The flaring blazar OP 313 reached an exceptional optical brightness
ATel #17184; Alessandro Marchini (Astronomical Observatory, DSFTA, University of Siena - Italy); Joao Pedro Maria Savino, Leonardo Stiaccini, Gaia Verna (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, Milan - Italy); Ivo Peretto, Stefano Lora, Matilde Barbieri, William Rivato, Lorenzo Sassaro (MarSEC, Marana di Crespadoro, Vicenza - Italy); Davide Agnetti (Associazione Astrofili Spezzini, Aldo Agnetti Observatory, Lomazzo - Italy)
on 15 May 2025; 17:28 UT
Credential Certification: Gaia Verna (gaia.verna@unisi.it)
Subjects: Optical, AGN, Blazar, Transient
Referred to by ATel #: 17194
Last night, coordinated observations of 4 Italian telescopes recorded another optical flare of the flat spectrum radio quasar OP 313 (R.A. = 197.619 deg, Decl. = +32.345 deg; J2000; Johnston et al. 1995, AJ, 110, 880) at redshift z=0.997 (Schneider et al. 2010, AJ, 139, 2360). In the last few years, we have regularly monitored this blazar (Atel #16360, #16891, #16951, #16964, #16979), and we have recently reported an increased brightness in its optical emission (ATel #17173).
We report the maximum brightness recorded in the BVRI bands of the Johnson-Cousins photometric systems:
Civil Date(UT) Mag (dMag) Filter
2025 May 14.863 13.94 (0.01) B
2025 May 14.862 13.44 (0.01) V
2025 May 14.867 13.05 (0.01) R
2025 May 14.854 12.55 (0.01) I
Reported uncertainty is statistical only.
As a reference, these measurements are less than 0.5 mag fainter than the record R-band magnitude of 12.6 observed in July 2022 (see ATel #16360 and references therein). We also report evidence for intranight variability down to hours timescale.
Observations were conducted from the 0.30 m telescope of the Astronomical Observatory of the University of Siena (Siena, Italy - IAU MPC observatory code K54), the 0.53 m telescope of the Montarrenti Astronomical Observatory (Sovicille, Siena, Italy - C88), the 0.36 m telescope of the Marana Space Explorer Centre (MarSEC, Vicenza, Italy) and the 0.28 m telescope of the Aldo Agnetti Observatory (Lomazzo, Como, Italy - L53).
Any enquiry on these observations can be addressed either to Alessandro Marchini (marchini@unisi.it) or to Gaia Verna (gaia.verna@unisi.it). We will continue monitoring the source in the following nights. Multi-wavelength follow-up is strongly encouraged.
We acknowledge the excellent scientific cooperation and valuable support from the Whole Earth Blazar Telescope (WEBT) Collaboration.
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, on the website of the Unione Astrofili Senesi and on the page of the Seveso Astronomical Observatory within the website of the WEBT .
Last night (2025, May 14th-15th), R-band lightcurve of OP 313 from the four observatories: http://tiny.cc/OP313_lc_20250514
Last months' BVRI lightcurves of OP 313 from the four observatories: http://tiny.cc/OP313_lc_2025
Astronomical Observatory of the University of Siena - Official Webpage
