BL Lac again in optical high state

ATel #14751; Felix Hemrich, Niels Bader, Matija Brown, Ben Horst, Jonas Ludwig, Felix Molz, David Reinhart, Korbinian Rosenlehner, Kilian Schoch, Remco Steineke, Dirk Seifert, Lukas Waller, Nils Zottmann, Martin Feige, Christian Lorey (all Friedrich-Koenig-Gymnasium / Hans-Haffner-Sternwarte), Adrian Scherbantin, Karl Mannheim (all Universitaet Wuerzburg), Dominik Elsaesser (TU Dortmund)
on 4 Jul 2021; 15:45 UT
Credential Certification: Dominik Elsaesser (dominik.elsaesser@tu-dortmund.de)

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For the fourth time within one year, BL Lacertae's (ICRS coords. (ep=J2000): RA 22 02 43.291 Dec +42 16 39.978) optical brightness in increasing significantly.
After a first big outburst in August and September 2020 (ATel#13930, ATel#13956, ATel# 13958, ATel# 14065, ATel# 14069, ATel #14081, ATel #14096), BL Lac had continued to reach high brightness values in January (ATel #14328 & #14329, ATel #14334, ATel #14343, ATel #14356, ATel #14467) and April 2021 (ATel#14548).
Now, about 3 months later, the brightness is again rising and has once more exceeded 12th magnitude in the R-Band.
We are using Bessel filters four our exposures 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 here report the following brightness values:


R - band magnitudes:

JD 2459377.4467: 13.108 ± 0.006
JD 2459378.3892: 12.868 ± 0.008
JD 2459378.5455: 12.917 ± 0.004
JD 2459385.4069: 12.866 ± 0.021
JD 2459392.5702: 12.427 ± 0.015
JD 2459395.3964: 12.437 ± 0.026
JD 2459398.4501: 11.993 ± 0.004
JD 2459399.5586: 11.978 ± 0.007


V - band magnitudes:

JD 2459377.4486: 13.696 ± 0.009
JD 2459378.3911: 13.426 ± 0.018
JD 2459378.5474: 13.488 ± 0.006
JD 2459385.4031: 13.287 ± 0.043
JD 2459392.5720: 13.022 ± 0.024
JD 2459395.3982: 13.081 ± 0.011
JD 2459398.4519: 12.552 ± 0.006
JD 2459399.5545: 12.534 ± 0.015


B - band magnitudes:

JD 2459377.4505: 14.783 ± 0.018
JD 2459378.3932: 14.635 ± 0.046
JD 2459378.5492: 14.565 ± 0.015
JD 2459385.4049: 14.537 ± 0.074
JD 2459392.5738: 14.052 ± 0.073
JD 2459395.4000: 14.164 ± 0.020
JD 2459398.4538: 13.600 ± 0.014
JD 2459399.5563: 13.686 ± 0.034


These measurements were 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 the TU Dortmund University with the 0.5m CDK astrograph at the school and university observatory Hans-Haffner-Sternwarte in D-97265 Hettstadt (Germany).

AGN Monitoring Program at the Hans-Haffner-Sternwarte in Hettstadt