Astrophysical shocks at all scales, from those in the heliosphere up to cosmological shock waves, are typically ‘collisionless’, because the thickness of their jump region is much shorter than the collisional mean free path. Across these jumps, electrons, protons and ions are expected to be heated at different temperatures. Supernova remnants (SNRs) are ideal targets to study collisionless processes because of their bright post-shock emission and fast shocks, but the actual dependence of the post-shock temperature on the particle mass is still widely debated1. We tackle this longstanding issue through the analysis of deep multi-epoch and high-resolution observations, made with the Chandra X-ray telescope, of the youngest nearby supernova remnant, SN 1987A. We introduce a data analysis method by studying the observed spectra in close comparison with a dedicated full three-dimensional hydrodynamic simulation that self-consistently reproduces the broadening of the spectral lines of many ions together. We measure the post-shock temperature of protons and ions through comparison of the model with observations. Our results show that the ratio of ion temperature to proton temperature is always significantly higher than one and increases linearly with the ion mass for a wide range of masses and shock parameters.

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The HD simulations adopted here are presented in detail in ref. 24. The Chandra dataset analysed are available in the Chandra Data Archive (http://cxc.harvard.edu/cda/). Other relevant data are available from the corresponding author upon reasonable request.

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The software used in this work was, in part, developed by the US Department of Energy-supported Advanced Simulation and Computing/Alliance Center for Astrophysical Thermonuclear Flashes at the University of Chicago. We acknowledge that the results of this research have been achieved using the PRACE Research Infrastructure resource MareNostrum III based in Spain at the Barcelona Supercomputing Center (PRACE Award no. 2012060993). The scientific results reported in this article are based to a significant degree on data obtained from the Chandra Data Archive. M.M., S.O., G.P. and F.B. acknowledge financial contribution from the agreement ASI-INAF n.2017-14-H.O. O.P. acknowledges partial support from the agreement 0118U004941.

Author information


  1. Dipartimento di Fisica e Chimica, Università degli Studi di Palermo, Palermo, Italy

    • Marco Miceli
    • , Costanza Argiroffi
    • , Fabio Reale
    •  & Giovanni Peres
  2. INAF-Osservatorio Astronomico di Palermo, Palermo, Italy

    • Marco Miceli
    • , Salvatore Orlando
    • , Costanza Argiroffi
    • , Fabio Reale
    • , Giovanni Peres
    •  & Fabrizio Bocchino
  3. Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA, USA

    • David N. Burrows
  4. Northwestern University, Technological Institute, Evanston, IL, USA

    • Kari A. Frank
  5. Institute for Applied Problems in Mechanics and Mathematics, Lviv, Ukraine

    • Oleh Petruk


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M.M. composed the text on the basis of inputs from all authors. M.M. designed the analysis procedure and led the analysis of the synthetic and actual X-ray spectra. S.O. led the set-up and run of the hydrodynamics simulation and the synthesis of X-ray spectra. D.N.B., K.A.F. and C.A. supported the X-ray data analysis process. F.R., G.P., O.P. and F.B. supported the analysis of the simulation and the synthesis of observables. All authors helped to discuss the results and to comment on the manuscript.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Marco Miceli.

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