Simultaneous ALMA–Hinode–IRIS Observations on Footpoint Signatures of a Soft X-Ray Loop-like Microflare

Microflares have been considered to be among the major energy input sources to form active solar corona. To investigate the response of the low atmosphere to events, we conducted an Atacama Large Millimeter/submillimeter Array (ALMA) observation at 3 mm, coordinated with Interface Region Imaging Spectrograph (IRIS) and Hinode observations, on 2017 March 19. During the observations, a soft X-ray loop-type microflare (active region transient brightening) was captured using the Hinode X-ray telescope in high temporal cadence. A brightening loop footpoint is located within narrow fields of view of ALMA, IRIS slit-jaw imager, and Hinode spectropolarimeter. Counterparts of the microflare at the footpoint were detected in Si iv and ALMA images, while the counterparts were less apparent in C ii and Mg ii k images. Their impulsive time profiles exhibit the Neupert effect pertaining to soft X-ray intensity evolution. The magnitude of thermal energy measured using ALMA was approximately 100 times smaller than that measured in the corona. These results suggest that impulsive counterparts can be detected in the transition region and upper chromosphere, where the plasma is thermally heated via impinging nonthermal particles. Our energy evaluation indicates a deficit of accelerated particles that impinge the footpoints for a small class of soft X-ray microflares. The footpoint counterparts consist of several brightening kernels, all of which are located in weak (void) magnetic areas formed in patchy distribution of strong magnetic flux at the photospheric level. The kernels provide a conceptual image in which the transient energy release occurs at multiple locations on the sheaths of magnetic flux bundles in the corona.

Thermal-nonthermal energy partition in solar flares derived from X-ray, EUV, and bolometric observations

Context. In solar flares, energy is released impulsively and is partly converted into thermal energy of hot plasmas and kinetic energy of accelerated nonthermal particles. It is crucial to constrain the partition of these two energy components to understand energy release and transport as well as particle acceleration in solar flares. Despite numerous efforts, no consensus on quantifying this energy balance has yet been reached. Aims. We aim to understand the reasons for the contradicting results on energy partition obtained by various recent studies. The overarching question we address is whether there is sufficient energy in nonthermal particles to account for the thermal flare component. Methods. We considered five recent studies that address the thermal-nonthermal energy partition in solar flares. Their results are reviewed, and their methods are compared and discussed in detail. Results. The main uncertainties in deriving the energy partition are identified as (a) the derivation of the differential emission measure distribution and (b) the role of the conductive energy loss for the thermal component, as well as (c) the determination of the low-energy cutoff for the injected electrons. The bolometric radiated energy, as a proxy for the total energy released in the flare, is a useful independent constraint on both thermal and nonthermal energetics. In most of the cases, the derived energetics are consistent with this constraint. There are indications that the thermal-nonthermal energy partition changes with flare strength: in weak flares, there appears to be a deficit of energetic electrons, while the injected nonthermal energy is sufficient to account for the thermal component in strong flares. This behavior is identified as the main cause of the dissimilar results in the studies we considered. The changing partition has two important consequences: (a) an additional direct (i.e. non-beam) heating mechanism has to be present, and (b) considering that the bolometric emission originates mainly from deeper atmospheric layers, conduction or waves are required as additional energy transport mechanisms.

Effects of transient nonthermal particles on the big bang nucleosynthesis

The effects of introducing a small amount of nonthermal distribution (NTD) of elements in big bang nucleosynthesis (BBN) are studied by allowing a fraction of the NTD to be time-dependent so that it contributes only during a certain period of the BBN evolution. The fraction is modeled as a Gaussian-shaped function of [Formula: see text], where [Formula: see text] is the temperature of the cosmos, and thus the function is specified by three parameters; the central temporal position, the width and the magnitude. The change in the average nuclear reaction rates due to the presence of the NTD is assumed to be proportional to the Maxwellian reaction rates but with temperature [Formula: see text], [Formula: see text] being another parameter of our model. By scanning a wide four-dimensional parametric space at about half a million points, we have found about 130 points with [Formula: see text], at which the predicted primordial abundances of light elements are consistent with the observations. The magnitude parameter [Formula: see text] of these points turns out to be scattered over a very wide range from [Formula: see text] to [Formula: see text], and the [Formula: see text]-parameter is found to be strongly correlated with the magnitude parameter [Formula: see text]. The temperature region with [Formula: see text] or the temporal region [Formula: see text][Formula: see text]s seems to play a central role in lowering [Formula: see text].