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

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°.

scholarly journals Simultaneous Kepler/K2 and XMM-Newton observations of superflares in the Pleiades

2019 ◽  
Vol 622 ◽  
pp. A210 ◽  
Author(s):  
M. G. Guarcello ◽  
G. Micela ◽  
S. Sciortino ◽  
J. López-Santiago ◽  
C. Argiroffi ◽  
...  
Keyword(s):  
Time Evolution ◽  
Energy Budget ◽  
Solar Flares ◽  
Light Curves ◽  
Integrated Analysis ◽  
Electromagnetic Spectrum ◽  
The Sun ◽  
X Rays ◽  
X Ray ◽  
Different Ages

Context. Flares are powerful events ignited by a sudden release of magnetic energy which triggers a cascade of interconnected phenomena, each resulting in emission in different electromagnetic bands. In fact, in the Sun flares are observed across the whole electromagnetic spectrum. Multi-band observations of stellar flares are instead rare. This limits our ability to extend what we learn from solar flares to the case of flares occurring in stars with different properties. Aims. With the aim of studying flares in the 125-Myr-old stars in the Pleiades observed simultaneously in optical and X-ray light, we obtained new XMM-Newton observations of this cluster during the observations of Kepler K2 Campaign 4. The objective of this paper is to characterize the most powerful flares observed in both bands and to constrain the energy released in the optical and X-ray, the geometry of the loops, and their time evolution. We also aim to compare our results to existing studies of flares occurring in the Sun and stars at different ages. Methods. We selected bright X-ray/optical flares that occurred in 12 known members of the Pleiades from their K2 and XMM-Newton light curves. The sample includes ten K-M stars, one F9 star, and one G8 star. Flare average properties were obtained from integrated analysis of the light curves during the flares. The time evolution of the plasma in the magnetic loops is constrained with time-resolved X-ray spectral analysis. Results. Most of the flares studied in this work emitted more energy in optical than in X-rays, as in most solar flares, even if the Pleiades flares output a larger fraction of their total energy in X-rays than typical solar flares do. Additionally, the energy budget in the two bands is weakly correlated. We also found comparable flare duration in optical and X-rays and observed that rapidly rotating stars (e.g., with rotation period shorter than 0.5 days) preferentially host short flares. We estimated the slope of the cooling path of the flares in the log(EM)-vs.-log(T) plane. The values we obtained are affected by large uncertainties, but their nominal values suggest that the flares analyzed in this paper are mainly due to single loops with no sustained heating occurring during the cooling phase. We also observed and analyzed oscillations with a period of 500 s during one of the flares. Conclusions. The flares observed in the Pleiades can be classified as “superflares” based on their energy budget in the optical, and share some of the properties of the flares observed in the Sun, despite being more energetic. For instance, as in most solar flares, more energy is typically released in the optical than in X-rays and the duration of the flares in the two bands is correlated. We have attempted a comparison between the X-ray flares observed in the Pleiades and those observed in clusters with different ages, but to firmly address any evolutionary pattern of flare characteristics, similar and uniform multi-wavelength analyses on more complete samples are necessary.

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 The Transient Highly Excited Solar Flare Plasma

1972 ◽  
Vol 14 ◽  
pp. 827-842 ◽  
Author(s):  
L. D. De Feiter
Keyword(s):  
Solar Flare ◽  
Radio Emission ◽  
Special Reference ◽  
Solar Flares ◽  
Energetic Particles ◽  
X Rays ◽  
Microwave Region ◽  
X Ray ◽  
Flare Plasma ◽  
Radiation Processes

AbstractRecent observations of the energetic particles produced in solar flares indicate that the production of electrons, with energies up to about 100 keV, is a fairly common feature of small flares. In those flares the acceleration of protons and other nuclei does not extend beyond about 1 MeV.The X-ray emission often exhibits two distinct components of which the first one is produced by non-thermal, the second by thermal electrons through bremsstrahlung collisions with the ambient ions. Along with these X rays, radio emission, in the microwave region, is observed. This radio emission is usually interpreted as due to gyrosynchrotron radiation from the same electrons.In this review a discussion is presented of the processes occurring in solar flares with special reference to the acceleration and radiation processes.

Development of Standard X-Ray Beams for Calibration of Radiobiology Cabinet and Conformal Irradiators

2021 ◽  
Author(s):  
Emily J. King ◽  
Natalie N. Viscariello ◽  
Larry A. DeWerd
Keyword(s):  
Monte Carlo Code ◽  
X Rays ◽  
Energy Agency ◽  
X Ray ◽  
Measurement Models ◽  
Dose Determination ◽  
University Of Wisconsin ◽  
Free Air ◽  
Accurate Dose ◽  
The University

This work seeks to develop standard X-ray beams that are matched to radiobiology X-ray irradiators. The calibration of detectors used for dose determination of these irradiators is performed with a set of standard X rays that are more heavily filtered and/or lower energy, which leads to a higher uncertainty in the dose measurement. Models of the XRad320, SARRP, and the X-ray tube at the University of Wisconsin Medical Radiation Research Center (UWMRRC) were created using the BEAMnrc user code of the EGSnrc Monte Carlo code system. These models were validated against measurements, and the resultant modeled spectra were used to determine the amount of added filtration needed to match the X-ray beams at the UWMRRC to those of the XRad320 and SARRP. The depth profiles and half-value layer (HVL) simulations performed using BEAMnrc agreed to measurements within 3% and 3.6%, respectively. A primary measurement device, a free-air chamber, was developed to measure air kerma in the medium energy range of X rays. The resultant spectra of the matched beams had HVL's that matched the HVL's of the radiobiology irradiators well within the 3% criteria recommended by the International Atomic Energy Agency (IAEA) and the average energies agreed within 2.4%. In conclusion, three standard X-ray beams were developed at the UWMRRC with spectra that more closely match the spectra of the XRad320 and SARRP radiobiology irradiators, which will aid in a more accurate dose determination during calibration of these irradiators.

