Journal
NATURE
Volume 582, Issue 7812, Pages 356-369Publisher
NATURE RESEARCH
DOI: 10.1038/s41586-020-2354-1
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Funding
- German Ministry for Education and Research (BMBF)
- Max Planck Society
- German Research Foundation (DFG)
- Helmholtz Association
- Alexander von Humboldt Foundation
- French Ministry of Higher Education, Research and Innovation
- Centre National de la Recherche Scientifique (CNRS/IN2P3)
- Centre National de la Recherche Scientifique (CNRS/INSU)
- Commissariat a l'energie atomique et aux energies alternatives (CEA)
- UK Science and Technology Facilities Council (STFC)
- Knut and Alice Wallenberg Foundation
- National Science Centre, Poland [2016/22/M/ST9/00382]
- South African Department of Science and Technology
- South African National Research Foundation
- University of Namibia
- National Commission on Research, Science and Technology of Namibia (NCRST)
- Austrian Federal Ministry of Education, Science and Research
- Austrian Science Fund (FWF)
- Australian Research Council (ARC)
- Japan Society for the Promotion of Science
- University of Amsterdam
- STFC [ST/S000453/1] Funding Source: UKRI
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The nearby radio galaxy Centaurus A belongs to a class of active galaxies that are luminous at radio wavelengths. Most show collimated relativistic outflows known as jets, which extend over hundreds of thousands of parsecs for the most powerful sources. Accretion of matter onto the central supermassive black hole is believed to fuel these jets and power their emission(1). Synchrotron radiation from relativistic electrons causes the radio emission, and it has been suggested that the X-ray emission from Centaurus A also originates in electron synchrotron processes(2-4). Another possible explanation is inverse Compton scattering with cosmic microwave background (CMB) soft photons(5-7). Synchrotron radiation needs ultrarelativistic electrons (about 50 teraelectronvolts) and, given their short cooling times, requires some continuous re-acceleration mechanism(8). Inverse Compton scattering, on the other hand, does not require very energetic electrons, but the jets must stay highly relativistic on large scales (exceeding 1 megaparsec). Some recent evidence disfavours inverse Compton-CMB models(9-12), although other work seems to be compatible with them(13,14). In principle, the detection of extended gamma-ray emission, which directly probes the presence of ultrarelativistic electrons, could distinguish between these options. At gigaelectronvolt energies there is also an unusual spectral hardening(15,16)in Centaurus A that has not yet been explained. Here we report observations of Centaurus A at teraelectronvolt energies that resolve its large-scale jet. We interpret the data as evidence for the acceleration of ultrarelativistic electrons in the jet, and favour the synchrotron explanation for the X-rays. Given that this jet is not exceptional in terms of power, length or speed, it is possible that ultrarelativistic electrons are commonplace in the large-scale jets of radio-loud active galaxies. Observations of the radio galaxy Centaurus A at teraelectronvolt energies resolve its large-scale jet and favour electron synchrotron processes as the source of its X-ray emission.
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