A Poisson-process AutoDecoder for Astrophysical, Time-variable, X-ray Sources

X-ray observing facilities such as the Chandra X-ray Observatory and the eROSITA all sky survey have detected millions of astronomical sources associated with high-energy phenomena. The arrival of photons as a function of time follows a Poisson process and can vary by orders-of-magnitude, presenting obstacles for downstream tasks such as source classification, physical property derivation and anomaly detection. Previous work has either failed to directly capture the Poisson nature of the data or only focuses on Poisson rate function reconstruction. In this work, we present Poisson Process AutoDecoder (PPAD). PPAD is a neural field decoder that maps fixed-length latent features to continuous Poisson rate functions across energy band and time via unsupervised learning. It reconstructs the rate function and yields a representation at the same time. We demonstrate the efficacy of PPAD reconstruction, regression, classification and anomaly detection experiments using the Chandra Source Catalog.