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Sample records for flare electron spectra

  1. The energy spectra of solar flare electrons

    NASA Technical Reports Server (NTRS)

    Evenson, P. A.; Hovestadt, D.; Meyer, P.; Moses, D.

    1985-01-01

    A survey of 50 electron energy spectra from .1 to 100 MeV originating from solar flares was made by the combination of data from two spectrometers onboard the International Sun Earth Explorer-3 spacecraft. The observed spectral shapes of flare events can be divided into two classes through the criteria of fit to an acceleration model. This standard two step acceleration model, which fits the spectral shape of the first class of flares, involves an impulsive step that accelerates particles up to 100 keV and a second step that further accelerates these particles up to 100 MeV by a single shock. This fit fails for the second class of flares that can be characterized as having excessively hard spectra above 1 MeV relative to the predictions of the model. Correlations with soft X-ray and meter radio observations imply that the acceleration of the high energy particles in the second class of flares is dominated by the impulsive phase of the flares.

  2. Collisional Relaxation of Electrons in a Warm Plasma and Accelerated Nonthermal Electron Spectra in Solar Flares

    NASA Astrophysics Data System (ADS)

    Kontar, Eduard P.; Jeffrey, Natasha L. S.; Emslie, A. Gordon; Bian, N. H.

    2015-08-01

    Extending previous studies of nonthermal electron transport in solar flares, which include the effects of collisional energy diffusion and thermalization of fast electrons, we present an analytic method to infer more accurate estimates of the accelerated electron spectrum in solar flares from observations of the hard X-ray spectrum. Unlike for the standard cold-target model, the spatial characteristics of the flaring region, especially the necessity to consider a finite volume of hot plasma in the source, need to be taken into account in order to correctly obtain the injected electron spectrum from the source-integrated electron flux spectrum (a quantity straightforwardly obtained from hard X-ray observations). We show that the effect of electron thermalization can be significant enough to nullify the need to introduce an ad hoc low-energy cutoff to the injected electron spectrum in order to keep the injected power in non-thermal electrons at a reasonable value. Rather, the suppression of the inferred low-energy end of the injected spectrum compared to that deduced from a cold-target analysis allows the inference from hard X-ray observations of a more realistic energy in injected non-thermal electrons in solar flares.

  3. Electron densities in a solar flare derived from X-ray spectra

    NASA Astrophysics Data System (ADS)

    McKenzie, D. L.; Broussard, R. M.; Landecker, P. B.; Rugge, H. R.; Young, R. M.; Doschek, G. A.; Feldman, U.

    1982-01-01

    A major solar flare was observed with the RAP crystal of the SOLEX B spectrometer. The spectra were obtained by scanning back and forth between Bragg angles of 17.4 deg and 61.7 deg (7.8 to 23 A) at a rate of 0.525 degrees-.15. A full scan took 84.5 sec. A line list identifying more than 100 lines observed in this flare was compiled. Measurements of the density sensitive O 7 lines near 22 A are discussed.

  4. High resolution solar flare X-ray spectra - The temporal behavior of electron density, temperature, and emission measure for two class M flares

    NASA Astrophysics Data System (ADS)

    Doschek, G. A.; Feldman, U.; Landecker, P. B.; McKenzie, D. L.

    1981-10-01

    High resolution soft X-ray flare spectra recorded by Naval Research Laboratory (NRL) and Aerospace Corporation Bragg crystal spectrometers flown on an orbiting spacecraft (P78-1) are combined and analyzed. The instruments were launched on t979 February 24 by the U.S. Air Force, and the data discussed in this paper cover the wavelength ranges, 1.82-1.97 Å, 3.143.24 Å, and 18.423.0 Å. The NRL experiment (SOLFLEX) covers the two short wavelength ranges (highly ionized Fe and Ca lines) and the Aerospace experiment (SOLEX) covers the t8.4-23.O Å range, which includes the Lyα O VIII line and the resonance, intercombination, and forbidden lines of O VII. We analyze the spectra of two flares which occurred on 1980 April 8 and May 9. Temporal coverage is fairly complete for both flares, including the rise and decay phases. Measurements of electron density Ne with rather high time resolution (about 1 minute) have been obtained throughout most of the lifetimes of the two flares. These measurements were obtained from the O VII lines and pertain to flare plasma at temperatures near 2 × 106 K. Peak density seems to occur slightly before the times of peak X-ray flux in the resonance lines of Fe XXV, Ca XIX, and O VII, and for both flares the peak density is about 1012 cm-3. Electron temperature Te as a function of time is determined from the Fe and Ca spectra. Peak temperature for both flares is about 18 × 106 K. Differential emission measures and volume emission measures are determined from the resonance lines of O VII, Ca XIX, and Fe XXV. The number of electrons NeΔV and the volume ΔV over which the O VII lines are formed are determined from the O VII volume emission measure Ne2ΔV and the density Ne. These quantities are determined as a function of time. The relationship of the low and high temperature regions is discussed.

