Infrared activity of the Seyfert galaxy NGC 4151 in 1995-1998

We present the results of infrared JHKL photometry of the Seyfert galaxy NG C 4151 during a period of activity in 1995-1998. In 1998, the "cold" variab le source of NGC 4151 was still; in an active phase, though its luminosity had decreased by about 15-20%. If the luminosity decrement (Delta L-c simil ar to 4 x 10(42) erg/s over two years) of the "cold" variable source of NGC 4151 remains unchanged, this source could return to an activity minimum by summer 2000, and the photometric parameters of this minimum should be the same as those for the 1985-1988 minimum. If the "cold" variable source of t he galaxy corresponds to a dust cloud heated by the central "hot" source, t his component should be optically thin to the radiation of the central sour ce, with its optical depth falling in the interval 0.05-0.15. In 1995-1998, during the active phase of the galactic nucleus, material at a distance of several parsecs was heated, so that we observed the near-IR radiation of d ust particles at 600-800 K. The mass of the radiating dust is estimated to be 5-20 M-.. If the gas-to-dust ratio near the nucleus is about 500, the ma ss of material that is several parsecs from the nucleus of NGC 4151 is abou t similar to 10(4)M(.).