Z+LIONS is a public, magnitude-limited survey that extends systematic spectroscopic classification in the Legacy Survey of Space and Time (LSST) era, building on the success of previous Zwicky Transient Facility (ZTF) classification efforts - the Bright Transient survey (BTS; Fremling et al., 2020, Perley et al., 2020, Rehemtulla et al., 2024 ) and Complete Astronomical Transient Survey within 150 Mpc (CATS150; 2025TNSAN..64....1D). The survey targets all transients detected by either the ZTF or LSST alert streams that peak brighter than 20th magnitude in the ~10,000 sq. deg. overlap, exploiting improved efficiency and throughput of the Next Generation Palomar Spectrograph (NGPS; 2024TNSAN.340....1K) on the Palomar 200-inch Hale telescope. All bright (<20 mag) transients identified in the ZTF+LSST overlap are reported, and all P60/SEDM classifications are submitted to TNS. We encourage community follow-up of all sources.
The primary science goals of Z+LIONS include constraining the faint end of the core-collapse supernova luminosity function, characterizing SN pre- and post-cursors, and discovering ultra-stripped supernovae, strongly-lensed supernovae, high mass core-collapse SNe progenitors, tidal disruption events, and superluminous supernovae. The systematic approach and high spectroscopic completeness of Z+LIONS, combined with the depth and cadence of ZTF+LSST observations, will make it a uniquely valuable source of well-characterized, spectroscopically-confirmed transients for training the next generation of machine-learning classifiers on the full LSST alert stream.
As of 02/24/2026, we have 79 transients in the sample, of which 35 are spectroscopically classified primarily by NGPS on the Palomar 200-inch. The sample consists of 30 Type Ia SNe, 3 Type IIn SNe, and 2 Type Ic SNe. Survey status and statistics can be found here: https://sites.astro.caltech.edu/LIONS/z+lions.html.
Note that starting February 6th, the ZTF public alert stream now only includes detections from our 1-day cadence gri survey overlapping the LSST footprint, maximizing synergy between the two surveys.
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; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; National Central University, Taiwan; DESY and DZY; Operations are conducted by Caltech's Optical Observatory (COO) and Caltech/IPAC.
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