Optical brightening of the flaring blazar PKS 2345-16

ATel #13234; Alessandro Marchini (Astronomical Observatory, Department of Physical Sciences, Earth and Environment (DSFTA), University of Siena - Italy), Giacomo Bonnoli, Lorenzo Bellizzi, Vincenzo Millucci, Riccardo Paoletti, Leonardo Stiaccini, Stefano Truzzi, Sofia Ventura (DSFTA, University of Siena - Italy), Massimo Conti, Claudio Vallerani (Astronomical Observatory, University of Siena - Italy), Pietro Aceti, Massimo Banfi (Osservatorio Astronomico Città di Seveso - Italy).
on 28 Oct 2019; 18:11 UT
Credential Certification: Giacomo Bonnoli (giacomo.bonnoli@unisi.it)

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We observed in the past weeks the Flat Spectrum Radio Quasar PKS 2345-16 (RA: 23 48 02.61 Dec: -16 31 12.02 J2000.0) at redshift z=0.576 (Tadhunter C.N. et al. 1993, MNRAS, 263, 999) from the Astronomical Observatory of the University of Siena and from the Osservatorio Astronomico Città di Seveso, both in Italy. Our interest was raised by ATel #13172 reporting a flare in gamma rays detected by the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope, and by subsequent ATel #13187 reporting an intense flare at infrared wavelengths as well.
The observations from Siena consist of series of 300 s exposures in the Johnson-Cousins R filter, taken in 2x2 binning with clear sky during dark time. After dark current subtraction and flat field correction the images for each visit were averaged and aperture photometry was performed on the average frame by means of the MaximDL software package. Reference and check stars in the field of view were selected from the APASS9 (Henden et al., 2016) catalogue. The reference R magnitudes were derived from those reported in the same APASS9 catalogue after conversion between the two different photometric systems, following a formula taken from Munari U., "Classical and Recurrent Novae", JAAVSO, 40 (2012). The observations in Seveso followed the same procedure without any significant deviation, except for worse weather conditions. The results of the preliminary analysis of our observations are reported in the following table:

Civil Date (UT) Rmag(dRmag) Observatory #of exposures
2019 Oct 17.86 15.69(0.02) Siena 5
2019 Oct 25.76 15.27(0.03) Siena 4
2019 Oct 25.85 15.18(0.05) Seveso 5


Quoted uncertainty is statistical only.
We conclude that the source is very active also in the optical band. 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).

A brief description of the instrumental setup at Siena Observatory is available at the official webpage of the Astronomical Observatory of the University of Siena (see link below). The instrumentation in Seveso consists of a 0.3 m, f/6.5 telescope equipped with a ST8 XME NABG SBig CCD.

Astronomical Observatory of the University of Siena - Official Webpage