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Astron. Astrophys. 351, 21-30 (1999)

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3. Light curves

Fig. 1 presents the light curve of the nucleus of NGC 1275, obtained by Lyuty (Nesterov et al., 1995) in 1968-1994. It shows week averaged fluxes (F, mJy). One can see that a period of high activity was observed in 1968-1980, and from the end of the seventies the nucleus is in the long minimum of brightness. Our two observing runs shown by brackets were made in the period of a gradual decrease of the nucleus brightness. Fig. 2 presents the light curves of the NGC 1275 nucleus, obtained at the first run (1982-1987) from observations in the spectral region [FORMULA] 5200 Å and at the second run (1989-1994) - from the UBVRI system. The data in Fig. 2 do not show a systematic trend of the flux variations with time. But variations of the nucleus brightness during the separate nights are clearly seen. The character of the variability is dominated by rapid outbursts, exceeding the luminosity of the quiescent state by more than 20%.

[FIGURE] Fig. 1. Light curve of the NGC 1275 nucleus, representing week averaged fluxes in filter V according to Nesterov et al. (1995). Two periods of Crimean observations are shown by two brackets.

[FIGURE] Fig. 2. Light curves of the NGC 1275 nucleus. Continuum flux near [FORMULA] 5200 Å was obtained in 1982-1987 by Merkulova et al. (1987, 1988, 1992), dimension of one circle equals to about [FORMULA]. UBVRI fluxes for 1989-1994 were obtained by Merkulova & Metik (1995, 1996), Pronik et al. (1998), dimension of one circle equals to about 3[FORMULA].

It is evident from Table 1, that the intranight activity of the nucleus of NGC 1275, when SD[FORMULA] 3 [FORMULA], was observed in 8% of the nights of observations during 1982-1987. One can conclude that the duty cycle of the intranight variations was 0.08.

We study the character of the flux variations of the NGC 1275 nucleus by means of SF analysis. It is a powerful tool to measure time variations of sources on different scales especially if the data are spaced rather inhomogeneous by time.

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© European Southern Observatory (ESO) 1999

Online publication: November 2, 1999