  5. The flares of August 1972. [solar flare characteristics and spectra

    NASA Technical Reports Server (NTRS)

    Zirin, H.; Tanaka, K.

    1973-01-01

    Observations of the August, 1972 flares at Big Bear and Tel Aviv, involving monochromatic movies, magnetograms, and spectra, are analyzed. The region (McMath 11976) showed inverted polarity from its inception on July 11; the great activity was due to extremely high shear and gradients in the magnetic field, as well as a constant invasion of one polarity into the opposite; observations in lambda 3835 show remarkable fast flashes in the impulsive flare of 18:38 UT on Aug. 2 with lifetimes of 5 sec, which may be due to dumping of particles in the lower chromosphere. Flare loops show evolutionary increases of their tilts to the neutral line in the flares of Aug. 4 and 7. Spectroscopic observations show red asymmetry and red shift of the H alpha emission in the flash phase of the Aug. 7 flare, as well as substantial velocity shear in the photosphere during the flare, somewhat like earthquake movement along a fault. Finally the total H alpha emission of the Aug. 7 flare could be measured accurately as about 2.5 x 10 to the 30th power erg, considerably less than coarser previous estimates for great flares.

  6. EMITTING ELECTRONS SPECTRA AND ACCELERATION PROCESSES IN THE JET OF Mrk 421: FROM THE LOW STATE TO THE GIANT FLARE STATE

    SciTech Connect

    Yan Dahai; Zhang Li; Fan Zhonghui; Zeng Houdun; Yuan Qiang

    2013-03-10

    We investigate the electron energy distributions (EEDs) and the acceleration processes in the jet of Mrk 421 through fitting the spectral energy distributions (SEDs) in different active states in the frame of a one-zone synchrotron self-Compton model. After assuming two possible EEDs formed in different acceleration models: the shock-accelerated power law with exponential cut-off (PLC) EED and the stochastic-turbulence-accelerated log-parabolic (LP) EED, we fit the observed SEDs of Mrk 421 in both low and giant flare states using the Markov Chain Monte Carlo method which constrains the model parameters in a more efficient way. The results from our calculations indicate that (1) the PLC and LP models give comparably good fits for the SED in the low state, but the variations of model parameters from low state to flaring can be reasonably explained only in the case of the PLC in the low state; and (2) the LP model gives better fits compared to the PLC model for the SED in the flare state, and the intra-day/night variability observed at GeV-TeV bands can be accommodated only in the LP model. The giant flare may be attributed to the stochastic turbulence re-acceleration of the shock-accelerated electrons in the low state. Therefore, we may conclude that shock acceleration is dominant in the low state, while stochastic turbulence acceleration is dominant in the flare state. Moreover, our result shows that the extrapolated TeV spectra from the best-fit SEDs from optical through GeV with the two EEDs are different. It should be considered with caution when such extrapolated TeV spectra are used to constrain extragalactic background light models.

  7. An upper limit on the hardness of the nonthermal electron spectra produced during the flash phase of solar flares.

    NASA Technical Reports Server (NTRS)

    Kane, S. R.

    1971-01-01

    The observations of impulsive solar-flare X-rays above 10 keV made with OGO-5 satellite have been analyzed in order to study the variation of the nonthermal electron spectrum from one flare to another. The X-ray spectrum at the maxima of 129 impulsive X-ray bursts is represented by KE to the minus-gamma power photons per sq cm per sec per keV, and the frequency of occurrence of bursts with different values of gamma is studied. It is found that for gamma less than 4.0 the frequency of bursts rapidly decreases with the decrease in the value of gamma. The probability of occurrence of a burst with gamma less than 2.3 is extremely small.

  8. First dynamic spectra of stellar microwave flares

    NASA Technical Reports Server (NTRS)

    Bastian, T. S.; Bookbinder, J. A.

    1987-01-01

    The VLA has been used in the spectral-line mode at 1.4 GHz to obtain the first dynamic spectra of stellar sources other than the sun. Two very intense, highly circularly polarized, microwave outbursts were observed on the dMe flare star UV Cet, in addition to a slowly varying, unpolarized component. One outburst was purely left circularly polarized and showed no variations as a function of frequency across the 41 MHz band, whereas the other was as much as 70 percent right-circularly polarized and showed distinct variations with frequency. Although the slowly varying emission is probably due to incoherent gyrosynchrotron emission, the two flaring events are the result of coherent mechanisms. The coherent emission is interpreted in terms of plasma radiation and the cyclotron maser instability.

  9. Soft X-ray flare spectra. [existence of high temperature plasmas in solar flares

    NASA Technical Reports Server (NTRS)

    Doschek, G. A.; Meekins, J. F.

    1973-01-01

    Large solar flares produce intense soft X-ray emission, indicating the existence of high temperature plasmas that coexist in time with the plasmas responsible for the normally observed brightenings in H-alpha. The time behavior of the X-ray flux, as revealed, for example, by ion chamber detectors on the series of Solrad monitoring satellites, appears to roughly mimic the intensity-time behavior of the H-alpha flare, insofar as start times, times of maximum flux, and approximate decay times are concerned. In recent years, soft X-ray spectra of both active regions and solar flares have been obtained by instruments flown on spacecraft such as the Orbiting Solar Observatory (OSO) series. The disbursing elements used were Bragg crystals, and in the 8 Angstrom region the resolution is typically approximately 1200. This paper discusses the observed characteristics of X-ray flare spectra and spectroscopic diagnostics for determining electron temperatures, electron densities, and departures from ionization equilibrium within the soft X-ray emitting plasma.

  10. Solar flare soft-X-ray spectra from Very Low Frequency observations of ionospheric modulations: Possibility of uninterrupted observation of non-thermal electron-plasma interaction in solar atmosphere.

    NASA Astrophysics Data System (ADS)

    Palit, Sourav; Chakrabarti, Sandip Kumar; Ray, Suman

    2016-07-01

    The hard and soft X-ray regions of a solar flare spectrum are the manifestation of interaction, namely of bremsstrahlung radiation of the non-thermal electrons moving inward in the denser part of the solar atmosphere with the plasma heated by those energetic electrons. The continuous and uninterrupted knowledge of X-ray photon spectra of flares are of great importance to derive information on the electron acceleration and hence time-evolution of energy transport and physics during solar flares. Satellite observations of solar X-ray spectrum are often limited by the restricted windows in each duty cycle to avoid the interaction of detectors and instruments with harmful energetic charge particles. In this work we have tried to tackle the problem by examining the possibility of using Earth's ionosphere and atmosphere as the detector of such transient events. Earth's lower ionosphere and upper atmosphere are the places where the X-rays and gamma-rays from such astronomical sources are absorbed. The electron-ion production rates due to the ionization of such energetic photons at different heights depend on the intensity and wavelength of the injected spectra and hence vary from one source to another. Obviously the electron and ion density vs. altitude profile has the imprint of the incident photon spectrum. As a preliminary exercise we developed a novel deconvolution method to extract the soft X-ray part of spectra of some solar flares of different classes from the electron density profiles obtained from Very Low Frequency (VLF) observation of lower ionosphere during those events. The method presented here is useful to carry out a similar exercise to infer the higher energy part of solar flare spectra and spectra of more energetic events such as the GRBs, SGRs etc. with the possibilities of probing even lower parts of the atmosphere.

  11. Directionality of bremsstrahlung from relativistic electrons in solar flares

    NASA Technical Reports Server (NTRS)

    Dermer, C. D.; Ramaty, R.

    1985-01-01

    Angular and energy spectra of bremsstrahlung have been calculated from anisotropic electron distributions in solar flares. Results have been compared to observations of gamma-ray limb-brightening and to data on the variation of the gamma-ray spectrum with flare position on the sun.

  12. Relativistic electrons associated with solar flares.

    NASA Technical Reports Server (NTRS)

    Sakurai, K.

    1972-01-01

    Solar flares which produce relativistic electrons generally occur within sunspot groups which are active in the emission of meter type I noise storms. It is suggested that relativistic electrons in solar flares are accelerated from the keV-energy electrons responsible for the type I noise storms. The relationship between flare developments and the ejection of keV-electrons is briefly considered.

  13. Stochastic Acceleration of Electrons in Solar Flares

    NASA Astrophysics Data System (ADS)

    Pongkitiwanichakul, P.; Chandran, B. D.

    2012-12-01

    Stochastic particle acceleration (SPA) is a process in which turbulent fluctuations or randomly phased waves energize particles. We develop an SPA model for electron acceleration in solar flares based on turbulent fast magnetosonic waves and transit-time damping. Our model is two dimensional in both velocity space and wavenumber space, so that it takes into account anisotropy in the wave power spectrum P and electron distribution function f. We use quasilinear theory to obtain a set of equations that describes the coupled evolution of P and f. We solve these equations numerically, and find that the electron distribution function develops a power-law-like non-thermal tail between energies Emin and Emax. We obtain approximate analytic expressions for Emin and Emax that describe how these minimum and maximum energies depend upon plasma parameters such as the electron temperature and number density. We compare our results to previous studies that assume that P and f are isotropic and use our analysis to explain the observed hard x-ray spectrum seen in the June 27, 1980 flare. In our numerical simulations, the power-law indices of the electron energy spectra range from -2.3 to -4.4. The absolute values of these indices are larger than the corresponding values in studies with isotropic P and f and closer to the observed values in solar flares.

  14. Fast electrons in small solar flares

    NASA Technical Reports Server (NTRS)

    Lin, R. P.

    1975-01-01

    This review summarizes both the direct spacecraft observations of nonrelativistic solar electrons, and observations of the X-ray and radio emission generated by these particles at the sun and in the interplanetary medium. These observations bear on the basic astrophysical process of particle acceleration in tenuous plasmas. We find that in many small solar flares, the nearly 5-100 keV electrons accelerated during flash phase constitute the bulk of the total flare energy. Thus the basic flare mechanism in these flares essentially converts the available flare energy into fast electrons. These electrons may produce the other flare electromagnetic emissions through their interactions with the solar atmosphere. In large proton flares these electrons may provide the energy to eject material from the sun and to create a shock wave which could accelerate nuclei and electrons to much higher energies.

  15. Observations of solar flare photon energy spectra from 20 keV to 7 MeV

    NASA Technical Reports Server (NTRS)

    Yoshimori, M.; Watanabe, H.; Nitta, N.

    1985-01-01

    Solar flare photon energy spectra in the 20 keV to 7 MeV range are derived from the Apr. 1, Apr. 4, apr. 27 and May 13, 1981 flares. The flares were observed with a hard X-ray and a gamma-ray spectrometers on board the Hinotori satellite. The results show that the spectral shape varies from flare to flare and the spectra harden in energies above about 400 keV. Effects of nuclear line emission on the continuum and of higher energy electron bremsstrahlung are considered to explain the spectral hardening.

  16. Two types of electron events in solar flares

    NASA Technical Reports Server (NTRS)

    Daibog, E. I.; Kurt, V. G.; Logachev, Y. I.; Stolpovsky, V. G.

    1985-01-01

    The fluxes and spectra of the flare electrons measured on board Venera-I3 and I4 space probes are compared with the parameters of the hard (E sub x approximately 55 keV) and thermal X-ray bursts. The electron flux amplitude has been found to correlate with flare importance in the thermal X-ray range (r approximately 0.8). The following two types of flare events have been found in the electron component of SCR. The electron flux increase is accompanied by a hard X-ray burst and the electron spectrum index in the approximately 25 to 200 keV energy range is gamma approximately 2 to 3. The electron flux increase is not accompanied by a hard X-ray burst and the electron spectrum is softer (Delta gamma approximately 0.7 to 1.0).

