A Hybrid Framework for Kilonova Anomaly Detection using Single-Epoch SEDs from the 7-Dimensional Telescope

TL;DR

This paper presents a hybrid machine learning framework that effectively detects kilonovae anomalies using single-epoch medium-band photometry from the 7-Dimensional Telescope, enabling rapid and interpretable transient classification.

Contribution

The study introduces a novel hybrid anomaly detection and classification framework tailored for 7DT data, demonstrating high accuracy and practical follow-up strategies for kilonova detection.

Findings

Recovers over 90% of simulated and observed kilonovae with low contamination.

Using half of the most informative filters maintains near-baseline accuracy.

Combining top filters with a single LSST band achieves similar performance to full models.

Abstract

We develop a hybrid framework to identify kilonovae (KNe), using single-epoch, medium-band spectral energy distributions from the 7-Dimensional Telescope (7DT). The framework integrates an unsupervised anomaly classifier (\texttt{Isolation Forest}) to flag unusual events with a supervised multi-class classifier (\texttt{XGBoost}) that characterizes eight common transient types. Trained on realistically simulated 7DT photometry accounting for per-filter sensitivity, the classifier achieves macro $F_{1}\sim0.80$ ($\sim0.82$) with 20 (40) filters across eight classes, Type~Ia/Ibc/II SNe, SLSNe, TDEs, AGN, stellar variables, and asteroids. Without direct training, the anomaly detector recovers $>$90\% of simulated and observed optically detectable KNe (AT~2017gfo) with a low contamination fraction, with a caveat of limitations of the training sample such as limited redshift range of SNe ($z < 0.15$), and a relatively small number of early non-KNe spectra. A SHAP-based feature analysis reveals that only $\sim$40--50\% of the most informative filters are sufficient to retain near-baseline performance, while red-end filters contribute little. Combining the top-ranked half of the 40 7DT filters with a single LSST band reproduces the full-model accuracy within 1--2\%, suggesting practical follow-up strategies. These results demonstrate that 7DT's medium-band system enables rapid, interpretable classifications and reliable anomaly alerts from single-epoch data -- promising for gravitational-wave follow-up, Rubin alert stream filtering, and serendipitous transient discovery in the 7DT survey.