Very high energy γ-ray emission from two blazars of unknown redshift and upper limits on their distance
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 multi-wavelength observations with Fermi/LAT, XRT and UVOT on board the Swift satellite, and ATOM. Based on an extrapolation of the Fermi/LAT spectrum towards the VHE γ-ray regime, we deduce a 95% 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 for PKS 1440-389 to 0.14 z < 0.53.
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