A deep spectromorphological study of the γ -ray emission surrounding the young massive stellar cluster Westerlund 1

Aharonian F, Ashkar H, Backes M, Martins VB, Becherini Y, Berge D, Bi B, Böttcher M, De Lavergne MDB, Bradascio F, Brose R, Brun F, Bulik T, Burger-Scheidlin C, Cangemi F, Caroff S, Casanova S, Cerruti M, Chand T, Chandra S, Chen A, Chibueze O, Cristofari P, Mbarubucyeye JD, Djannati-Ataï A, Ernenwein JP, Feijen K, De Clairfontaine GF, Fontaine G, Funk S, Gabici S, Gallant YA, Ghafourizadeh S, Giavitto G, Giunti L, Glawion D, Glicenstein JF, Goswami P, Grondin MH, Härer LK, Haupt M, Hinton JA, Hörbe M, Hofmann W, Holch TL, Holler M, Horns D, Jamrozy M, Joshi V, Jung-Richardt I, Kasai E, Katarzyński K, Katz U, Khélifi B, Kluźniak W, Komin N, Kosack K, Kostunin D, Mezek GK, Lang RG, Le Stum S, Lemière A, Lemoine-Goumard M, Lenain JP, Leuschner F, Lohse T, Luashvili A, Lypova I, Mackey J, Majumdar J, Malyshev D, Marandon V, Marchegiani P, Marcowith A, Martí-Devesa G, Marx R, Maurin G, Meyer M, Mitchell A, Moderski R, Mohrmann L, Montanari A, Moulin E, Muller J, Murach T, Nakashima K, De Naurois M, Nayerhoda A, Niemiec J, Ohm S, Olivera-Nieto L, Wilhelmi EDO, Ostrowski M, Panny S, Panter M, Parsons RD, Peron G, Prokhorov DA, Pühlhofer G, Punch M, Quirrenbach A, Rauth R, Reichherzer P, Reimer A, Reimer O, Renaud M, Reville B, Rieger F, Rowell G, Rudak B, Ruiz-Velasco E, Sahakian V, Salzmann H, Sanchez DA, Santangelo A, Sasaki M, Schüssler F, Schutte HM, Schwanke U, Shapopi JNS, Specovius A, Spencer S, Stawarz Ł, Steenkamp R, Steinmassl S, Steppa C, Sushch I, Suzuki H, Takahashi T, Tanaka T, Terrier R, Thorpe-Morgan C, Tsirou M, Tsuji N, Tuffs R, Unbehaun T, van Eldik C, Van Soelen B, Vecchi M, Veh J, Venter C, Vink J, Wagner SJ, White R, Wierzcholska A, Wong YW, Zacharias M, Zargaryan D, Zdziarski AA, Zhu SJ, Zouari S, Żywucka N, Blackwell R, Braiding C, Burton M, Cubuk K, Filipović M, Tothill N, Wong G (2022)

Publication Language: English

Publication Type: Journal article

Publication year: 2022

Journal

Book Volume: 666

Article Number: A124

DOI: 10.1051/0004-6361/202244323

Abstract

Context. Young massive stellar clusters are extreme environments and potentially provide the means for efficient particle acceleration. Indeed, they are increasingly considered as being responsible for a significant fraction of cosmic rays (CRs) that are accelerated within the Milky Way. Westerlund 1, the most massive known young stellar cluster in our Galaxy, is a prime candidate for studying this hypothesis. While the very-high-energy γ-ray source HESS J1646-458 has been detected in the vicinity of Westerlund 1 in the past, its association could not be firmly identified. Aims. We aim to identify the physical processes responsible for the γ-ray emission around Westerlund 1 and thus to understand the role of massive stellar clusters in the acceleration of Galactic CRs better. Methods. Using 164 h of data recorded with the High Energy Stereoscopic System (H.E.S.S.), we carried out a deep spectromorphological study of the γ-ray emission of HESS J1646-458. We furthermore employed H I and CO observations of the region to infer the presence of gas that could serve as target material for interactions of accelerated CRs. Results. We detected large-scale (~2 diameter) γ-ray emission with a complex morphology, exhibiting a shell-like structure and showing no significant variation with γ-ray energy. The combined energy spectrum of the emission extends to several tens of TeV, and it is uniform across the entire source region. We did not find a clear correlation of the γ-ray emission with gas clouds as identified through H I and CO observations. Conclusions. We conclude that, of the known objects within the region, only Westerlund 1 can explain the majority of the γ-ray emission. Several CR acceleration sites and mechanisms are conceivable and discussed in detail. While it seems clear that Westerlund 1 acts as a powerful particle accelerator, no firm conclusions on the contribution of massive stellar clusters to the flux of Galactic CRs in general can be drawn at this point.

