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Observation of inverse Compton emission from a long γ-ray burst


Long-duration γ-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterized by an initial phase of bright and highly variable radiation in the kiloelectronvolt-to-megaelectronvolt band, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission1,2. Subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands1,2,3,4,5,6. The afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock7,8,9. Recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from GRB 190114C10,11. Here we report multi-frequency observations of GRB 190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from 5 × 10−6 to 1012 electronvolts. We find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. This component is associated with the afterglow and is satisfactorily explained by inverse Compton up-scattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed teraelectronvolt component are typical for GRBs, supporting the possibility that inverse Compton emission is commonly produced in GRBs.

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Fig. 1: Multi-wavelength light curves of GRB 190114C.
Fig. 2: Multi-band spectra in the time interval 68–2,400 s.
Fig. 3: Modelling of the broadband spectra in the time intervals 68–110 s and 110–180 s.

Data availability

Data are available from the corresponding authors upon request.

Code availability

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. Source data for Figs. 2, 3 are provided with the paper.


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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 MINECO (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, FPA201790566REDC), 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 grant number 320045. This work was also supported by the Spanish Centro de Excelencia ‘Severo Ochoa’ through grants 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, 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. L. Nava acknowledges funding from the European Union’s Horizon 2020 Research and Innovation programme under the Marie Skłodowska-Curie grant agreement number 664931. E. Moretti acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement number 665919. This study used the following ALMA data: ADS/JAO.ALMA#2018.A.00020.T, ADS/JAO.ALMA#2018.1.01410.T. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. C.C.T., A.d.U.P. and D.A.K. acknowledge support from the Spanish research project AYA2017-89384-P. C.C.T and A.d.U.P. acknowledge support from funding associated with Ramón y Cajal fellowships (RyC-2012-09984 and RyC-2012-09975). D.A.K. acknowledges support from funding associated with Juan de la Cierva Incorporación fellowships (IJCI-2015-26153). The JCMT is operated by the East Asian Observatory on behalf of The National Astronomical Observatory of Japan, Academia Sinica Institute of Astronomy and Astrophysics, the Korea Astronomy and Space Science Institute, and Center for Astronomical Mega-Science (as well as the National Key R&D Program of China via grant number 2017YFA0402700). Additional funding support is provided by the Science and Technology Facilities Council of the UK and participating universities in the UK and Canada. The JCMT data reported here were obtained under project M18BP040 (principal investigator D.A.P.). We thank M. Rawlings, K. Silva, S. Urquart and the JCMT staff for support for these observations. The Liverpool Telescope, located on the island of La Palma, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, is operated by Liverpool John Moores University with financial support from the UK Science and Technology Facilities Council. The Australia Telescope Compact Array is part of the Australia Telescope National Facility, which is funded by the Australian Government for operation as a National Facility managed by CSIRO. G.E.A. is the recipient of an Australian Research Council Discovery Early Career Researcher Award (project number DE180100346) and J.C.A.M.-J. is the recipient of an Australian Research Council Future Fellowship (project number FT140101082) funded by the Australian Government. Support for the German contribution to GBM was provided by the Bundesministerium für Bildung und Forschung (BMBF) via the Deutsches Zentrum für Luft und Raumfahrt (DLR) under grant number 50 QV 0301. The University of Alabama in Huntsville (UAH) coauthors acknowledge NASA funding from cooperative agreement NNM11AA01A. C.A.W.-H. and C.M.H. acknowledge NASA funding through the Fermi-GBM project. The Fermi LAT Collaboration acknowledges support from a number of agencies and institutes that have supported both the development and the operation of the LAT, as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy (DOE) in the USA; the Commissariat à l’Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France; the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy; the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan; and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. We acknowledge additional support for science analysis during the operations phase from the Istituto Nazionale di Astrofisica in Italy and the Centre National d’Études Spatiales in France. This work was performed in part under DOE contract DE-AC02-76SF00515. Part of the funding for GROND (both hardware and personnel) was granted from the Leibniz-Prize to G. Hasinger (DFG grant HA 1850/28-1). Swift data were retrieved from the Swift archive at HEASARC/NASA-GSFC and from the UK Swift Science Data Centre. Support for Swift in the UK is provided by the UK Space Agency. This work is based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. This work is partially based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 199.D-0143. The work is partly based on observations made with the GTC, installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma. This work is partially based on observations made with the NOT (programme 58-502), operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofísica de Canarias. This work is partially based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 102.D-0662. This work is partially based on observations collected through the ESO programme 199.D-0143 ePESSTO. M. Gromadzki is supported by the Polish NCN MAESTRO grant 2014/14/A/ST9/00121. M.N. is supported by a Royal Astronomical Society Research Fellowship M.G.B., S. Campana, A. Melandri and P.D’A. acknowledge ASI grant I/004/11/3. S. Campana acknowledges support from agreement ASI-INAF number 2017-14-H.0. S.J.S. acknowledges funding from STFC grant ST/P000312/1. N.P.M.K. acknowledges support by the UK Space Agency under grant ST/P002323/1 and the UK Science and Technology Facilities Council under grant ST/N00811/1. L.P. and S. Lotti acknowledge partial support from agreement ASI-INAF number 2017-14-H.0. A.F.V. acknowledges RFBR 18-29-21030 for support. A.J.C.-T. acknowledges support from the Junta de Andalucía (Project P07-TIC-03094) and from the Spanish Ministry Projects AYA2012-39727-C03-01 and 2015-71718R. K. Misra acknowledges support from the Department of Science and Technology (DST), Government of India and the Indo-US Science and Technology Forum (IUSSTF) for the WISTEMM fellowship and Departnment of Physics, UC Davis, where a part of this work was carried out. S.B.P. and K. Misra acknowledge BRICS (Brazil, Russia, India, China and South Africa) grant DST/IMRCD/BRICS/Pilotcall/ProFCheap/2017(G) for this work. M.J.M. acknowledges the support of the National Science Centre, Poland, through grant 2018/30/E/ST9/00208. V.J. and L.R. acknowledge support from grant EMR/2016/007127 from the Department of Science and Technology, India. K. Maguire acknowledges support from H2020 through an ERC starting grant (758638). L.I. acknowledges M. Della Valle for support in the operation of the telescope.

