VARIABLE RADIO ECHOES FROM A JET IN QSO-0957+561

Time delay determinations in astrophysics are used most often to find time delays between flux density variations of different spectral band s and/or spectral lines in AGNs and different images of gravitationall y lensed QSOs. Here we consider a new algorithm for a complex case, wh en the time delay is itself a linear function of time and the intensit y of echo response is power function of the delay. We apply this metho d to investigate optical-to-radio delay in the double quasar 0957+561, which is a generally accepted case of gravitational lensing. Radio-op tical correlation in QSO 0957+561 was first reported by Oknyanskij and Beskin (1993, hereafter OB) on the basis of radio observations made i n the years 1979 to 1990. OB used an idea to take into account the kno wn gravitational lensing time delay to get combined radio and optical light curves and then to use them for determination of the possible ra dio-from-optical time delay. It was found this way that radio variatio ns (5 MHz) followed optical ones by about 6.4 years with high level of correlation (approximate to 0.87). Using new radio data (Haarsma et a l., 1996), for the interval 1979-1994 we find nearly the same value fo r the optical-to-radio delay as has been found before. Additionally we suspect that the time delay value is linearly increasing at about 110 days per year while the portion of reradiated flux in the radiorespon se is decreasing. Obtained results indicate that the optical and radio emitting regions are physically related, but have distinct size scale s, locations and possibly radiation mechanisms. We conclude that the r esults can be explained by simple model were the variable radio source is ejected from the central part of the QSO compact component and tha t the changing time delay between the optical and radio light curves i s consequence of light travel effect.