AstroNote 2025-348

AT 2025afsj/ZTF18aaxqitv (RA=12:55:07.09, Dec=+34:08:46.70) was discovered by the ZTF survey on 2025-11-23 (MJD=61002.54), in the Seyfert galaxy SDSS J125507.07+340846.6 at a redshift of z = 0.1654. It has been suggested as a TDE candidate by POTICA on 2025-12-18 based on its ZTF light curves (AstroNote 2025-341). We triggered optical spectroscopic observations of AT2025afsj using YFOSC on board the Lijiang 2.4 m telescope on 2025-12-20 (MJD 61029). The spectrum shows a significantly bluer continuum compared to the archival SDSS spectrum of the host galaxy and exhibits a prominent broad He II λ4686 emission line, along with a substantial increase in the flux of broad Balmer lines. These spectral characteristics are consistent with those of tidal disruption events (TDE-H+He).

We immediately triggered Swift ToO observations of AT2025afsj following its spectroscopic classification based on the Lijiang 2.4m spectrum. The first epoch was observed on 2025-12-25 (MJD=61034.74). No significant X-ray emission was detected, and a 3-sigma upper limit of 3.454e-13 erg s⁻¹ cm⁻² was derived for the 0.3–10 keV flux. In contrast, the source is clearly detected in the UVOT UV bands, with AB magnitudes of UVW2 = 17.93 ± 0.04 mag and UVM2 = 18.05 ± 0.08, after correcting for Galactic extinction and subtracting the host-galaxy contribution based on SED fitting. Adopting the SDSS spectroscopic redshift of 0.1654, the UV–optical SED can be well fit by a blackbody with a temperature of 22069 ± 519 K, consistent with typical TDEs.

We tentatively classified AT2025afsj as a TDE in AGN given its He II λ4686 emission line and blue continuum. Continued monitoring of this source is ongoing.