Plasma Diagnostics of Microflares observed by STIX and AIA

Solar flares are generally thought to be the impulsive release of magnetic energy giving rise to a wide range of solar phenomena that influence the heliosphere and in some cases even conditions of earth. Part of this liberated energy is used for particle acceleration and to heat up the solar plasma. The Spectrometer/Telescope for Imaging X-rays (STIX) instrument onboard the Solar Orbiter mission launched on February 10th 2020 promises advances in the study of solar flares of various sizes. It is capable of measuring X-ray spectra from 4 to 150 keV with 1 keV resolution binned into 32 energy bins before downlinking. With this energy range and sensitivity, STIX is capable of sampling thermal plasma with temperatures of&#8819;10 MK, and to diagnose the nonthermal bremsstrahlung emission of flare-accelerated electrons. During the spacecraft commissioning phase in the first half of the year 2020, STIX observed 68 microflares. Of this set, 26 events could clearly be identified in at least two energy channels, all of which originated in an active region that was also visible from earth. These events provided a great opportunity to combine the STIX observations with the multi-band EUV imagery from the Atmospheric Imaging Assembly (AIA) instrument on board the earth orbiting Solar Dynamics Observatory (SDO). For the microflares that could be identified in two STIX science energy bands, it was possible to derive the temperature and emission measure (EM) of the flaring plasma assuming an isothermal source. For larger events where more detailed spectra could be derived, a more accurate analysis was performed by fitting the spectra assuming various thermal and nonthermal sources. These results are compared to the diagnostics derived from AIA images. To this aim, the Differential EmissionMeasure (DEM) was reconstructed from AIA observations to infer plasma temperatures and EM in the flaring regions. Combined with the the relative timing between the emission seen by STIX and AIA, this allows us to get deeper insight into the flare energy release and transport processes.

Download Full-text

First results of the STIX hard X-ray telescope onboard Solar Orbiter

10.5194/egusphere-egu21-4390 ◽

2021 ◽

Author(s):

Andrea Francesco Battaglia ◽

Jonas Saqri ◽

Ewan Dickson ◽

Hualin Xiao ◽

Astrid Veronig ◽

...

Keyword(s):

Solar Flares ◽

Magnetic Energy ◽

Imaging Spectroscopy ◽

X Rays ◽

X Ray ◽

X Ray Imaging ◽

First Results ◽

Early Peak ◽

Accelerated Particles ◽

Magnetic Energy Release

With the launch and commissioning of Solar Orbiter, the Spectrometer/Telescope for Imaging X-rays (STIX) is the latest hard X-ray telescope to study solar flares over a large range of flare sizes. STIX uses hard X-ray imaging spectroscopy in the range from 4 to 150 keV to diagnose the hottest temperature of solar flare plasma and the related nonthermal accelerated electrons. The unique orbit away from the Earth-Sun line in combination with the opportunity of joint observations with other Solar Orbiter instruments, STIX will provide new inputs into understanding the magnetic energy release and particle acceleration in solar flares. Commissioning observations showed that STIX is working as designed and therefore we report on the first solar microflare observations recorded on June 2020, when the spacecraft was at 0.52 AU from the Sun. STIX&#8217;s measurements are compared with Earth-orbiting observatories, such as GOES and SDO/AIA, for which we investigate and interpret the different temporal evolution. The detected early peak of the STIX profiles relative to GOES is due either by nonthermal X-ray emission of accelerated particles interacting with the dense chromosphere or the higher sensitivity of STIX toward hotter plasma.

