Highly Polarized Emission from the E-Hotspot in DA240

Extract

The hotspot in the eastern lobe of the nearby giant radio galaxy DA240 (z=0.0356) provides a rare opportunity to examine the detailed polarization structure of a hotspot. Maps have been made with the Cambridge 5-km telescope at 2.7 and 5.0 GHz. The 5.0-GHz maps are shown in Figs 1 and 2. The main characteristics are: (a) The hotspot has an overall size in the 2.7-GHz map of 10×18 kpc². It blends smoothly at its outer edge into the background of the extended lobe. The 5.0 GHz total intensity map shows a yet more compact region (subcomponent A). It has not been fully resolved in the direction of the minor axis and has a size <1×2.5 kpc². There is a second much weaker and diffuse region (subcomponent B). Both subcomponents are superimposed on a broad plateau of emission. The hotspot has spectral index α(0.61–5.0)=0.52, minimum total energy E_min=3×10⁵⁶ ergs and equipartition magnetic field B_eq=2×10⁻⁵ G, values typical of other hotspots, although its projected distance from the nucleus is very large (0.65 Mpc);