arXiv subjects

Markus Aschwanden

Publications and source records attributed to Markus Aschwanden.

4 recordsLinked to original sources

arXiv2025

Universal Constants and Energy Integral in Self-Organized Criticality Systems

The occurrence frequency distributions of fluxes (F) and fluences or energies (E) observed in astrophysical observations are found to be consistent with the predictions of the fractal-diffusive self-organized criticality (FD-SOC) model, which predicts power law slopes with universal constants of $α_F=(9/5)=1.80$ for the flux and $α_E=(5/3)\approx 1.67$ for the fluence. The energy integrated over the power law-like (size distribution) energy range is found to be finite for these power law slopes with $α_E < 2$, which refutes earlier claims of a divergent energy integral that has been postulated in the energy budget of solar and stellar nanoflare scenarios. The theoretial FD-SOC model approximates the microscopic cellular automaton models satisfactorily with the macroscopic scaling law of classical diffusion. The universal scaling laws predict the size distributions of numerous astrophysical phenomena, such as solar flares, stellar flares, coronal mass ejections (CME), auroras, blazars, galactic fast radio bursts (FRB), active galactic nuclei (AGN), gamma-ray bursts (GRB), soft gamma-ray repeaters (SGB), and black-hole systems (BH), while coherent solar radio bursts, random radio bursts, solar energetic partices (SEP), cosmic rays, and pulsar glitches require non-standard SOC models.

astro-ph.HE↗

arXiv2024

Testing the Universality of Self-Organized Criticality in Galactic, Extra-Galactic, and Black-Hole Systems

In this study we are testing whether the power law slopes ($α_F$, $α_E$) of fluxes $(F)$, fluences or energies $(E)$ are universal in their size distributions, $N(F) \propto F^{-α_F}$ and $N(E) \propto E^{-α_E}$, in astrophysical observations of galactic, extragalactic, and black-hole systems. This is a test of fundamental importance for self-organized criticality (SOC) systems. The test decides whether (i) power laws are a natural consequence of the scale-freeness and inherent universality of SOC systems, or (ii) if they depend on more complex physical scaling laws. The former criterion allows quantitative predictions of the power law-like size distributions, while the later criterion requires individual physical modeling for each SOC variable and data set. Our statistical test, carried out with 61 published data sets, yields strong support for the former option, which implies that observed power laws can simply be derived from the scale-freeness and do not require specific physical models to understand their statistical distributions. The observations show a mean and standard deviation of $α_F=1.78\pm0.29$ for SOC fluxes, and $α_E=1.66\pm0.22$ for SOC fluences, and thus are consistent with the prediction of the fractal-diffusive SOC model, with $α_F=1.80$ and $α_E=1.67$.

astro-ph.HE↗

arXiv2019

Global Energetics of Solar Flares: VIII. The Low-Energy Cutoff

One of the key problems in solar flare physics is the determination of the low-energy cut-off; the value that determines the energy of nonthermal electrons and hence flare energetics. We discuss different approaches to determine the low-energy cut-off in the spectrum of accelerated electrons: (i) the total electron number model, (ii) the time-of-flight model (based on the equivalence of the time-of-flight and the collisional deflection time); (iii) the warm target model of Kontar et al.~(2015), and (iv) the model of the spectral cross-over between thermal and nonthermal components. We find that the first three models are consistent with a low-energy cutoff with a mean value of $\approx 10$ keV, while the cross-over model provides an upper limit for the low-energy cutoff with a mean value of $ \approx 21$ keV. Combining the first three models we find that the ratio of the nonthermal energy to the dissipated magnetic energy in solar flares has a mean value of $q_E=0.57\pm0.08$, which is consistent with an earlier study based on the simplified approximation of the warm target model alone ($q_E=0.51\pm0.17$). This study corroborates the self-consistency between three different low-energy cutoff models in the calculation of nonthermal flare energies.

astro-ph.SR↗

arXiv2010

Uncovering Mechanisms of Coronal Magnetism via Advanced 3D Modeling of Flares and Active Regions

The coming decade will see the routine use of solar data of unprecedented spatial and spectral resolution, time cadence, and completeness. To capitalize on the new (or soon to be available) facilities such as SDO, ATST and FASR, and the challenges they present in the visualization and synthesis of multi-wavelength datasets, we propose that realistic, sophisticated, 3D active region and flare modeling is timely and critical, and will be a forefront of coronal studies over the coming decade. To make such modeling a reality, a broad, concerted effort is needed to capture the wealth of information resulting from the data, develop a synergistic modeling effort, and generate the necessary visualization, interpretation and model-data comparison tools to accurately extract the key physics.

astro-ph.SR↗