Download Full-text

Late Ordovician geographic patterns of extinction compared with simulations of astrophysical ionizing radiation damage

Paleobiology ◽

10.1666/0094-8373-35.3.311 ◽

2009 ◽

Vol 35 (3) ◽

pp. 311-320 ◽

Cited By ~ 41

Author(s):

Adrian L. Melott ◽

Brian C. Thomas

Keyword(s):

Solar Flares ◽

Gamma Ray ◽

High Energy ◽

Gamma Ray Bursts ◽

X Rays ◽

Mass Extinctions ◽

Observable Universe ◽

Variable Intensity ◽

High Rotational Speed ◽

Wide Range

Terrestrial mass extinctions have been attributed to a wide range of causes. Some of them are external to Earth, such as bolide impacts (as widely discussed for the K/T boundary) and radiation events. Among radiation events, there are possible large solar flares, nearby supernovae, gamma-ray bursts (GRBs), and others. These have variable intensity, duration, and probability of occurrence, although some generalizations are possible in understanding their effects (Ejzak et al. 2007). Here we focus on gamma-ray bursts (Thorsett 1995; Scalo and Wheeler 2002), a proposed causal agent for the end-Ordovician extinction. These are the most remote and infrequent of events, but by virtue of their power, a threat approximately competitive with, for example, that of nearby supernovae. A GRB of the most powerful type (Woosley and Bloom 2006) is thought to result from a supernova at the end of stellar evolution for very massive stars with high rotational speed. Much of their energy is channeled into beams, or jets, which include very high energy electromagnetic energy, i.e., gamma-rays and X-rays. It is a testament to the power of these events, far across the observable universe, that they were first detected in the 1969–1970 results from monitoring satellites designed to detect nuclear explosions on Earth's surface. It was not until the 1990s, when the distance to the events became known, that their power became apparent. Several such events occur every day in the observable universe. Other kinds of events are also potentially damaging, such as so-called short bursts and solar flares, but rate information is only now beginning to clarify how much threat is likely from such sources.

Download Full-text

Validation of computed extreme ultraviolet emission spectra during solar flares

Earth Planets and Space ◽

10.1186/s40623-021-01402-7 ◽

2021 ◽

Vol 73 (1) ◽

Author(s):

Shohei Nishimoto ◽

Kyoko Watanabe ◽

Toshiki Kawai ◽

Shinsuke Imada ◽

Tomoko Kawate

Keyword(s):

Solar Flares ◽

Rise Time ◽

Extreme Ultraviolet ◽

Emission Spectra ◽

Physical Models ◽

Spectral Irradiance ◽

X Rays ◽

Solar Dynamics Observatory ◽

Ultraviolet Emission ◽

Proposed Model

AbstractX-rays and extreme ultraviolet (EUV) emissions from solar flares rapidly change the physical composition of the Earth’s thermosphere and ionosphere, thereby causing space weather phenomena such as communication failures. Numerous empirical and physical models have been developed to estimate the effects of flare emissions on the Earth’s upper atmosphere. We verified the reproduction of the flare emission spectra using a one-dimensional hydrodynamic calculation and the CHIANTI atomic database. To validate the proposed model, we used the observed EUV spectra obtained by the Extreme ultraviolet variability experiment (EVE) on board the Solar Dynamics Observatory (SDO). We examined the “EUV flare time-integrated irradiance” and “EUV flare line rise time” of the EUV emissions for 21 events by comparing the calculation results of the proposed model and observed EUV spectral data. The proposed model successfully reproduced the EUV flare time-integrated irradiance of the Fe VIII 131 Å, Fe XVIII 94 Å, and Fe XX133 Å, as well as the 55–355 Å and 55–135 Å bands. For the EUV flare line rise time, there was an acceptable correlation between the proposed model estimations and observations for all Fe flare emission lines. These results demonstrate that the proposed model can reproduce the EUV flare emission spectra from the emitting plasma with a relatively high formation temperature. This indicates that the physics-based model is effective for the accurate reproduction of the EUV spectral irradiance.

