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From: atel@astronomerstelegram.org
Subject: ATel  17566
Message-Id: <20251230070623.268472880793@server.astronomerstelegram.org>
Date: Tue, 30 Dec 2025 02:06:23 -0500 (EST)

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Posted: Within the last 24 hours
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ATEL #17566							     ATEL #17566

Title:	Exceptionally high optical brightness of the BL Lac object
		PKS 1749+096 in recent nights
Author:	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)
Queries:	dominik.elsaesser@tu-dortmund.de
Posted:	29 Dec 2025; 17:45 UT
Subjects:Optical, AGN, Blazar

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 &#177; 0.043 mag
on October 15, 2025 (JD 2460964.31478) to 14.964 &#177; 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
&#177; 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 &#177; 0.043

JD 2460984.24078: 16.850 &#177; 0.075

JD 2460991.26747: 16.228 &#177; 0.027

JD 2461001.26875: 16.427 &#177; 0.028

JD 2461028.21433: 15.309 &#177; 0.053

JD 2461034.73003: 15.161 &#177; 0.016

JD 2461035.20585: 15.135 &#177; 0.040

JD 2461035.72367: 15.032 &#177; 0.012

JD 2461036.20480: 15.058 &#177; 0.033

JD 2461036.72471: 15.107 &#177; 0.010

JD 2461036.73166: 15.111 &#177; 0.012

JD 2461038.72185: 14.972 &#177; 0.008

JD 2461038.73220: 14.964 &#177; 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: https://schuelerlabor-wuerzburg.de/en/observatory/
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Password Certification: Dominik Elsaesser (dominik.elsaesser@tu-dortmund.de)
https://www.astronomerstelegram.org/?read=17566
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