Optical evolution of the flaring blazar TXS 0025+197

ATel #13370; Alessandro Marchini (Astronomical Observatory, Department of Physical Sciences, Earth and Environment (DSFTA), University of Siena - Italy), Giacomo Bonnoli, Lorenzo Bellizzi, Eleonora Bernardi, Vincenzo Millucci, Riccardo Paoletti, Leonella Filippa Saya, Leonardo Stiaccini, Stefano Truzzi, Sofia Ventura (DSFTA, University of Siena - Italy), Massimo Conti, Massimo Damiani, Claudio Vallerani (Astronomical Observatory, University of Siena - Italy)
on 24 Dec 2019; 15:31 UT
Credential Certification: Giacomo Bonnoli (giacomo.bonnoli@unisi.it)

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We observed in the last weeks the Flat Spectrum Radio Quasar TXS 0025+197 (RA: 00 27 29.8 Dec: +20 00 27 J2000.0) at redshift z=1.55 (Alam et al., 2015, ApJS, 219, 12) from the Astronomical Observatory of the University of Siena, in the framework of our program dedicated to the optical monitoring of blazars that, being either established or potential emitters of very high energy (VHE, E > 30 GeV) gamma rays, are potential targets for the MAGIC Telescopes. Earlier this year our interest was triggered by ATel #13032 reporting a flare in gamma rays detected by the Large Area Telescope (LAT) onboard the Fermi satellite in August. Activity in optical and NIR was thereafter reported (ATel #13038,#13045).
Our observations consist at each visit of 3-9 x 300 s exposures in the Johnson-Cousins R, taken in 2x2 binning with clear sky. Sky brightness varied from night to night, depending on moon illumination firstly. 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 results of our observations of this source (including also the ones already reported in our previous ATel #13038) are reported in the following table:

Civil Date (UT) Rmag(dRmag)
2019 Aug 16.11 17.06(0.03)
2019 Aug 17.04 16.76(0.03)
2019 Aug 19.13 16.78(0.04)
2019 Nov 30.73 16.25(0.02)
2019 Dec 10.72 17.05(0.06)
2019 Dec 21.72 16.86(0.05)
2019 Dec 23.74 16.73(0.02)

Quoted uncertainty is statistical only. The optical brightness is at the level of our previous ATel #13038, and is less than half of a magnitude dimmer than our record value on November 30.73, indicating that the active phase is still ongoing. 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 acknowledge excellent scientific cooperation with, and valuable support from, the WEBT Collaboration, the Tuorla Observatory and the MAGIC Collaboration. Eleonora Bernardi and Leonella Filippa Saya contributed to these observations and to the photometric analysis in the framework of their training program about observational astronomy as undergraduate students in Physics and Advanced Technologies at the University of Siena.

A brief description of our instrumental setup is available at the official webpage of the Astronomical Observatory of the University of Siena (see link below).

Astronomical Observatory of the University of Siena - Official Webpage