Download Full-text

Validation of Computed Extreme Ultraviolet Emission Spectra During Solar Flares

10.21203/rs.3.rs-52084/v2 ◽

2020 ◽

Author(s):

Shohei Nishimoto ◽

Kyoko Watanabe ◽

Toshiki Kawai ◽

Shinsuke Imada ◽

Tomoko Kawate

Keyword(s):

Solar Flares ◽

Rise Time ◽

Extreme Ultraviolet ◽

Emission Spectra ◽

Physical Models ◽

X Rays ◽

Solar Dynamics Observatory ◽

Ultraviolet Emission ◽

Proposed Model ◽

Solar Dynamics

Abstract X-rays and extreme ultraviolet (EUV) emissions from solar flares rapidly change the physical composition of the Earth’s thermosphere and ionosphere, thereby causing space weather phenomena such as communication failures. To predict the effects of flare emissions on the Earth’s upper atmosphere, numerous empirical and physical models have been developed. We verify the extent of reproducing the flare emission spectra using a one-dimensional hydrodynamic calculation and the CHIANTI atomic database. To verify the proposed model, we use the observed EUV spectra obtained by the extreme ultraviolet variability (EVE) on board the Solar Dynamics Observatory (SDO). We examined the “EUV flare time-integrated irradiance” and “EUV flare line rise time” of the EUV emissions for 21 events by comparing the calculation results of the proposed model and observed EUV spectral data. The proposed model succeeded in reproducing the EUV flare time-integrated irradiance of the Fe VIII 131 Å , Fe XVIII 94 Å, and Fe XX 133 Å, as well as the 55 to 355 Å and 55 to 135 Å bands. For the EUV flare line rise time, there was acceptable correlation between the proposed model estimations and observations for all Fe flare emission lines. These results demonstrate that the proposed model can reproduce the EUV flare emission spectra from the emitting plasma with relatively high formation temperature. This indicates that the physics-based model is effective for the accurate reproduction of EUV spectral flux.

Download Full-text

Energetic electrons in solar flares: observational support for acceleration processes linked to magnetic reconnection

10.5194/egusphere-egu21-15019 ◽

2021 ◽

Author(s):

Nicole Vilmer ◽

Sophie Musset

Keyword(s):

Solar Flares ◽

Magnetic Energy ◽

Imaging Spectroscopy ◽

Active Regions ◽

Coronal Magnetic Field ◽

High Energy ◽

X Rays ◽

Energetic Electrons ◽

Radio Imaging ◽

Gyrosynchrotron Emission

Efficient electron (and ion) acceleration is produced in association with solar flares. Energetic particles play a major role in the active Sun since they contain a large amount of the magnetic energy released during flares. Energetic electrons (and ions) interact with the solar atmosphere and produce high-energy X-rays and &#947;-rays. Energetic electrons also produce radio emission in a large frequency band through gyrosynchrotron emission processes in the magnetic fields of flaring active regions and conversion of plasma waves when e.g. propagating to the high corona towards the interplanetary medium. It is currently admitted that solar flares are powered by magnetic energy previously stored in the coronal magnetic field and that magnetic energy release is likely to occur on coronal currents sheets along regions of strong gradient of magnetic connectivity. However, understanding the connection between particle acceleration processes and the topology of the complex magnetic structures present in the corona is still a challenging issue. In this talk, we shall review some recent results derived from X-ray and radio imaging spectroscopy of solar flares bringing some new observational constraints on the localization of HXR/radio sources with respect to current sheets, termination shocks in the corona derived from EUV observations.

Download Full-text

Recent Observations of Energetic Electrons in Solar Flares

Symposium - International Astronomical Union ◽

10.1017/s0074180900067620 ◽

1980 ◽

Vol 91 ◽

pp. 227-230

Author(s):

S. R. Kane

Keyword(s):

