Nuclear variability of NGC 4151 in UVB and JHKL: A new cycle of activity

Details Nuclear variability of NGC 4151 in UVB and JHKL: A new cycle of activity Nuclear variability of NGC 4151 in UVB and JHKL: A new cycle of activity

Mar 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998astl...24..199l&link_type=abstract

Astronomy Letters, Volume 24, Issue 2, March 1998, pp.199-205; Pis'ma v Astronomicheskii Zhurnal, Vol. 24, p. 243

Astronomy and Astrophysics

Astronomy

6

Scientific paper

The coordinated UBV and JHKL observations of the Seyfert Galaxy NGC 4151 during a new cycle of activity (1985-1997) after the deep minimum of 1984 are analyzed. The variability amplitude is ~~ 2.5m in U and ~1m in K; the light variations are correlated in all bands. The emission from a variable source in the nucleus has been separated in the wavelength range 0.36-3.5 microns by subtracting the constant flux from the underlying galaxy that was obtained from multiaperture photometry. The emission of the underlying galaxy through a 12" aperture (14 Mpc for H_0 = 75) has been decomposed: ~80% of the light comes from stars, and the remaining emission is produced by gas and dust at temperatures of ~1100 and ~420 K, respectively. The contribution of the variable source is very small in UBV at minimum light (1985-1988) and almost zero in JHKL. At maximum light (1995-1996), three variable sources are clearly separated in the spectral energy distribution: (1) a compact hot source (a radius of ~ 7 x 10^14 cm, a temperature of ~ 30 000 K, L_0.36-3.5 ~ 2.4 x 10^44 erg s^-1); (2) an intermediate source (~ 3 x 10^15, ~ 7000, L_0.36-3.5 ~ 3 x 10^43); and (3) a cold source (~ 4 x 10^16, ~1500, L_0.36-3.5 ~ 1 x 10^43). If the infrared emission is the reradiation of energy of the compact hot source, then the infrared source cannot be spherically symmetric, but rather has a flattened structure with h / r ~ 0.15.

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