Abstract
ABSTRACT We report on the detection of very high energy (VHE; E > 100 GeV) γ-ray emission from the BL Lac objects KUV 00311−1938 and PKS 1440−389 with the High Energy Stereoscopic System (H.E.S.S.). H.E.S.S. observations were accompanied or preceded by multiwavelength observations with Fermi/LAT, XRT and UVOT onboard the Swift satellite, and ATOM. Based on an extrapolation of the Fermi/LAT spectrum towards the VHE γ-ray regime, we deduce a 95 per cent confidence level upper limit on the unknown redshift of KUV 00311−1938 of $z$ < 0.98 and of PKS 1440−389 of $z$ < 0.53. When combined with previous spectroscopy results, the redshift of KUV 00311−1938 is constrained to 0.51 ≤ $z$ < 0.98 and of PKS 1440−389 to 0.14 ⪅ $z$ < 0.53.
Highlights
The extragalactic γ -ray sky is strongly dominated by blazars, a class of radio-loud jet-dominated active galactic nuclei (AGNs) in which the relativistic jet is oriented at a small angle with respect to the line of sight
In this paper we present the detection with H.E.S.S. in the very high energy (VHE) regime of two blazars, selected for their hard Fermi/Large Area Telescope (LAT) spectra and large upper limits on their redshift, KUV 00311−1938 and PKS 1440−389
The spectral parameters of sources within the inner 3◦ of the region of interest were left free during the fit, all others were fixed to their 3FGL values
Summary
The extragalactic γ -ray sky is strongly dominated by blazars, a class of radio-loud jet-dominated active galactic nuclei (AGNs) in which the relativistic jet is oriented at a small angle with respect to the line of sight. This alignment leads to strong Doppler enhancement of the observed flux across the entire electromagnetic spectrum as well as a shortening of the apparent variability, which has been observed to be as short as a few minutes (e.g. Gaidos et al 1996; Aharonian et al 2007; Albert et al 2007; Arlen et al 2013). Measurements of blazar SEDs and their variability provide a unique laboratory for probing the microphysical processes of particle acceleration and radiative cooling in AGN jets
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