Possible Variations of λ=10 µm Radiation from NGC 4151

Abstract

THE nucleus of the Seyfert galaxy NGC 4151 was observed at λ=3.5 µm and λ = 11.5 µm on June 21, 1969, with one of the 36-inch telescopes at Kitt Peak National Observatory. The purpose of the observations was to look for possible variations in the infrared flux from these objects. Calculations of radiation processes applied to the infrared flux from Seyfert galaxies and the quasi-stellar object 3C 273 indicate that it would be highly unlikely that radiation from dust could be the source of this radiation, if any significant variation were found to occur at λ = 10 µm (unpublished work of Burbidge and Stein, and of Rees, Silk, Werner and Wickramasinghe). The results of the observations of June 21, 1969, indicate that it is likely that a significant variation of the λ = 10 µm flux from NGC 4151 has occurred in the past one to two years. These results are preliminary, but significant enough to indicate that this object should be carefully monitored for variations at infrared wavelengths in the near future.