# STACCATO: A Novel Solution to Supernova Photometric Classification with Biased Training Sets

## TL;DR

This paper introduces STACCATO, a method that synthetically augments biased supernova training data using Gaussian processes, significantly improving classification accuracy of Type Ia supernovae from light curves.

## Contribution

The paper presents STACCATO, a novel data augmentation technique that enhances supernova classification accuracy with biased training sets by generating synthetic light curves based on Gaussian processes.

## Key findings

- STACCATO improves AUC from 0.93 to 0.96.
- Method increases true positive rate for high-redshift SNe by up to 50.
- Performance approaches that of an unbiased training set.

## Abstract

We present a new solution to the problem of classifying Type Ia supernovae from their light curves alone given a spectroscopically confirmed but biased training set, circumventing the need to obtain an observationally expensive unbiased training set. We use Gaussian processes (GPs) to model the supernovae's (SN) light curves, and demonstrate that the choice of covariance function has only a small influence on the GPs ability to accurately classify SNe. We extend and improve the approach of Richards et al (2012} -- a diffusion map combined with a random forest classifier -- to deal specifically with the case of biassed training sets. We propose a novel method, called STACCATO (SynThetically Augmented Light Curve ClassificATiOn') that synthetically augments a biased training set by generating additional training data from the fitted GPs. Key to the success of the method is the partitioning of the observations into subgroups based on their propensity score of being included in the training set. Using simulated light curve data, we show that STACCATO increases performance, as measured by the area under the Receiver Operating Characteristic curve (AUC), from 0.93 to 0.96, close to the AUC of 0.977 obtained using the 'gold standard' of an unbiased training set and significantly improving on the previous best result of 0.88. STACCATO also increases the true positive rate for SNIa classification by up to a factor of 50 for high-redshift/low brightness SNe.