AstroNote 2025-120

AT 2023uqm (https://alerce.online/object/ZTF23abikzfr) was discovered by ATLAS on October 10, 2023 at RA = 23:10:39.010, Dec = +34:54:10.63 (J2000) and reported to TNS by the ATLAS team (Tonry et al. 2023). It was spectroscopically classified as an AGN based on an optical spectrum taken on November 5, 2023 by ePESSTO+ using ESO-NTT/EFOSC2 (Ramsden et al. 2023), with a redshift z = 0.238 derived from galaxy lines (Ramsden et al. 2023b).

AT 2023uqm / ZTF23abikzfr had its first alert in the public ZTF alert stream on October 7, 2023, with an r-band difference magnitude 19.24+-0.11 mag. It rose to a peak r-band difference magnitude of 19.05+-0.17 mag, 8 days after first ZTF detection. Prior to the re-brightening or new event, the last detection in the public ZTF alert stream was on November 13, 2023 with a r-band difference magnitude 20.02+-0.16 mag. It had no detections in the public ZTF alert stream until 510 days later (or 547 days after first ZTF detection), on April 6, 2025 with a r-band difference magnitude of 19.28+-0.16 mag. It had its most recent detection on April 16, 2025 with a r-band difference magnitude 19.15+-0.15 mag.

We attach figures that display the AT 2023uqm / ZTF23abikzfr light curve, based on PSF forced photometry on ZTF difference images (Masci et al. 2023) at its mean location. Such data reveal that AT 2023uqm / ZTF23abikzfr has mean apparent magnitudes of 20.09, 19.11 and 18.60 mag in g-, r- and i- bands, respectively, and shows no signs of fainter events between the two brightenings seen in alerts; however, prior to the first ZTF alert, there are three flaring events with smaller amplitudes (up to 1 mag in g-band). These five events last around 40-60 rest-frame days, and hint at a tentative periodicity of around 420 rest-frame days.

AT 2023uqm / ZTF23abikzfr is located towards the center of SDSS J231039.01+345410.9, photometrically classified as a galaxy in SDSS DR16 (Ahumada et al. 2020). We encourage additional follow-up observations of this event.

This report is based on observations obtained with the Samuel Oschin 48-inch Telescope and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant #12540303 (PI: M. J. Graham). We acknowledge the use of the ALeRCE broker (Forster et al. 2021), in particular its Web Interface and the ZTF Forced Photometry Notebook.