Searching for Unmodeled Sources Using the Earth Occultation Data from the Fermi GBM

TL;DR

This paper introduces an imaging algorithm using Fermi GBM Earth Occultation data to detect unmodeled x-ray and gamma-ray sources, providing all-sky images over 2.5 years in specific energy bands.

Contribution

The paper develops a novel imaging method to identify new sources in GBM data, expanding beyond catalog-based flux measurements.

Findings

All-sky images generated in 12-25 keV and 100-300 keV bands

Detection of unmodeled sources in the data

Demonstrated over 2.5 years of observations

Abstract

Employing the 12 NaI detectors in the Fermi GBM, the Earth Occultation Technique (EOT) can be used to measure the fluxes of x-ray and gamma-ray sources. Each time a source passes behind the Earth (or emerges from behind the Earth), a step-like feature is produced in the detector count rate. With a predefined catalog of source positions, the times of the occultation steps can be calculated, the individual steps fit, and the fluxes derived. However, in order to find new sources and generate a complete catalog, a method is needed for generating an image of the sky. An imaging algorithm has been developed to generate all-sky images using the GBM data. Here we present imaging results from ~2.5 years of data in the 12-25 keV and 100-300 keV energy bands.