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H.E.S.S. detection of very high-energy γ-ray emission from the quasar PKS 0736+017

H. Abdalla R. Adam 1 F. Aharonian F. Ait Benkhali E. O. Angüner 2 M. Arakawa C. Arcaro C. Armand 3 H. Ashkar 4 M. Backes V. Barbosa Martins 5 M. Barnard Y. Becherini D. Berge 5 K. Bernlöhr R. Blackwell M. Böttcher C. Boisson 6 J. Bolmont 7 S. Bonnefoy 5 J. Bregeon 8 M. Breuhaus F. Brun 4 P. Brun 4 M. Bryan M. Büchele T. Bulik T. Bylund M. Capasso S. Caroff 7 A. Carosi 3 S. Casanova M. Cerruti 7, * T. Chand S. Chandra A. Chen S. Colafrancesco M. Curyło I. D. Davids C. Deil J. Devin 9 P. Dewilt L. Dirson A. Djannati-Ataï 10 A. Dmytriiev 6 A. Donath V. Doroshenko L. O’c. Drury J. Dyks K. Egberts G. Emery 7 J.-P. Ernenwein 2 S. Eschbach K. Feijen S. Fegan 1 A. Fiasson 3 G. Fontaine 1 S. Funk M. Füßling 5 S. Gabici 10 Y. A. Gallant 8 F. Gaté 3 G. Giavitto 5 D. Glawion J. F. Glicenstein 4 D. Gottschall M.-H. Grondin 9 J. Hahn M. Haupt 5 G. Heinzelmann G. Henri 11 G. Hermann J. A. Hinton W. Hofmann C. Hoischen T. L. Holch M. Holler D. Horns D. Huber H. Iwasaki M. Jamrozy D. Jankowsky F. Jankowsky A. Jardin-Blicq I. Jung-Richardt M. A. Kastendieck K. Katarzyński M. Katsuragawa U. Katz D. Khangulyan B. Khélifi 10 J. King S. Klepser 5 W. Kluźniak Nu. Komin K. Kosack 4 D. Kostunin 5 M. Kraus G. Lamanna 3 J. Lau A. Lemière 10 M. Lemoine-Goumard 9 J.-P. Lenain 7 E. Leser 5 C. Levy 7 T. Lohse I. Lypova 5 J. Mackey J. Majumdar 5 D. Malyshev V. Marandon A. Marcowith 8 A. Mares 9 C. Mariaud 1 G. Martí-Devesa R. Marx G. Maurin 3 P. J. Meintjes A. M. W. Mitchell R. Moderski M. Mohamed L. Mohrmann J. Muller 1 C. Moore Emmanuel Moulin 4 T. Murach 5 S. Nakashima M. de Naurois 1 H. Ndiyavala F. Niederwanger J. Niemiec L. Oakes P. O’brien H. Odaka S. Ohm 5 E. de Oña Wilhelmi 5 M. Ostrowski I. Oya 5 M. Panter R. D. Parsons C. Perennes 7 P.-O. Petrucci 11 B. Peyaud 4 Q. Piel 3 S. Pita 10 V. Poireau 3 A. Priyana Noel D. A. Prokhorov H. Prokoph 5, * G. Pühlhofer M. Punch 10 A. Quirrenbach S. Raab R. Rauth A. Reimer O. Reimer Q. Remy 8 M. Renaud 8 F. Rieger L. Rinchiuso 4 C. Romoli G. Rowell B. Rudak E. Ruiz-Velasco V. Sahakian S. Saito D. A. Sanchez 3 A. Santangelo M. Sasaki R. Schlickeiser F. Schüssler 4 A. Schulz 5 H. Schutte U. Schwanke S. Schwemmer M. Seglar-Arroyo 4 M. Senniappan A. S. Seyffert N. Shafi K. Shiningayamwe R. Simoni A. Sinha 10 H. Sol 6 A. Specovius M. Spir-Jacob 10 Ł. Stawarz R. Steenkamp C. Stegmann 5 C. Steppa T. Takahashi 12 T. Tavernier 4 A. M. Taylor 5 R. Terrier 10 D. Tiziani M. Tluczykont C. Trichard 1 M. Tsirou 8 N. Tsuji R. Tuffs Y. Uchiyama D. J. van der Walt C. van Eldik C. van Rensburg B. van Soelen G. Vasileiadis 8 J. Veh C. Venter P. Vincent 7 J. Vink F. Voisin H. J. Völk T. Vuillaume 3 Z. Wadiasingh S. J. Wagner R. White 13 A. Wierzcholska R. Yang 13 H. Yoneda M. Zacharias R. Zanin A. A. Zdziarski A. Zech 6 A. Ziegler J. Zorn N. Żywucka P. S. Smith
Abstract : Context. Flat-spectrum radio-quasars (FSRQs) are rarely detected at very high energies (E ≥ 100 GeV) due to their low-frequency-peaked spectral energy distributions. At present, only six FSRQs are known to emit very high-energy (VHE) photons, representing only 7% of the VHE extragalactic catalog, which is largely dominated by high-frequency-peaked BL Lacertae objects.Aims. Following the detection of MeV–GeV γ-ray flaring activity from the FSRQ PKS 0736+017 (z = 0.189) with Fermi-LAT, the H.E.S.S. array of Cherenkov telescopes triggered target-of-opportunity (ToO) observations on February 18, 2015, with the goal of studying the γ-ray emission in the VHE band.Methods. H.E.S.S. ToO observations were carried out during the nights of February 18, 19, 21, and 24, 2015. Together with Fermi-LAT, the multi-wavelength coverage of the flare includes Swift observations in soft X-ray and optical-UV bands, and optical monitoring (photometry and spectro-polarimetry) by the Steward Observatory, and the ATOM, the KAIT, and the ASAS-SN telescopes.Results. VHE emission from PKS 0736+017 was detected with H.E.S.S. only during the night of February 19, 2015. Fermi-LAT data indicate the presence of a γ-ray flare, peaking at the time of the H.E.S.S. detection, with a flux doubling timescale of around six hours. The γ-ray flare was accompanied by at least a 1 mag brightening of the non-thermal optical continuum. No simultaneous observations at longer wavelengths are available for the night of the H.E.S.S. detection. The γ-ray observations with H.E.S.S. and Fermi-LAT are used to put constraints on the location of the γ-ray emitting region during the flare: it is constrained to be just outside the radius of the broad-line region rBLR with a bulk Lorentz factor Γ ≃ 20, or at the level of the radius of the dusty torus rtorus with Γ ≃ 60.Conclusions. PKS 0736+017 is the seventh FSRQ known to emit VHE photons, and at z = 0.189 is the nearest so far. The location of the γ-ray emitting region during the flare can be tightly constrained thanks to opacity, variability, and collimation arguments.
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H. Abdalla, R. Adam, F. Aharonian, F. Ait Benkhali, E. O. Angüner, et al.. H.E.S.S. detection of very high-energy γ-ray emission from the quasar PKS 0736+017. Astronomy and Astrophysics - A&A, EDP Sciences, 2020, 633, pp.A162. ⟨10.1051/0004-6361/201935906⟩. ⟨cea-02458766⟩

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