THE LONG-TERM PERIODIC OSCILLATION OF THE NGC-4151 NUCLEUS

The hypothesis that the luminosity of the nucleus of the Seyfert 1 gal axy NGC 4151 varies with a period of P-0 approximate to 160.0101 minut es is revised. In 1987-1994 a series of photometric observations of th e NGC 4151 has been carried out in the U and V filters at several inst ruments. In the total sample of 27 nights, the U data of 15 nights sho wed an appreciable intranight variability of the AGN flux. Being detre nded and folded with the a priori period P-0, those data exhibited sig nificant P-0 signal coinciding in phase with that found in previous st udies. Nearly the same result is obtained for 39 nights in the V-filte r. The average harmonic amplitudes of the P-0 oscillation (for the tot al interval 1968-1994) are found to be approximate to 7 and approximat e to 2 mmag in the U and V filters, respectively. The power spectrum w as computed for the total data series 1968-1994 (in all 2771 measureme nts including X-ray data from Ariel 5, EXOSAT, and Ginga satellites). It reveals a prominent peak corresponding to a period of 160.0104 +/- 0.0005 minutes (with the lower level of confidence 3.6 sigma). The lat ter fairly well coincides with the P-0 period discovered much earlier in the power spectrum of global oscillations of the Sun. This analysis thus strongly supports a cosmological interpretation of the ''ubiquit ous'' oscillation with the P-0 period.