On instrument response functionP8R2_SOURCE_V6. The recently updated PASS8

On board the Fermi satellite, LAT is a pair-conversion telescopedesigned to detect HE ?-rays in the energy range 20 MeV – 300GeV. Operating since August 4, 2008, it is always in the surveymode by default, scanning the entire sky every ~3 hours, therebyproviding continuous monitoring of ?-ray sources. Details aboutthe Fermi LAT can be found in Atwood et al. (2009).In the current paper we analyze the data accumulated for 8 years,from the beginning of the Fermi LAT mission up to August 8,2016 (MET 239557417-460339204). Fermi LAT Science Toolversion v10r0p5 is used with the instrument response functionP8R2_SOURCE_V6. The recently updated PASS8 version of thedata in the energy range between 100 MeV – 300 GeV is analyzed.The entire data set is filtered with gtselect and gtmktimetools and only the events with a high probability of being photonsevclass=128, evtype=3 have been considered. The zenithangle cutoff > 90?is made to exclude atmospheric ?-rays fromthe Earth limb that can be a significant source of background.The photons from a circular Region of Interest (ROI) centered onVLBI radio positions of 3C 120 (RA,dec) = (68.296, 5.354) areused in the analysis. The photons are binned within 14.1?×14.1?square regions with gtbin tool, with a stereographic projectioninto 0.1? × 0.1? pixels. In order to account for the emissionfrom other sources within ROI, the model file is generated usingthe Fermi-LAT third source catalog (Acero et al. 2015) and thesources within 10? +5?from the position of 3C 120 are includedin the model file. Since 3C 120 is not included in the catalog,a point-like source in the known location of 3C 120 was addedto the model file. The Galactic background component is modeledusing the LAT standard diffuse background model gll_ iem_ v05_ rev1 and iso_source_v05 – for the isotropic ?-ray background.The normalization of background models as well as thefluxes and spectral indices of the sources within 10?are left asfree parameters during the analysis.


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