Scrutinizing the 2020 multiwavelength outburst of PKS 0903 - 57 through observations with H.E.S.S․

Acharyya A, Aharonian F, Ait Benkhali F, Alkan A, Ashkar H, Backes M, Barbosa Martins V, Batzofin R, Becherini Y, Berge D, Bernlöhr K, Bi B, Böttcher M, Boisson C, Bolmont J, Borowska J, Brose R, Brown A, Brun F, Bruno B, Bulik T, Burger-Scheidlin C, Casanova S, Celic J, Cerruti M, Chandra S, Chen A, Chernyakova M, Chibueze JO, Chibueze O, Cornejo B, Cotter G, Cozzolongo G, Damascene Mbarubucyeye J, de Assis Scarpin J, de Naurois M, de Oña Wilhelmi E, Delgado Giler AG, Devin J, Djannati-Ataï A, Djuvsland J, Dmytriiev A, Doroshenko V, Egg K, Einecke S, Ernenwein JP, Escañuela Nieves C, Feijen K, Filipovic MD, Fontaine G, Funk S, Gabici S, Gallant YA, Genaro M, Glicenstein JF, Goswami P, Grolleron G, Haerer L, Heckmann L, Hermann G, Heß B, Hinton JA, Hofmann W, Holch TL, Holler M, Horns D, Jamrozy M, Jankowsky F, Jung-Richardt I, Kasai E, Katarzyński K, Kerszberg D, Khatoon R, Khélifi B, Kluźniak W, Komin N, Kostunin D, Guedes Lang R, Lemière A, Lenain JP, Luashvili A, Mackey J, Malyshev D, Marandon V, Martí-Devesa G, Marx R, Mayer M, Mehta A, Mitchell A, Moderski R, Moghadam MO, Mohrmann L, Montanari A, Moulin E, Moyeni D, Niemiec J, Olivera-Nieto L, Panny S, Panter M, Parsons RD, Pensec U, Pita S, Pühlhofer G, Quirrenbach A, Regeard M, Reimer A, Reimer O, Ren HX, Reville B, Rieger F, Rowell G, Rudak B, Sabri K, Sahakian V, Salzmann H, Sasaki M, Schäfer J, Schüssler F, Schutte HM, Shapopi JN, Sharma A, Si Said W, Sol H, Spencer S, Stawarz , Steenkamp R, Steinmassl S, Steppa C, Takahashi T, Tanaka T, Taylor AM, van Eldik C, Vecchi M, Vink J, Wach T, Wagner SJ, Wierzcholska A, Zacharias M, Zdziarski AA, Zech A, Zywucka N (2026)

Publication Type: Journal article

Publication year: 2026

Journal

Book Volume: 53

Article Number: 100599

DOI: 10.1016/j.jheap.2026.100599

Abstract

The blazar PKS 0903 - 57 has recently been classified as a flat spectrum radio quasar at a redshift of z=0.2621. In March and April 2020, Fermi -LAT and AGILE reported tremendous activity in high-energy γ rays with the flux increasing by ∼ 2 orders of magnitude compared to quiescence. The flare was observed with H.E.S.S. in very-high-energy γ rays for six nights with a total observation time of 13.1 h, resulting in the discovery of PKS 0903 - 57 in this energy band with an average flux of 1.5×10⁻¹⁰ph cm⁻²s⁻¹ above an energy threshold of ∼ 180 GeV corresponding to 60% of the Crab Nebula flux above the same threshold. The very-high-energy γ -ray flux was strongly variable. X-ray and optical data were collected with Swift and ATOM, and also indicate significant variability. The observed multiwavelength flux and spectral variability during the H.E.S.S. observation window suggest variability time scales on the order of a few hours and reveal complex correlation patterns. The lack of absorption beyond that of the extragalactic background light in the γ -ray domain suggests that the emission region was located outside of the broad-line region. A leptonic one-zone modeling of the six H.E.S.S. observation nights using the dusty torus as seed photons for the inverse-Compton scattering, results in a low magnetization of the emission region. This implies that shock acceleration is likely the main driver during the event.

Authors with CRIS profile

Involved external institutions

University of Oxford United Kingdom (GB) Humboldt-Universität zu Berlin Germany (DE) Noordwes-Universiteit / North-West University South Africa (ZA) Institute of Research into the Fundamental Laws of the Universe / Institut de recherche sur les lois fondamentales de l'univers (IRFU) France (FR) Deutsches Elektronen-Synchrotron DESY Germany (DE) Nicolaus Copernicus Astronomical Centre of the Polish Academy of Sciences Poland (PL) DIAS Dunsink Observatory Ireland (IE) University of Montpellier / Université Montpellier France (FR) Université Paris Cité France (FR) Max-Planck-Institut für Kernphysik (MPIK) / Max Planck Institute for Nuclear Physics Germany (DE) Ruprecht-Karls-Universität Heidelberg Germany (DE) Universität Potsdam Germany (DE) Konan University / 甲南大学 Japan (JP) Eberhard Karls Universität Tübingen Germany (DE) Leopold-Franzens-Universität Innsbruck / University of Innsbruck Austria (AT) University of Namibia (UNAM) Namibia (NA) Paris Observatory / Observatoire de Paris France (FR) Universität Hamburg (UHH) Germany (DE) Jagiellonian University / Uniwersytet Jagielloński (UJ) Poland (PL) Laboratoire Leprince-Ringuet (LLR) France (FR) University of Southern Denmark / Syddansk Universitet Denmark (DK) Sorbonne Université France (FR) University of Adelaide Australia (AU) University of the Witwatersrand (WITS) South Africa (ZA) Polska Akademia Nauk (PAN) / Polish Academy of Sciences Poland (PL) Yerevan Physics Institute (YerPhI) / Երևանի Ֆիզիկայի Ինստիտուտ Armenia (AM) University of Amsterdam Netherlands (NL) University of Warsaw / Uniwersytet Warszawski Poland (PL) University of Groningen / Rijksuniversiteit Groningen Netherlands (NL) Institut national de physique nucléaire et de physique des particules (IN2P3) France (FR) University of Tokyo Japan (JP) Nicolaus Copernicus University (NCU) / Uniwersytet Mikołaja Kopernika w Toruniu (UMK) Poland (PL) University of Western Sydney Australia (AU)

How to cite

APA:

Acharyya, A., Aharonian, F., Ait Benkhali, F., Alkan, A., Ashkar, H., Backes, M.,... Zywucka, N. (2026). Scrutinizing the 2020 multiwavelength outburst of PKS 0903 - 57 through observations with H.E.S.S․. Journal of High Energy Astrophysics, 53. https://doi.org/10.1016/j.jheap.2026.100599

MLA:

Acharyya, A., et al. "Scrutinizing the 2020 multiwavelength outburst of PKS 0903 - 57 through observations with H.E.S.S․." Journal of High Energy Astrophysics 53 (2026).

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