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Extremely bright optical state of the flaring blazar PKS 0346-27

ATel #12479; 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), Paolo Da Vela (INFN-Pisa).
on 6 Feb 2019; 21:33 UT
Credential Certification: Giacomo Bonnoli (giacomo.bonnoli@unisi.it)

Subjects: Optical, Blazar, Transient

We observed yesterday and again few hours ago the Flat Spectrum Radio Quasar PKS 0346-27 (RA: 03 48 38.14 Dec: -27 49 13.57 J2000.0) at redshift z=0.991 (White et al. 1988 ApJ, 327, 561) from the Astronomical Observatory of the University of Siena.

PKS 0346-27 is showing intense activity at all wavelengths from NIR to HE gamma rays since February 2018, as reported by many observers (ATel #11251,#11269,#11337,#11455) with later episodes of renewed activity (ATel #11644) and a recent recrudescence in December (ATel #12310,#12324,#12336). The source belongs to the "LAT Monitored Sources" list, therefore preliminary, uncalibrated estimations of the daily gamma-ray flux observed by Fermi LAT are publicly available at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_0346-27 . The reported daily-averaged gamma-ray flux above 100 MeV was often above the level of 1.0e-6 cm^-2 s^-1 in the last weeks, with a recent record grazing 2.0e-6 cm^-2 s^-1.

Our 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. The source is observable from Siena below 19 degrees of elevation at the culmination, and our seeing was 5" and 6" (FWHM) today and yesterday respectively. After dark current subtraction and flat field correction the images for each night 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 results of our observations are gathered in the following table:

Civil Date (UT) Rmag(dRmag)
2019 Feb 05.76 15.28(0.05)
2019 Feb 06.77 15.32(0.02)


Quoted uncertainty is statistical only. To the best of our knowledge such a bright magnitude in the R band, corresponding to a flux density around 1.0e-11 erg cm^-2 s^-1 at the 0.64 um effective wavelength of the filter, is unprecedented for this source. 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).

These observations were performed in the context of a guidance project about astrophysics involving high school students from the "Liceo Scientifico G. Marconi" (Grosseto). We thank all of them for their enthusiastic participation in the observations and photometric analyses performed along their guidance project: Stefano Cericola, Leonardo Fabbrini, Rita Fedele, Lucia Iezzi, Pierfrancesco Lacorte, Martin Simon Liechti, Benedetta Mancini, Giulio Periccioli, Elisa Romualdi, Leonardo Scavuzzo e Gian Luca Schiano.

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