ИСТИНА

The eclipsing system SS 433 (V1343 Aql) with moving emission lines in the spectrum consists of an A4-A8 giant (Gies et al., 2002) and a neutron star (Goranskij, 2013). The moving components of Balmer and He I lines are formed by a pair of oppositely directed, highly collimated and precessing relativistic jets of gas moving with a velocity of 0.26 c. The orbital period of 13.082 day, the jet precession period 162 days, and jet nodding period 6.28 day are present in both photometric and spectroscopic data. The star is located in the center of radio structure W50 interpreted as a 10000-year old supernova remnant. We present the results of forty-year monitoring, which includes multicolor photometry and synoptic observations analyzed along with fragmentary spectroscopic and radio data. Photometry shows secular trend towards decreasing amplitudes of all periodic variations by about 40 percent. We observed episodes of eclipse disappearance during several orbital periods. We explain such episodes as consequence of a sporadically forming common envelope, when Roche lobe of the neutron star is overfilled. Then gas flows in the circumbinary extended and precessing disk (earlier described by Barnes et al., 2002) through the Lagrangian point L2. We observed also episodes of blocking the jets by the common envelope, the explosive ejection of the common envelope, and recovery of the jets. These phenomena suggest that the mass transfer from the A-type companion passes into a dynamical timescale.