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

ATel #11196; Alessandro Marchini (Astronomical Observatory, Department of Physical Sciences, Earth and Environment (DSFTA), University of Siena - Italy), Giacomo Bonnoli, Vincenzo Millucci, Bartolomeo Trefoloni (DSFTA, University of Siena - Italy)
on 18 Jan 2018; 12:13 UT
Credential Certification: Giacomo Bonnoli (giacomo.bonnoli@unisi.it)

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We observed tonight 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. This observation was performed within the frame of a guidance project about astrophysics involving high school students from the Liceo "Tito Sarrocchi" (Siena) and Liceo "Carlo Cattaneo" (Follonica).

Observation of this target was triggered by the recent alerts issued by the Fermi/LAT collaboration (ATel #11189) and by the REM telescope (ATel #11190) reporting a flaring state of the source both in gamma rays and in optical-NIR. 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. After dark current subtraction and flat field correction images were averaged and preliminary photometric analysis was performed by means of the MaximDL software package. Reference and check stars in the field of view were taken from the finding chart made available by Landessternwarte Koenigstuhl at https://www.lsw.uni-heidelberg.de/projects/extragalactic/charts/1253-055.html . The reference R magnitudes for these stars are taken from Villata et al., A&AS 130, 305 (1998).

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). Quoted uncertainty is statistical only. Measurement comes from a preliminary photometric analysis and may be subject to later refinement. 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.

Any enquiry on these observations can be addressed either to Alessandro Marchini (alessandro.marchini@unisi.it) or to Giacomo Bonnoli (giacomo.bonnoli@unisi.it).

We thank all the involved high school students for their enthusiastic participation in the observations and photometric analyses performed along their guidance project: G. Astorino, D. Cangiolini, G. Ciavarella, F. Corridori, L. Donato, A. Gepponi, T. Gotti, C. Margheriti, F. Marri, G. Masini, F. Materozzi, C. Montomoli, M. Morgantetti, F. Paggetti, A. Viti, S. Viti.

The Astronomical Observatory of the University of Siena runs a remotely operated 0.3 m f/5.6 Maksutov-Cassegrain reflector, installed on a German equatorial mount. The instrument is hosted in a dome on the roof of the Department building, 0.7 km southwards of the city center (43°18'45"N 11°20'12"E) site elevation is around 300 m above sea level. The telescope is equipped with a Johnson-Cousins BVRI filter wheel and a STL-6303 SBig CCD (3072 x 2048 9 μm pixels) capable of imaging a 58 x 38 arcmin² field of view with a plate scale of 2.3"/pixel (in binning 2x2).