AstroNote 2026-266

We report the classification of optical transient ZTF26abmlfan/AT 2026yxi 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.

ZTF26abmlfan/AT 2026yxi was first detected by ZTF on 2026-08-05 as an alert. It was first reported as a transient to TNS by ATLAS on 2026-08-14 under the name ATLAS26kaq (TNS Discovery Report 2026-3299), and later reported by ZTF on 2026-08-15. The transient was rising at the time of discovery, and has remained persistently blue (g-r=-0.3 mag) since discovery with no clear colour evolution. The candidate was first identified as a likely TDE by tdescore on 2026-08-15, and assigned for follow-up.

The first low-resolution spectrum of AT 2026yxi was taken by SEDm on 2026-08-16, revealing a blue continuum with no obvious supernova features. A later spectrum with higher-resolution was taken using the Next Generation Palomar Spectrograph (NGPS) at the Palomar 200-in Hale Telescope on 2026-08-31 (PI: Graham), confirming a blue continuum without clear emission features. Ca II absorption features indicate a redshift of z=0.109. 

AT 2026yxi reached a peak magnitude of mg=18.0 on 2026-08-31, and has since slowly faded. With the apparent redshift, the peak magnitude of AT 2026yxi would be Mg=-20.6. The post-peak lightcurve of AT 2026yxi has continued to stay blue, with no evidence of any cooling. The source remains optically bright, at a g-band magnitude of 18.1.

The luminosity, spectrum, lightcurve evolution, and nuclear location are all indicative of a TDE origin for this flare. We therefore classify AT 2026yxi as a likely featureless TDE.

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 Grants No. AST-1440341, AST-2034437, and currently Award #2407588. ZTF receives additional funding from the ZTF partnership. Current members include Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, 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, German Center for Astrophysics, Germany, and OKC, University of Stockholm, Sweden. Operations are conducted by Caltech's Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA.