arXiv subjects

G. Vasalos

Publications and source records attributed to G. Vasalos.

3 recordsLinked to original sources

arXiv2026

Evidence of flare and coronal mass ejection-driven shock acceleration of relativistic protons on 21 November 2024

On 21 November 2024 at 17:55 UTC, a solar flare erupted from far-side active region (AR) 13892, with enhanced hard X-ray flux measured by Solar Orbiter (SO). It was associated with a coronal mass ejection (CME) travelling at 1436 km/s along the limb. This event produced a strong and widespread solar energetic particle (SEP) event at Earth, STEREO-A and SO, with proton energies exceeding 100 MeV. We investigate the relativistic particle acceleration during this event, focusing on separating flare- and shock-related contributions and linking spectral evolution to the CME-driven shock properties. We combine multi-spacecraft energetic-particle observations with velocity dispersion analysis (VDA), three-dimensional CME-driven shock reconstruction, and magnetic connectivity modelling. Radio observations and SEP composition provided independent diagnostics of shock- and flare-associated particle acceleration, respectively. VDA yields solar release times (SRTs) consistent with an early flare-accelerated particle population at all three observers, despite their broad range of helio-longitudes. At STEREO-A, the early release is followed immediately by magnetic connection to an efficient CME-driven shock. A 3D reconstruction of the type II radio burst location confirms a connection between Earth and an efficient shock-acceleration region several minutes later. Within the adopted models, the SO release precedes magnetic connection to the reconstructed front, disfavouring acceleration at the connected shock as the source of the earliest particles. Despite this diversity, STEREO-A and SO show similar spectral evolution, while the near-Earth spectrum extends to relativistic energies and exhibits a high-energy rollover. SEP abundances also show signatures of flare-related acceleration at all three observers. The analysis suggests multiple acceleration processes acting non-uniformly across observers.

astro-ph.SR↗

arXiv2026

Catalogue and statistics of greater than 100 MeV solar proton events during solar cycles 23-25 from SOHO-ERNE observations

The SPEARHEAD (specification, analysis, and re-calibration of high-energy particle data) project, funded by the European Union Horizon Europe programme, enhances the accuracy and usability of high-energy particle measurements. It investigates particle acceleration, release, and transport during solar eruptions by refining instrument response functions and cross-calibrating datasets. We present a comprehensive catalogue of greater than 100 MeV proton events identified from May 1996 to August 2024 using SOHO-ERNE penetrating-particle rates, together with associated solar phenomena derived from multi-instrument observations. The SEP events were detected through a systematic scan of ERNE-HED counter data and cross-calibrated with SOHO-EPHIN to derive peak fluxes and fluences. Each event was associated with its likely parent eruption using X-ray (XR) (GOES-XRS, RHESSI, SolO-STIX), radio (Wind-WAVES, STEREO-WAVES, ground-based observatories), and gamma-ray (Fermi-LAT) observations, CMEs (SOHO-LASCO), and ground-level enhancements (GLEs) (neutron monitors). Timings and physical properties were systematically compared to investigate the relationships between SEP onset, flare evolution, CME kinematics, and radio signatures. Statistical analyses reveal that most SEP releases closely follow flare and CME onsets, with moderate SEP-XR-CME correlations, and a strong SEP-GLE fluence link. These results indicate that high-energy SEP events are typically associated with strong solar activity signatures, with the observed intensities and timings strongly modulated by magnetic connectivity and coronal conditions. This catalogue provides the most extensive reference to date for high-energy SEP events over solar cycles 23-25, establishing a unified framework for future investigations of extreme particle acceleration.

astro-ph.SR↗

arXiv2025

The high-energy protons of the ground level enhancement (GLE74) event on 11 May 2024

High energy solar protons were observed by particle detectors aboard spacecraft in near-Earth orbit on May 11, 2024 and produced the 74th ground level enhancement (GLE74) event registered by ground-based neutron monitors. This study involves a detailed reconstruction of the neutron monitor response, along with the identification of the solar eruption responsible for the emission of the primary particles, utilizing both in situ and remote-sensing. Observations spanning proton energies from a few MeV to around 1.64 GeV, collected from the Solar and Heliospheric Observatory (SOHO), the Geostationary Operational Environmental Satellite (GOES), the Solar Terrestrial Relations Observatory (STEREO-A), and neutron monitors, were integrated with records of the associated solar soft X-ray flare, coronal mass ejection, and radio bursts, to identify the solar origin of the GLE74. Additionally, a time-shift analysis was conducted to link the detected particles to their solar sources. Finally, a comparison of GLE74 to previous ones is carried out. GLE74 reached a maximum particle rigidity of at least 2.4 GV and was associated with a series of type III, type II, and type IV radio bursts. The release time of the primary solar energetic particles (SEPs) with an energy of 500 MeV was estimated to be around 01:21 UT. A significant SEP flux was observed from the anti-Sun direction with a relatively broad angular distribution, rather than a narrow, beam-like pattern, particularly during the main phase at the particle peak flux. Comparisons with previous GLEs suggest that GLE74 was a typical event in terms of solar eruption dynamics.

astro-ph.SR↗