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Gigaelectronvolt emission from a compact binary merger

Nature volume 612, pages 236–239 (2022)Cite this article

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Abstract

An energetic γ-ray burst (GRB), GRB 211211A, was observed on 11 December 20211,2. Despite its long duration, typically associated with bursts produced by the collapse of massive stars, the observation of an optical-infrared kilonova points to a compact binary merger origin3. Here we report observations of a significant (more than five sigma) transient-like emission in the high-energy γ-rays of GRB 211211A (more than 0.1 gigaelectronvolts) starting 103 seconds after the burst. After an initial phase with a roughly constant flux (about 5 × 10−10 erg per second per square centimetre) lasting about 2 × 104 seconds, the flux started decreasing and soon went undetected. Our detailed modelling of public and dedicated multi-wavelength observations demonstrates that gigaelectronvolt emission from GRB 211211A is in excess with respect to the flux predicted by the state-of-the-art afterglow model at such late time. We explore the possibility that the gigaelectronvolt excess is inverse Compton emission owing to the interaction of a late-time, low-power jet with an external source of photons, and find that kilonova emission can provide the seed photons. Our results open perspectives for observing binary neutron star mergers.

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Fig. 1: Fermi/LAT detection of GRB 211211A.
Fig. 2: High-energy light curves of GRBs observed by Fermi/LAT.
Fig. 3: Multi-wavelength light curves and spectra of GRB 211211A.
Fig. 4: External inverse Compton model contribution.
Fig. 5: The interaction between the low-power jet and the kilonova.

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Data availability

Swift/XRT raw data are public and available from the UK Swift Science Data Centre at the University of Leicester. The light-curve data were taken from https://www.swift.ac.uk/xrt_curves/GRB_ID/flux.qdp, where GRB_ID is the GRB observation ID. The spectra were obtained from https://www.swift.ac.uk/xrt_spectra/addspec.php?targ=GRB_ID where GRB_ID is the GRB observation ID. The details of the automatic spectral analysis can be found at https://www.swift.ac.uk/xrt_spectra/docs.php. Swift/UVOT raw data are available at https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/swift.pl. Fermi/LAT raw data are public and can be downloaded using the software GTBURST available at https://fermi.gsfc.nasa.gov/ssc/data/analysis/scitools/gtburst.html. The Fermi/LAT second GRB catalogue data are available at https://www-glast.stanford.edu/pub_data/953/. The VLA data are available at the public repository https://data.nrao.edu/portal/#/. The observation code is 21B-370. XMM-Newton raw data are available at https://www.cosmos.esa.int/web/xmm-newton/xsa. The TNG data are available from the corresponding author upon reasonable request.

Code availability

HEASOFT, XSPEC and PYXSPEC are freely available online at https://heasarc.gsfc.nasa.gov/docs/software/heasoft/, https://heasarc.gsfc.nasa.gov/xanadu/xspec/ and https://heasarc.gsfc.nasa.gov/docs/xanadu/xspec/python/html/index.html. GTBURST is part of the Fermi Science Tools package, freely available at https://fermi.gsfc.nasa.gov/ssc/data/analysis/software/. The details of the GTBURST analysis can be found at https://fermi.gsfc.nasa.gov/ssc/data/analysis/scitools/gtburst.html. The XMM-Newton Science Analysis Software is freely available at https://www.cosmos.esa.int/web/xmm-newton/sas-download. SOSTA is part of the XIMAGE software package, freely available at https://heasarc.gsfc.nasa.gov/xanadu/ximage/ximage.html. The ESO eclipse package is available https://www.eso.org/sci/software/eclipse/. The CASA software is available at https://casa.nrao.edu/casa_obtaining.shtml. A tutorial on how to use CASA can be found at https://casaguides.nrao.edu/index.php?title=VLA_Continuum_Tutorial_3C391-CASA6.2.0. emcee is a Python package, available at https://emcee.readthedocs.io/en/stable/user/install/. AFTERGLOWPY is a Python package, available at https://github.com/geoffryan/afterglowpy. All reduced data and computer code are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank A. Celotti, G. Ghisellini, A. Segreto, E. Ambrosi and M. Grazia Bernardini for discussions. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. P.D. and S.C. thank N. Schartel for granting XMM-Newton DDT observations. M.B. acknowledges financial support from the Italian Ministry of University and Research (MUR, PRIN 2020 grant 2020KB33TP). M.B. and G.O. acknowledge financial support from the AHEAD2020 project (grant agreement number 871158). B.B., M.B. and P.D. acknowledge financial support from MUR (PRIN 2017 grant 20179ZF5KS). O.S.S. thanks MUR grant 2017MB8AEZ for financial support. P.D. and S.C. acknowledge support from ASI grant I/004/11/5. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.

