A Fast Algorithm for Finding Point Sources in the Fermi Data Stream: FermiFAST

TL;DR

FermiFAST is a rapid algorithm that efficiently identifies gamma-ray point sources in Fermi data by using a hierarchical data structure and likelihood analysis, enabling quick catalog construction and data exploration.

Contribution

The paper introduces FermiFAST, a novel fast algorithm for detecting gamma-ray sources in Fermi data, significantly reducing computation time compared to previous methods.

Findings

Can find half of the 3FGL catalog in minutes with 80% purity.

Achieves high detection significance for most sources outside the galaxy plane.

Enables rapid data exploration and source parameter estimation.

Abstract

We present a new and efficient algorithm for finding point sources in the photon event data stream from the Fermi Gamma-Ray Space Telescope, FermiFAST. The key advantage of FermiFAST is that it constructs a catalogue of potential sources very fast by arranging the photon data in a hierarchical data structure. Using this structure FermiFAST rapidly finds the photons that could have originated from a potential gamma-ray source. It calculates a likehihood ratio for the contribution of the potential source using the angular distribution of the photons within the region of interest. It can find within a few minutes the most significant half of the Fermi Third Point Source catalogue (3FGL) with nearly 80\% purity from the four years of data used to construct the catalogue. If a higher purity sample is desirable, one can achieve a sample that includes the most significant third of the Fermi 3FGL with only five percent of the sources unassociated with Fermi sources. Outside the galaxy plane, all but eight of the 580 FermiFAST detections are associated with 3FGL sources. And of these eight, six yield significant detections of greater than five sigma when a further binned likelihood analysis is performed. This software allows for rapid exploration of the Fermi data, simulation of the source detection to calculate the selection function of various sources and the errors in the obtained parameters of the sources detected.