WNB0313- ANALYSIS OF A NEWLY DISCOVERED GIANT RADIO GALAXY(683 )

We present the results of a detailed analysis of the newly discovered 15' large radio galaxy WNB 0313+683. It has been discovered in the WEN SS and NVSS radio surveys, and has been identified with an optical gal axy at a redshift of 0.0901 +/- 0.0002. The linear size of the radio s tructure is 2.0 Mpc, which places it in the class of Giant Radio Galax ies (GRGs). Radio observations have been carried out with the WSRT at 1.4 GHz and with the 92-cm broadband system, with the 100-m Effelsberg telescope at 10.45 GHz and with the VLA at 1.4 GHz and 5 GHz. At 10.4 5 GHz the core is the dominant source structure, emitting similar to 2 5% Of the total flux. It has an inverted spectrum with a spectral inde x of alpha = +0.42 +/- 0.03 (S-nu proportional to nu(alpha)) between 1 .4 GHz and 10.45 GHz, suggesting a very compact structure, although we can not rule out variability of the core luminosity. The Rotation Mea sure distribution has been mapped using a new method and has been foun d to be very uniformly distributed over the source. It is therefore pr obably galactic in origin, with only a small contribution from the (su rroundings of the:) source itself. From the spectral index distributio n we have de;ermined an upper limit on the spectral age of 1.4 +/- 0.1 x 10(8) yrs. The particle density of the ambient medium, using ram-pr essure equilibrium at the hotspots, is greater than or similar to 1.6 x 10(-6) cm(-3) for the southern lobe and greater than or similar to 5 .8 x 10(-7) cm(-3) for the northern lobe. An independent measure of th e external density has been determined using the amount of depolarizat ion towards the southern lobe. This gives a density, averaged along th e line of sight, which is a factor of 10 higher (2.0 x 10(-5) cm(-3)) than the density near the head of the lobes found using the ram-pressu re arguments. This discrepancy might at least partly be the result of a contribution from internal depolarization, which we can not exclude on basis of our radio data. From spectroscopical observations of the h ost galaxy we find that the Hoc emission line has a broad component, a nd that the extinction must be large with colour index E(B - V) = 0.98 +/- 0.10 mag. Since the galactic latitude is +9.degrees 8, the extinc tion is probably mostly galactic in origin. We further find that WNB 0 313+683 has a very large optical emission line flux with respect to it s estimated jet power, when compared with the correlation between thes e two properties found by Rawlings Br Saunders (1991). We argue that t his, together with the relatively high radio power and the inverted ra dio spectrum of the radio core, is suggestive of a new phase of radio activity in WNB 0313+683.