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HESS and Suzaku observations of the Vela X pulsar wind nebula

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journal contribution
posted on 2019-08-05, 15:06 authored by H Abdalla, F Aharonian, FA Benkhali, EO Anguner, M Arakawa, C Arcaro, C Armand, M Backes, M Barnard, Y Becherini, D Berge, K Bernloehr, R Blackwell, M Bottcher, C Boisson, J Bolmont, S Bonnefoy, J Bregeon, F Brun, P Brun, M Bryan, M Buechele, T Bulik, T Bylund, M Capasso, S Caroff, A Carosi, S Casanova, M Cerruti, N Chakraborty, T Chand, S Chandra, RCG Chaves, A Chen, S Colafrancesco, B Condon, ID Davids, C Deil, J Devin, P deWilt, L Dirson, A Djannati-Atai, A Dmytriiev, A Donath, V Doroshenko, LO Drury, J Dyks, K Egberts, G Emery, J-P Ernenwein, S Eschbach, K Feijen, S Fegan, A Fiasson, G Fontaine, S Funk, M Fuessling, S Gabici, YA Gallant, F Gate, G Giavitto, D Glawion, JF Glicenstein, D Gottschall, M-H Grondin, J Hahn, M Haupt, G Heinzelmann, G Henri, G Hermann, JA Hinton, W Hofmann, C Hoischen, TL Holch, M Holler, D Horns, D Huber, H Iwasaki, A Jacholkowska, M Jamrozy, D Jankowsky, F Jankowsky, L Jouvin, I Jung-Richardt, MA Kastendieck, K Katarzynski, M Katsuragawa, U Katz, D Khangulyan, B Khelifi, J King, S Klepser, W Kluzniak, N Komin, K Kosack, D Kostunin, M Kraus, G Lamanna, J Lau, A Lemiere, M Lemoine-Goumard, J-P Lenain, E Leser, T Lohse, R Lopez-Coto, I Lypova, D Malyshev, V Marandon, A Marcowith, C Mariaud, G Marti-Devesa, R Marx, G Maurin, N Maxted, PJ Meintjes, AMW Mitchell, R Moderski, M Mohamed, L Mohrmann, C Moore, E Moulin, T Murach, S Nakashima, M de Naurois, H Ndiyavala, F Niederwanger, J Niemiec, L Oakes, P O'Brien, H Odaka, S Ohm, EDO Wilhelmi, M Ostrowski, I Oya, M Panter, RD Parsons, C Perennes, P-O Petrucci, B Peyaud, Q Piel, S Pita, V Poireau, AP Noel, DA Prokhorov, H Prokoph, G Puehlhofer, M Punch, A Quirrenbach, S Raab, R Rauth, A Reimer, O Reimer, M Renaud, F Rieger, L Rinchiuso, C Romoli, G Rowell, B Rudak, E Ruiz-Velasco, V Sahakian, S Saito, DA Sanchez, A Santangelo, M Sasaki, R Schlickeiser, F Schussler, A Schulz, H Schutte, U Schwanke, S Schwemmer, M Seglar-Arroyo, M Senniappan, AS Seyffert, N Shafi, I Shilon, K Shiningayamwe, R Simoni, A Sinha, H Sol, A Specovius, M Spir-Jacob, L Stawarz, R Steenkamp, C Stegmann, C Steppa, T Takahashi, J-P Tavernet, T Tavernier, AM Taylor, R Terrier, L Tibaldo, D Tiziani, M Tluczykont, C Trichard, M Tsirou, N Tsuji, R Tuffs, Y Uchiyama, DJ van der Walt, C van Eldik, C van Rensburg, B van Soelen, G Vasileiadis, J Veh, C Venter, P Vincent, J Vink, F Voisin, HJ Voelk, T Vuillaume, Z Wadiasingh, SJ Wagner, R White, A Wierzcholska, R Yang, H Yoneda, D Zaborov, M Zacharias, R Zanin, AA Zdziarski, A Zech, A Ziegler, J Zorn, N Zywucka
Context. Pulsar wind nebulae (PWNe) represent the most prominent population of Galactic very-high-energy gamma-ray sources and are thought to be an efficient source of leptonic cosmic rays. Vela X is a nearby middle-aged PWN, which shows bright X-ray and TeV gamma-ray emission towards an elongated structure called the cocoon. Aims. Since TeV emission is likely inverse-Compton emission of electrons, predominantly from interactions with the cosmic microwave background, while X-ray emission is synchrotron radiation of the same electrons, we aim to derive the properties of the relativistic particles and of magnetic fields with minimal modelling. Methods. We used data from the Suzaku XIS to derive the spectra from three compact regions in Vela X covering distances from 0.3 to 4 pc from the pulsar along the cocoon. We obtained gamma-ray spectra of the same regions from H.E.S.S. observations and fitted a radiative model to the multi-wavelength spectra. Results. The TeV electron spectra and magnetic field strengths are consistent within the uncertainties for the three regions, with energy densities of the order 10−12 erg cm−3. The data indicate the presence of a cutoff in the electron spectrum at energies of ~ 100 TeV and a magnetic field strength of ~6 μG. Constraints on the presence of turbulent magnetic fields are weak. Conclusions. The pressure of TeV electrons and magnetic fields in the cocoon is dynamically negligible, requiring the presence of another dominant pressure component to balance the pulsar wind at the termination shock. Sub-TeV electrons cannot completely account for the missing pressure, which may be provided either by relativistic ions or from mixing of the ejecta with the pulsar wind. The electron spectra are consistent with expectations from transport scenarios dominated either by advection via the reverse shock or by diffusion, but for the latter the role of radiative losses near the termination shock needs to be further investigated in the light of the measured cutoff energies. Constraints on turbulent magnetic fields and the shape of the electron cutoff can be improved by spectral measurements in the energy range ≳ 10 keV.


