Proton acceleration in thermonuclear nova explosions revealed by gamma rays

Acciari, V. A., et al (MAGIC Collaboration)Classical novae are cataclysmic binary star systems in which the matter of a companion star is accreted on a white dwarf. Accumulation of hydrogen in a layer eventually causes a thermonuclear explosion on the surface of the white dwarf, brightening the white dwarf to ~10 solar luminosities and triggering ejection of the accumulated matter. Novae provide the extreme conditions required to accelerate particles, electrons or protons, to high energies. Here we present the detection of gamma rays by the MAGIC telescopes from the 2021 outburst of RS Ophiuchi, a recurrent nova with a red giant companion, which allowed us to accurately characterize the emission from a nova in the 60 GeV to 250 GeV energy range. The theoretical interpretation of the combined Fermi LAT and MAGIC data suggests that protons are accelerated to hundreds of gigaelectronvolts in the nova shock. Such protons should create bubbles of enhanced cosmic ray density, of the order of 10 pc, from the recurrent novae. © 2022, The Author(s), under exclusive licence to Springer Nature Limited.The financial support of the German BMBF, MPG and HGF; the Italian INFN and INAF; the Swiss National Fund SNF; the ERDF under the Spanish Ministerio de Ciencia e Innovación (MICINN) (PID2019-104114RB-C31, PID2019-104114RB-C32, PID2019-104114RB-C33, PID2019-105510GB-C31,PID2019-107847RB-C41, PID2019-107847RB-C42, PID2019-107847RB-C44, PID2019-107988GB-C22); the Indian Department of Atomic Energy; the Japanese ICRR, the University of Tokyo, JSPS and MEXT; the Bulgarian Ministry of Education and Science, National RI Roadmap Project DO1-400/18.12.2020, and the Academy of Finland grant number 320045 is gratefully acknowledged. This work was also supported by the Spanish Centro de Excelencia Severo Ochoa (SEV-2016-0588, SEV-2017-0709, CEX2019-000920-S), the Unidad de Excelencia María de Maeztu (CEX2019-000918-M, MDM-2015-0509-18-2) and the CERCA programme of the Generalitat de Catalunya; by the Croatian Science Foundation (HrZZ) project IP-2016-06-9782 and the University of Rijeka Project uniri-prirod-18-48; by the DFG Collaborative Research Centres SFB823/C4 and SFB876/C3; by the Polish National Research Centre grant UMO-2016/22/M/ST9/00382 and by the Brazilian MCTIC, CNPq and FAPERJ. The TJO of the Montsec Observatory (OdM) is owned by the Catalan Government and operated by the Institute for Space Studies of Catalonia (IEEC). We acknowledge with thanks the variable star observations from the AAVSO International Database contributed by observers worldwide and used in this research. We gratefully acknowledge the prompt response to the alert and the data provided by the CAOS Team. We acknowledge with thanks the ARAS database27 (https://aras-database.github.io/database/index.html). The observers who contributed worldwide data used in this research are O. Garde, V. Lecoq, L. Franco, F. Teyssier, O. Thizy, C. Boussin, P. A. Dubovsky and D. Boyd. We thank G. Principe for the advice in extending the Fermi LAT analysis below 100 MeV and F. D’Ammando for his comments on the manuscript. R.L.-C.’s work was financially supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement 754496—FELLINI.Peer reviewe