THE MASSIVE BLACK-HOLE IN THE CENTER OF THE ACTIVE GALAXY MRK421

We report the observation of a dramatic outburst in the optical band f rom the active galaxy Markarian 421 (Mrk 421). During this outburst, t he brightness of Mrk 421 increased rapidly by 1.34mag from B=15.67 to B=14.32 in 26 minutes. Another interesting fact is that this extremely rapid burst in the optical band is similar to the dramatic outburst o f TeV photons which was obtained by Gaidos et al. (1996) in every esse ntial respect, for example, the time scales on which they vary, and th e shapes of the light curves. These data in the optical band and TeV g amma-ray suggest that they are both produced in the same emission regi on, and that the emission region is extremely small, R approximate to 1.23 x 10(14) cm. With these results, we prove that there is a massive black hole with M = 2 x 10(6) M. in the centre of Mrk 421. We obtaine d also a important result R=205R(g) > 200R(g) (Sunyaev 1975). This cou ld provide a new challenge for current theoretical model of such emiss ions. We prove that the origin of TeV gamma-ray is by Synchrotron self -Compton.