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The MAGIC telescope system was designed and constructed by the MAGIC Collaboration. Operation, data processing, calibration, Monte Carlo simulations of the detector and of theoretical models, and data analyses were performed by the members of the MAGIC Collaboration, who also discussed and approved the scientific results. L. Nava coordinated the collection of the data, developed the theoretical interpretation and wrote the main section and the section on afterglow modelling. E. Moretti coordinated the analysis of the MAGIC data, wrote the relevant sections and, together with F. Longo, coordinated the collaboration with the Fermi team. D. Miceli, Y.S. and S.F. performed the analysis of the MAGIC data. S. Covino provided support with the analysis of the optical data and the writing of the corresponding sections. Z.B. performed calculations for the contribution of prompt emission to the teraelectronvolt radiation and wrote the corresponding section. A. Stamerra, D.P. and S.I. contributed to structuring and editing the paper. A. Berti contributed to editing and finalizing the manuscript. R.M. coordinated and supervised the writing of the paper. All MAGIC collaborators contributed to the editing of and provided comments on the final version of the manuscript. S. Campana and M.G.B. extracted the spectra and performed the spectral analysis of the Swift-BAT and Swift-XRT data. N.P.M.K. derived the photometry for the Swift-UVOT event mode data and the UV grism exposure. M.H.S. derived the image-mode Swift-UVOT photometry. A.d.U.P. was principal investigator of ALMA programme 2018.1A.00020.T, triggered these observations and performed photometry. S. Martin reduced the ALMA Band 6 data. C.C.T., S. Schulze, D.A.K. and M. Michałowski participated in the ALMA DDT proposal preparation, observations and scientific analysis of the data. D.A.P. was principal investigator of ALMA programme 2018.1.01410.T and triggered these observations and was principal investigator of the LT and JCMT programmes. A.M.C. analysed the ALMA Band 3 and LT data and wrote the LT text. S. Schulze contributed to the development of the ALMA Band 3 observing programme. I.A.S. triggered the JCMT programme, analysed the data and wrote the associated text. N.R.T. contributed to the development of the JCMT programme. D.A.K. and C.C.T. triggered and coordinated the X-shooter observations. D.A.K. independently checked the optical light curve analysis. K. Misra was the principal investigator of the GMRT programme 35_018. S.V.C. and V.J. analysed the data. L.R. contributed to the observation plan and data analysis. E. Tremou, I.H. and R.D. performed the MeerKAT data analysis. G.E.A., A. Moin, S. Schulze and E. Troja were principal investigators of ATCA programme CX424. G.E.A., M. Wieringa and J. Stevens carried out the observations. G.E.A., G. Bernardi, S.K., M. Marongiu, A. Moin, R.R. and M. Wieringa analysed these data. J.C.A.M.-J. and L.P. participated in the ATCA proposal preparation and the scientific analysis of the data. The ePESSTO project was delivered by the following, who contributed to managing, executing, reducing, analysing ESO/NTT data and provided comments to the manuscript: J.P.A., N.C.S., P.D’A., M. Gromadzki, C.I., E.K., K. Maguire, M.N., F.R. and S.J.S.; A. Melandri and A. Rossi reduced and analysed REM data and provided comments to the manuscript. J. Bolmer was responsible for observing the GRB with GROND and for the data reduction and calibration. J. Bolmer and J. Greiner contributed to the analysis of the data and writing of the text. E. Troja triggered the NuSTAR TOO observations performed under the DDT programme, L.P. requested the XMM-Newton data, obtained under a DDT programme, and carried out the scientific analysis of the XMM-Newton and NuSTAR data. S. Lotti analysed the NuSTAR data and wrote the associated text. A. Tiengo and G. Novara analysed the XMM-Newton data and wrote the associated text. A.J.C.-T. led the observing BOOTES and GTC programmes. A. Castellón, C.J.P.d.P., E.F.-G., I.M.C., S.B.P. and X.Y.L. analysed the BOOTES data, and A.F.V., M.D.C.-G., R.S.-R., Y.-D.H. and V.V.S. analysed the GTC data and interpreted them accordingly. N.R.T. created the X-shooter and AlFOSC figures. J.P.U.F. and J.J. performed the analysis of the X-shooter and AlFOSC spectra. D.X. and P.J. contributed to the NOT programme and triggering. D. Malesani performed photometric analysis of NOT data. E. Peretti contributed to the development of the code for modelling afterglow radiation. L.I. triggered and analysed the OASDG data, and A.D.D. and A.N. performed the observations at the telescope.

