Physical sciences: Variations in the 10 μm flux from NGC 1068

ALTHOUGH there is considerable evidence of rapid variability of the intense infrared sources in the nuclei of galaxies and quasars, conclusive data have been lacking. NGC 1068 is one of the most powerful of the extragalactic infrared sources (L_IR = 6×10⁴⁵ erg s^-1) and, with the exception of M82 which is extended, has the highest signal-to-noise ratio at 10 μm. We have therefore monitored NGC 1068 for several years to look for variations. The pertinent observations are summarized in Fig. 1, where data obtained during the past 3 yr have been combined into four points. The results of the individual observations are given in Table 1.