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Astron. Astrophys. 334, L29-L31 (1998)

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Letter to the Editor

The massive black hole in the center of the active galaxy Mrk 421

G.Z. Xie 1, 2, J.M. Bai 1, X. Zhang 1, 4 and J.H. Fan 3

1 Yunnan Astronomical Observatory, The Chinese Academy of Sciences, Kunming, 650011, P.R. China (gzxie@public.km.yn.cn)
2 United Laboratory of Optical Astronomy, The Chinese Academy of Sciences (ULOAC)
3 Astrophysical Center, Guangzhou Teacher's College, Guangzhou 510400, P.R. China
4 Department of physics of Yunnan Normal University, Kunming, P.R. China

Received 11 March 1998 / Accepted 31 March 1998


We report the observation of a dramatic outburst in the optical band from the active galaxy Markarian 421 (Mrk 421). During this outburst, the 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 of TeV photons which was obtained by Gaidos et al. (1996) in every essential respect, for example, the time scales on which they vary, and the shapes of the light curves. These data in the optical band and TeV [FORMULA] -ray suggest that they are both produced in the same emission region, and that the emission region is extremely small, [FORMULA] cm. With these results, we prove that there is a massive black hole with [FORMULA] in the centre of Mrk 421. We obtained also a important result R=205 [FORMULA] (Sunyaev 1975). This could provide a new challenge for current theoretical model of such emissions. We prove that the origin of TeV [FORMULA] -ray is by Synchrotron self-Compton.

Key words: BL Lacertae objects: individual: Mrk 421 – fl-rays: theory – galaxy: photometry

Send offprint requests to: J.M. Bai

© European Southern Observatory (ESO) 1998

Online publication: May 12, 1998