Optical Brightening of the blazar S5 0716+714

ATel #11107; Alessandro Marchini (Astronomical Observatory, Department of Physical Sciences, Earth and Environment (DSFTA), University of Siena - Italy), Giacomo Bonnoli (DSFTA, University of Siena - Italy)
on 29 Dec 2017; 14:23 UT
Credential Certification: Giacomo Bonnoli (giacomo.bonnoli@unisi.it)

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We observed the blazar S5 0716+714 (RA: 07:21:53.45, Dec: +71:20:36.36, J2000.0) with the 0.3 m telescope at the Astronomical Observatory of the University of Siena, triggered by ATel #11100 issued by the MAGIC collaboration reporting unprecedented activity in VHE (E>100 GeV) gamma rays from the source. Observations consist of 3 x 300 s exposures in the Johnson-Cousins R filter, taken in 2x2 binning under good observing conditions with clear sky, high (~ 80% RH) humidity and seeing 4.5" (FWHM), starting at MJD 58115.905116 (civil date 2017-12-28 h. 21:43 UTC)). 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 Königstuhl at https://www.lsw.uni-heidelberg.de/projects/extragalactic/charts/0716+714.html . The reference R magnitudes for these stars are taken from Villata et al., A&AS 130, 305 (1998). We derive for S5 0716+714 a magnitude R=12.76 +/- 0.01 at MJD=58115.910556 (civil date 2017-12-28 h. 21.51 UTC). Quoted uncertainty is statistical only. Measurement comes from a preliminary photometric analysis and may be subject to later refinement. This magnitude is the brightest since the first quarter of 2016 if compared to the measurements reported by the Tuorla Observatory in their blazar monitoring program; a plot is publicly available at http://users.utu.fi/kani/1m/S5_0716+714.html . Moreover this measurement is ~1 magnitude brighter than the last publicly available measurement from the same monitoring program (R=~13.7, on Nov 1st). We infer that the source is in a relatively active state at optical wavelengths too, even if still far from the minimal magnitude reported in the long term (R~11.6, Jan 2015, see also ATel #6999 and ATel #6953). We will continue monitoring the source in the following nights. Multi-wavelength follow-up is warmly 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) 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 pixel ) capable of imaging a 58 x 38 arcmin^2 field of view with a resolution of 1.15”/pixel.