Fermi Gamma-ray Space Telescope

A Search for Counterparts to the Fermi Unassociated Sources using the Swift X-ray Telescope

Amanpreet Kaur
(Abe D. Falcone)


The Fermi Gamma Ray Observatory has revolutionized gamma-ray astronomy by discovering thousands of sources since its launch in 2008. However, the unidentified population of these sources in the Fermi catalogs is still substantial, e.g. one third of the Fermi sources in the latest 3FGL catalog are unidentified. Swift-XRT observations of these Fermi unassociated fields have found possible X-ray counterparts in ~30% of these Fermi unassociated uncertainty regions, and approximately half of these sources were previously uncataloged in either radio/optical/X-ray catalogs. The main objective of this work is to identify the nature of these possible counterparts, utilizing the properties of known Fermi sources coupled with the X-ray source properties. The majority of the known sources in the Fermi catalogs are blazars, which constitute the bulk of the extragalactic gamma-ray source population. The galactic population on the other hand is dominated by pulsars. Overall, these two categories constitute the majority of all gamma-ray objects. Blazars and pulsars occupy different parameter space when X-ray fluxes are compared with various gamma-ray properties. In our work, we utilize the X-ray observations performed with Swift-XRT telescope for the unknown Fermi sources and compare their X-ray and gamma-ray properties to differentiate between the two source classes. These initial investigations can help discriminate between blazars and pulsars, and will be further investigated by utilizing the principles of multivariate principle component analysis as well as machine learning techniques.