Unveiling the nature of the unidentified gamma-ray sources. IV. The Swift catalog of potential X-ray counterparts. (2013)
Keywords :
catalogs - galaxies active - gamma rays: galaxies - radiation mechanisms: non-thermal - X-rays: galaxies
Abstract:A significant fraction (~30%) of the high-energy {gamma}-ray sources listed in the second Fermi Large Area Telescope (LAT) catalog are still of unknown origin, having not yet been associated with counterparts at lower energies. To investigate the nature of these enigmatic sources, we present an extensive search of X-ray sources lying in the positional uncertainty region of a selected sample of these unidentified gamma-ray sources (UGSs) that makes use of all available observations performed by the Swift X-ray Telescope before 2013 March 31, available for 205 UGSs. To detect the fainter sources, we merged all the observations covering the Fermi LAT positional uncertainty region at a 95% level of confidence of each UGS. This
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The initial sample considered in our analysis is constituted by the
299 unidentified gamma-ray sources (UGSs) in the 2FGL catalog that do
not present any {gamma}-ray analysis flag (Nolan et al. 2012,
Cat. J/ApJS/199/31).
After Fermi was launched, the Swift XRT Survey of Fermi Unassociated
Sources was started in order to perform follow-up observations of the
unidentified gamma-ray sources (UGSs) in an attempt to find their
potential X-ray counterparts (PI: A. Falcone). We analyze all data
collected between the beginning of the follow-up program until 2013
March 31. We note that 203 of the 205 UGSs that constitute our sample
have been also observed in the optical and UV by UVOT. We then
produced for each X-ray observation the corresponding merged UVOT
event files, adopting standard procedures.
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