Exceptionally high optical brightness of the BL Lac object PKS 1749+096 in recent nights

ATel #17566; R. Steineke, D. Reinhart, S. Duerr, F. Lach, D. Paulini, D. Schneider, S. Ankara, M. Grischy, O. Koppitz, S. Krauth, B. Lehmann, L. Lehmann; J. Meiler, L. Neisser, N. Zottmann, M. Feige, C. Lorey (all Hans-Haffner-Sternwarte, Friedrich-Koenig-Gymnasium, Wuerzburg, Germany) J. Hessdoerfer, M. Kadler, L. Haury, K. Mannheim, F. Roesch W. Schulga (all University of Wurzburg, Germany) D. Elsaesser (TU Dortmund, Germany)
on 29 Dec 2025; 17:45 UT
Credential Certification: Dominik Elsaesser (dominik.elsaesser@tu-dortmund.de)

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The BL Lac object PKS 1749+096, also known as OT 081 or 4C 09.57, with ICRS J2000 coordinates RA.: 17 51 32.819 Dec.: +09 39 00.728 and redshift z=0.322 (Simbad astronomical database), has shown exceptionally high optical brightness in recent nights, at levels not observed for several years.
For two and a half months, the optical brightness of this object in the R band has increased by more than 2.7 mag from 17.749 ± 0.043 mag on October 15, 2025 (JD 2460964.31478) to 14.964 ± 0.008 mag this morning (December 29, 2025; JD 2461038.73220).
More than 10 years ago, in July 2016, very unusual activity was detected in this object in various wavelength ranges (ATel #9267; ATel #9260; ATel #9259; ATel #9231). At that time, the source reached an optical brightness of R = 14.9 mag (ATel #9259), similar to the current level.
Five and a half years later, at the end of 2021, the object was observed by TELAMON in a rather low radio state (ATel #15075). In the following weeks, we measured a strong increase in brightness and on March 1, 2022 (JD 2459639.62912) we recorded a peak brightness in the R band of 14.739 ± 0.007 mag.
Since then, this source has behaved rather inconspicuously in the optical range with values in the R band of 16–18 mag, until it steadily increased in brightness from mid-October this year.

We report the following preliminary R-band magnitudes:

JD 2460964.31478: 17.749 ± 0.043
JD 2460984.24078: 16.850 ± 0.075
JD 2460991.26747: 16.228 ± 0.027
JD 2461001.26875: 16.427 ± 0.028
JD 2461028.21433: 15.309 ± 0.053
JD 2461034.73003: 15.161 ± 0.016
JD 2461035.20585: 15.135 ± 0.040
JD 2461035.72367: 15.032 ± 0.012
JD 2461036.20480: 15.058 ± 0.033
JD 2461036.72471: 15.107 ± 0.010
JD 2461036.73166: 15.111 ± 0.012
JD 2461038.72185: 14.972 ± 0.008
JD 2461038.73220: 14.964 ± 0.008

Our 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 University.
Comparison stars and their magnitudes were taken from P. S. Smith, T. J. Balonek, PASP 1998, 110, 1164-1171.
The optical data were acquired through a Bessel R filter (Chroma) with a 0.5m CDK-astrograph (PlaneWave) and a Moravian C4-16000EC camera at the school and university observatory Hans-Haffner-Sternwarte in 97265 Hettstadt, Germany (https://schuelerlabor-wuerzburg.de/en/observatory/).

Hans-Haffner-Sternwarte