Issue |
A&A
Volume 612, April 2018
H.E.S.S. phase-I observations of the plane of the Milky Way
|
|
---|---|---|
Article Number | A9 | |
Number of page(s) | 13 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/201730824 | |
Published online | 09 April 2018 |
Characterising the VHE diffuse emission in the central 200 parsecs of our Galaxy with H.E.S.S.
1
Centre for Space Research, North-West University,
2520 Potchefstroom,
South Africa
2
Universität Hamburg,
Institut für Experimentalphysik,
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
University of Namibia, Department of Physics,
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
GRAPPA, Anton Pannekoek Institute for Astronomy and Institute of High-Energy Physics, University of Amsterdam,
Science Park 904,
1098 XH Amsterdam,
The Netherlands
13
Institut für Astro- und Teilchenphysik,
Leopold-Franzens-Universität Innsbruck, 6020 Innsbruck,
Austria
14
School of Physical Sciences, University of Adelaide,
5005 Adelaide,
Australia
15
LUTH, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot,
5 place Jules Janssen,
92190 Meudon,
France
16
Sorbonne Universités,
UPMC Université Paris 06,
Université Paris Diderot,
Sorbonne Paris Cité, CNRS, Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE),
4 place Jussieu,
75252 Paris Cedex 5,
France
17
Laboratoire Univers et Particules de Montpellier,
Université Montpellier,
CNRS/IN2P3,
CC 72, Place Eugène Bataillon,
34095 Montpellier Cedex 5,
France
18
DSM/Irfu,
CEA Saclay,
91191 Gif-Sur-Yvette Cedex,
France
19
Astronomical Observatory, The University of Warsaw,
Al. Ujazdowskie 4,
00-478 Warsaw,
Poland
20
Aix-Marseille Université,
CNRS/IN2P3, CPPM UMR 7346,
13288 Marseille,
France
21
Instytut Fizyki Ja̧drowej PAN,
ul. Radzikowskiego 152,
31-342 Kraków,
Poland
22
Funded by EU FP7 Marie Curie, grant agreement No. PIEF-GA-2012-332350
23
School of Physics, University of the Witwatersrand,
1 Jan Smuts Avenue,
Braamfontein, 2050 Johannesburg,
South Africa
24
Laboratoire d’Annecy-le-Vieux de Physiquedes Particules,
Université Savoie Mont-Blanc, CNRS/IN2P3,
74941 Annecy-le-Vieux,
France
25
Landessternwarte,
Universität Heidelberg, Königstuhl,
69117 Heidelberg,
Germany
26
Université Bordeaux,
CNRS/IN2P3, Centre d’Études Nucléaires de Bordeaux Gradignan,
33175 Gradignan,
France
27
Oskar Klein Centre, Department of Physics, Stockholm University, Albanova University Center,
10691 Stockholm,
Sweden
28
Wallenberg Academy Fellow
29
Institut für Astronomie und Astrophysik,
Universität Tübingen,
Sand 1,
72076 Tübingen,
Germany
30
Laboratoire Leprince-Ringuet,
École Polytechnique, CNRS/IN2P3,
91128 Palaiseau,
France
31
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
32
Univ. Grenoble Alpes,
IPAG; CNRS, IPAG,
38000 Grenoble,
France
33
Department of Physics and Astronomy, The University of Leicester, University Road,
Leicester, LE1 7RH,
UK
34
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences,
ul. Bartycka 18,
00-716 Warsaw,
Poland
35
Institut für Physik und Astronomie,
Universität Potsdam,
Karl-Liebknecht-Strasse 24/25,
14476 Potsdam,
Germany
36
Friedrich-Alexander-Universität Erlangen-Nürnberg,
Erlangen Centre for Astroparticle Physics,
Erwin-Rommel-Str. 1,
91058 Erlangen,
Germany
37
DESY,
15738 Zeuthen,
Germany
38
Obserwatorium Astronomiczne,
Uniwersytet Jagielloński,
ul. Orla 171,
30-244 Kraków,
Poland
39
Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University,
Grudziadzka 5,
87-100 Torun, Poland
40
Department of Physics, University of the Free State,
PO Box 339,
9300 Bloemfontein,
South Africa
41
Heisenberg Fellow (DFG),
ITAUniversität Heidelberg,
69120 Heidelberg,
Germany
42
GRAPPA, Institute of High-Energy Physics, University of Amsterdam,
Science Park 904,
1098 XH Amsterdam,
The Netherlands
43
Department of Physics, Rikkyo University,
3-34-1 Nishi-Ikebukuro,
Toshima-ku,
171-8501 Tokyo,
Japan
44
Japan Aerospace Exploration Agency (JAXA), Institute of Space and Astronautical Science (ISAS),
3-1-1 Yoshinodai,
Chuo-ku, Sagamihara,
229-8510 Kanagawa,
Japan
45
Now at The School of Physics, The University of New South Wales,
2052 Sydney,
Australia
★ Corresponding author: H.E.S.S. Collaboration,
e-mail: contact.hess@hess-experiment.eu
Received:
20
March
2017
Accepted:
7
June
2017
The diffuse very high-energy (VHE; >100 GeV) γ-ray emission observed in the central 200 pc of the Milky Way by H.E.S.S. was found to follow dense matter distribution in the central molecular zone (CMZ) up to a longitudinal distance of about 130 pc to the Galactic centre (GC), where the flux rapidly decreases. This was initially interpreted as the result of a burst-like injection of energetic particles 104 yr ago, but a recent more sensitive H.E.S.S. analysis revealed that the cosmic-ray (CR) density profile drops with the distance to the centre, making data compatible with a steady cosmic PeVatron at the GC. In this paper, we extend this analysis to obtain, for the first time, a detailed characterisation of the correlation with matter and to search for additional features and individual γ-ray sources in the inner 200 pc. Taking advantage of 250 h of H.E.S.S. data and improved analysis techniques, we perform a detailed morphology study of the diffuse VHE emission observed from the GC ridge and reconstruct its total spectrum. To test the various contributions to the total γ-ray emission, we used an iterative 2D maximum-likelihood approach that allows us to build a phenomenological model of the emission by summing a number of different spatial components. We show that the emission correlated with dense matter covers the full CMZ and that its flux is about half the total diffuse emission flux. We also detect some emission at higher latitude that is likely produced by hadronic collisions of CRs in less dense regions of the GC interstellar medium. We detect an additional emission component centred on the GC and extending over about 15 pc that is consistent with the existence of a strong CR density gradient and confirms the presence of a CR accelerator at the very centre of our Galaxy. We show that the spectrum of full ridge diffuse emission is compatible with that previously derived from the central regions, suggesting that a single population of particles fills the entire CMZ. Finally, we report the discovery of a VHE γ-ray source near the GC radio arc and argue that it is produced by the pulsar wind nebula candidate G0.13−0.11.
Key words: gamma rays: general / gamma rays: ISM / Galaxy: center / cosmic rays
© ESO 2018
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