Authors with CRIS profile

Involved external institutions

Noordwes-Universiteit / North-West University South Africa (ZA) Institute of Nuclear Physics Polish Academy of Sciences / Instytut Fizyki Jądrowej im. Henryka Niewodniczańskiego Polskiej Akademii Nauk Poland (PL) University of Paris 4 - Paris-Sorbonne / Université paris IV Paris-Sorbonne France (FR) Université de Paris France (FR) Deutsches Elektronen-Synchrotron DESY Germany (DE) Institut national de physique nucléaire et de physique des particules (IN2P3) France (FR) University of Savoy Mont Blanc / Université Savoie Mont Blanc France (FR) École Polytechnique - Université Paris-Saclay France (FR) Dublin Institute for Advanced Studies (DIAS) Ireland (IE) University of Adelaide Australia (AU) Leopold-Franzens-Universität Innsbruck / University of Innsbruck Austria (AT) University of Montpellier / Université Montpellier France (FR) Max-Planck-Institut für Kernphysik (MPIK) / Max Planck Institute for Nuclear Physics Germany (DE) University of Namibia (UNAM) Namibia (NA) Aix-Marseille University / Aix-Marseille Université France (FR) University of New South Wales (UNSW) Australia (AU) Eberhard Karls Universität Tübingen Germany (DE) Yerevan Physics Institute (YerPhI) / Երևանի Ֆիզիկայի Ինստիտուտ Armenia (AM) Universität Potsdam Germany (DE) University of Warsaw / Uniwersytet Warszawski Poland (PL) University of the Witwatersrand (WITS) South Africa (ZA) Universität Hamburg (UHH) Germany (DE) Ruprecht-Karls-Universität Heidelberg Germany (DE) Humboldt-Universität zu Berlin Germany (DE) Konan University / 甲南大学 Japan (JP) Jagiellonian University / Uniwersytet Jagielloński (UJ) Poland (PL) University of Tokyo Japan (JP) University of Western Sydney Australia (AU) Riken Institute of Physical and Chemical Research / 理化学研究所 Japan (JP) University of Amsterdam Netherlands (NL) University of Oxford United Kingdom (GB) Nicolaus Copernicus University (NCU) / Uniwersytet Mikołaja Kopernika w Toruniu (UMK) Poland (PL) Linnaeus University (LNU) / Linnéuniversitetet Sweden (SE) Armagh Observatory United Kingdom (GB) Polska Akademia Nauk (PAN) / Polish Academy of Sciences Poland (PL) Nicolaus Copernicus Astronomical Centre of the Polish Academy of Sciences Poland (PL) University of the Free State South Africa (ZA) Laboratoire Univers et Théories (LUTH) / Laboratory of the Universe and Theories France (FR)

How to cite

APA:

Aharonian, F., Ashkar, H., Backes, M., Martins, V.B., Becherini, Y., Berge, D.,... Wong, G. (2022). A deep spectromorphological study of the γ -ray emission surrounding the young massive stellar cluster Westerlund 1. Astronomy & Astrophysics, 666. https://doi.org/10.1051/0004-6361/202244323

MLA:

Aharonian, F., et al. "A deep spectromorphological study of the γ -ray emission surrounding the young massive stellar cluster Westerlund 1." Astronomy & Astrophysics 666 (2022).

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