Particle transport within the pulsar wind nebula HESS J1825–137^★

¹ Centre for Space Research, North-West University, Potchefstroom 2520, South Africa
² Institut für Experimentalphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
³ Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
⁴ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
⁵ National Academy of Sciences of the Republic of Armenia, Marshall Baghramian Avenue, 24, 0019 Yerevan, Armenia
⁶ Yerevan Physics Institute, 2 Alikhanian Brothers St., 375036 Yerevan, Armenia
⁷ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
⁸ Department of Physics, University of Namibia, Private Bag 13301, Windhoek, Namibia
⁹ GRAPPA, Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹⁰ Department of Physics and Electrical Engineering, Linnaeus University, 351 95 Växjö, Sweden
¹¹ Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
¹² Institut für Astro- und Teilchenphysik, Leopold-Franzens-Universität Innsbruck, 6020 Innsbruck, Austria
¹³ School of Physical Sciences, University of Adelaide, Adelaide 5005, Australia
¹⁴ LUTH, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, 5 Place Jules Janssen, 92190 Meudon, France
¹⁵ Laboratoire de Physique Nucléaire et de Hautes Energies, Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité, CNRS/IN2P3, 4 Place Jussieu, 75252 Paris, France
¹⁶ Laboratoire Univers et Particules de Montpellier, Université Montpellier, CNRS/IN2P3, CC 72, Place Eugéne Bataillon, 34095 Montpellier Cedex 5, France
¹⁷ IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
¹⁸ Astronomical Observatory, The University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw, Poland
¹⁹ Aix-Marseille Université, CNRS/IN2P3, CPPM, Marseille, France
²⁰ Instytut Fizyki Ja̧drowej PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland
²¹ School of Physics, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, Johannesburg, 2050 South Africa
²² Laboratoire d’Annecy de Physique des Particules, Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, LAPP, 74000 Annecy, France
²³ Landessternwarte, Universität Heidelberg, Königstuhl, D 69117 Heidelberg, Germany
²⁴ CNRS/IN2P3, Centre d’Études Nucléaires de Bordeaux Gradignan, Université Bordeaux, 33175 Gradignan, France
²⁵ Oskar Klein Centre, Department of Physics, Stockholm University, Albanova University Center, 10691 Stockholm, Sweden
²⁶ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
²⁷ Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3, 91128 Palaiseau, France
²⁸ APC, AstroParticule et Cosmologie, Université Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de Paris, Sorbonne Paris Cité, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France
²⁹ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³⁰ Department of Physics and Astronomy, The University of Leicester, University Road, Leicester, LE1 7RH, UK
³¹ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul.Bartycka 18, 00-716 Warsaw, Poland
³² Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany
³³ Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Centre for Astroparticle Physics, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany
³⁴ DESY, 15738 Zeuthen, Germany
³⁵ Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171, 30-244 Kraków, Poland
³⁶ Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland
³⁷ Department of Physics, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa
³⁸ ITA, Universität Heidelberg, Heidelberg, Germany
³⁹ Department of Physics, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan
⁴⁰ Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo Institutes for Advanced Study, The University of Tokyo, 5-1-5 Kashiwa-no-Ha, Kashiwa City, Chiba 277-8583, Japan
⁴¹ Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
⁴² RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
⁴³ Physik Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland

Received: 28 September 2018
Accepted: 25 October 2018

Abstract

Context. We present a detailed view of the pulsar wind nebula (PWN) HESS J1825–137. We aim to constrain the mechanisms dominating the particle transport within the nebula, accounting for its anomalously large size and spectral characteristics.

Aims. The nebula was studied using a deep exposure from over 12 years of H.E.S.S. I operation, together with data from H.E.S.S. II that improve the low-energy sensitivity. Enhanced energy-dependent morphological and spatially resolved spectral analyses probe the very high energy (VHE, E > 0.1 TeV) γ-ray properties of the nebula.

Methods. The nebula emission is revealed to extend out to 1.5° from the pulsar, ~1.5 times farther than previously seen, making HESS J1825–137, with an intrinsic diameter of ~100 pc, potentially the largest γ-ray PWN currently known. Characterising the strongly energy-dependent morphology of the nebula enables us to constrain the particle transport mechanisms. A dependence of the nebula extent with energy of R ∝ E^α with α = −0.29 ± 0.04_stat ± 0.05_sys disfavours a pure diffusion scenario for particle transport within the nebula. The total γ-ray flux of the nebula above 1 TeV is found to be (1.12 ± 0.03_stat ± 0.25_sys) × 10⁻¹¹ cm⁻² s⁻¹, corresponding to ~64% of the flux of the Crab nebula.

Results. HESS J1825–137 is a PWN with clearly energy-dependent morphology at VHE γ-ray energies. This source is used as a laboratory to investigate particle transport within intermediate-age PWNe. Based on deep observations of this highly spatially extended PWN, we produce a spectral map of the region that provides insights into the spectral variation within the nebula.