Very high energy γ-ray emission from two blazars of unknown redshift and upper limits on their distance
Authors: Abdalla H , Adam R , Aharonian F , Ait Benkhali F , Angüner E O , Arakawa M , Arcaro C , Armand C , Armstrong T , Ashkar H , Backes M , Baghmanyan V , Barbosa Martins V , Barnacka A , Barnard M , Becherini Y , Berge D , Bernlöhr K , Böttcher M , Boisson C , Bolmont J , Bonnefoy S , Bregeon J , Breuhaus M , Brun F , Brun P , Bryan M , Büchele M , Bulik T , Bylund T , Caroff S , Carosi A , Casanova S , Chand T , Chandra S , Chen A , Cotter G , Curyło M , Davids I D , Davies J , Deil C , Devin J , deWilt P , Dirson L , Djannati-Ataï A , Dmytriiev A , Donath A , Doroshenko V , Dyks J , Egberts K , Eichhorn F , Emery G , Ernenwein J -P , Feijen K , Fegan S , Fiasson A , Fontaine G , Funk S , Füßling M , Gabici S , Gallant Y A , Giavitto G , Giunti L , Glawion D , Glicenstein J F , Gottschall D , Grondin M -H , Hahn J , Haupt M , Hermann G , Hinton J A , Hofmann W , Hoischen C , Holch T L , Holler M , Hörbe M , Horns D , Huber D , Iwasaki H , Jamrozy M , Jankowsky D , Jankowsky F , Jardin-Blicq A , Joshi V , Jung-Richardt I , Kastendieck M A , Katarzyński K , Katsuragawa M , Katz U , Khangulyan D , Khélifi B , Klepser S , Kluźniak W , Komin Nu , Konno R , Kosack K , Kostunin D , Kreter M , Lamanna G , Lemière A , Lemoine-Goumard M , Lenain J -P , Leser E , Levy C , Lohse T , Lypova I , Mackey J , Majumdar J , Malyshev D , Malyshev D , Marandon V , Marchegiani P , Marcowith A , Mares A , Martí-Devesa G , Marx R , Maurin G , Meintjes P J , Moderski R , Mohamed M , Mohrmann L , Moore C , Morris P , Moulin E , Muller J , Murach T , Nakashima S , Nakashima K , de Naurois M , Ndiyavala H , Niederwanger F , Niemiec J , Oakes L , O’Brien P , Odaka H , Ohm S , de Oña Wilhelmi E , Ostrowski M , Panter M , Parsons R D , Peyaud B , Piel Q , Pita S , Poireau V , Noel A P , Prokhorov D A , Prokoph H , Pühlhofer G , Punch M , Quirrenbach A , Raab S , Rauth R , Reimer A , Reimer O , Remy Q , Renaud M , Rieger F , Rinchiuso L , Romoli C , Rowell G , Rudak B , Ruiz-Velasco E , Sahakian V , Sailer S , Saito S , Sanchez D A , Santangelo A , Sasaki M , Scalici M , Schüssler F , Schutte H M , Schwanke U , Schwemmer S , Seglar-Arroyo M , Senniappan M , Seyffert A S , Shafi N , Shiningayamwe K , Simoni R , Sinha A , Sol H , Specovius A , Spencer S , Spir-Jacob M , Stawarz Ł , Steenkamp R , Stegmann C , Steppa C , Takahashi T , Tavernier T , Taylor A M , Terrier R , Tiziani D , Tluczykont M , Tomankova L , Trichard C , Tsirou M , Tsuji N , Tuffs R , Uchiyama Y , van der Walt D J , van Eldik C , van Rensburg C , van Soelen B , Vasileiadis G , Veh J , Venter C , Vincent P , Vink J , Völk H J , Vuillaume T , Wadiasingh Z , Wagner S J , Watson J , Werner F , White R , Wierzcholska A , Yang R , Yoneda H , Zacharias M , Zanin R , Zargaryan D , Zdziarski A A , Zech A , Zhu S J , Zorn J , Żywucka N , Cerruti M 
Published: April 2020

ABSTRACT
We report on the detection of very high energy (VHE; E &gt; 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 $z$ &lt; 0.98 and of PKS 1440−389 of $z$ &lt; 0.53. When combined with previous spectroscopy results, the redshift of KUV 00311−1938 is constrained to 0.51 ≤ $z$ &lt; 0.98 and of PKS 1440−389 to 0.14 ⪅ $z$ &lt; 0.53.