Search for superrapid variability and UBVR-photometry of A0620-00

Electrophotometrical observations of A0620-00 system, whose compact element is probably a black hole, have been made within the framework of MANIA experiment on the 6-m telescope of the SAO, USSR AS. Four extremely fast events - double superrapid flares of 0.5-5 ms duration and 0.1-1ms duration of the leading fronts have been detected. Low estimates of the brightness temperature in the zones of flare generation are 109-1011 K. These data show evidence for probable realization of nonthermal processes in A0620-00 system in course of accretion onto a black hole. In the following observations no variability in the range 5x10-7-60s has been detected. The restrictions of relative power of the variable component are 90% to 3%, respectively. Using the results of UBVR-photometry of A0620-00 the contribution of the disk radiation around the component into the total luminosity system is estimated