scholarly journals Another Clue About Particle Acceleration in Impulsive Hard X-Ray/Microwave Bursts

1994 ◽  
Vol 142 ◽  
pp. 697-700
Author(s):  
David Batchelor
Keyword(s):  
Thermal Conduction ◽  
Microwave Emission ◽  
Spectral Information ◽  
Acceleration Of Particles ◽  
X Rays ◽  
Radio Radiation ◽  
X Ray ◽  
Structure And Dynamics ◽  
Source Structure ◽  
Microwave Bursts

AbstractIn a sample of impulsive bursts with rise times less than 30 s, a correlation between burst rise times and the frequency of maximum microwave emission has been found. The implications for source structure and dynamics are discussed in this paper. Previously evidence was found that such bursts are caused by some propagating disturbance such as a shock wave or thermal conduction front. Combining that evidence with the microwave and hard X-ray spectral information suggests that the most rapid bursts are emitted from the most compact and intensely magnetized sources. The most rapid bursts also exhibited the hardest X-ray spectra, as published previously. These facts are important clues to understanding the physical process responsible for impulsive bursts. A model for the bursts is suggested, based on the observations and inferences described.Subject headings: acceleration of particles — Sun: radio radiation — X-rays: bursts

scholarly journals X-Ray Free-Electron Lasers for the Structure and Dynamics of Macromolecules

2019 ◽  
Vol 88 (1) ◽  
pp. 35-58 ◽  
Author(s):  
Henry N. Chapman
Keyword(s):  
Free Electron ◽  
Conformational Dynamics ◽  
Cryogenic Cooling ◽  
X Rays ◽  
Free Electron Lasers ◽  
X Ray ◽  
Virus Particles ◽  
Structure And Dynamics ◽  
Small Crystals ◽  
Serial Crystallography

X-ray free-electron lasers provide femtosecond-duration pulses of hard X-rays with a peak brightness approximately one billion times greater than is available at synchrotron radiation facilities. One motivation for the development of such X-ray sources was the proposal to obtain structures of macromolecules, macromolecular complexes, and virus particles, without the need for crystallization, through diffraction measurements of single noncrystalline objects. Initial explorations of this idea and of outrunning radiation damage with femtosecond pulses led to the development of serial crystallography and the ability to obtain high-resolution structures of small crystals without the need for cryogenic cooling. This technique allows the understanding of conformational dynamics and enzymatics and the resolution of intermediate states in reactions over timescales of 100 fs to minutes. The promise of more photons per atom recorded in a diffraction pattern than electrons per atom contributing to an electron micrograph may enable diffraction measurements of single molecules, although challenges remain.

scholarly journals An Observed Correlation Between the Flux Densities of Extended Hard X-ray and Microwave Solar Bursts

1980 ◽  
Vol 86 ◽  
pp. 281-283
Author(s):  
R. T. Stewart ◽  
G. J. Nelson
Keyword(s):  
Second Phase ◽  
Acceleration Process ◽  
X Rays ◽  
Turnover Frequency ◽  
Thin Target ◽  
X Ray ◽  
Time Profiles ◽  
Solar Bursts ◽  
Phase Acceleration ◽  
Microwave Bursts

Crannell et al. (1978) have reported an observed correlation between the time profiles and flux densities of impulsive hard x-ray and microwave solar bursts. We report here on a significant correlation between the fluxes of extended bursts of hard x-rays and microwaves. The significance of our observations follows from the suggestion of Wild, Smerd and Weiss (1963) that the extended bursts are evidence for a second phase acceleration process in the corona. We show that the observed characteristics of these extended microwave bursts (viz. rather a flat spectrum below a turnover frequency which is independent of intensity) can be explained by gyrosynchrotron radiation from the same population of energetic (E ~ 100 keV) electrons as those emitting thin-target x-ray bremsstrahlung.

scholarly journals Materials Imaging and Dynamics (MID) instrument at the European X-ray Free-Electron Laser Facility

2021 ◽  
Vol 28 (2) ◽  
pp. 637-649
Author(s):  
A. Madsen ◽  
J. Hallmann ◽  
G. Ansaldi ◽  
T. Roth ◽  
W. Lu ◽  
...  
Keyword(s):  
Free Electron ◽  
Free Electron Laser ◽  
Condensed Matter ◽  
Coherent Scattering ◽  
X Rays ◽  
Structured Materials ◽  
X Ray ◽  
Structure And Dynamics ◽  
Laser Facility

The Materials Imaging and Dynamics (MID) instrument at the European X-ray Free-Electron Laser (EuXFEL) facility is described. EuXFEL is the first hard X-ray free-electron laser operating in the MHz repetition range which provides novel science opportunities. The aim of MID is to enable studies of nano-structured materials, liquids, and soft- and hard-condensed matter using the bright X-ray beams generated by EuXFEL. Particular emphasis is on studies of structure and dynamics in materials by coherent scattering and imaging using hard X-rays. Commission of MID started at the end of 2018 and first experiments were performed in 2019.