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Extended data figures and tables

Extended Data Fig. 1 Prompt-emission light curves for different detectors.

af, Light curves for Super-AGILE (a; 20–60 keV), Swift-BAT (b; 15–150 keV), Fermi-GBM (c; 10–1,000 keV), AGILE-MCAL (d; 0.4–1.4 MeV), AGILE-MCAL (e; 1.4–100 MeV) and Fermi-LAT (f; 0.1–10 GeV). The light curve of AGILE-MCAL is split into two bands to show the energy dependence of the first peak. Error bars show 1σ statistical errors.

Extended Data Fig. 2 MAGIC time-integrated SEDs in the time interval 62–2,400 s after T0.

The green (yellow, blue) points and band show the results of the Monte Carlo (MC) simulations for the nominal and the varied light scale cases (+15%, −15%), which define the limits of the systematic uncertainties. The contour regions are drawn from the 1σ error of their best-fit power-law functions. The vertical bars of the data points show the 1σ errors on the flux.

Extended Data Fig. 3 Afterglow light curves of GRB 190114C.

Flux density at different frequencies as a function of the time since the initial burst, T − T0. a, Observation in the NIR, optical and UV bands. The flux has been corrected for extinction in the host and in our Galaxy. The contribution of the host galaxy and its companion has been subtracted. Fluxes have been rescaled (except for the r-band filter). b, Radio and submillimetre observations from 1.3 GHz to 670 GHz. ‘Instr.’, instrument.

