BL Lac reaches a new optical all-time maximum

ATel #14820; Lukas Kunkel, Adrian Scherbantin, Karl Mannheim (all Universitaet Wuerzburg), Fiona Kaplan, Niels Bader, Erik Heidemann, Felix Hemrich, Ben Horst, Alexander Lessing, Jonas Ludwig, Felix Molz, David Reinhart, Korbinian Rosenlehner, Kilian Schoch, Remco Steineke, Lukas Waller, Nils Zottmann, Martin Feige, Christian Lorey (all Friedrich-Koenig-Gymnasium / Hans-Haffner-Sternwarte), Dominik Elsaesser (TU Dortmund)
on 31 Jul 2021; 07:18 UT
Credential Certification: Dominik Elsaesser (dominik.elsaesser@tu-dortmund.de)

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Since BL Lac's major brightness outburst in the summer of 2020, we have observed a flare from this object roughly every three to three and a half months, each time reaching an even greater maximum brightness in the optical spectral range.
The current outbreak began in early July 2021 (ATel #14751, ATel #14773) and has been observed in different wavelength bands (ATel #14774, ATel #14777, ATel #14782, ATel #14783).
Tonight we measured a rapid increase in optical brightness (R-Band) from 11.433 ± 0.004 mag (21:30 UTC - JD 2459426.3956) to 11.315 ± 0.003 mag (22:12 UTC - JD 2459426.4252). Over the next hour and a half, the brightness then slowly increased (with fluctuations) to 11.271 ± 0.003 mag (23.50 UTC - JD 2459426.4930), which is a new all-time high state for this AGN, as far as our coverage is concerned. By dawn in Hettstadt, the brightness slowly decreased to 11.444 ± 0.008 mag (02:44 UTC - JD 2459426.6142).

We are using Bessel filters and for the aperture photometry we are using the specifications of the GASP list of WEBT (https://www.oato.inaf.it/blazars/webt/gasp/fc/2200fc.html).

We strongly encourage further observations of this record optical flare.

These measurements are carried out as part of the long-term AGN monitoring program of the Naturwissenschaftliches Labor fuer Schueler am Friedrich-Koenig-Gymnasium (FKG), the Universitaet Wuerzburg, and TU Dortmund with the 0.5m CDK-astrograph at the school and university observatory Hans-Haffner-Sternwarte in D-97265 Hettstadt (Germany).

NATUR­WISSEN­SCHAFT­LICHES LABOR FÜR SCHÜLER AM FKG E.V.