Evidence of Attenuation of VHE Blazar Spectra by Extragalactic Background Light

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Allen, Cameron
Blazar; EBL; Attenuation; Cherenkov; VERITAS; Fermi; Cosmology, Relativity, and Gravity; External Galaxies; Other Astrophysics and Astronomy
article description
The spectrum of two blazar objects, 1ES 1959+650 and 1ES 2344+514, are analyzed for evidence of interactions with the Extragalactic Background Light (EBL), using combined data from the Very Energetic Radiation Imaging Telescope Array System and the Fermi Gamma-ray Space Telescope, By analyzing the distinct curvature across the combined spectrum, we infer that the very-high energy (VHE) gamma-rays must be attenuated by interactions with the EBL. We also find that the measured 1ES 1959+650 spectrum is sensitive to the intrinsic blazar model, with a preference for a power-law with an exponential cutoff (EPWL). The measured curvature is a combination of the EBL attenuation and the exponential cut-off, as determined by statistical tests assuming that there is no EBL. Finally, a test of the optical depth due to the EBL indicates that the two blazars are consistent with the amount of EBL given by the Franceschini model of intergalactic optical depth.