Spatial Resolution ◽

Solar Flares ◽

Electron Distribution ◽

Energetic Electron ◽

Low Energy ◽

Thermal Source ◽

X Rays ◽

Energetic Electrons ◽

X Ray ◽

Wide Range

SummaryIt has been apparent for the last few years that a large fraction of the total energy released during a solar flare appears initially in the form of energetic electrons accelerated during the impulsive phase. An estimate of the energy of these electrons is based on the observed hard x-ray spectra as well as the assumed form (thermal or non-thermal) of the electron distribution. Even after the basic form of the electron distribution is assumed, additional assumptions, such as the low energy cut-off in the case of the power law energy spectrum or existence of a multi-thermal source in the case of the thermal spectrum, are usually required. In order to test these assumptions, measurements of the hard x-ray spectrum with spatial resolution and covering a wide range of x-ray energy are essential. In absence of good spatial resolution, as is the case with most of the presently available hard x-ray observations, the impulsive x-ray emission at energies hv ≲ 10 keV is often unobservable because of the presence of a large background of relatively intense gradual emission associated with most flares. Observations made in the past suffered either because of the lack of a clearly identifiable impulsive x-ray emission at low energies (Peterson et al, 1973) or an adequate spectral resolution (Kahler, 1973). Thus so far it has not been possible to measure unambiguously the spectrum of impulsive x-rays ≲ 10 keV and hence to deduce a possible low energy cut-off in the energetic electron spectrum. Here we report briefly such an observation made with the ISEE-3 x-ray spectrometer experiment and its implications with regard to the characteristics of energetic electrons in solar flares.

Download Full-text

The Relationship between Hard and Soft X-Ray Bursts Observed by OSO 7

Symposium - International Astronomical Union ◽

10.1017/s0074180900071692 ◽

1975 ◽

Vol 68 ◽

pp. 191-208

Author(s):

Dayton W. Datlowe

Keyword(s):

Time Evolution ◽

Solar Flares ◽

Emission Measure ◽

University Of California ◽

X Rays ◽

X Ray ◽

Cooling Mechanism ◽

Flare Plasma ◽

The University ◽

The Relationship

Solar X-rays in the energy range 1–100 keV originate in hot plasmas and streams of energetic electrons in solar flares, and since these phenomena may represent a significant fraction of the energy in a flare, an understanding of them is important for any flare theory. This paper presents the results of the University of California, San Diego, solar X-ray instrument on the OSO-7 satellite. Study of the time evolution of the emission measure in a typical burst indicates that the growth of soft X-ray emission is due to the addition of new hot material to the flare plasma, and the study of the time evolution of the temperature of the plasma indicates that conduction is the dominant cooling mechanism. Comparison of the hard (10–100 keV) and soft (5–10 keV) data indicates that the main heat input to the flare plasma is not collisions by the electrons which make the hard X-rays. The fraction of soft X-ray bursts observed by the instrument which also have a detectable hard X-ray component is this result is the same for bursts which occured near the center of the disk (θ < 60°) and for those bursts believed to have been partly occulted by the limb, indicating that hard X-ray emission comes at least part from high in the corona. For a sample of 62 hard X-ray bursts which occurred near or beyond the limb, the spectral index of the hard X-ray power law was significantly larger, as compared with the spectra of a comparable number which occurred at solar longitudes less than 60°.

Download Full-text

Validation of Extreme Ultraviolet Emission Spectra During Solar Flares

10.21203/rs.3.rs-52084/v1 ◽

2020 ◽

Author(s):

Shohei Nishimoto ◽

Kyoko Watanabe ◽

Toshiki Kawai ◽

Shinsuke Imada ◽

Tomoko Kawate

Keyword(s):

