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


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Characteristics of the variability of the nucleus of NGC 1275 in the optical in 1982-1994

I.I. Pronik, N.I. Merkulova and L.P. Metik

Crimean Astrophysical Observatory, Crimea, Ukraine and Isaac Newton Institute of Chile, Crimean Branch

Received 26 August 1997 / Accepted 26 April 1999

Abstract

We study the variability of the nucleus of NGC 1275 in the optical region using two samples of the photoelectric observations obtained with the 1.25-m telescope of the Crimean Astrophysical Observatory. The first sample contains one series of 379 measurements of the nucleus brightness obtained with the scanning spectrophotometer during 35 nights from 12.XI.1982 to 23.X.1987. The slit [FORMULA] = 80 Å was centered at the wavelength [FORMULA] 5200 Å. The second sample contains 5 series of 820 measurements obtained simultaneously in each of the UBVRI bands during 37 nights from 22.XII.1989 to 29.XII.1994. The observations during one night lasted from 0.5 up to 8.7 hours. Each of the 6 independent observational series was analyzed separately.

An analysis has been made of the variations both on a time scale of years and of single nights (intra-night). Ratios of Standard Deviations (SD) of the variable flux to the error of the observations ([FORMULA]) were calculated for each night, and the parameters of Structure Functions (SF) were used as indications of the intranight variability. We assume that the intranight variations of the flux are real, when SD [FORMULA] 3[FORMULA]. There were 8% of such nights in 1982-1987, and about 40% of nights showed intranight variability in 1989-1994.

SFs of the intranight variations for all series of observations are characterized by the two slopes log(SF) [FORMULA] b log dt: for time scales less than 4 hours the slope is in the range 0.25[FORMULA]b[FORMULA]0.66, for the time scales less than 9 hours it is in the range 0.66[FORMULA]b[FORMULA]1.19. These data allow us to conclude that during 1982-1994 two processes operated in the nucleus of the NGC 1275 galaxy, causing variations of its flux in the optical on a time scale of several hours. One of the processes was a mixture of shot-noise and flicker-noise, and the second one was nearer to pure shot-noise.

The SF slopes for the time scale of years were in the range of 0.06-0.14. They evidenced that on the time scale years the process was absent, or a pure flicker-noise is operated. The evolution of the processes acting in the nucleus from 1968-1980 to 1982-1994 is mentioned. A years process is evolved in accordance with the general flux variations, but an activity of the intranight variations is increased with the decreasing of the general brightness of the nucleus. All obtained data are discussed from the point of view of the current models of a powering mechanism.

Key words: galaxies: individual: NGC 1275 – galaxies: Seyfert – instabilities

Send offprint requests to: I. Pronik (ipronik@crao.crimea.ua)

© European Southern Observatory (ESO) 1999

Online publication: November 2, 1999

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