AstroNote 2026-37

We report the classification of  ZTF26aafpwna (AT2026dmt) and ZTF26aadsfxv (AT2026chm) as a tidal disruption events (TDEs), plus an additional spectrum for ZTF26aabpzxh (TDE2026amv). The sources were 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.

ZTF26aafpwna/AT2026dmt was first detected by ZTF on 2026-02-05 as an alert with a detection of g = 20.18 mag, and reported as a transient to TNS on 2026-02-17. The transient is still rising with g-r ~ -0.346 and no clear color evolution. We obtained a spectrum on 2026-02-16 with LRIS (PI: Chornock), which revealed a blue continuum and broad feature near λ ~ 4686 Å. The redshift was secured from narrow host galaxy emission (z=0.147). With this spectrum, coupled with the persistent blue light curve, we classify ZTF26aafpwna/AT2026dmt as TDE-He.

ZTF26aadsfxv/AT2026chm was first detected by ZTF on 2026-01-25 as an alert with a detection of g = 20.177 mag, and reported as a transient to TNS on 2026-01-25. It was reported as a possible TDE candidate by POTICA and NEEDLE on 2026-02-13 (AN 2026-32, AN 2026-33 respectively). Forced photometry reveals additional early detections of this source beginning on 2026-01-20, with similar evolution and color. It has remained persistently blue (g-r = -0.37 mag) since discovery with no clear color evolution and is currently near peak. An initial spectrum was taken with the Kast spectrograph on the Shane telescope on 2026-02-10 (PI: Chornock), which showed a blue continuum and narrow host emission at z=0.191. We obtained a spectrum with LRIS on 2026-02-16, which revealed a steep blue continuum and no obvious broad emission features, consistent with the TDE-featureless class. Host narrow emission lines confirm the redshift to be z = 0.191. With this spectrum, coupled with the blue light curve and lack of obvious AGN signatures, we classify ZTF26aadsfxv/AT2026chm as TDE-featureless. 

ZTF26aabpzxh/TDE2026amv was first detected by ZTF on 2026-01-14 as an alert with a detection of g = 20.419 mag, and reported as a transient to TNS on 2025-01-14. It was noted as a potential TDE candidate by NEEDLE on 2026-02-13 (AN 2026-33). The transient was rising at the time of discovery and has remained persistently blue (g-r ~ -0.31 mag) since discovery with no clear color evolution. We obtained an initial spectrum with the SOAR Goodman High Throughput Spectrograph (GHTS, PI: Carney) on 2026-01-19, which showed a mostly featureless continuum and host stellar absorption lines at z = 0.091. We obtained an additional spectrum with the Low Resolution Imaging Spectrometer (LRIS) at Keck-I on 2026-02-16. The spectrum reveals a blue continuum with narrow host galaxy emission consistent with star-formation (z=0.091) and a possible broad emission feature near λ ~ 4640 Å, which may be N III. TDE2026amv was classified as a TDE in TNSCR #22991, noting a similar broad feature. With this spectrum, coupled with the persistent blue light curve, we also classify ZTF26aabpzxh/AT2026amv as a likely TDE. The transient is still rising, 34 days after discovery. The possible broad feature near λ ~ 4640 Å may imply that this transient is a member of the TDE-Bowen class.

ZTF26aadtozg/AT2026dmu was first detected by ZTF on 2026-01-14 as an alert with a detection of g = 20.577 mag, and reported as a transient to TNS on 2026-02-17. It has remained persistently blue (g-r ~ -0.29 mag) since discovery with no clear color evolution and is currently near peak. We obtained a spectrum with LRIS on 2026-02-16, which revealed a blue continuum, intermediate width Balmer lines (FWHM ~ 2500-3000 km/s), and He II + N III plus strong O III 3133. However, no strong narrow lines indicative of pre-existing AGN activity (e.g., [O III] 5008) are present. Host stellar absorption lines confirm the redshift to be z = 0.169. The width of the Balmer lines, coupled with the presence of He II, N III, and O III are reminiscent of Bowen Fluorescence Flares (BFFs; Trakhtenbrot+2019, doi: 10.1038/s41550-018-0661-3). We therefore classify ZTF26aadtozg/AT2026dmu as a Bowen Fluorescence Flare at z = 0.169.

We also determined redshifts for two objects previously identified as likely TDEs. ZTF25abuovxv/AT 2025zmb was identified as a candidate TDE by NEEDLE (AN 2025-307) and was spectroscopically classified as an overluminous featureless TDE by Bochenek et al. (AN 2025-327), but with an unknown redshift. Subsequent spectroscopic monitoring with the Kast spectrograph on the Lick 3 m telescope and LRIS on the Keck-I telescope has shown a continued featureless spectrum from the transient. However, weak stellar absorption features such as Ca II H+K and Na I D, diluted by the continuum of the transient, are detected at a consistent redshift of z=0.345 in several epochs of spectroscopy, including one taken 2026-02-16 with LRIS. At this redshift, the peak absolute magnitude of the transient is M_g~-24 AB mag (corrected for substantial Galactic extinction), indicating that this is a very luminous transient.

In addition, ZTF25acfyeke/TDE 2025afvr was previously identified as a likely TDE-featureless by Charalampopoulos (AN 2025-340), although with an uncertain redshift. An optical spectrum taken with Keck-I LRIS on 2026-01-19 displays a featureless blue continuum with weak Mg II absorption lines, as well as superposed Ca II H+K and Na I D absorption from star light in the host galaxy at a consistent redshift of z=0.403. At this redshift, the optical transient peaked at M_g ~-23.8 AB mag.

Both of these events are highly luminous, are spatially coincident with the centroids of faint host galaxies, have featureless optical spectra, and appear to have hosts with older stellar populations lacking any detected narrow emission lines. These properties are consistent with the TDE-featureless classifications previously reported.

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.