scholarly journals The observation of 10–50 KeV solar flare X-rays by the OGO satellites and their correlation with solar radio and energetic particle emission

1968 ◽  
Vol 35 ◽  
pp. 490-509
Author(s):  
R. L. Arnoldy ◽  
S. R. Kane ◽  
J. R. Winckler
Keyword(s):  
Magnetic Field ◽  
Solar Flare ◽  
Radio Emission ◽  
Total Energy ◽  
Total Duration ◽  
Microwave Emission ◽  
X Rays ◽  
Ionization Chambers ◽  
X Ray ◽  
Peak Intensity

More than 70 cases have been observed of energetic solar flare X-ray bursts by large ionization chambers on the OGO satellites in space. The ionization chambers have an energy range between 10 and 50 KeV for X-rays and are also sensitive to solar protons and electrons. A study has been made of the X-ray microwave relationship, and it is found that the total energy released in the form of X-rays between 10 and 50 KeV is approximately proportional to the peak or total energy simultaneously released in the form of microwave emission. For a given burst the rise time, decay time and total duration are similar for the 10–50 KeV X-rays and the 3 to 10 cm radio emission. Roughly exponential decay phases are observed for both emissions with time constants between 1 and 10 min. All 3 or 10 cm radio bursts with peak intensity greater than 80 solar flux units are accompanied by an X-ray burst greater than 3 × 10−7 ergs cm−2 sec−1 peak intensity. The probability of detecting such X-ray events is low unless the radio spectrum extends into the centimetric range of wavelengths. The best correlation between cm-λ and energetic X-rays is observed for the first event in a flare. Subsequent structure and second bursts may not correspond even when the radio emission is rich in the microwave component. The mechanism for the energetic X-rays is shown to be bremsstrahlung probably of fast electrons on a cooler plasma. If the radio emission is assumed to be synchrotron radiation then a relationship is developed between density and magnetic field which meets the observed quantitative results. One finds, on the average, that 5 × 10−54 joules m−2 (CPS)−1 of microwave energy at the Earth are required per electron at the Sun to provide the radio emission for the various events.A strong correlation between interplanetary solar flare electrons observed by satellite and X-ray bursts is shown to exist. This correlation is weak for solar proton events. One may infer a strong propagation asymmetry for solar flare electrons along the spiral interplanetary magnetic field.

scholarly journals On the Thermal Interpretation of Hard X-Ray Bursts from Solar Flares

1974 ◽  
Vol 57 ◽  
pp. 395-412 ◽  
Author(s):  
John C. Brown
Keyword(s):  
Solar Flares ◽  
Thermal Conduction ◽  
Temperature Structure ◽  
X Rays ◽  
X Ray ◽  
Time Variations ◽  
Relationship Of ◽  
First Time ◽  
The Relationship ◽  
Continuous Temperature

The possible validity of thermal bremsstrahlung models of flare hard X-ray bursts is investigated quantitatively. In particular, the problem of rapid thermal conduction in ‘multi-temperature’ models is adequately examined for the first time by using a continuous temperature distribution consistent with the observed X-ray spectrum. This distribution is obtained from a general analytic solution for the temperature structure required to mimick any ‘non-thermal’ spectrum, the method being equally applicable to cosmic sources.It is concluded that the thermal interpretation might extend to X-rays of hundreds of keV, a result with important consequences for flare energetics. The relationship of such a model to observations of X-ray polarization and rapid time variations is also considered.

scholarly journals Solar Microwave Emission in Active Regions

1985 ◽  
Vol 107 ◽  
pp. 225-230
Author(s):  
B. Lokanadham ◽  
P. K. Subramanian ◽  
M. Sateesh Reddy ◽  
B. M. Reddy ◽  
D. R. Lakshmi
Keyword(s):  
Solar Maximum ◽  
Active Regions ◽  
Peak Frequency ◽  
Microwave Emission ◽  
Emission Mechanism ◽  
Strong Magnetic Fields ◽  
X Ray ◽  
Maximum Period ◽  
Solar Microwave ◽  
Microwave Bursts

Multi–frequency Observations of Solar Microwave bursts recorded during solar maximum period 1980–81 are analysed and compared with x–ray data for studying the nature of microwave emissions from active regions. Most of the microwave burst spectra showed that the spectral index below the peak frequency is always less than 2.The magneto-ionic conditions of the burst sources and the electron energies as obtained from these multi-frequency observations of the bursts showed that the centimetric and x-ray observations are satisfactorily explained, if the emitting regions are dense, hot and compact associated with strong magnetic fields of a few hundred gauss, suggesting that the thermal gyroresonance process is the most likely emission mechanism involved in the emission of microwave and x-ray radiations from the active regions of sun.

scholarly journals Three discoveries of γ Cas analogues from dedicated XMM–Newton observations of Be stars

