Constraints on particle acceleration in SS433/W50 from MAGIC and H.E.S.S. observations

¹ ETH Zurich, 8093 Zurich, Switzerland
² Università di Udine, and INFN Trieste, 33100 Udine, Italy
³ INAF National Institute for Astrophysics, 00136 Rome, Italy
⁴ Università di Padova and INFN, 35131 Padova, Italy
⁵ Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka, University of Split – FESB, University of Zagreb – FER, University of Osijek, 10000 Zagreb, Croatia
⁶ Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Salt Lake, Sector-1, 700064 Kolkata, India
⁷ Max-Planck-Institut für Physik, 80805 München, Germany
⁸ Universidad Complutense, 28040 Madrid, Spain
⁹ Inst. de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
¹⁰ Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
¹¹ University of Łódź, 90236 Lodz, Poland
¹² Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
¹³ Institut de Fisica d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB, 08193 Bellaterra (Barcelona), Spain
¹⁴ Università di Siena, and INFN Pisa, 53100 Siena, Italy
¹⁵ Institute for Space Sciences (CSIC/IEEC), 08193 Barcelona, Spain
¹⁶ Technische Universität Dortmund, 44221 Dortmund, Germany
¹⁷ Universität Würzburg, 97074 Würzburg, Germany
¹⁸ Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Astronomy Division, University of Oulu, 90014 Oulu, Finland
¹⁹ Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
²⁰ Universitat de Barcelona, ICC, IEEC-UB, 08028 Barcelona, Spain
²¹ Japanese MAGIC Consortium, ICRR, The University of Tokyo, Department of Physics and Hakubi Center, Kyoto University, Tokai University, The University of Tokushima, 770-8501 Tokushima, Japan
²² Inst. for Nucl. Research and Nucl. Energy, 1784 Sofia, Bulgaria
²³ Università di Pisa, and INFN Pisa, 56126 Pisa, Italy
²⁴ ICREA and Institute for Space Sciences (CSIC/IEEC), 08193 Barcelona, Spain
²⁵ Also at the Departmentof Physics of Kyoto University, 606-8501 Kyoto, Japan
²⁶ Now at Centro Brasileiro de Pesquisas Físicas (CBPF/MCTI), R. Dr. Xavier Sigaud, 150 – Urca, Rio de Janeiro – RJ, 22290-180, Brazil
²⁷ Now at NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
²⁸ Department of Physics and Department of Astronomy, University of Maryland, College Park, MD 20742, USA
²⁹ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
³⁰ Also at University of Trieste
³¹ Also at Japanese MAGIC Consortium
³² Now at Finnish Centre for Astronomy with ESO (FINCA), Turku, Finland
³³ Also at INAF-Trieste and Dept. of Physics & Astronomy, University of Bologna, 40126 Bologna, Italy
³⁴ Now at Laboratoire AIM (UMR 7158 CEA/DSM, CNRS, Université Paris Diderot), Irfu/Service d’Astrophysique, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
³⁵ Now at INAF/IAPS-Roma, 00133 Roma, Italy; Centre for Space Research, North-West University, 2520 Potchefstroom, South Africa
³⁶ Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
³⁷ Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
³⁸ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
³⁹ National Academy of Sciences of the Republic of Armenia, Marshall Baghramian Avenue, 24, 0019 Yerevan, Republic of Armenia
⁴⁰ Yerevan Physics Institute, 2 Alikhanian Brothers St., 375036 Yerevan, Armenia
⁴¹ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
⁴² University of Namibia, Department of Physics, 13301 Private Bag, Windhoek, Namibia
⁴³ GRAPPA, Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
⁴⁴ Department of Physics and Electrical Engineering, Linnaeus University, 351 95 Växjö, Sweden
⁴⁵ Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
⁴⁶ GRAPPA, Anton Pannekoek Institute for Astronomy and Institute of High-Energy Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
⁴⁷ Institut für Astro- und Teilchenphysik, Leopold-Franzens-Universität Innsbruck, 6020 Innsbruck, Austria
⁴⁸ School of Physical Sciences, University of Adelaide, 5005 Adelaide, Australia
⁴⁹ LUTH, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
⁵⁰ Sorbonne Universités, UPMC Université Paris 06, Université Paris Diderot, Sorbonne Paris Cité, CNRS, Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE), 4 place Jussieu, 75252 Paris Cedex 5, France
⁵¹ Laboratoire Univers et Particules de Montpellier, Université Montpellier, CNRS/IN2P3, CC 72, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France
⁵² DSM/Irfu, CEA Saclay, 91191 Gif-Sur-Yvette Cedex, France
⁵³ Astronomical Observatory, The University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw, Poland
⁵⁴ Aix-Marseille Université, CNRS/IN2P3, CPPM UMR 7346, 13288 Marseille, France
⁵⁵ Instytut Fizyki Ja̧drowej PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland
⁵⁶ Funded by EU FP7 Marie Curie, grant agreement No. PIEF-GA-2012-332350
⁵⁷ School of Physics, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, 2050 Johannesburg, South Africa
⁵⁸ Laboratoire d’Annecy-le-Vieux de Physique des Particules, Université Savoie Mont-Blanc, CNRS/IN2P3, 74941 Annecy-le-Vieux, France
⁵⁹ Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
⁶⁰ Université Bordeaux, CNRS/IN2P3, Centre d’Études Nucléaires de Bordeaux Gradignan, 33175 Gradignan, France
⁶¹ Oskar Klein Centre, Department of Physics, Stockholm University, Albanova University Center, 10691 Stockholm, Sweden
⁶² Wallenberg Academy Fellow
⁶³ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
⁶⁴ Laboratoire Leprince-Ringuet, École Polytechnique, CNRS/IN2P3, 91128 Palaiseau, France
⁶⁵ 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
⁶⁶ Univ. Grenoble Alpes, IPAG, 38000 Grenoble, France; CNRS, IPAG, 38000 Grenoble, France
⁶⁷ Department of Physics and Astronomy, The University of Leicester, University Road, Leicester, LE1 7RH, UK
⁶⁸ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warsaw, Poland
⁶⁹ Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany
⁷⁰ Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Centre for Astroparticle Physics, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany
⁷¹ DESY, 15738 Zeuthen, Germany
⁷² Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171, 30-244 Kraków, Poland
⁷³ Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland
⁷⁴ Department of Physics, University of the Free State, PO Box 339, 9300 Bloemfontein, South Africa
⁷⁵ Heisenberg Fellow (DFG), ITA Universität Heidelberg, Germany
⁷⁶ GRAPPA, Institute of High-Energy Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
⁷⁷ Department of Physics, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima-ku, 171-8501 Tokyo, Japan
⁷⁸ Japan Aerpspace Exploration Agency (JAXA), Institute of Space and Astronautical Science (ISAS), 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, 229-8510 Kanagawa, Japan
⁷⁹ Now at Santa Cruz Institute for Particle Physics and Department of Physics, University of California at Santa Cruz, Santa Cruz, CA 95064, USA
⁸⁰ Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2, Canada

