AstroNote 2025-118

We report the classification of optical transient ZTF25aajmtzs/AT 2025fak as a tidal disruption event (TDE). The source was selected by the tdescore ML classifier (Stein+2024, doi: 10.3847/2041-8213/ad3337) as a candidate TDE, primarily due to their persistent blue colour and the lack of AGN-like host signatures.

ZTF25aajmtzs/AT 2025fak was first detected by ZTF on 2025-03-20 08:25:03 as an alert, and reported as a transient to TNS on 2025-03-20 17:13:13. The transient was near its peak at the time of discovery and only detected in g-band. Forced photometry revealed additional early detections of this source, beginning 2025-02-24, and a blue (g-r =-0.1) color near peak. The candidate was first identified as a likely TDE by tdescore on 2025-03-24, and assigned for spectroscopic follow-up. ATLAS forced photometry reveals additional early detections of this source.

A spectrum of  ZTF25aajmtzs was taken with the Goodman High Throughput Spectrograph on the 4m SOAR telescope on 2025-04-02 (PI: Andreoni), which exhibited a blue continuum. A redshift of z=0.136 was derived from narrow nebular emission lines from the host galaxy. A broad feature consistent with He II 4686 at this redshift is also present.

ToO observations were completed by the Neil Gehrels Swift Observatory on 2025-04-09. These observations reveal a bright UV source at the location of ZTF25aajmtzs. No sources were detected at the location of ZTF25aajmtzs in multiple previous serendipitous observations of the same field. These observations suggest that ZTF25aajmtzs is UV-bright, as expected for a TDE.

ZTF25aajmtzs reached a peak magnitude of mg=19.8 on 2025-03-26, and has since slowly faded. With the apparent redshift, the peak magnitude of ZTF25aajmtzs would be Mg=-19.4. The source continues to be detected, at a g-band magnitude of 20.0 as of 14 days post-peak.

The luminosity, spectrum, lightcurve evolution, nuclear location and UV brightness are all indicative of a TDE origin for this flare. We therefore classify ZTF25aajmtzs/AT 2025fak as a likely TDE-He.

Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; Operations are conducted by Caltech's Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA.