Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Modelling the coincident observation of a high-energy neutrino and a bright blazar flare


In September 2017, the IceCube Neutrino Observatory recorded a very-high-energy neutrino in directional coincidence with a blazar in an unusually bright gamma-ray state, TXS0506 + 056 (refs1,2). Blazars are prominent photon sources in the Universe because they harbour a relativistic jet whose radiation is strongly collimated and amplified. High-energy atomic nuclei known as cosmic rays can produce neutrinos; thus, the recent detection may help in identifying the sources of the diffuse neutrino flux3 and the energetic cosmic rays. Here we report a self-consistent analysis of the physical relation between the observed neutrino and the blazar, in particular the time evolution and spectral behaviour of neutrino and photon emission. We demonstrate that a moderate enhancement in the number of cosmic rays during the flare can yield a very strong increase in the neutrino flux, which is limited by co-produced hard X-rays and teraelectronvolt gamma rays. We also test typical radiation models4,5 for compatibility and identify several model classes6,7 as incompatible with the observations. We investigate to what degree the findings can be generalized to the entire population of blazars, determine the relation between their output in photons, neutrinos and cosmic rays, and suggest how to optimize the strategy of future observations.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Prices vary by article type



Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Illustration of the emission region of TXS0506 + 056 travelling at relativistic speed.
Fig. 2: Spectral energy flux from TXS0506 + 056 flare for two hypothetical scenarios.
Fig. 3: Energy flux from TXS0506 + 056 across the electromagnetic spectrum and for neutrinos.
Fig. 4: Time-dependent simulation of the light curve during the flare.

Data availability

The historical observations analysed during the current study are available in the SED Builder Tool of the Space Science Data Center (SSDC) and from the NASA/IPAC Extragalactic Database (NED). The data that support the plots within this paper and other findings of this study are available from S.G. and A.F. upon reasonable request.


  1. Blaufuss, E. IceCube-170922A—Icecube Observation of a High-Energy Neutrino Candidate Event GCN Circular 21916 (2017).

  2. Aartsen, M. et al. Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922a. Science 361, eaat1378 (2018).

    ADS  Google Scholar 

  3. Aartsen, M. et al. Observation and characterization of a cosmic muon neutrino flux from the northern hemisphere using six years of IceCube data. Astrophys. J. 833, 3 (2016).

    Article  ADS  Google Scholar 

  4. Urry, C. M. & Padovani, P. Unified schemes for radio-loud active galactic nuclei. Publ. Astron. Soc. Pacif. 107, 803 (1995).

    Article  ADS  Google Scholar 

  5. Böttcher, M., Reimer, A., Sweeney, K. & Prakash, A. Leptonic and hadronic modeling of Fermi-detected blazars. Astrophys. J. 768, 54 (2013).

    Article  ADS  Google Scholar 

  6. Mannheim, K. & Biermann, P. L. Gamma-ray flaring of 3C 279—a proton-initiated cascade in the jet? Astron. Astrophys. 253, L21–L24 (1992).

    ADS  Google Scholar 

  7. Mücke, A. & Protheroe, R. J. A proton synchrotron blazar model for flaring in Markarian 501. Astropart. Phys. 15, 121–136 (2001).

    Article  ADS  Google Scholar 

  8. Mücke, A., Engel, R., Rachen, J. P., Protheroe, R. J. & Stanev, T. SOPHIA: Monte Carlo simulations of photohadronic processes in astrophysics. Comput. Phys. Commun. 124, 290–314 (2000).

    Article  ADS  Google Scholar 

  9. Hümmer, S., Rüger, M., Spanier, F. & Winter, W. Simplified models for photohadronic interactions in cosmic accelerators. Astrophys. J. 721, 630–652 (2010).

    Article  ADS  Google Scholar 

  10. Kadler, M. et al. Coincidence of a high-fluence blazar outburst with a PeV-energy neutrino event. Nat. Phys. 12, 807–814 (2016).

    Article  Google Scholar 

  11. Gao, S., Pohl, M. & Winter, W. On the direct correlation between gamma-rays and PeV neutrinos from blazars. Astrophys. J. 843, 109 (2017).

    Article  ADS  Google Scholar 

  12. Petropoulou, M., Dimitrakoudis, S., Padovani, P., Mastichiadis, A. & Resconi, E. Photohadronic origin of γ-ray BL Lac emission: implications for IceCube neutrinos. Mon. Not. R. Astron. Soc. 448, 2412–2429 (2015).

    Article  ADS  Google Scholar 

  13. Cerruti, M., Zech, A., Boisson, C. & Inoue, S. A hadronic origin for ultra-high-frequency-peaked BL Lac objects. Mon. Not. R. Astron. Soc. 448, 910–927 (2015).

    Article  ADS  Google Scholar 

  14. Sadowski, A. & Narayan, R. Powerful radiative jets in supercritical accretion discs around non-spinning black holes. Mon. Not. R. Astron. Soc. 453, 3213–3221 (2015).

    Article  ADS  Google Scholar 

  15. van Marle, A. J., Casse, F. & Marcowith, A. On magnetic field amplification and particle acceleration near non-relativistic astrophysical shocks: particles in MHD cells simulations. Mon. Not. R. Astron. Soc. 473, 3394–3409 (2018).

    Article  ADS  Google Scholar 

  16. Cerruti, M., Zech, A., Emery, G. & Guarin, D. Hadronic modeling of TeV AGN: gammas and neutrinos. AIP Conf. Proc. 1792, 050027 (2017).

    Article  Google Scholar 

  17. Krawczynski, H. et al. Multiwavelength observations of strong flares from the TeV blazar 1ES 1959+650. Astrophys. J. 601, 151–164 (2004).

    Article  ADS  Google Scholar 

  18. Archambault, S. et al. Deep broadband observations of the distant gamma-ray blazar PKS 1424+240. Astrophys. J. Lett. 785, L16 (2014).

    Article  ADS  Google Scholar 

  19. Sánchez-Conde, M. A., Paneque, D., Bloom, E., Prada, F. & Domnguez, A. Hints of the existence of axionlike particles from the gamma-ray spectra of cosmological sources. Phys. Rev. D 79, 123511 (2009).

    Article  ADS  Google Scholar 

  20. Essey, W. & Kusenko, A. A new interpretation of the gamma-ray observations of distant active galactic nuclei. Astropart. Phys. 33, 81–85 (2010).

    Article  ADS  Google Scholar 

  21. Abeysekara, A. U. et al. VERITAS observations of the BL Lac object TXS 0506+056. Astrophys. J. Lett. 861, L20 (2018).

    Article  ADS  Google Scholar 

  22. Aartsen, M. G. et al. All-sky search for time-integrated neutrino emission from astrophysical sources with 7 yr of IceCube data. Astrophys. J. 835, 151 (2017).

    Article  ADS  Google Scholar 

  23. Abdollahi, S. et al. The second catalog of flaring gamma-ray sources from the Fermi All-sky Variability Analysis. Astrophys. J. 846, 34 (2017).

    Article  ADS  Google Scholar 

  24. Chen, X., Pohl, M. & Böttcher, M. Particle diffusion and localized acceleration in inhomogeneous AGN jets—I. Steady-state spectra. Mon. Not. R. Astron. Soc. 447, 530–544 (2015).

    Article  ADS  Google Scholar 

  25. Chen, X., Pohl, M., Böttcher, M. & Gao, S. Particle diffusion and localized acceleration in inhomogeneous AGN jets—II. Stochastic variation. Mon. Not. R. Astron. Soc. 458, 3260–3271 (2016).

    Article  ADS  Google Scholar 

  26. Paiano, S., Falomo, R., Treves, A. & Scarpa, R. The redshift of the BL Lac object TXS 0506+056. Astrophys. J. 854, L32 (2018).

    Article  ADS  Google Scholar 

  27. Aartsen, M. G. et al. A search for neutrino emission from fast radio bursts with six years of IceCube data. Astrophys. J. 857, 117 (2018).

    Article  ADS  Google Scholar 

  28. Fedynitch, A., Engel, R., Gaisser, T. K., Riehn, F. & Stanev, T. Calculation of conventional and prompt lepton fluxes at very high energy. EPJ Web Conf. 99, 08001 (2015).

    Article  Google Scholar 

  29. Dembinski, H. P. et al. Data-driven model of the cosmic-ray flux and mass composition from 10 GeV to 1011 GeV. PoS ICRC2017, 533 (2017).

    ADS  Google Scholar 

  30. Riehn, F. et al. The hadronic interaction model SIBYLL 2.3c and Feynman scaling. In 35th International Cosmic Ray Conference (ICRC2017) (Proceedings of Science, 2017).

  31. Palladino, A. & Winter, W. A multi-component model for the observed astrophysical neutrinos. Astron. Astrophys. 615, A168 (2018).

    Article  ADS  Google Scholar 

  32. Inoue, Y. et al. Extragalactic background light from hierarchical galaxy formation: gamma-ray attenuation up to the epoch of cosmic reionization and the first stars. Astrophys. J. 768, 197 (2013).

    Article  ADS  Google Scholar 

Download references


We thank A. Taylor, A. Palladino and E. Bernardini for discussions and comments. S.G., A.F. and W.W. have received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant no. 646623).

Author information

Authors and Affiliations



S.G. performed the numerical modelling and created the artwork. A.F. extracted and analysed the data. S.G. and A.F. provided first technical documentation. All authors contributed to development of the theoretical ideas and interpretation of the results. The final manuscript was written by M.P., W.W. and A.F. with contributions from S.G.

Corresponding author

Correspondence to Anatoli Fedynitch.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figures 1–4, Supplementary Table 1, Supplementary References 1–5

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Gao, S., Fedynitch, A., Winter, W. et al. Modelling the coincident observation of a high-energy neutrino and a bright blazar flare. Nat Astron 3, 88–92 (2019).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing