Researchers have identified significant time gaps in emissions in solar flares that challenge the accuracy of current models of solar flares, and point to possible alternative energy transfer mechanisms
A new study has revealed gaps between simulation predictions and real observations of the dynamics of solar flares, mainly in the timing of emissions from the chromosphere.
Solar flares are very powerful events that occur in the Sun's atmosphere and last from a few minutes to a few hours. According to the standard flare model, the energy driving the flares is transferred by accelerated electrons moving from the coronal magnetic fusion region into the chromosphere.
When these electrons collide with the plasma in the chromosphere, they release their energy, heating and ionizing the plasma. This interaction also creates strong radiation at all wavelengths of the electromagnetic spectrum. The areas where this energy is released are called the "footpoints" of the solar flares, and they usually occur in magnetically linked pairs.
A new study aims to test the validity of the Standard Model by comparing the results of computer simulations based on the model and observational data provided by the McMath-Pierce Telescope during the solar flare SOL2014-09-24T17:50. The research focused on measuring time gaps between AA emissions from a pair of sources in the chromosphere during the eruption.
"We found a significant difference between the observation data from the telescope and the behavior predicted by the model. In the observational data, the tracer pair appeared as two very luminous regions of the chromosphere. The striking electrons exited from the same region of the corona and moved in similar trajectories, so the two spots should have shone almost simultaneously in the chromosphere according to the model, but the observational data show a time difference of 0.75 between them," said Paulo José de Aguirre Simoinç, the first author of the article from Brazil .
A gap of 0.75 seconds may seem irrelevant, but the researchers calculated that the maximum gap according to the model should be 0.42 seconds when all possible geometric configurations are taken into account. The real number was almost 80% percent higher. "We used a sophisticated statistical technique to infer the time gaps between pairs of trace points, and estimated the uncertainties of these values using the Monte Carlo method. In addition, the results were checked using electron transfer simulations and radiative-hydrodynamic simulations. By using all these resources, we were able to construct different scenarios of the flight time of the electrons between the corona and the chromosphere and the creation time of the AA radiation. All the scenarios that were based on the simulations showed much smaller time gaps than the observational data," Simoinesh said.
One of the scenarios tested was of spiral motion and magnetic trapping of electrons in the corona. "Using simulations of electron transfer, we investigated scenarios that included magnetic asymmetry between trace points of the eruption. We expected that the differences between the penetration times of the electrons into the chromosphere would be proportional to the difference in the strength of the magnetic field between the trace points, which would also increase the difference in the number of electrons that reach the chromosphere due to the magnetic trapping effect. But the analysis of the X-ray observation data that we did showed that the intensities of the trace points were very similar, which indicates the deposition of similar amounts of electrons in these regions and excludes this as the cause of the time differences in the observed emission," he said.
The radiative-hydrodynamic simulations also showed that the ionization and recombination timelines in the chromosphere were too short to explain the time gaps. "Imagine the timeline of the emission of the AA. We calculated the transfer of electrons to the chromosphere, the deposition of the electron energy, and its effects on the plasma: heating; spread; ionization and fusion of the hydrogen and helium atoms; The radiation created on the spot, which causes the release of excess energy. AA radiation is created as a result of the increase in electron density in the chromosphere due to the ionization of hydrogen, which is initially in a neutral state in the plasma. The simulations showed that ionization and the AA emissions occur almost immediately due to the penetration of the accelerated electrons, and therefore cannot explain the gap of 0.75 seconds between the emissions of the tracking points," Simoinsh said.
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