Classification of X-ray counterparts of 3FGL sources Virtual Observatory Resource

Authors
  1. Kaur A.
  2. Falcone A.D.
  3. Stroh M.D.
  4. Kennea J.A.
  5. Ferrara E.C.
  6. Published by
    CDS
Abstract

Approximately one-third of the gamma-ray sources in the third Fermi-LAT catalog are unidentified or unassociated with objects at other wavelengths. Observations with the X-Ray Telescope on the Neil Gehrels Swift Observatory (Swift-XRT) have yielded possible counterparts in ~30% of these source regions. The objective of this work is to identify the nature of these possible counterparts, utilizing their gamma-ray properties coupled with the Swift derived X-ray 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 this work, we utilize the X-ray observations performed with the Swift-XRT for the unknown Fermi sources and compare their X-ray and gamma-ray properties to differentiate between the two source classes. We employ two machine-learning algorithms, decision tree and random forest (RF) classifier, to our high signal-to-noise ratio sample of 217 sources, each of which corresponds to Fermi unassociated regions. The accuracy scores for both methods were found to be 97% and 99%, respectively. The RF classifier, which is based on the application of a multitude of decision trees, associated a probability value (P_bzr_) for each source to be a blazar. This yielded 173 blazar candidates from this source sample, with P_bzr_>=90% for each of these sources, and 134 of these possible blazar source associations had P_bzr_>=99%. The results yielded 13 sources with P_bzr_<=10%, which we deemed as reasonable candidates for pulsars, seven of which result with P_bzr_<=1%. There were 31 sources that exhibited intermediate probabilities and were termed ambiguous due to their unclear characterization as a pulsar or a blazar.

Keywords
  1. gamma-ray-astronomy
  2. x-ray-sources
  3. active-galactic-nuclei
  4. pulsars
Bibliographic source Bibcode
2019ApJ...887...18K
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https://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/887/18
IVOA Identifier IVOID
ivo://CDS.VizieR/J/ApJ/887/18
Document Object Identifer DOI
doi:10.26093/cds/vizier.18870018

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History

2021-06-04T10:35:26Z
Resource record created
2021-06-04T10:35:26Z
Created
2024-10-07T20:11:08Z
Updated

Contact

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