39 research outputs found
Saddle-shaped solar flare arcades
Arcades of flare loops form as a consequence of magnetic reconnection
powering solar flares and eruptions. We analyse the morphology and evolution of
flare arcades that formed during five well-known eruptive flares. We show that
the arcades have a common saddle-like shape. The saddles occur despite the fact
that the flares were of different classes (C to X), occurred in different
magnetic environments, and were observed in various projections. The saddles
are related to the presence of longer, relatively-higher, and inclined flare
loops, consistently observed at the ends of the arcades, which we term
`cantles'. Our observations indicate that cantles typically join straight
portions of flare ribbons with hooked extensions of the conjugate ribbons. The
origin of the cantles is investigated in stereoscopic observations of the 2011
May 9 eruptive flare carried out by the Atmospheric Imaging Assembly (AIA) and
Extreme Ultraviolet Imager (EUVI). The mutual separation of the instruments led
to ideal observational conditions allowing for simultaneous analysis of the
evolving cantle and the underlying ribbon hook. Based on our analysis we
suggest that the formation of one of the cantles can be explained by magnetic
reconnection between the erupting structure and its overlying arcades. We
propose that the morphology of flare arcades can provide information about the
reconnection geometries in which the individual flare loops originate.Comment: 9 pages, 5 figure
Plasma Diagnostics From Active Region and Quiet Sun Spectra Observed by Hinode/EIS: Quantifying the Departures from a Maxwellian Distribution
We perform plasma diagnostics, including that of the non-Maxwellian
-distributions, in several structures observed in the solar corona by
the Extreme-Ultraviolet Imaging Spectrometer (EIS) onboard the Hinode
spacecraft. To prevent uncertainties due to the in-flight calibration of EIS,
we selected spectral atlases observed shortly after the launch of the mission.
One spectral atlas contains an observation of an active region, while the other
is an off-limb quiet Sun region. To minimize the uncertainties of the
diagnostics, we rely only on strong lines and we average the signal over a
spatial area within selected structures. Multiple plasma parameters are
diagnosed, such as the electron density, differential emission measure, and the
non-Maxwellian parameter . To do that, we use a simple, well-converging
iterative scheme based on refining the initial density estimates via the DEM
and . We find that while the quiet Sun spectra are consistent with a
Maxwellian distribution, the coronal loops and moss observed within active
region are strongly non-Maxwellian with 3. These results
were checked by calculating synthetic ratios using DEMs obtained as a function
of . Ratios predicted using the DEMs assuming -distributions
converged to the ratios observed in the quiet Sun and coronal loops. To our
knowledge, this work presents a strong evidence of a presence of different
electron distributions between two physically distinct parts of the solar
corona.Comment: 23 pages, 8 figures, 4 table
Non-Equilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind \textit{(Invited Review)}
We review the presence and signatures of the non-equilibrium processes, both
non-Maxwellian distributions and non-equilibrium ionization, in the solar
transition region, corona, solar wind, and flares. Basic properties of the
non-Maxwellian distributions are described together with their influence on the
heat flux as well as on the rates of individual collisional processes and the
resulting optically thin synthetic spectra. Constraints on the presence of
high-energy electrons from observations are reviewed, including positive
detection of non-Maxwellian distributions in the solar corona, transition
region, flares, and wind. Occurrence of non-equilibrium ionization is reviewed
as well, especially in connection to hydrodynamic and generalized
collisional-radiative modelling. Predicted spectroscopic signatures of
non-equilibrium ionization depending on the assumed plasma conditions are
summarized. Finally, we discuss the future remote-sensing instrumentation that
can be used for detection of these non-equilibrium phenomena in various
spectral ranges.Comment: Solar Physics, accepte
Spectral Imager of the Solar Atmosphere: The First Extreme-Ultraviolet Solar Integral Field Spectrograph Using Slicers
Particle acceleration, and the thermalisation of energetic particles, are fundamental processes across the universe. Whilst the Sun is an excellent object to study this phenomenon, since it is the most energetic particle accelerator in the Solar System, this phenomenon arises in many other astrophysical objects, such as active galactic nuclei, black holes, neutron stars, gamma ray bursts, solar and stellar coronae, accretion disks and planetary magnetospheres. Observations in the Extreme Ultraviolet (EUV) are essential for these studies but can only be made from space. Current spectrographs operating in the EUV use an entrance slit and cover the required field of view using a scanning mechanism. This results in a relatively slow image cadence in the order of minutes to capture inherently rapid and transient processes, and/or in the spectrograph slit âmissing the actionâ. The application of image slicers for EUV integral field spectrographs is therefore revolutionary. The development of this technology will enable the observations of EUV spectra from an entire 2D field of view in seconds, over two orders of magnitude faster than what is currently possible. The Spectral Imaging of the Solar Atmosphere (SISA) instrument is the first integral field spectrograph proposed for observations at âŒ180 Ă
combining the image slicer technology and curved diffraction gratings in a highly efficient and compact layout, while providing important spectroscopic diagnostics for the characterisation of solar coronal and flare plasmas. SISAâs characteristics, main challenges, and the on-going activities to enable the image slicer technology for EUV applications are presented in this paper
The First Flight of the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS)
The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) sounding rocket
experiment launched on July 30, 2021 from the White Sands Missile Range in New
Mexico. MaGIXS is a unique solar observing telescope developed to capture X-ray
spectral images, in the 6 - 24 Angstrom wavelength range, of coronal active
regions. Its novel design takes advantage of recent technological advances
related to fabricating and optimizing X-ray optical systems as well as
breakthroughs in inversion methodologies necessary to create spectrally pure
maps from overlapping spectral images. MaGIXS is the first instrument of its
kind to provide spatially resolved soft X-ray spectra across a wide field of
view. The plasma diagnostics available in this spectral regime make this
instrument a powerful tool for probing solar coronal heating. This paper
presents details from the first MaGIXS flight, the captured observations, the
data processing and inversion techniques, and the first science results.Comment: 20 pages, 18 figure
The Solar Particle Acceleration Radiation and Kinetics (SPARK) Mission Concept
© 2023by the authors. Licensee MDPI, Basel, Switzerland. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Particle acceleration is a fundamental process arising in many astrophysical objects, including active galactic nuclei, black holes, neutron stars, gamma-ray bursts, accretion disks, solar and stellar coronae, and planetary magnetospheres. Its ubiquity means energetic particles permeate the Universe and influence the conditions for the emergence and continuation of life. In our solar system, the Sun is the most energetic particle accelerator, and its proximity makes it a unique laboratory in which to explore astrophysical particle acceleration. However, despite its importance, the physics underlying solar particle acceleration remain poorly understood. The SPARK mission will reveal new discoveries about particle acceleration through a uniquely powerful and complete combination of Îł-ray, X-ray, and EUV imaging and spectroscopy at high spectral, spatial, and temporal resolutions. SPARKâs instruments will provide a step change in observational capability, enabling fundamental breakthroughs in our understanding of solar particle acceleration and the phenomena associated with it, such as the evolution of solar eruptive events. By providing essential diagnostics of the processes that drive the onset and evolution of solar flares and coronal mass ejections, SPARK will elucidate the underlying physics of space weather events that can damage satellites and power grids, disrupt telecommunications and GPS navigation, and endanger astronauts in space. The prediction of such events and the mitigation of their potential impacts are crucial in protecting our terrestrial and space-based infrastructure.Peer reviewe