Infrared variability properties of the blazar 3C 279

The long-term (about 27 years) near-infrared K light curve is constructed from the published literature for the blazar 3C 279. The Jurkevich method is adopted to analyse the periodicity, and a strong 7.1±0.44 yr period is found, suggesting that the next near-infrared outburst will occur in 2002/03. The correlation between colour index (spectral index) and magnitude is discussed, and a significant correlation between ( J ? H ) and K is found with a correlation coefficient r =0.72 ( p =2.0×10^?10), which is consistent with Brown et al.'s proposal.