^★ Corresponding author: H.E.S.S. Collaboration, e-mail: contact.hess@hess-experiment.eu ; MAGIC Collaboration, e-mail: aloramas@iac.es; pere.munar@iaps.inaf.it

Received: 10 February 2017
Accepted: 14 July 2017

Abstract

Context. The large jet kinetic power and non-thermal processes occurring in the microquasar SS 433 make this source a good candidate for a very high-energy (VHE) gamma-ray emitter. Gamma-ray fluxes above the sensitivity limits of current Cherenkov telescopes have been predicted for both the central X-ray binary system and the interaction regions of SS 433 jets with the surrounding W50 nebula. Non-thermal emission at lower energies has been previously reported, indicating that efficient particle acceleration is taking place in the system.

Aim. We explore the capability of SS 433 to emit VHE gamma rays during periods in which the expected flux attenuation due to periodic eclipses (P_orb~ 13.1 days) and precession of the circumstellar disk (P_pre ~ 162 days) periodically covering the central binary system is expected to be at its minimum. The eastern and western SS 433/W50 interaction regions are also examined using the whole data set available. We aim to constrain some theoretical models previously developed for this system with our observations.

Methods. We made use of dedicated observations from the Major Atmospheric Gamma Imaging Cherenkov telescopes (MAGIC) and High Energy Spectroscopic System (H.E.S.S.) of SS 433 taken from 2006 to 2011. These observation were combined for the first time and accounted for a total effective observation time of 16.5 h, which were scheduled considering the expected phases of minimum absorption of the putative VHE emission. Gamma-ray attenuation does not affect the jet/medium interaction regions. In this case, the analysis of a larger data set amounting to ~40–80 h, depending on the region, was employed.

Results. No evidence of VHE gamma-ray emission either from the central binary system or from the eastern/western interaction regions was found. Upper limits were computed for the combined data set. Differential fluxes from the central system are found to be ≲ 10⁻¹²–10⁻¹³ TeV⁻¹ cm⁻² s⁻¹ in an energy interval ranging from ~few × 100 GeV to ~few TeV. Integral flux limits down to ~ 10⁻¹²–10⁻¹³ ph cm⁻² s⁻¹ and ~ 10⁻¹³–10⁻¹⁴ ph cm⁻² s⁻¹ are obtainedat 300 and 800 GeV, respectively. Our results are used to place constraints on the particle acceleration fraction at the inner jetregions and on the physics of the jet/medium interactions.

Conclusions. Our findings suggest that the fraction of the jet kinetic power that is transferred to relativistic protons must be relatively small in SS 433, q_p ≤ 2.5 × 10⁻⁵, to explain the lack of TeV and neutrino emission from the central system. At the SS 433/W50 interface, the presence of magnetic fields ≳10 μG is derived assuming a synchrotron origin for the observed X-ray emission. This also implies the presence of high-energy electrons with E_e⁻ up to 50 TeV, preventing an efficient production of gamma-ray fluxes in these interaction regions.