Optical Flares of the blazars OP 313 and PG 1553+113
ATel #17173; Alessandro Marchini (Astronomical Observatory, University of Siena - Italy); 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 8 May 2025; 00:11 UT
Credential Certification: Gaia Verna (gaia.verna@unisi.it)
Subjects: Optical, Request for Observations, AGN, Blazar, Transient
We regularly monitor a set of VHE gamma-ray emitting blazars including 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) and the high-peaked BL Lac PG 1553+113 (R.A. = 238.929 deg, Decl. = 11.190 deg; J2000; Gaia EDR3, 2020) at redshift 0.408 < z < 0.436 (J. D. Jones et al. 2022, MNRAS 509, 4330â4343). Photometric observations are performed in the optical band from a network of observatories including 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 Center (MarSEC, Vicenza, Italy) and the 0.28 m telescope of the Aldo Agnetti Observatory (Lomazzo, Como, Italy - L53).
For OP 313 a gamma-ray flare has been very recently reported by the Fermi/LAT Collaboration (ATel #17167).
The following tables collect a selection of our latest measurements in the R filter of the Johnson-Cousins photometric system. An average value for each night is reported. Quoted uncertainty is statistical only.
OP 313
Civil Date(UT) Mag (dMag) - Observatory
2025 apr. 23.836 14.95 (0.02) - Siena
2025 apr. 24.838 14.70 (0.03) - Montarrenti
2025 apr. 24.876 14.81 (0.01) - Lomazzo
2025 apr. 25.903 14.70 (0.01) - Lomazzo
2025 apr. 28.833 14.75 (0.02) - MarSEC
2025 may 01.816 14.37 (0.01) - Siena
2025 may 02.957 14.47 (0.06) - Montarrenti
2025 may 06.895 13.82 (0.01) - Montarrenti
2025 may 07.079 13.85 (0.02) - Siena
PG 1553+113
Civil Date(UT) Mag (dMag) - Observatory
2025 apr. 23.912 13.69 (0.01) - Siena
2025 apr. 24.960 13.74 (0.01) - Lomazzo
2025 apr. 25.984 13.72 (0.01) - Lomazzo
2025 apr. 30.913 13.57 (0.01) - MarSEC
2025 may 01.871 13.50 (0.01) - MarSEC
2025 may 02.997 13.48 (0.01) - Montarrenti
2025 may 07.092 13.41 (0.02) - Siena
We notice that both blazars brightened significantly in the last few days and reached high optical states in the R band. The full data sets, containing our measurements in the B, V, R and I filters of the Johnson-Cousins photometric system for both blazars are under study and can be made available upon request.
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.
Plots of OP 313 and PG 1553+113 from the four observatories during the last months can be found at: http://tiny.cc/OP313_lc_20250507 http://tiny.cc/PG1553_lc_20250507
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