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Authors and Affiliations

  1. Gran Sasso Science Institute, L’Aquila, Italy

    Alessio Mei, Biswajit Banerjee, Gor Oganesyan, Marica Branchesi & Samuele Ronchini

  2. INFN - Laboratori Nazionali del Gran Sasso, L’Aquila, Italy

    Alessio Mei, Biswajit Banerjee, Gor Oganesyan, Marica Branchesi & Samuele Ronchini

  3. Università degli Studi di Milano-Bicocca, Milan, Italy

    Om Sharan Salafia

  4. INFN - Sezione di Milano-Bicocca, Milan, Italy

    Om Sharan Salafia & Giancarlo Ghirlanda

  5. INAF - Osservatorio Astronomico di Brera, Merate, Italy

    Om Sharan Salafia, Paolo D’Avanzo, Sergio Campana & Giancarlo Ghirlanda

  6. INAF - Istituto di Radioastronomia, Bologna, Italy

    Stefano Giarratana

  7. Department of Physics and Astronomy, University of Bologna, Bologna, Italy

    Stefano Giarratana

  8. Department of Astronomy, Astrophysics and Space Engineering, Indian Institute of Technology Indore, Indore, India

    Amit Shukla & Pawan Tiwari

Authors
  1. Alessio Mei
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  2. Biswajit Banerjee
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  3. Gor Oganesyan
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  4. Om Sharan Salafia
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  5. Stefano Giarratana
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  6. Marica Branchesi
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  7. Paolo D’Avanzo
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  8. Sergio Campana
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  9. Giancarlo Ghirlanda
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  10. Samuele Ronchini
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  11. Amit Shukla
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  12. Pawan Tiwari
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Contributions

A.M., B.B. and G.O. carried out LAT data reduction and analysis, and lead the GeV discovery. O.S.S. performed the multi-wavelength afterglow modelling. G.O. and O.S.S. developed the theoretical model used to interpret the high-energy excess. A.M., B.B., G.O. and O.S.S. lead the paper writing. G.G., M.B., S.G., P.D. and S.R. gave significant inputs on data interpretation. M.B. and G.G. gave major contributions to the paper writing. All authors contributed to discussions and editing of the paper. P.D. is the principal investigator of the XMM-Newton observations, and collected and analysed the optical and UV data. P.D. and S.C. reduced and analysed the XMM data and edited the corresponding text in the paper. S.G. is the principal investigator of the VLA observations. He reduced and analysed the radio data, and edited the corresponding text in the paper. P.T. and A.S. contributed to the LAT analysis providing computational tools. B.B. produced Fig. 1 and Extended Data Fig. 1. A.M. produced Fig. 2 and Extended Data Fig. 2. O.S.S. produced Figs. 3 and 5 and Extended Data Figs. 3–8. S.R. produced Fig. 5.

Corresponding author

Correspondence to Alessio Mei.

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Extended data figures and tables

Extended Data Fig. 1 Time-averaged broadband spectrum of 4FGL J1410.4+2820.

The two arrows represent the 3σ upper limits for the BL Lac flux obtained using one month of observation by Fermi/LAT before and after the GRB (in yellow and purple, respectively). The green band in the GeV energies represents the time-averaged GeV emission from 12 years of observation55. The emission from the blazar is at least two orders of magnitude weaker than the emission from the GRB.

Extended Data Fig. 2 Comparisons with other GRBs observed by Fermi/LAT.

Long (in green) and short (in blue) bursts emissions from the second Fermi/LAT GRB catalogue27 compared to GRB 211211A (in brown). a, LAT detection time from the burst versus the GRB duration T90 computed with Fermi/GBM data. The dashed lines separate GRBs that are detected during (below) or after (above) the prompt emission. Note that in some cases, including GRB 211211A, the Fermi/LAT observation started after the prompt phase, and we cannot exclude an emission starting before the detection time shown in the plot. b, LAT photon index versus LAT flux (0.1–10 GeV), both obtained through time-integrated analysis in ref. 27.

Extended Data Fig. 3 Corner plot of the 12-dimensional posterior obtained from MCMC sampling.

The meaning of the parameters is explained in the text. The histograms on the diagonal show the one-dimensional marginalized posterior probability density for each parameter, with the red line showing the best fit and the dashed lines bracketing 90% (or 95% in case of upper limits) credible ranges. Contours in the remaining two-dimensional plots show the one-, two- and three-sigma equivalent bounds of the joint posteriors of parameter pairs, while dots show qualitatively the distribution of posterior samples outside the three-sigma boundaries. The red lines and dots show the position of the best fit.

Extended Data Fig. 4 Details on the kilonova photon transverse diffusion.

a, Kilonova luminosity that can diffuse from the jet-kilonova ‘walls’ above the jet dissipation region, located at Rj, at post-merger time t = 104 s. b, Kilonova luminosity available for up-scattering within the jet dissipation region (red solid line), compared to the total kilonova luminosity (blue dashed line), assuming Rj = 1013 cm.

Extended Data Fig. 5 Light curves as SEDs with models, showing the synchrotron emission from the low-power jet.

a, b, Same as Fig. 3, but showing the model-predicted synchrotron emission from the low-power jet with dot-dashed lines in b.

Extended Data Fig. 6 Comparison with the afterglow modelling in ref. 3.

a, b, Light curves (a) and SEDs (b) with the best-fit parameters from ref. 3.

Extended Data Fig. 7 Comparison with the afterglow modelling in ref. 107.

a, b, Light curves (a) and SEDs (b) with the best-fit parameters from ref. 107.

Extended Data Fig. 8 Comparison with the afterglow modelling in ref.26.

a, b, Light curves (a) and SEDs (b) with the best-fit parameters from ref. 26.

Extended Data Table 1 High-energy photons from GRB 211211A detected by Fermi/LAT
Full size table
Extended Data Table 2 Results of the forward shock + kilonova model fit
Full size table

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Mei, A., Banerjee, B., Oganesyan, G. et al. Gigaelectronvolt emission from a compact binary merger. Nature 612, 236–239 (2022). https://doi.org/10.1038/s41586-022-05404-7

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