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Resolving the Crab pulsar wind nebula at teraelectronvolt energies

Abstract

The Crab nebula is one of the most-studied cosmic particle accelerators, shining brightly across the entire electromagnetic spectrum up to very-high-energy gamma rays1,2. It is known from observations in the radio to gamma-ray part of the spectrum that the nebula is powered by a pulsar, which converts most of its rotational energy losses into a highly relativistic outflow. This outflow powers a pulsar wind nebula, a region of up to ten light-years across, filled with relativistic electrons and positrons. These particles emit synchrotron photons in the ambient magnetic field and produce very-high-energy gamma rays by Compton up-scattering of ambient low-energy photons. Although the synchrotron morphology of the nebula is well established, it has not been known from which region the very-high-energy gamma rays are emitted3,4,5,6,7,8. Here we report that the Crab nebula has an angular extension at gamma-ray energies of 52 arcseconds (assuming a Gaussian source width), much larger than at X-ray energies. This result closes a gap in the multi-wavelength coverage of the nebula, revealing the emission region of the highest-energy gamma rays. These gamma rays enable us to probe a previously inaccessible electron and positron energy range. We find that simulations of the electromagnetic emission reproduce our measurement, providing a non-trivial test of our understanding of particle acceleration in the Crab nebula.

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Fig. 1: Images of the Crab nebula.
Fig. 2: SED, with the measured and predicted extensions of the Crab PWN.
Fig. 3: Projected event distribution from the direction of the Crab nebula.

Data availability

The raw data and the code used in this study are not public but belong to the H.E.S.S. Collaboration. All derived higher-level data that are shown in plots will be made available on the H.E.S.S. Collaboration’s website (https://www.mpi-hd.mpg.de/hfm/HESS/pages/publications/pubs_jour.shtml) upon publication of this study.

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Acknowledgements

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 Helmholtz Association, the Alexander von Humboldt Foundation, the French Ministry of Higher Education, Research and Innovation, the Centre National de la Recherche Scientifique (CNRS/IN2P3 and CNRS/INSU), the Commissariat à l’énergie atomique et aux énergies alternatives (CEA), the UK Science and Technology Facilities Council (STFC), the Knut and Alice Wallenberg Foundation, the National Science Centre, Poland (grant number 2016/22/M/ST9/00382), the South African Department of Science and Technology and the National Research Foundation, the University of Namibia, the National Commission on Research, Science and Technology of Namibia (NCRST), the Austrian Federal Ministry of Education, Science and Research and the Austrian Science Fund (FWF), the Australian Research Council (ARC), the Japan Society for the Promotion of Science and the University of Amsterdam. We appreciate the excellent work of the technical support staff in Berlin, Zeuthen, Heidelberg, Palaiseau, Paris, Saclay, Tübingen and 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. R.C.G.C. was funded by EU FP7 Marie Curie (grant agreement number PIEF-GA-2012-332350).

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D.B., J.H., M. Holler, D.K. and R.D.P. analysed and interpreted the data, and prepared the manuscript. The whole of the H.E.S.S. collaboration contributed to the publication with involvement at various stages ranging from the design, construction and operation of the instrument, to the development and maintenance of all software for data handling, data reduction and data analysis. All authors reviewed, discussed, and commented on the present results and on the manuscript.

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Supplementary Figures 1-2, Supplementary Tables 1-2, Supplementary References 1-13

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H.E.S.S. Collaboration. Resolving the Crab pulsar wind nebula at teraelectronvolt energies. Nat Astron 4, 167–173 (2020). https://doi.org/10.1038/s41550-019-0910-0

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