2020 ◽  
Vol 493 (2) ◽  
pp. 2511-2517 ◽  
Author(s):  
Yaël Nazé ◽  
Christian Motch ◽  
Gregor Rauw ◽  
Shami Kumar ◽  
Jan Robrade ◽  
...  
Keyword(s):  
Spectral Characterization ◽  
Spectral Information ◽  
X Rays ◽  
Be Stars ◽  
Spectral Variability ◽  
Short Term ◽  
X Ray ◽  
Long Term Variations

ABSTRACT In the last years, a peculiarity of some Be stars – their association with unusually hard and intense X-ray emission – was shown to extend beyond a mere few cases. In this paper, we continue our search for new cases by performing a limited survey of 18 Be stars using XMM–Newton. The targets were selected either on the basis of a previous X-ray detection (exosat,rosat, XMM-slew survey) without spectral information available or because of the presence of a peculiar spectral variability. Only two targets remain undetected in the new observations and three other stars display only faint and soft X-rays. Short-term and/or long-term variations were found in one third of the sample. The spectral characterization of the X-ray brightest 13 stars of the sample led to the discovery of three new γ Cas (HD 44458, HD 45995, and V558 Lyr), bringing the total to 25 known cases, and another γ Cas candidate (HD 120678), bringing the total to two.

scholarly journals Relation of Microwave Emission to X-Ray Emission from Solar Flares

1975 ◽  
Vol 68 ◽  
pp. 299-313 ◽  
Author(s):  
Tatsuo Takakura
Keyword(s):  
Solar Flares ◽  
Microwave Emission ◽  
Radio Sources ◽  
X Rays ◽  
Radio Emissions ◽  
Energetic Electrons ◽  
X Ray ◽  
Time Histories ◽  
Temporal And Spatial

Recent observations of impulsive microwave and hard X-ray emissions during the early phase of the flares are briefly reviewed in order to deduce the dynamics of energetic electrons consistently from two view points of the microwaves and X-rays. An emphasis is put on the necessity of distinction between temporal and spatial variations so far confused in the interpretation of the time histories of the X-ray and radio emissions. The role of plasma turbulence on the dynamics of the energetic electrons is shown to be important in deducing the model of X-ray and radio sources.

An Observed Correlation between the Flux Densities of Extended Hard X-ray and Microwave Solar Bursts

1979 ◽  
Vol 3 (6) ◽  
pp. 390-392 ◽  
Author(s):  
R. T. Stewart ◽  
G. J. Nelson
Keyword(s):  
Companion Paper ◽  
Source Model ◽  
Second Phase ◽  
Acceleration Process ◽  
X Rays ◽  
X Ray ◽  
Time Profiles ◽  
Solar Bursts ◽  
Phase Acceleration ◽  
Microwave Bursts

Crannell et al. (1978) have reported an observed correlation between the time profiles and flux densities of impulsive hard X-ray and microwave solar bursts. We report here on a significant correlation between the flux density of extended bursts of hard X-rays and micowaves. These extended events follow after impulsive bursts and last much longer (see e.g. Fig. 1, Frost and Dennis 1971). However, as extended bursts only occur during very large flares the number of cases available for study is small. The significance of our observations follows from the suggestion of Wild et al. (1963) that the extended bursts are evidence for a second-phase acceleration process in the corona. We show that the observed characteristics of these extended microwave bursts (viz. a rather flat spectrum below a turnover frequency which is independent of intensity) can be explained by gyro-synchrotron radiation from the same population of energetic (E ≈ 100 keV) electrons as those emitting (thin-target) X-ray bremsstrahlung. A detailed source model is discussed in a companion paper (Nelson and Stewart 1979 — Paper B).

White-Light Coronal Structures: Streamers and CMEs

1994 ◽  
Vol 144 ◽  
pp. 82
Author(s):  
E. Hildner
Keyword(s):  
Emission Line ◽  
Electron Density ◽  
White Light ◽  
Coronal Mass Ejections ◽  
X Rays ◽  
Solar Cycles ◽  
Temperature Function ◽  
X Ray ◽  
Eclipse Observations ◽  
Coronal Structures

AbstractOver the last twenty years, orbiting coronagraphs have vastly increased the amount of observational material for the whitelight corona. Spanning almost two solar cycles, and augmented by ground-based K-coronameter, emission-line, and eclipse observations, these data allow us to assess,inter alia: the typical and atypical behavior of the corona; how the corona evolves on time scales from minutes to a decade; and (in some respects) the relation between photospheric, coronal, and interplanetary features. This talk will review recent results on these three topics. A remark or two will attempt to relate the whitelight corona between 1.5 and 6 R⊙to the corona seen at lower altitudes in soft X-rays (e.g., with Yohkoh). The whitelight emission depends only on integrated electron density independent of temperature, whereas the soft X-ray emission depends upon the integral of electron density squared times a temperature function. The properties of coronal mass ejections (CMEs) will be reviewed briefly and their relationships to other solar and interplanetary phenomena will be noted.

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