Optical evolution of the current active state of the blazar 3C 279

We observed the z=0.5632 (Marziani et al. 1996, ApJS, 104, 37) flat-spectrum radio quasar 3C 279 (with FK5 coordinates RA 12 56 11.167 Dec -05 47 21.52 J2000.0) with the 0.3 m telescope at the Astronomical Observatory of the University of Siena. Observation consists of 4 x 300 s exposures in the Johnson-Cousins R filter, taken in 2x2 binning under good observing conditions with clear sky and seeing 4.8" (FWHM), starting at JD=2458136.6377 (civil date 2018-01-18 h. 3:18 UT). The source altitude was about 39 degrees during the observation. We obtained for 3C 279 a magnitude R=13.87 +- 0.02 at JD=2458136.6452 (civil date 2018-01-18 h. 03:29 UT). This magnitude is compatible with the R-band measurement provided on January 17 by the REM telescope (ATel #11190). We can also compare this measurement with two previous measurements taken within our blazar monitoring program on January 3 and January 12: Date UT JD mag_R dmag_R Notes 2018-01-03 3:14 2458121.6349 15.38 0.04 strong moon, poor sky 2018-01-13 4:05 2458131.6705 14.70 0.02 2018-01-18 3:29 2458136.6452 13.87 0.02 These values are compatible with the recent onset of an increasing trend of the flux at optical wavelengths. We will continue monitoring the source in the following nights. Multi-wavelength follow-up is encouraged.