.