Plasma Diagnostics of Microflares observed by STIX and AIA

2021 ◽  
Author(s):  
Jonas Saqri ◽  
Astrid Veronig ◽  
Ewan Dickson ◽  
Säm Krucker ◽  
Andrea Francesco Battaglia ◽  
...  
Keyword(s):  
Solar Flares ◽  
Magnetic Energy ◽  
Emission Measure ◽  
Transport Processes ◽  
X Rays ◽  
Solar Dynamics Observatory ◽  
Energy Bands ◽  
Accurate Analysis ◽  
Great Opportunity ◽  
Wide Range

&lt;p&gt;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&amp;#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.&lt;/p&gt;

scholarly journals Production of Different Non-Thermal Electron Groups in Small Solar Flares

1972 ◽  
Vol 14 ◽  
pp. 822-823
Author(s):  
S. R. Kane
Keyword(s):  
Electron Emission ◽  
Solar Flares ◽  
Electron Acceleration ◽  
X Rays ◽  
Thermal Electron ◽  
X Ray ◽  
Type Iii

Using the measurements of impulsive solar X-rays made with the OGO-5 satellite to identify the flash phase electron acceleration in solar flares of Hα-importance ≲ 1, the satellite and ground based observations are analyzed to study the origin of the different groups of non-thermal electrons responsible for the impulsive X-ray, impulsive microwave, type III radio and interplanetary electron emission.

Honesty Requiring a Self-Initiated Response

1980 ◽  
Vol 46 (1) ◽  
pp. 87-90 ◽  
Author(s):  
Ron Hays
Keyword(s):  
University Of California ◽  
External Knowledge ◽  
Dollar Bill ◽  
Student Union ◽  
Subject Variables ◽  
The Subject ◽  
And Behavior ◽  
The University ◽  
The Relationship

33 patrons of the University of California, Riverside student union were given $1.05 in change for a dollar bill (three quarters, two dimes, and two nickels). Honesty was assessed by the criterion of self-initiating the return of the extra nickel, and behavior was examined as a function of sex, age, and manner of dress. Results indicate that the over-all honesty of patrons was low (45%), but no significant findings for the relationship between the subject variables and honesty were shown. The 45% rate of honesty indicates that subjects who believe there will not be any external knowledge of their dishonesty are likely to exhibit dishonest behavior.

scholarly journals Magnetic fields, winds and X-rays of massive stars in the Orion nebula cluster

2010 ◽  
Vol 6 (S272) ◽  
pp. 208-209 ◽  
Author(s):  
Véronique Petit ◽  
Gregg A. Wade ◽  
Evelyne Alecian ◽  
Laurent Drissen ◽  
Thierry Montmerle ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Massive Stars ◽  
Theoretical Models ◽  
Magnetic Star ◽  
X Rays ◽  
Orion Nebula ◽  
X Ray ◽  
Ob Stars ◽  
The Impact ◽  
The Relationship

AbstractIn some massive stars, magnetic fields are thought to confine the outflowing radiatively-driven wind. Although theoretical models and MHD simulations are able to illustrate the dynamics of such a magnetized wind, the impact of this wind-field interaction on the observable properties of a magnetic star - X-ray emission, photometric and spectral variability - is still unclear. The aim of this study is to examine the relationship between magnetism, stellar winds and X-ray emission of OB stars, by providing empirical observations and confronting theory. In conjunction with the COUP survey of the Orion Nebula Cluster, we carried out spectropolarimatric ESPaDOnS observations to determine the magnetic properties of massive OB stars of this cluster.

scholarly journals Electrons and X-Ray Emission of Solar Flares

1990 ◽  
Vol 142 ◽  
pp. 409-413
Author(s):  
V. G. Kurt
Keyword(s):  
Solar Activity ◽  
Statistical Analysis ◽  
Solar Flare ◽  
Frequency Dependence ◽  
Power Law ◽  
Solar Flares ◽  
X Rays ◽  
Fast Electrons ◽  
X Ray ◽  
Flare Frequency

A statistical analysis of solar flare X-rays and interplanetary particle fluxes, measured onboard VENERA-13, 14 Spacecraft, was performed. The correlation of fluences for different manifestations of solar flares is strong, especially for fast electrons and hard and soft X-ray emissions. Frequency dependence on fluence value ϵi for practically all Kinds of solar flare emission can be described by power law ν (ϵ > ϵO) ∼ ϵ−0.45±0.15 which does not change significantly with solar activity. For different Hα flare importances the values of ϵi were obtained. It is proposed that appearance of certain energy flare frequency is strongly dependent on some scale factor.

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