Rapid variability of active galactic nuclei: The 160min periodicity in NGC 3516, NGC 4151 and Quasar 3C 273

The analysis of all the available data between 1968 and 1991 on rapid variability of optical and X-ray luminosity of three AGNs, NGC 3516, NGC 4151 and 3C 273, shows the presence of small-amplitude (˜ 1 %) but statistically confident (≈︁ 5s̀) periodicity of 160.0105 (± 6) min. Within the error limits it coincides with the period P₀ = 160.0101 (± 1) min of global oscillations of the Sun. An independence of the observed period on AGN red shift z favours the hypothesis about a cosmological origin of the 160min oscillation.     

The Splitting Or Disappearance of the Solar 160-Min Mode?

The CrAO-WSO-network experiment was designed for detection of low-degree oscillations of the Sun representing either its normal g -modes or those driven by, e.g., rapid (hypothetical) rotation of the central solar core. The Doppler-shift measurements were made in 1974–1995 at both sites during about 13600 hr, in all. Taking into account the upper limit (0.08 m s^-1) for amplitudes of potential g-modes, attention is paid to the Sun's behaviour at frequencies near the 9th daily harmonic (period P 160.The two main issues follow from analysis of the combined CrAO-WSO data: (a) in 1974–1982 the primary period of solar pulsation was P ₀160.0099 ± 0.0016 ± 0.0016 min, but (b) during the last 13 yr it attained a new value, P ₁ 159.9654 ± 0.0010 min, which happens to be a near-annual sidelobe of P ₀. We find therefore that the phase stability of the 160-min mode is no longer present: it appears to be splitted at least into a pair of oscillations,P ₀ and P ₁, having perhaps different physical origins. But the most striking is the fair coincidence of the strongest peaks in the two data sets: CrAO (1974–1995): P = 159.9662 ±0.0006 min, WSO (1977–1994): P = 159.9663 ± 0.0007 min. The existence of two frequencies,P ^-1 ₀ and P ^-1 ₁, with their separation corresponding to 1-yr period, seems to be difficult to explain in terms of gravity g modes.     

Oscillations of the Sun: Results of observations in 1974–2007

Doppler measurements of the photosphere of the entire Sun carried out at the Crimean Astrophysical Observatory (CrAO) in 1974–2007 by the differential technique showed the presence of an enigmatic periodicity of P ₁ = 159.967(4) min. The phase of this oscillation was constant over the entire 34-year of surveys and interval. The true nature of this phenomenon is unknown. Pulsation with the former period P ₀ = 160.0101(15) min has been reliably detected only in the first nine years, from 1974 to 1982. It is noted that (a) the average amplitude of the P ₁ oscillation in the first half of the data was nearly 34% higher than in the second half and (b) the beat period of 400(14) d of these two pulsations is equal within error to the Jovian synodic period (399 d). A hypothesis is discussed relating the P ₁ oscillation to the superfast rotation of the inner solar core.     

160-min pulsation of the Sun: New observational results

The 1974–1988 Crimean measurements of the solar line-of-sight velocity continue to show the presence of a statistically significant periodicity P ₁ = 160.009 (±) min with an average harmonic amplitude of about 21 cm s^–1. The period is supposed to be that of the global pulsation of the Sun but with a little-known physical mechanism of excitation.The new observations give some evidence for the existence of a second periodicity, P ₁ = 160.014 (±) min. It is hypothesized that the appearance of P ₁ might be a sidelobe mode (of the P ₀-oscillation) induced by rapid rotation of the central solar core.It is also noted that the spacing, in frequency, between P ₀ and P ₁, corresponds to a beat period of 10 ± 3 yr, which happens to be in good agreement with the average duration of the 11 yr cycle of the magnetic activity of the Sun. Accordingly, we suppose that the phase shift of the P ₀-mode between the 1974–1982 and 1986–1988 time intervals reflects a remarkable change of the general magnetic field of the Sun in the course of the 22 yr solar cycle.