Solar Flares ◽

Rise Time ◽

Extreme Ultraviolet ◽

Emission Spectra ◽

Physical Models ◽

X Rays ◽

Solar Dynamics Observatory ◽

Ultraviolet Emission ◽

Proposed Model ◽

Solar Dynamics

Abstract X-rays and extreme ultraviolet (EUV) emissions from solar flares rapidly change the physical composition of the Earth’s thermosphere and ionosphere, thereby causing space weather phenomena such as communication failures. To predict the effects of flare emissions on the Earth’s upper atmosphere, numerous empirical and physical models have been developed. We verify the extent of reproducing the flare emission spectra using a one-dimensional hydrodynamic calculation and the CHIANTI atomic database. To verify the proposed model, we use the observed EUV spectra obtained by the extreme ultraviolet variability (EVE) on board the Solar Dynamics Observatory (SDO). We examined the “EUV flare time-integrated irradiance” and “EUV flare line rise time” of the EUV emissions for 21 events by comparing the calculation results of the proposed model and observed EUV spectral data. The proposed model succeeded in reproducing the EUV flare time-integrated irradiance of the Fe VIII 131 Å, Fe XVIII 94 Å, and Fe XX 133 Å, as well as the 55 to 355 Å and 55 to 135 Å bands. For the EUV flare line rise time, there was acceptable correlation between the proposed model estimations and observations for all Fe flare emission lines. These results demonstrate that the proposed model can reproduce the EUV flare emission spectra from the emitting plasma with relatively high formation temperature. This indicates that the physics-based model is effective for the accurate reproduction of EUV spectral flux.

Download Full-text

Radio and X-ray Observations of Short-lived Episodes of Electron Acceleration in a Solar Microflare

10.5194/egusphere-egu21-14293 ◽

2021 ◽

Author(s):

Rohit Sharma ◽

Marina Battaglia ◽

Yingjie Luo ◽

Bin Chen ◽

Sijie Yu

Keyword(s):

Extreme Ultraviolet ◽

Magnetic Energy ◽

Electron Acceleration ◽

High Energy ◽

Nonthermal Electron ◽

X Rays ◽

Solar Dynamics Observatory ◽

Lower Corona ◽

X Ray ◽

Multi Wavelength

Solar flares release enormous magnetic energy into the corona, producing the heating of ambient plasma and acceleration of particles. The flaring process is complex and often shows multiple spatially separated temporal individual episodes of energy releases, which can be hard to resolve based on the instrument capability. We analysed the multi-wavelength imaging and spectroscopy observations of multiple electron acceleration episodes during a GOES B1.7-class two-ribbon flare observed simultaneously with the Karl G. Jansky Very Large Array (VLA) at 1--2 GHz, the Reuven Ramatay High Energy Solar Spectroscopic Imager (RHESSI) in X-rays, and the Solar Dynamics Observatory in extreme ultraviolet (EUV). We observed a total of six radio bursts. First three bursts were co-temporal, but not co-spatial nonthermal X-ray source and represent multiple electron acceleration episodes. We model the radio spectra by optically thick gyrosynchrotron emission and estimate the magnetic field strength and nonthermal electron spectral parameters in each acceleration episode. We note that the nonthermal parameters derived from X-rays differ considerably from the nonthermal parameters inferred from the radio and originates in the lower corona. Although co-temporal, our multi-wavelength analysis shows that different electron populations produce multiple acceleration episodes in radio and X-rays wavelengths.&#160;

Download Full-text

A Color Coded STEM/SEM Image Storage System

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100097880 ◽

1981 ◽

Vol 39 ◽

pp. 272-273

Author(s):

Y. Kokubo ◽

W. H. Hardy ◽

J. Dance ◽

K. Jones

Keyword(s):

Image Processing ◽

Electron Beam ◽

Storage System ◽

Particle Analysis ◽

Specific Information ◽

X Rays ◽

Sem Image ◽

Backscattered Electrons ◽

Wide Range ◽

Scanning Electron

A color coded digital image processing is accomplished by using JEM100CX TEM SCAN and ORTEC’s LSI-11 computer based multi-channel analyzer (EEDS-II-System III) for image analysis and display. Color coding of the recorded image enables enhanced visualization of the image using mathematical techniques such as compression, gray scale expansion, gamma-processing, filtering, etc., without subjecting the sample to further electron beam irradiation once images have been stored in the memory.The powerful combination between a scanning electron microscope and computer is starting to be widely used 1) - 4) for the purpose of image processing and particle analysis. Especially, in scanning electron microscopy it is possible to get all information resulting from the interactions between the electron beam and specimen materials, by using different detectors for signals such as secondary electron, backscattered electrons, elastic scattered electrons, inelastic scattered electrons, un-scattered electrons, X-rays, etc., each of which contains specific information arising from their physical origin, study of a wide range of effects becomes possible.

Download Full-text