Machine learning application to Fermi-LAT data: sharpening all-sky map and emphasizing variable sources

TL;DR

This paper introduces machine learning algorithms to enhance all-sky gamma-ray maps from Fermi-LAT data, improving image quality and enabling detection of variable sources like AGNs without relying on emission models.

Contribution

It demonstrates the application of ML image processing to generate sharper all-sky maps from limited data and highlights its potential for detecting variable and transient sources.

Findings

ML improves all-sky map quality compared to standard methods

Diffuse galactic emission can be reconstructed from short observations

ML methods can detect variable sources like AGNs

Abstract

A novel application of machine-learning (ML) based image processing algorithms is proposed to analyze an all-sky map (ASM) obtained using the Fermi Gamma-ray Space Telescope. An attempt was made to simulate a one-year ASM from a short-exposure ASM generated from one-week observation by applying three ML based image processing algorithms: dictionary learning, U-net, and Noise2Noise. Although the inference based on ML is less clear compared to standard likelihood analysis, the quality of the ASM was generally improved. In particular, the complicated diffuse emission associated with the galactic plane was successfully reproduced only from one-week observation data to mimic a ground truth (GT) generated from a one-year observation. Such ML algorithms can be implemented relatively easily to provide sharper images without various assumptions of emission models. In contrast, large deviations between simulated ML maps and GT map were found, which are attributed to the significant temporal variability of blazar-type active galactic nuclei (AGNs) over a year. Thus, the proposed ML methods are viable not only to improve the image quality of an ASM, but also to detect variable sources, such as AGNs, algorithmically, i.e., without human bias. Moreover, we argue that this approach is widely applicable to ASMs obtained by various other missions; thus, it has the potential to examine giant structures and transient events, both of which are rarely found in pointing observations.