Time-dependent Acceleration and Escape of Charged Particles at Traveling Shocks in the near-Sun environment: the case of the Sept 5th 2022 Parker Solar Probe event
Year: 2025
Type: conference-paper
Abstract: The Parker Solar Probe (PSP) approaches to the Sun in the past 6 years unveiled a broad variety of Traveling shocks (Ts) in the near-Sun environment, from the very weak Ts that would have been unlikely classified as shocks at 1 AU and are not associated with significant enhancement of energized particles, to the fastest ever Ts in-situ measured in the heliosphere, with unprecedented early-on signatures of particle (ions and electrons) acceleration. The interpretation of these measurements requires models for the time-evolution of particle acceleration and the escape from the source. We present the time-dependent version of a 1D transport model that incorporates particle escape at all supra- and non-thermal energies (not only the highest energies) into the diffusive shock acceleration (DSA) model via an energy- and position- dependent escape time. If the scattering is dominated by pre-existing solar wind turbulence the average time scale for particle acceleration at various heliocentric distances, from 1 AU down to the inner heliosphere (< 0.1 AU), is shorter than in the no-escape case as higher energy particles have a shorter time to accelerate before leaking out into the upstream and never return. A simple scaling with time of the time-dependent energy spectrum is provided. Finally, we compare the ``nose'' structure at a few hundreds keV protons first measured in situ by PSP in crossing the very fast September 5th 2022 Ts at 0.07 AU. We find that the nose is reasonably well explained by a lack of the highest energy particles not yet produced by the young shock by both our model and the no-escape DSA version. A larger sample of such events by PSP will help identify the conditions in the Ts lifetime of an escape-dominated regime.
DOI: 10.22323/1.501.0040
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
Awards: G1390571956, EAGER: Novel Approach to Acceleration and Escape of Charged Particles at Interplanetary and Astrophysical Shock Waves, G2819165414, G3145826106, G3561758408, G3815726687, THE PARTICLE ACCELERATION AT INTERPLANETARY SHOCKS HAS BEEN AN ACTIVE FIELD OF OBSERVATIONAL AND THEORETICAL INVESTIGATION IN THE PAST FIVE DECADES; HOWEVER THE SPATIAL DISTRIBUTION OF ENERGETIC PARTICLES ACROSS THE SHOCK CAN NOT BE REPRODUCED BY CURRENT THEORETICAL MODELS IN SEVERAL CASES. WE PROPOSE TO INVESTIGATE THE LOCAL INTENSITY ENHANCEMENTS AT THE SHOCK (SO-CALLED "SPIKES") OF SUPRA-THERMAL PARTICLES HAVING A SPEED WITHIN ONE ORDER OF MAGNITUDE GREATER THAN THE SHOCK SPEED IN THE UPSTREAM FLUID REST FRAME. THIS REGIME HOLDS BEYOND THE VALIDITY OF THE STANDARD DIFFUSIVE SHOCK ACCELERATION MODEL AND HAS BEEN POORLY STUDIED SO FAR. WE CONSIDER THIS WORK AN OVERDUE AND INNOVATIVE APPROACH TO THE SO-CALLED "INJECTION PROBLEM". WE PROPOSE A DATA-GUIDED STUDY TO COMBINE: 1) ANALYSIS AND INTERPRETATION OF INTERPLANETARY SHOCKS HIGH TIME RESOLUTION DATA COLLECTED BY ENERGETIC PARTICLE DETECTORS AND MAGNETOMETERS AT 1 AU ONBOARD ACE (ADVANCED COMPOSITION EXPLORER) AND STEREO (SOLAR TERRESTRIAL RELATIONS OBSERVATORY) A/B; 2) THEORY AND ADVANCED NUMERICAL SIMULATIONS AT SHOCKS PROPAGATING IN A TURBULENT MEDIUM TO INTERPRET THE AVAILABLE DATA. AN ANALYSIS RECENTLY CONDUCTED HAS SUGGESTED THAT THE OBSERVED ANISOTROPY AT SHOCK SPIKES RESULTS FROM BIDIRECTIONAL STREAMING OF IONS ALONG FIELD LINES THAT CROSS THE SHOCK MULTIPLE TIMES AT ODDS WITH A PREVIOUS INTERPRETATION BASED ON PILE-UP OF REFLECTED IONS; WE WILL COMPARE SUCH INTERPRETATIONS IN DETAIL. WE HAVE IDENTIFIED TWO CASES OF SHOCK SPIKE THAT WE WILL ANALYZE IN DETAIL AND WE WILL LOOK FOR OTHER CASES FROM EXISTING AND UPCOMING SPACECRAFT ARCHIVES. WE WILL COMPARE THOSE DATA WITH OUR MULTIPLE-APPROACH SIMULATIONS TO INVESTIGATE THE ORIGIN OF THE SHOCK SPIKES THEIR ANISOTROPY AND TIME-EVOLUTION., REU Site: Solar Physics at the Harvard-Smithsonian Center for Astrophysics, G5780980149, G5966779717, G6386376961, G8457443216, G8493109902
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