Pandora cluster Lensing, AGN, and Transient Exploration (PLATE) from JWST Multi-Epoch Imaging. I. Discovery of a type II supernova candidate in a spiral galaxy at $z=0.7$

Yuxuan Pang, Xin Wang, Ping Chen, Subo Dong, Hang Zhou, Shengzhe Wang, Qianqiao Zhou, Xunda Sun, Jifeng Liu, Hu Zhan, Karl Glazebrook, Ivo Labbé, Themiya Nanayakkara, David A. Coulter, Justin D. R. Pierel, Armin Rest, Jujia Zhang

First listed 2026-08-24 | Last updated 2026-08-21

Abstract

We report the discovery and multi-wavelength analysis of a $z\sim0.7$ transient PLATE-23a in the Abell 2744 field, as the first results of the Pandora Lensing, AGN, and Transient Exploration (PLATE) project. Using multi-epoch JWST NIRCam imaging spanning from 2022 to 2025, we detect PLATE-23a in 12 filters. Difference-imaging analysis reveals its rising and declining phases. The host galaxy of PLATE-23a is a barred spiral at $z=0.688$ with a stellar mass of $\sim 10^{10.4}M_{\odot}$ and a star formation rate of $\sim5.1M_{\odot}~\rm yr^{-1}$, placing it on the star-forming main sequence. Bayesian light-curve classification strongly favors a type IIP supernova (SN) origin. It lies $\sim 13\rm kpc$ (after lensing correction) from the galaxy center in a region of low local star formation, suggesting the progenitor may have migrated from a distant star-forming clump. Physical properties derived from blackbody modeling indicate a temperature decreasing from $\sim8010\rm K$ to $\sim6100\rm K$ at around 65 days after the explosion; the late-time SED is consistent with entering the radioactive decay phase at about one rest-frame year. This work demonstrates the power of deep, multi-epoch JWST observations for studying transients at cosmological distances.

Short digest

Pang et al. present PLATE-23a, a transient discovered through difference imaging of roughly 10,000 JWST/NIRCam exposures in the Abell 2744 field, with 12-filter coverage across 2022–2025. The event is hosted by a barred, main-sequence spiral at z=0.688, but occurs at a lensing-corrected projected offset of about 13 kpc in a locally low-star-formation region, suggesting a progenitor displaced from a more actively star-forming clump. Bayesian fits to the early multiband light curve strongly favor a Type IIP interpretation, while the cooling blackbody evolution from about 8010 K to 6100 K by roughly 65 rest-frame days and a late SED consistent with radioactive decay trace the expected Type II evolution. As a first PLATE result, the paper illustrates how deep, irregularly cadenced JWST imaging can recover and physically characterize ordinary core-collapse supernovae at cosmological distance.

Key figures to inspect

• Figure 1. Difference images directly establish PLATE-23a as a real variable source by showing both its brightening and fading in F444W, making this the clearest visual introduction to the transient discovery.
• Figure 3. The resolved host maps place the supernova in context: they show that PLATE-23a lies outside the locally strongest star-forming regions despite residing in a star-forming barred spiral, supporting the inferred displaced-progenitor scenario.
• Figure 4. This is the central classification diagnostic, comparing the observed early multiband evolution with Type Ia, Ib/c, and Type II templates and identifying the Type IIP-like SN 2006iw model as the preferred match.
• Figure 6. The multi-epoch SED fits provide the physical evolution behind the classification, showing early blackbody-like emission and the later departure from an optically thick continuum toward a Type IIP-like late-time spectrum.
• Figure 8. The full light-curve synthesis connects the early Type IIP template to the late-time radioactive-decay model, making the paper's interpretation of the event over its extended rest-frame baseline explicit.