THE HOST OF B2-0828+32, A RADIO GALAXY WITH 2 SETS OF RADIO LOBES

B2 0828+32 is one of the few radio galaxies with two double lobe radio structures of different ages and oriented at widely different angles, indicating that the direction of the radio jet has changed with time. Recent spectral index maps set an age for the particles in the old lo bes of 70 Myears which is therefore also the maximum age of the young lobes. This sets a constraint on the time scale of the phenomenon whic h caused the change of radio axis direction. We have obtained deep CCD images, in V and R, of the host galaxy of B2 0828+32 in a search for signatures of a recent merger event. We find that the galaxy shows a r egular morphology with no signs of a recent major merger. It has no do uble core or companion brighter than M(v) = -16.7, within 38 kpc. This is in contrast with the best known radio galaxies of this type, 3C 31 5 and B2 0055+26, which both belong to a close pair of ellipticals. Th e luminosity profile follows the de Vaucouleurs r(1/4) profile with so me discrepancy at radii less than similar to 15 arcsec which could be a weak sign of a merger less than or similar to 10(8) years ago. We co nsider the scenario where the radio source is powered by a rotating bl ack hole and the radio axis is aligned along the spin axis of the blac k hole. We discuss the case where the change of the radio axis directi on was caused by accretion by the black hole following a merger event. The direction of the radio axis is changed when the accreted material arrives at the black hole with an angular momentum axis very differen t from the spin axis of the black hole and is at least equal to the in itial black hole mass. The minimum mass doubling time of a black hole corresponds to the Eddington accretion rate and is t similar to 31 Mye ars (independent of the mass). The maximum age of the young lobes, 70 Myears, constrains the accretion rate to be of the order of the Edding ton rate. The present luminosity of the radio galaxy is much below the Eddington luminosity of even a small 10(6) M(.) black hole, suggestin g that the fuel is now exhausted.