Extended Data Fig. 4 Images of the localization region of GRB 190114C.

a, All-sky image captured with the CASANDRA-1 camera at the BOOTES-1 station. The image (30 s exposure, unfiltered) was taken at T0 + 14.8 s, and was severely affected by the moon. At the GRB190114C location (red dot) no prompt optical emission is detected. Inset, magnification (inverted colours) containing a 10′-diametercircle centred on the optical position. b, Three-colour image of the host of GRB 190114C, obtained with the HST. The host galaxy is a spiral galaxy, and the green circle indicates the location of the transient close to its host nucleus. The image is 8″ across; north is up and east is to the left. ce, Images of the GRB 190114C field taken with the HST, obtained with the F850LP filter (covering roughly the region from 800 to 1,100 nm). Two epochs, 11 February and 12 March 2019, are shown (images are 4″ across); the right-most image is the result of the difference image. A faint transient is visible close to the nucleus of the galaxy, and we identify this as the late-time afterglow of the burst.

Extended Data Fig. 5 Optical–NIR spectra of GRB 190114C.

a, NOT/AlFOSC spectrum obtained at mid-time (i.e., the epoch corresponding to a half of the exposure length) 1 h post-burst. The continuum is afterglow-dominated at this time, and shows strong absorption features of Ca ii and Na i (in addition to telluric absorption). b, Normalized GTC (+OSIRIS) spectrum obtained on 14 January 2019, 23:32:03 ut with the R1000B and R2500I grisms. The emission lines of the underlying host galaxy are noticeable, besides the Ca ii absorption lines in the afterglow spectrum. c, Visible-light region of the VLT–X-shooter spectrum obtained approximately 3.2 d post-burst, showing strong emission lines from the star-forming host galaxy.

Extended Data Fig. 6 SEDs from radio frequencies to X-rays at different epochs.

The synchrotron frequency νm crosses the optical band, moving from higher to lower frequencies. The break between 108 and 1010 Hz is caused by the self-absorption synchrotron frequency, νsa. Optical (X-ray) data have been corrected for extinction (absorption). The data points are taken from the following telescopes (from lower to higher frequencies): filled and empty triangle symbols, GMRT and MeerKAT; stars, ATCA; violet filled circle, ALMA, down arrows, JCMT 1σ upper limits; filled circles, LT (yellow) and GROND (all the other colours). Error bars for all data points define the 1σ error. Coloured stripes show the best fit of the XRT data extrapolated to the time of each SED. Their vertical width is obtained from the error (90% confidence level) on the best-fit normalization. Solid lines show the model SEDs for the case s = 2.

Extended Data Fig. 7 Modelling of broadband light curves.

Modelling results of forward shock emission are compared to observations at different frequencies (see key). The model shown with solid and dashed lines is optimized to describe the high-energy radiation (teraelectronvolt, gigaelectronvolt and X-ray) and has been obtained with the following parameters: s = 0, εe = 0.07, εB = 8 × 10−5, p = 2.6, n0 = 0.5 and Ek = 8 × 1053 erg. Solid lines show the total flux (synchrotron and SSC) and the dashed line refers to the SSC contribution only. Dotted curves correspond to a better modelling of observations at lower frequencies, but fail to explain the behaviour of the teraelectronvolt light curve; they are obtained with the following model parameters: s = 2, εe = 0.6, εB = 10−4, p = 2.4, A. = 0.1 and Ek = 4 × 1053 erg. Vertical bars on the data points show the 1σ errors on the flux, and horizontal bars represent the duration of the observation.

Extended Data Table 1 MAGIC spectral-fit parameters for GRB 190114C
Extended Data Table 2 GROND photometry
Extended Data Table 3 LT, NOT and UVOT observations
Extended Data Table 4 Observations of the host galaxy
Extended Data Table 5 Observations of GRB 190114C by ATCA and JCMT SCUBA-2

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MAGIC Collaboration., Acciari, V.A., Ansoldi, S. et al. Observation of inverse Compton emission from a long γ-ray burst. Nature 575, 459–463 (2019).

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