Long-duration γ-ray bursts (GRBs) are the most luminous sources of electromagnetic radiation known in the Universe. They arise from outflows of plasma with velocities near the speed of light that are ejected by newly formed neutron stars or black holes (of stellar mass) at cosmological distances1,2. Prompt flashes of megaelectronvolt-energy γ-rays are followed by a longer-lasting afterglow emission in a wide range of energies (from radio waves to gigaelectronvolt γ-rays), which originates from synchrotron radiation generated by energetic electrons in the accompanying shock waves3,4. Although emission of γ-rays at even higher (teraelectronvolt) energies by other radiation mechanisms has been theoretically predicted5,6,7,8, it has not been previously detected7,8. Here we report observations of teraelectronvolt emission from the γ-ray burst GRB 190114C. γ-rays were observed in the energy range 0.2–1 teraelectronvolt from about one minute after the burst (at more than 50 standard deviations in the first 20 minutes), revealing a distinct emission component of the afterglow with power comparable to that of the synchrotron component. The observed similarity in the radiated power and temporal behaviour of the teraelectronvolt and X-ray bands points to processes such as inverse Compton upscattering as the mechanism of the teraelectronvolt emission9,10,11. By contrast, processes such as synchrotron emission by ultrahigh-energy protons10,12,13 are not favoured because of their low radiative efficiency. These results are anticipated to be a step towards a deeper understanding of the physics of GRBs and relativistic shock waves.
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Proprietary data reconstruction codes were generated at the MAGIC telescope large-scale facility. Information supporting the findings of this study is available from the corresponding authors upon request.
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We are grateful to G. Sinnis for remarks that helped us improve the format and content of this manuscript. We dedicate this paper to the memory of E. Lorenz. With his innovative spirit, infinite enthusiasm and vast knowledge of experimental methods, techniques and materials, he played a key role in optimizing the design of MAGIC, specifically for observations of GRBs. We thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. We acknowledge financial support by the German BMBF and MPG, the Italian INFN and INAF, the Swiss National Fund (SNF), the ERDF under the Spanish Ministry of Economy and Competitiveness (FPA2017-87859-P, FPA2017-85668-P,FPA2017-82729-C6-2-R, FPA2017-82729-C6-6-R, FPA2017-82729-C6-5-R, AYA2015-71042-P,AYA2016-76012-C3-1-P,ESP2017-87055-C2-2-P,FPA2017-90566-REDC), the Indian Department of Atomic Energy, the Japanese JSPS and MEXT, the Bulgarian Ministry of Education and Science, National RI Roadmap Project DO1-153/28.08.2018, and the Academy of Finland for grant number 320045. This work was also supported by the Spanish Centro de Excelencia ‘Severo Ochoa’ SEV-2016-0588 and SEV-2015-0548 and Unidad de Excelencia ‘María de Maeztu’ MDM-2014-0369, by the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782 and the University of Rijeka Project 22.214.171.124.02, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, the Polish National Research Centre grant UMO-2016/22/M/ST9/00382, and by the Brazilian MCTIC, CNPq and FAPERJ. S.I. is supported by JSPS KAKENHI grant number JP17K05460, MEXT, Japan, the RIKEN iTHEMS programme and the joint research programme of ICRR, University of Tokyo. L. Nava acknowledges funding from the European Union’s Horizon 2020 Research and Innovation programme under the Marie Skłodowska-Curie grant agreement number 664931. K. Noda is supported by JSPS KAKENHI grant number JP19K21043, MEXT, Japan. A. Berti acknowledges support from the Physics Department of the University of Torino (through funding from the Department of Excellence) and from the Torino division of the Italian INFN. E. Moretti acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement number 665919.
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Peer review information Nature thanks Gus Sinnis and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Extended data figures and tables
Extended Data Fig. 1 Light curves in the teraelectronvolt and kiloelectronvolt bands for GRB 190114C.
Photon flux light curve above 0.3 TeV measured by MAGIC (red; from T0 + 62 s to T0 + 210 s), compared with that between 15 keV and 50 keV measured by Swift-BAT73 (grey; from T0 to T0 + 210 s) and the photon flux above 0.3 TeV of the Crab Nebula (blue dashed line). The errors on the MAGIC photon fluxes correspond to one standard deviation. Vertical lines indicate the times when the alert was received (T0 + 22 s) by MAGIC, when the tracking of the GRB by the telescopes started (T0 + 50 s), when the data acquisition started (T0 + 57 s), and when the data acquisition system (DAQ) became stable (T0 + 62 s; dotted line).
Extended Data Fig. 2 Significance of the γ-ray signal between T0 + 62 s and T0 + 1,227 s for GRB 190114C.
Distribution of the squared angular distance, θ2, for the MAGIC data (points) and background events (grey shaded area). θ2 is defined as the squared angular distance between the nominal position of the source and the reconstructed arrival direction of the events. The dashed vertical line represents the value of the cut on θ2. This defines the signal region, where the number of events coming from the source (Non) and from the background (Noff) are computed. The errors for ‘on’ events are derived from Poissonian statistics. From Non and Noff, the number of excess events (Nex) is computed. The significance is calculated using the Li & Ma method42.
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Acciari, V.A., Ansoldi, S., Antonelli, L.A. et al. Teraelectronvolt emission from the γ-ray burst GRB 190114C. Nature 575, 455–458 (2019) doi:10.1038/s41586-019-1750-x