arXiv subjects

Immanuel Jebaraj

Publications and source records attributed to Immanuel Jebaraj.

4 recordsLinked to original sources

arXiv2026

Solar energetic particles and their association with radio emissions

Energetic particle populations are ubiquitous throughout the Universe. In our solar system, the most prominent sources of energetic particles are solar flares or collisionless shocks often driven by huge eruptions of magnetised plasma called coronal mass ejections (CMEs). Remotely, low energy electrons from the Sun can be observed as solar radio bursts that are produced by accelerated electron beams undergoing beam-plasma interactions. There are still many open questions on the generation of solar energetic particles (SEP): how and where are SEPs accelerated during solar flares and CMEs and how they escape the solar atmosphere? Another important question is: what is the link between the solar radio bursts and the observed SEPs at spacecraft? SKA can provide high-resolution radio images combined with spectroscopic observations to determine the acceleration time, trajectory and escape of low energy electrons from the solar corona. The synergy between SKA and current space missions will help investigate solar activity and energetic particles across a wide range of wavelengths and particle energies. Particle data from spacecraft can be used to make a connection between radio bursts and SEPs by comparing SEP inferred injection times and energies to those of electrons generating radio bursts at the Sun. Radio observations in turn can be used to distinguish between flare and shock acceleration since different radio bursts pinpoint towards different energetic processes. Since the acceleration region and origin of SEPs of various properties is still largely debated, radio observations have the potential to be an invaluable tool in unraveling these processes.

astro-ph.SR↗

arXiv2026

Magnetic Pumping: Plasma Heating to Particle Acceleration

One of the earliest mechanisms proposed for plasma heating was magnetic pumping (MP). However, its significance for astrophysical phenomena, including particle acceleration, has yet to be appreciated. MP-energized particles tap energy from magnetic-field oscillations. A particle's momentum component perpendicular to the local B-field increases during field growth by virtue of the adiabatic invariant $p_{\perp}^{2}/B=const$. The gained $p_{\perp}$ is then partially scattered elastically into the parallel momentum, $p_{\parallel}$, with $p^{2}=p_{\parallel}^{2}+p_{\perp}^{2}=const$, thereby retaining some fraction of the gained energy before the field decreases to its minimum. This scattering breaks the reversibility of energy exchange between particles and oscillating magnetic fields, thereby increasing the particle energy after each MP cycle. Field oscillations are often assumed to be sinusoidal, and the resulting MP is treated perturbatively. These simplifications restrict astrophysical applications, leaving objects with strong magnetic perturbations outside the scope of adequate treatment. We develop a nonperturbative approach to MP that is suitable for a broad spectrum of magnetic turbulence. The treatment comprises two steps. The first step is common: converting a kinetic equation into an infinite hierarchy of moments of the particle distribution function. The second step is new in MP treatments: we find an exact closure at an arbitrary level of the moment system. The heating is treated exactly at the second-moment closure. Particle acceleration generally requires a higher-level closure to determine the power-law index and the maximum energy of accelerated particles. We propose a method for extracting these crucial acceleration data from the second moment for a broadband random field.

astro-ph.HE↗

arXiv2025

Coronal flux tube illuminated by strong shock spot: New Year's Eve solar eruption of 2023-Dec-31

Powerful solar eruptions are known to produce fast and wide shock waves in the solar corona and inner heliosphere. The relationship between the coronal shock waves, solar energetic particles and different types of radio emission is a subject of long-lasting research activity. In this work, we perform a case study of 31 December 2023 eruption that occurred near eastern limb of the Sun. It produced a X5.0 class X-ray flare, a global EUV wave, a fast $\sim3000$ km/s Coronal Mass Ejection, strong radio emissions (including several type III and type II bursts), solar energetic particles in-situ, and long duration high-energy gamma-ray emission. We employ a technique that combines the reconstructed coronal shock from observations with background coronal MHD simulations to produce shock-mediated synthetic radio spectrum, assuming local emission at plasma frequency. We show that transient high Mach number and quasi-perpendicular coronal shock region explains both a ``hot flux tube'' precursor seen in EUV observations and reverse drifting radio spectral features observed by ground-based facilities. The occurrence of this evanescent strong shock patch was observed when it propagated across pseudo-streamer's cusp where the magnetic field was particularly low. We also find evidence that, at higher coronal altitudes, the low-frequency type II radio burst detected by several spacecraft, is triggered by the interaction of the shock with the heliospheric current sheet. This study provides additional evidence that high-$M_A$ regions of coronal shock surface are instrumental in energetic particle phenomenology.

astro-ph.SR↗

arXiv2023

Observation of solar radio burst events from Mars orbit with the Shallow Radar instrument

Multispacecraft and multiwavelength observations of solar eruptions such as flares and coronal mass ejections are essential to understand the complex processes behind these events. The study of solar burst events in the radio-frequency spectrum has relied almost exclusively on data from ground-based observations and a few dedicated heliophysics missions such as STEREO or Wind. Reanalysing existing data from the Mars Reconnaissance Orbiter (MRO) Shallow Radar (SHARAD) instrument, a Martian planetary radar sounder, we have discovered the instrument was also capable of detecting solar radio bursts, and was able to do so with unprecedented resolution for a space-based solar instrument. In this study we aim at demonstrating the reliability and value of SHARAD as a new solar radio-observatory. We characterised the sensitivity of the instrument to type-III solar radio bursts through a statistical analysis of correlated observations, using STEREO and Wind as references. Using 38 correlated detections, we establish the conditions under which SHARAD can observe solar bursts in terms of acquisition geometry. As an example of scientific application, we also present the first analysis of type-III characteristic times at high resolution beyond 1 AU. A simple logistic model based purely on geometrical acquisition parameters can predict burst show vs. no-show in SHARAD data with an accuracy of 79.2%, demonstrating the reliability of the instrument for detecting solar bursts and laying the foundation for using SHARAD as a solar radio-observatory. The extremely high resolution of the instrument, both in temporal and frequency directions, its bandwidth, and its position in the solar system enable SHARAD to make significant contributions to heliophysics; it could inform on plasma processes on the site of the burst generation and along the propagation path of associated fast electron beams.

astro-ph.SR↗