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H.E.S.S. detection and multi-wavelength study of the z ∼ 1 blazar PKS 0346−27

Context. PKS 0346-27 is a low synchrotron peaked blazar at redshift 0.991. The very high energy (VHE; E > 100 GeV) spectra of blazars are always affected by γγ absorption by the extragalactic background light (EBL), and subsequently no blazars have been detected in VHE γ-rays at redshifts exceedi...

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Main Authors: Aharonian, Felix A. (Author) , Bernlöhr, Konrad (Author) , Goswami, Pranjupriya (Author) , Hinton, James Anthony (Author) , Hofmann, Werner (Author) , Jankowsky, Felix (Author) , Montanari, Alessandro (Author) , Quirrenbach, Andreas (Author) , Taylor, Gabrielle (Author) , Wagner, Stefan (Author) , Zacharias, Michael (Author)
Format: Article (Journal)
Language:English
Published: February 2026
In: Astronomy and astrophysics
Year: 2026, Volume: 706, Pages: 1-12
ISSN:1432-0746
DOI:10.1051/0004-6361/202557228
Online Access:Verlag, kostenfrei, Volltext: https://doi.org/10.1051/0004-6361/202557228
Verlag, kostenfrei, Volltext: https://www.aanda.org/articles/aa/abs/2026/02/aa57228-25/aa57228-25.html
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Author Notes:F. Aharonian, M. Backes, R. Batzofin, Y. Becherini, D. Berge, K. Bernlöhr, B. Bi, M. Böttcher, C. Boisson, J. Bolmont, F. Brun, B. Bruno, C. Burger-Scheidlin, D. Cecchin Momesso, J. Celic, M. Cerruti, A. Chen, M. Chernyakova, J.O. Chibueze, O. Chibueze, B. Cornejo, G. Cotter, J. Damascene Mbarubucyeye, I.D. Davids, J. de Assis Scarpin, M. de Bony de Lavergne, M. de Naurois, E. de Oña Wilhelmi, A.G. Delgado Giler, J. Devin, A. Djannati-Ataï, A. Dmytriiev, K. Egberts, K. Egg, J.-P. Ernenwein, C. Esca nuela Nieves, K. Feijen, M.D. Filipovic, G. Fontaine, S. Funk, S. Gabici, M. Genaro, J.F. Glicenstein, J. Glombitza, P. Goswami, L. Heckmann, B. Hess, J.A. Hinton, W. Hofmann, T.L. Holch, M. Holler, D. Horns, M. Jamrozy, F. Jankowsky, I. Jaroschewski, I. Jung-Richardt, K. Kasprzak, K. Katarzyński, D. Kerszberg, B. Khélifi, N. Komin, K. Kosack, D. Kostunin, R.G. Lang, S. Lazarević, A. Lemière, J.-P. Lenain, P. Liniewicz, A. Luashvili, J. Mackey, D. Malyshev, V. Marandon, M. Mayer, A. Mehta, A.M.W. Mitchell, R. Moderski, L. Mohrmann, A. Montanari, E. Moulin, J. Niemiec, M.O. Moghadam, S. Panny, R.D. Parsons, U. Pensec, P. Pichard, T. Preis, G. Pühlhofer, M. Punch, A. Quirrenbach, A. Reimer, O. Reimer, I. Reis, B. Rudak, K. Sabri, V. Sahakian, D. Jimeno, A. Santangelo, M. Sasaki, F. Schüssler, J.N.S. Shapopi, W. Si Said, Ł Stawarz, S. Steinmassl, T. Takahashi, T. Tanaka, A.M. Taylor, G.L. Taylor, R. Terrier, T. Unbehaun, C. van Eldik, M. Vecchi, C. Venter, J. Vink, T. Wach, S.J. Wagner, A. Wierzcholska, M. Zacharias, A. Zech, and W. Zhong
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Summary:Context. PKS 0346-27 is a low synchrotron peaked blazar at redshift 0.991. The very high energy (VHE; E > 100 GeV) spectra of blazars are always affected by γγ absorption by the extragalactic background light (EBL), and subsequently no blazars have been detected in VHE γ-rays at redshifts exceeding 1. Aims. This is the goal of a target-of-opportunity (ToO) programme by H.E.S.S.: to observe flaring high-redshift (z ≳ 1) blazars. Importantly, extending the redshift range of VHE-detected blazars to z ≳ 1 will yield insights into the cosmological evolution of both the VHE blazar population and the EBL. Methods. We report H.E.S.S. ToO and multi-wavelength observations of the blazar PKS 0346−27. We analysed and modelled the H.E.S.S. data together with simultaneous data from Fermi-LAT, Swift (XRT and UVOT), using single-zone leptonic and hadronic models. Results. PKS 0346-27 was detected by H.E.S.S. at a significance of 6.3 σ during one night on 3 November 2021, while for other nights before and after this day, upper limits on the VHE flux have been determined. No evidence for intra-night γ-ray variability has been found. A flare in high-energy (E > 100 MeV) y-rays detected by Fermi-LAT preceded the H.E.S.S. detection by 2 days. A fit with a single-zone emission model to the contemporaneous spectral energy distribution during the detection night was possible with a proton-synchrotron-dominated hadronic model, requiring a proton-kinetic-energy-dominated jet power temporarily exceeding the source’s Eddington limit, although alternative (e.g. multi-zone) models cannot be ruled out. A one-zone leptonic model is, in principle, also able to fit the flare-state spectral energy distribution. However, it requires implausible parameter choices, in particular, extreme Doppler and bulk Lorentz factors of ≳80.
Item Description:Online veröffentlicht: 13. Februar 2026
Gesehen am 16.04.2026
Physical Description:Online Resource
ISSN:1432-0746
DOI:10.1051/0004-6361/202557228

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