1. Analysis of strong outbursts in selected blazars. Pyatunina T.B., Kudryavtseva N.A., Gabuzda D.C., Jorstad S.G., Aller M.F., Aller H.D., Terasranta H.

2. Two types of outbursts (Pyatunina et al., 2000, A&A, 358,451; Zhou et al. 2000, ApJ, 540, L13) Core outbursts : show frequency-dependent time-delays; are associated with core’s brightening due to primary perturbation. Jet outbursts : arise nearly simultaneously at all frequencies; are connected with structure evolution due to propagation of the perturbation down the jet.

3. What can be found? Frequency dependent time lags can be used for testing models of non-thermal emission (Lobanov, 1998, A&A, 330, 79; Marscher 2001, ASP Conf.Ser.,224, 23) Interval between two subsequent core outbursts defines a time scale of activity cycle as a whole (from origin primary perturbation to it’s drowing in quiescent jet).

4. Monitoring Data Radio Astronomical Observatory of the Michigan University, USA (Aller H.D., Aller M.F., Latimer G.E., Hodge P.E. 1985, ApJS 59,513) Metsahovi Radio Observatory, Finland (Terasranta H., et al. 1992, A&AS, 94, 121)

5. 0458-020 “A” –core outburst; “B” and “C” – jet outbursts. Activity time scale ≥ 15 yr. ● - 37 GHz ● - 22 GHz ● - 14.5 GHz ● - 8 GHz ● - 4.8 GHz AA B B  C C 

6. 0528+134 Total duration of activity cycle may be ≤14 yr (1976-1990; 1990-2004). The period (1976-1990) can be classified as a period of high core activity due to ejection of several new components and the core flux density variations ( Britzen et al. 1999,A&A, 341, 418). Next period of high activity (1990-2004) reveals numerous narrow outbursts, or rather “spikes” in some composite event as spectral evolution testifies (Pyatunina et al. in prep.)

7. 0528+134 The spikes D,E and F show convincing time-lags and are classified as “core outbursts”. Higher frequency data are necessary for determination of time-lags for spikes A,B and C, as can be seen from evolution of their spectra (Pyatunina et al. in prep. ).

8. 1730-130, NRAO 530 Extremely narrow feature has been observed in 1995 at 230 GHz (Bower et al. 1997, ApJ, 484, 118, brown ). The fine structure is unresolved at lower frequency and time-lags are determined for the outburst as a whole. Core outburst

9. 2230+114, CTA 102 Three periods of activity with maxima near 1981, 1989 and 1997 are seen in the light curves of the source. Emission during active state consists of a sequence of narrow outbursts or rather “spikes” of variable amplitude.

10. 2230+114 Quasi-periodicity at mm- (left) and cm-wavelengths (right). Spikes A and B show frequency-dependent time-lags and can be classified as core outbursts. Spikes C and D are unresolved at cm-wavelength and their time-lags are uncertain.

11. 2230+114 Correlation between amplitudes of outbursts and time-lags: time-lags are longer for more powerful outbursts. Period 2: Amplitude of A2 spike at 37 GHz – 1.65 Jy Amplitude of B2 spike at 37 GHz – 1.75 Jy Period 3: amplitude of A3 spike at 37 GHz – 3.65 Jy amplitude of B2 spike at 37 GHz – 3.65 Jy

12. 2230+114 Due to dependence of time lags on frequency and amplitude of outbursts periodicity in appearance of spikes can be observed only on average.

13. Conclusions Frequency dependent time-lags are defined and approximated by exponential function of frequency; Delay of 4.8 GHz outburst relative to 37 GHz outburst varies from 0.3 to ~1.2 yr; Index of exponential function changes from -0.3 to 2.2; Outbursts in sources 0528+134 and 2230+114 split into narrow (~ 1 yr) spikes; Both time-lags and indexes of exponential functions changes from one spike to another.

14. 2230+114, CTA 102 Quasi-period in activity Bright outbursts in emission of CTA 102 repeat every (8.04±0.30) yr. First maximum in the next bright outburst is expected near 2005.5. Amplitudes of individual spikes within outbursts change but their relative positions are preserved. There is s correlation between time-lags and amplitudes of activity: brighter outbursts show greater time-lags.