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J.T. Marcy, S.G. Stegman, E.F. Guinan, S.G. Engle, G.P. McCook (Villanova University)
NGC 4151 is one of the brightest and best studied Seyfert-1/AGN galaxies. NGC 4151 is a ~12th (V)mag Barred Spiral galaxy (d ~16 Mpc) with a highly luminous and active nucleus. Because of its brightness and complex variability at all wavelengths, NGC 4151 has become the ``Posterchild Galaxy'' for Active Galactic Nucleus (AGN) galaxies and has been the subject of numerous studies that cover wavelengths from gamma rays to radio. These studies show variability on all time scales, from minutes to years. Like other AGN, NGC 4151 is a powerful X-ray source with very strong UV, and radio emissions that are best explained by accretion processes occurring in the disk in proximity to its assumed super-massive ~109 M\odot blackhole nucleus.
We report on intensive UVBRI photoelectric photometry being carried out on NGC 4151 since February 2001. The photometry is being conducted with the 0.8m Four College Automatic Photoelectric Telescope (FCAPT) located in southern Arizona. Observations have been obtained on over 260 nights so far. Examination of the photometry reveals surprising eclipse-like decreases in brightness that are especially prominent in the U- and B-bands. Fast Fourier Transform (FFT) and periodogram analyses of the photometry were carried out. These reveal a prominent period of P \approx 294 ± 8 days. One of several possibilities being explored to explain this behavior is that the eclipse-like events (if confirmed by observations during the next few months) could arise from recently accreted absorbing material orbiting in the outer region of the nuclei's inner accretion disk. We are carrying out a global analysis of all available observations to investigate possible correlations of our photometry with contemporaneous X-ray, UV, and ground-based spectroscopy. The results of this study are discussed. This research is supported by RUI/NSF Grants to Villanova University.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.