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

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

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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