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Spectral energy distribution and its variability are basic tools forunderstanding the physical processes operating in active galactic nuclei (AGN).In this paper we report the results of a one-year near infra red (NIR) andoptical monitoring of a sample of 22 AGN known to be gamma-ray emitters, aimedat discovering correlations between optical and gamma-ray emission. We observedour objects with the Rapid Eye Mount (REM) telescope in J, H, K, and R bandsnearly twice every month during their visibility window and derived lightcurves and spectral indexes. We also analyzed the gamma-ray data from the Fermigamma-ray Space Telescope, making weekly averages. Six sources were neverdetected during our monitoring, proving to be fainter than their historical Twomicron all sky survey (2MASS) level. All of the sixteen detected sources showedmarked flux density variability, while the spectral indexes remained unchangedwithin our sensitivity limits. Steeper sources showed, on average, a largervariability. From the NIR light curves we also computed a variability speedindex for each detected source. Only one source (PKS 0208-512) underwent an NIRflare during our monitoring. Half of the sources showed a regular flux densitytrend on a one-year time scale, but do not show any other peculiarcharacteristic. The broadband spectral index alpha_ro appears to be a goodproxy of the NIR spectral index only for BL Lac objects. No clear correlationbetween NIR and gamma-ray data is evident in our data, save for PKS 0537-441,PKS 0521-360, PKS 2155-304, and PKS 1424-418. The gamma-ray/NIR flux ratioshowed a large spread, QSO being generally gamma-louder than BL Lac, with amarked correlation with the estimated peak frequency nu_peak of the synchrotronemission.

Near infrared and gamma-ray monitoring of TANAMI gamma-ray bright sources