The major SOL2001-08-25 event produced a fast coronal mass ejection (CME: 1430 km s
−1
), strong flare emissions in hard X-rays and
γ
-rays extending to high energies, and neutrons detected both on ...spacecraft and by a low-latitude neutron monitor. To supplement the probable picture of this outstanding event, we reconstruct kinematic plots of the eruption and the shock-wave history. The hard X-ray and
γ
-ray emissions exhibited soft-hard-soft evolution. The emissions were strongest and hardest during a two-minute interval soon after the highest change rate of the magnetic flux within the flare ribbons of
2.6
×
10
19
Mx s
−1
, which was simultaneous with the reconstructed acceleration of the erupting flux rope. We reveal an indication of accelerated electrons injected into the erupting flux rope that then precipitated far from the main flare site, producing a hard X-ray source that moved along the footprint of a stretching flux-rope leg. These results suggest that the particle acceleration was governed by magnetic reconnection during the eruption. As in a typical situation, a piston shock was excited early in the impulsive phase and gradually transformed into a bow shock later. The frequency drift of a Type-II burst is shown to be proportional to a power of frequency
f
,
d
f
/
d
t
∝
−
f
ϵ
, with a typical range of
ϵ
being between 5/3 and 2. Overall, the SOL2011-08-25 event was a typical eruptive two-ribbon flare. Its strength was determined mainly by the intensity of the reconnection processes.
Since the launch of the
Fermi
mission in 2008, it has become possible to study high-energy solar
γ
-rays with an unprecedented imaging capability. In particular, the position of the
>
100
MeV
γ
-ray ...source can shed light on the origin of high-energy protons that is still controversial. However, the imaging of solar
γ
-ray sources with the
Fermi Large Area Telescope
(LAT) is a complex multi-stage process influenced by a number of factors and instrumental effects, which is difficult to fully comprehend a priori. The SOL2014-09-01 behind-the-limb event was significant, for which the
γ
-ray source position was not firmly established at once. Following the methodology outlined by the
Fermi
/LAT team, we estimated the proton power-law indices and
γ
-ray centroid positions at two temporal intervals of this event, separated by one hour. Our estimates for the first interval are comparable to estimates recently updated by the
Fermi
/LAT team, thereby confirming the consistency of the analysis applied. Although, in the second interval, corresponding to the decay phase of the flare, the proton power-law index clearly hardened, the presumable position of the fading
γ
-ray source remained unchanged. Its constancy in both temporal intervals and its proximity to the bases of long coronal loops connected to the flare site support the flare origin of high-energy protons injected into these loops along with electrons and trapped there for a long time. Our experience analyzing
Fermi
/LAT data clarifies their complex handling and will hopefully benefit the solar community in their wider use.
The SOL2001-12-26 moderate solar eruptive event (GOES importance M7.1, microwaves up to 4000 sfu at 9.4 GHz, coronal mass ejection (CME) speed 1446 km s
−1
) produced strong fluxes of solar energetic ...particles and ground-level enhancement (GLE) of cosmic-ray intensity (GLE63). To find a possible reason for the atypically high proton outcome of this event, we study multi-wavelength images and dynamic radio spectra and quantitatively reconcile the findings with each other. An additional eruption probably occurred in the same active region about half an hour before the main eruption. The latter produced two blast-wave-like shocks during the impulsive phase. The two shock waves eventually merged around the radial direction into a single shock traced up to
25
R
⊙
as a halo ahead of the expanding CME body, in agreement with an interplanetary Type II event recorded by the
Radio and Plasma Wave Investigation
(WAVES) experiment on the
Wind
spacecraft. The shape and kinematics of the halo indicate an intermediate regime of the shock between the blast wave and bow shock at these distances. The results show that i) the shock wave appeared during the flare rise and could accelerate particles earlier than usually assumed; ii) the particle event could be amplified by the preceding eruption, which stretched closed structures above the developing CME, facilitated its lift-off and escape of flare-accelerated particles, enabled a higher CME speed and stronger shock ahead; iii) escape of flare-accelerated particles could be additionally facilitated by reconnection of the flux rope, where they were trapped, with a large coronal hole; and iv) the first eruption supplied a rich seed population accelerated by a trailing shock wave.
The high-energy conventional atmospheric neutrino fluxes are calculated with the hadronic interaction models: Kimel & Mokhov, QGSJET II-03(04), SIBYL 2.1(2.3), EPOS LHC. The influence of ...hadron-nuclear interactions on the neutrino flux ratios, v/v¯,(vμ+v¯μ)/(ve+v¯e) , is studied. A comparison of calculations obtained with use of two different approaches, Z(E,h) -functions method and the Matrix Cascade Equations (MCEQ), demonstrates close agreement in whole but some of partial contrubutions. The comparison of calculated muon neutrino spectra with the latest experimental data justifies reliability of performed computation which describes correctly the atmospheric neutrino production. The calculation made with the model EPOS LHC, combined with Hillas & Gaisser parametrization of the cosmic ray spectrum, is in close agreement with the best fit of IceCube for energy spetrum of atmospheric muon neutrinos in the energy range 1-500 TeV.