The support of the Namibian authorities and of the University of Namibia in facilitating the construction and operation of H.E.S.S. is gratefully acknowledged, as is the support by the German Ministry for Education and Research (BMBF), the Max Planck Society, the German Research Foundation (DFG), the Alexander von Humboldt Foundation, the Deutsche Forschungsgemeinschaft, the French Ministry for Research, the CNRS-IN2P3 and the Astroparticle Interdisciplinary Programme of the CNRS, the U.K. Science and Technology Facilities Council (STFC), the IPNP of the Charles University, the Czech Science Foundation, the Polish National Science Centre, the South African Department of Science and Technology and National Research Foundation, the University of Namibia, the National Commission on Research, Science & Technology of Namibia (NCRST), the Innsbruck University, the Austrian Science Fund (FWF), and the Austrian Federal Ministry for Science, Research and Economy, the University of Adelaide and the Australian Research Council, the Japan Society for the Promotion of Science and by the University of Amsterdam. We appreciate the excellent work of the technical support staff in Berlin, Durham, Hamburg, Heidelberg, Palaiseau, Paris, Saclay, and in Namibia in the construction and operation of the equipment. This work benefited from services provided by the H.E.S.S. Virtual Organisation, supported by the national resource providers of the EGI Federation. This research has made use of data obtained from the Suzaku satellite, a collaborative mission between the space agencies of Japan (JAXA) and the USA (NASA). We acknowledge the usage of the following open-source software: aplpy (Robitaille & Bressert 2012), astropy (Astropy Collaboration 2018), corner (Foreman-Mackey 2016), emcee (Foreman-Mackey et al. 2013), matplotlib (Hunter 2007), naima (Zabalza 2015).



Astronomy and Astrophysics, 2019, 627, A100

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Appendix A: Additional information from the H.E.S.S. spectral fitting Appendix B: Contributions from infrared fields to inverse-Compton emission from Vela X Appendix C: Probability density distributions of radiative model parameters fit to the multi-wavelength data