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The recent flare of the blazar 3C 345 reached an exceptional optical magnitude at R=15.2

ATel #16306; Alessandro Marchini (Astronomical Observatory, University of Siena - Italy); Leonardo Stiaccini, (Department of Physical Sciences, Earth and Environment (DSFTA), University of Siena - Italy); Simone Leonini, Massimo Conti, Paolo Rosi, Luz Marina Tinjaca Ramirez (Montarrenti Observatory, Sovicille (Siena - Italy)); Giacomo Bonnoli (INAF - Brera Astronomical Observatory)
on 23 Oct 2023; 14:41 UT
Credential Certification: Giacomo Bonnoli (giacomo.bonnoli@inaf.it)

Subjects: Optical, Gamma Ray, AGN, Blazar, Transient

Referred to by ATel #: 16309, 16320

We observed along the past weeks the blazar 3C 345 (R.A.=16 42 58.81 Dec.=+39 48 36.99, J2000.0; z=0.5928) in response to the trigger sent by the LAT Collaboration (ATel #16274) reporting renewed gamma-ray activity from the source, within the framework of our blazar monitoring program. Our brightest measurement at R=15.22 (on October 11) is to the best of our knowledge rather exceptional for this source (see. e.g. ATels #15341, #11624). We note that this value is in substantial agreement with the slightly dimmer measurements obtained at Sierra Nevada Observatory on the same night and reported in ATel #16305.

The following table reports our B, V, R and I (Johnson-Cousins) measurements:

Civil Date(UT) Mag (dMag) - Observatory
2023 Oct. 11.742 B= 16.21 (0.03) - Montarrenti
2023 Oct. 12.745 B= 17.23 (0.08) - Montarrenti
2023 Oct. 13.740 B= 17.47 (0.12) - Montarrenti
2023 Oct. 14.746 B= 16.88 (0.15) - Montarrenti
2023 Oct. 15.751 B= 16.57 (0.17) - Montarrenti

2023 Oct. 11.736 V= 15.70 (0.03) - Montarrenti
2023 Oct. 12.742 V= 16.75 (0.08) - Montarrenti
2023 Oct. 12.777 V= 16.68 (0.09) - Siena
2023 Oct. 13.741 V= 16.97 (0.10) - Montarrenti
2023 Oct. 14.746 V= 16.31 (0.12) - Montarrenti
2023 Oct. 15.752 V= 16.06 (0.16) - Montarrenti

2023 Oct. 11.736 R= 15.22 (0.02) - Montarrenti
2023 Oct. 12.742 R= 16.26 (0.05) - Montarrenti
2023 Oct. 12.779 R= 16.24 (0.07) - Siena
2023 Oct. 13.740 R= 16.46 (0.06) - Montarrenti
2023 Oct. 14.747 R= 15.78 (0.07) - Montarrenti
2023 Oct. 15.754 R= 15.48 (0.12) - Montarrenti
2023 Oct. 19.763 R= 15.96 (0.09) - Siena
2023 Oct. 22.834 R= 16.70 (0.09) - Siena

2023 Oct. 11.737 I= 14.59 (0.02) - Montarrenti
2023 Oct. 12.744 I= 15.53 (0.05) - Montarrenti
2023 Oct. 12.781 I= 15.47 (0.04) - Siena
2023 Oct. 13.742 I= 15.68 (0.06) - Montarrenti
2023 Oct. 14.745 I= 15.05 (0.06) - Montarrenti
2023 Oct. 15.753 I= 14.90 (0.14) - Montarrenti

These measurements were obtained using the photometric sequence made publicly available by the WEBT Collaboration. Quoted uncertainties are statistical only.

Any enquiry on these observations can be addressed either to Alessandro Marchini (marchini@unisi.it) or to Giacomo Bonnoli (giacomo.bonnoli@inaf.it). We will continue monitoring the source in the following nights. Multi-wavelength follow-up is encouraged.

We acknowledge excellent scientific cooperation with, and valuable support from, the WEBT Collaboration.

Our blazar monitoring program is carried out with the 0.30 m telescope at the Astronomical Observatory of the University of Siena (K54) and with the 0.53 m telescope at Montarrenti Observatory (C88), both located in Siena (Italy).

Brief descriptions of the instrumental setups used for the reported observations are available at the official webpage of the Astronomical Observatory of the University of Siena and on the website of the Unione Astrofili Senesi.