AstroNote 2026-217

We report the identification and spectroscopic follow-up of low luminosity transients detected in the ZTF and Rubin/LSST alert streams. We selected alerts using the Babamulevent broker with the BOOM infrastructure (du Laz+ 2025) and custom filters designed to identify low luminosity transients in D<100 Mpc galaxies. Spectroscopic classification efforts are facilitated through our designated Keck and Gemini programs (PI: Jacobson-Galan) for classifying precursor emission before supernovae occur. Additional spectroscopic observations are conducted through the Z+LIONS Survey (Hinds+ 2026). We thank the Gemini staff for conducting these observations.

1.) ZTF26abgbpyv / 2026sfn: Slow-rising transient currently at M = -14.5 mag (z = 0.0177), confirmed in ZTF forced photometry. GMOS-S spectrum shows narrow Balmer series emission lines with electron-scattering redward “wing,” similar to other precursor events such as 2009ip and 2023ldh (Pastorello+ 2025). Given the spectroscopic and photometric similarities to “Event A” of SN 2023ldh, the terminal explosion could occur within the next ~60 days. 

2.) ZTF26abctnjz / 2026srw / 170587107396419675: Flat ZTF+LSST light curve with approximate absolute magnitude of M = -11.5 mag (z=0.0053). Gemini GMOS-S and P200 NGPS spectra confirms transient redshift and shows an Halpha emission line profile with potential symmetric Lorentzian wings (i.e., IIn-like), which would be indicative of some form of CSM interaction.

3.) 2026qzl / 170591540574421162: Flat LSST light curve with approximate absolute magnitude of M = -12.1 mag (z = 0.0154) and potential earlier ZTF forced photometry detections. Spectroscopic follow-up is planned.

This AstroNote is 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; 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.