DETECTION OF EXTENDED OPTICAL-EMISSION ASSOCIATED WITH THE NORTHERN RADIO HOT-SPOT OF 3C-390.3

We present deep V, R, and I broadband CCD images of the northern radio lobe associated with the radio galaxy 3C 390.3. Spatially resolved em ission coincident with the brightest region of the northern lobe (hot spot B) is detected in all filters, with surface brightness V = 24.6 m ag arcsec(-2) and V-I color similar to 0.8. The new optical data, toge ther with the available radio and X-ray data for the hot spot, are com patible with a straight synchrotron spectrum of power-law index simila r to -0.8. The source of optical emission is extended, and its shape a nd size are in good agreement with those seen at radio wavelengths. Th e second brightest region in the northern lobe (head A) was not detect ed in any of the filters. The upper limit to its brightness is I simil ar to 23 mag.