AstroNote 2026-7

The transient AT 2025aljd/ZTF25aclckzl was first detected in the ZTF public stream on 2025 Dec 18 UT with an apparent magnitude of g=20.7 AB mag and first reported to TNS on 2026 Jan 09 (Sollerman et al.; Transient Report No. 286142). The light curve has slowly risen to an apparent peak near g~19.4 AB mag with persistent blue colors (g-r ~ -0.45 mag). The transient was flagged by the ML classifier tdescore (Stein et al., 2024, ApJL, 965, L14) due to its blue colors and lack of evidence for past variability or AGN activity in the host galaxy, and assigned for spectroscopic follow-up on 2026 Jan 08. This transient was later independently identified as a TDE candidate by NEEDLE (Sheng et al., AstroNote 2026-6).

We obtained a spectrum of AT 2025aljd on 2026 Jan 12.5 UT using the Kast Spectrograph on the Shane 3 m telescope at Lick Observatory covering the range 3500-10500 Angs. The spectrum reveals a very blue continuum, with some host galaxy emission superposed that is consistent with star light from an early-type galaxy at redshift z=0.150 (e.g., Ca II H+K). No narrow nebular emission lines are detected. The transient spectrum is blue and largely featureless, with no clear broad features present at the Balmer lines. A broad emission feature may be present near He II 4686, although subtraction of the host galaxy star light will be necessary to be secure. We therefore classify this transient as a TDE, likely of the featureless or TDE-He subtype.

Swift follow-up observations have been requested.

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; 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, 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.