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The Long-Term Periodic Oscillation of the NGC 4151 Nucleus

The hypothesis that the luminosity of the nucleus of the Seyfert 1 galaxy NGC 4151 varies with a period of P0 ≈ 160.0101 minutes is revised. In 1987-1994 a series of photometric observations of the NGC 4151 has been carried out in the U and V filters at several instruments. In the total sample of 27 nights, the U data of 15 nights showed an appreciable intranight variability of the AGN flux. Being detrended and folded with the a priori period P0, those data exhibited significant P0 signal coinciding in phase with that found in previous studies. Nearly the same result is obtained for 39 nights in the V-filter. The average harmonic amplitudes of the P0 oscillation (for the total interval 1968-1994) are found to be ≈ 7 and ≈ 2 mmag in the U and V filters, respectively. The power spectrum was computed for the total data series 1968-1994 (in all 2771 measurements 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 σ). The latter fairly well coincides with the P0 period discovered much earlier in the power spectrum of global oscillations of the Sun. This analysis thus strongly supports a cosmological interpretation of the “ubiquitous” oscillation with the P0 period.