The far-side solar eruptive event SOL2014-09-01 produced hard electromagnetic and radio emissions that were observed with detectors at near-Earth vantage points. Especially challenging was a ...long-duration > 100 MeV
γ
-ray burst that was probably produced by accelerated protons exceeding 300 MeV. This observation raised the question how high-energy protons could reach the Earth-facing solar surface. Some preceding studies discussed a scenario in which protons accelerated by a shock driven by a coronal mass ejection high in the corona return to the solar surface. We continue with the analysis of this challenging event, involving radio images from the
Nançay Radioheliograph
and hard X-ray data from the
High Energy Neutron Detector
(HEND) of the
Gamma-Ray Spectrometer
onboard the
Mars Odyssey
space observatory located near Mars. HEND recorded unocculted flare emission. The results indicate that the emissions observed from the Earth’s direction were generated by flare-accelerated electrons and protons trapped in static long coronal loops. They can be reaccelerated in these loops by a shock wave that was excited by the eruption, being initially not driven by a coronal mass ejection. The results highlight ways to address the remaining questions.
Ground level enhancements (GLEs) of cosmic-ray intensity occur, on average, once a year. Because they are rare, studying the solar sources of GLEs is especially important to approach understanding ...their origin. The SOL2001-12-26 eruptive-flare event responsible for GLE63 seems to be challenging in some aspects. Deficient observations limited our understanding of it. Analysis of additional observations found for this event provided new results that shed light on the flare configuration and evolution. This article addresses the observations of this flare with the
Siberian Solar Radio Telescope
(SSRT). Taking advantage of its instrumental characteristics, we analyze the detailed SSRT observations of a major long-duration flare at 5.7 GHz without cleaning the images. The analysis confirms that the source of GLE63 was associated with an event in active region 9742 that comprised two flares. The first flare (04:30 – 05:03 UT) reached a GOES importance of about M1.6. Two microwave sources were observed, whose brightness temperatures at 5.7 GHz exceeded 10 MK. The main flare, up to an importance of M7.1, started at 05:04 UT and occurred in strong magnetic fields. The observed microwave sources reached a brightness temperature of about 250 MK. They were not static. After appearing on the weaker-field periphery of the active region, the microwave sources moved toward each other nearly along the magnetic neutral line, approaching the stronger-field core of the active region, and then moved away from the neutral line like expanding ribbons. These motions rule out an association of the non-thermal microwave sources with a single flaring loop.
Our analysis of the observations of the SOL2001-12-26 event, which was related to ground-level enhancement of cosmic-ray intensity GLE63, including microwave spectra and images from the
Nobeyama ...Radioheliograph
at 17 and 34 GHz, from the
Siberian Solar Radio Telescope
at 5.7 GHz, and from the
Transition Region and Coronal Explorer
in 1600 Å, has led to the following results: A flare ribbon overlapped with the sunspot umbra, which is typical of large particle events. Atypical were i) the long duration of the flare, which lasted more than one hour; ii) the moderate intensity of the microwave burst, which was about
10
4
sfu
; iii) the low peak frequency of the gyrosynchrotron spectrum, which was about 6 GHz; and its insensitivity to the flux increase by more than one order of magnitude. This was accompanied by a nearly constant ratio of the flux emitted by the volume in the high-frequency part of the spectrum to its elevated low-frequency part determined by the area of the source. With the self-similarity of the spectrum, a similarity was observed between the moving microwave sources and the brightest parts of the flare ribbons in 1600 Å images. We compared the 17 GHz and 1600 Å images and confirm that the microwave sources were associated with multiple flare loops, whose footpoints appeared in the ultraviolet as intermittent bright kernels. To understand the properties of the event, we simulated its microwave emission using a system of several homogeneous gyrosynchrotron sources above the ribbons. The scatter between the spectra and the sizes of the individual sources is determined by the inhomogeneity of the magnetic field within the ribbons. The microwave flux is mainly governed by the magnetic flux passing through the ribbons and the sources. The apparent simplicity of the microwave structures is caused by a poorer spatial resolution and dynamic range of the microwave imaging. The results indicate that microwave manifestations of accelerated electrons correspond to the structures observed in thermal emissions, as well-known models predict.
Recently the atmospheric muon spectra at high energies were reconstructed for two ranges of zenith angles, basing on the events collected with the IceCube detector. These measurements reach high ...energies at which the contribution to atmospheric muon fluxes from decays of short-lived hadrons is expected. Latest IceCube measurements of the high-energy atmospheric muon spectrum indicate the presence of prompt muon component at energies above 500 TeV.
We study the development of a coronal mass ejection (CME) caused by a prominence eruption on 24 February 2011 and properties of a related interplanetary CME (ICME). The prominence destabilized, ...accelerated, and produced an M3.5 flare, a fast CME, and a shock wave. The eruption at the east limb was observed in quadrature by the
Atmospheric Imaging Assembly
(AIA) on board the
Solar Dynamics Observatory
(SDO) and by the
Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI) instrument suite on board the
Solar-Terrestrial Relations Observatory
(STEREO). The ICME produced by the SOL2011-02-24 event was measured
in situ
on STEREO-B two days later. The diagnostics made from multi-wavelength SDO/AIA images reveals a pre-eruptive heating of the prominence to about 7 MK and its subsequent heating during the eruption by flare-accelerated particles to about 10 MK. The hot plasma was detected in the related ICME as an enhancement in the ionic charge state of Fe, whose evolution was reproduced in the modeling. The analysis of the solar source region allows for predicting the variations of magnetic components in the ICME, while the flux-rope rotation by about
40
∘
was indicated by observations. The magnetic-cloud propagation appears to be ballistic.
New results are presented from experimental studies of the nonthermal effect high-power (high-voltage) nanosecond electromagnetic pulses have on the development of microdefects in rock samples. ...Scanning electron microscopy is used to assess microstructural modifications in samples, along with X-ray microtomography for coal. Sizes of the gaps in microcracks are measured, their structural features are analyzed, and a possible mechanism of miсrodefect formation is discussed.
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