TY - JOUR
T1 - The relativistic solar particle event on 28 October 2021
T2 - Evidence of particle acceleration within and escape from the solar corona
AU - Klein, Karl Ludwig
AU - Musset, Sophie
AU - Vilmer, Nicole
AU - Briand, Carine
AU - Krucker, Säm
AU - Francesco Battaglia, Andrea
AU - Dresing, Nina
AU - Palmroos, Christian
AU - Gary, Dale E.
N1 - Funding Information:
Acknowledgements. The authors acknowledge the providers of data used in this work: neutron monitors (NMDB consortium, the French Polar Institute IPEV), radio spectra (e-Callisto, Nançay and Owens Valley radio Observatories, Wind/WAVES, STEREO/SWAVES); Solar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA. The STIX instrument is an international collaboration between Switzerland, Poland, France, Czech Republic, Germany, Austria, Ireland, and Italy. This study has received funding from CNES and CNRS/INSU/PNST to the Paris Observatory team, the Swiss National Science Foundation Grant 200021L_189180, the grant ‘Activités Nationales Complémentaires dans le domaine spatial’ REF-1131-61001 for STIX, and of the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 101004159 (SERPENTINE) to the University of Turku team. N.D. is grateful for support by the Turku Collegium for Science, Medicine and Technology of the University of Turku, Finland. D.G. acknowledges support from NSF grant AGS-2130832 and NASA grant 80NSSC18K1128 to New Jersey Institute of Technology. KLK is grateful to the French Polar Institute IPEV for the operation of neutron monitors at Kerguelen Islands and Terre Adélie, and to the personnel at these stations for their dedicated work under difficult conditions. He acknowledges many helpful discussions with colleagues at Paris Observatory/LESIA and in the Solar Orbiter and International Space Science Institute (ISSI) working groups, with special thanks to N. Chrysaphi, H. Hudson, M. Maksimovic, A. Papaioannou, and V. Krupar. He is indebted to M. Pesce Rollins for information on Fermi/LAT observations, and to G. Mann for many discussions on coronal shock waves. The language editor is acknowledged for many constructive comments.
Publisher Copyright:
© K.-L. Klein et al. 2022.
PY - 2022/7/1
Y1 - 2022/7/1
N2 - Aims. We analyse particle, radio, and X-ray observations during the first relativistic proton event of solar cycle 25 detected on Earth. The aim is to gain insight into the relationship between relativistic solar particles detected in space and the processes of acceleration and propagation in solar eruptive events. Methods. To this end, we used ground-based neutron monitor measurements of relativistic nucleons and space-borne measurements of electrons with similar speed to determine the arrival times of the first particles at 1 AU and to infer their solar release times. We compared the release times with the time histories of non-thermal electrons in the solar atmosphere and their escape to interplanetary space, as traced by radio spectra and X-ray light curves and images. Results. Non-thermal electrons in the corona are found to be accelerated in different regions. Some are confined in closed magnetic structures expanding during the course of the event. Three episodes of electron escape to the interplanetary space are revealed by groups of decametric-to-kilometric type III bursts. The first group appears on the low-frequency side of a type II burst produced by a coronal shock wave. The two latter groups are accompanied at higher frequencies by bursts with rapid drifts to both lower and higher frequencies (forward- or reverse-drifting bursts). They are produced by electron beams that propagate both sunward and anti-sunward. The first relativistic electrons and nucleons observed near Earth are released with the third group of type III bursts, more than ten minutes after the first signatures of non-thermal electrons and of the formation of the shock wave in the corona. Although the eruptive active region is near the central meridian, several tens of degrees east of the footpoint of the nominal Parker spiral to the Earth, the kilometric spectrum of the type III bursts and the in situ detection of Langmuir waves demonstrate a direct magnetic connection between the L1 Lagrange point and the field lines onto which the electron beams are released at the Sun. Conclusions. We interpret the forward- and reverse-drifting radio bursts as evidence of reconnection between the closed expanding magnetic structures of an erupting flux rope and ambient open magnetic field lines. We discuss the origin of relativistic particles near the Earth across two scenarios: (1) acceleration at the CME-driven shock as it intercepts interplanetary magnetic field lines rooted in the western solar hemisphere and (2) an alternative where the relativistic particles are initially confined in the erupting magnetic fields and get access to the open field lines to the Earth through these reconnection events.
AB - Aims. We analyse particle, radio, and X-ray observations during the first relativistic proton event of solar cycle 25 detected on Earth. The aim is to gain insight into the relationship between relativistic solar particles detected in space and the processes of acceleration and propagation in solar eruptive events. Methods. To this end, we used ground-based neutron monitor measurements of relativistic nucleons and space-borne measurements of electrons with similar speed to determine the arrival times of the first particles at 1 AU and to infer their solar release times. We compared the release times with the time histories of non-thermal electrons in the solar atmosphere and their escape to interplanetary space, as traced by radio spectra and X-ray light curves and images. Results. Non-thermal electrons in the corona are found to be accelerated in different regions. Some are confined in closed magnetic structures expanding during the course of the event. Three episodes of electron escape to the interplanetary space are revealed by groups of decametric-to-kilometric type III bursts. The first group appears on the low-frequency side of a type II burst produced by a coronal shock wave. The two latter groups are accompanied at higher frequencies by bursts with rapid drifts to both lower and higher frequencies (forward- or reverse-drifting bursts). They are produced by electron beams that propagate both sunward and anti-sunward. The first relativistic electrons and nucleons observed near Earth are released with the third group of type III bursts, more than ten minutes after the first signatures of non-thermal electrons and of the formation of the shock wave in the corona. Although the eruptive active region is near the central meridian, several tens of degrees east of the footpoint of the nominal Parker spiral to the Earth, the kilometric spectrum of the type III bursts and the in situ detection of Langmuir waves demonstrate a direct magnetic connection between the L1 Lagrange point and the field lines onto which the electron beams are released at the Sun. Conclusions. We interpret the forward- and reverse-drifting radio bursts as evidence of reconnection between the closed expanding magnetic structures of an erupting flux rope and ambient open magnetic field lines. We discuss the origin of relativistic particles near the Earth across two scenarios: (1) acceleration at the CME-driven shock as it intercepts interplanetary magnetic field lines rooted in the western solar hemisphere and (2) an alternative where the relativistic particles are initially confined in the erupting magnetic fields and get access to the open field lines to the Earth through these reconnection events.
KW - Acceleration of particles
KW - Solar-terrestrial relations
KW - Sun: coronal mass ejections (CMEs)
KW - Sun: flares
KW - Sun: particle emission
KW - Sun: radio radiation
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U2 - 10.1051/0004-6361/202243903
DO - 10.1051/0004-6361/202243903
M3 - Article
AN - SCOPUS:85135194382
SN - 0004-6361
VL - 663
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A173
ER -