  17. Recent observations of energetic electrons in solar flares

    NASA Technical Reports Server (NTRS)

    Kane, S. R.

    1980-01-01

    The impulsive solar X-ray burst observed by the ISEE 3 X-ray spectrometer experiment on October 5, 1978 is discussed with consideration of energetic electrons in solar flares. The X-ray spectrum is consistent with a power law electron spectrum with no apparent low energy cut-off up to energies of around 5 keV. Although an explanation of the observed X-ray spectrum in terms of the emission from a multi-thermal electron spectrum cannot be ruled out, the observations lend support to the existence of nonthermal electron spectra during the impulsive phase of solar flares.

  18. Dynamic spectra of radio bursts from flare stars

    SciTech Connect

    Bastian, T.S.; Bookbinder, J.; Dulk, G.A.; Davis, M. Joint Institute for Laboratory Astrophysics, Boulder, CO Smithsonian Astrophysical Observatory, Cambridge, MA Colorado Univ., Boulder )

    1990-04-01

    The Arecibo 305 m telescope has been used to observe radio bursts from flare stars at 430 and 1415 MHz. Dynamic spectra of the emission with bandwidths of 10 MHz in the former case and 40 MHz in the latter are recorded. For AD Leo, the microwave burst emission was 100 percent right circularly polarized, achieved brightness temperatures near 10 to the 16th K, was generally broadband in character, but was superposed with finite structures in both frequency and time. Quasi-periodic pulsations were clearly present as well as a sudden reduction feature. For YZ CMi, the emission was 100 percent left circularly polarized and was relatively broadband with fine structures. Instabilities driven by anisotropies in the electron distribution, particularly the loss-cone distribution, are considered to account for the coherent radiation. 55 refs.

  19. Dynamic spectra of radio bursts from flare stars

    NASA Technical Reports Server (NTRS)

    Bastian, T. S.; Bookbinder, J.; Dulk, G. A.; Davis, M.

    1990-01-01

    The Arecibo 305 m telescope has been used to observe radio bursts from flare stars at 430 and 1415 MHz. Dynamic spectra of the emission with bandwidths of 10 MHz in the former case and 40 MHz in the latter are recorded. For AD Leo, the microwave burst emission was 100 percent right circularly polarized, achieved brightness temperatures near 10 to the 16th K, was generally broadband in character, but was superposed with finite structures in both frequency and time. Quasi-periodic pulsations were clearly present as well as a sudden reduction feature. For YZ CMi, the emission was 100 percent left circularly polarized and was relatively broadband with fine structures. Instabilities driven by anisotropies in the electron distribution, particularly the loss-cone distribution, are considered to account for the coherent radiation.

  20. IUE spectra of a flare in HR 5110: A flaring RS CVn or Algol system?

    NASA Technical Reports Server (NTRS)

    Simon, T.; Linsky, J. L.; Schiffer, F. H., III

    1981-01-01

    Ultraviolet spectra of the RS CVn type binary system HR 5110 were obtained with IUE on May 31, 1979 during a period of intense radio flaring of this star. High temperature transition region lines are present, but are not enhanced above observed quiescent strengths. The similarities of HR 5110 to the Algol system, As Eri, suggest that the 1979 May to June flare may involve mass exchange rather than annihilation of coronal magnetic fields.

  1. High-resolution X-ray spectra of solar flares. IV - General spectral properties of M type flares

    NASA Technical Reports Server (NTRS)

    Feldman, U.; Doschek, G. A.; Kreplin, R. W.; Mariska, J. T.

    1980-01-01

    The spectral characteristics in selected narrow regions of the X-ray spectrum of class M solar flares are analyzed. High-resolution spectra in the ranges 1.82-1.97, 2.98-3.07, 3.14-3.24 and 8.26-8.53 A, which contain lines important for the determination of electron temperature and departure from ionization equilibrium, were recorded by spaceborne Bragg crystal spectrometers. Temperatures of up to 20,000,000 K are obtained from line ratios during flare rise phases in M as well as X flares, while in the decay phase the calcium temperature can be as low as 8,000,000 K, which is significantly lower than in X flares. Large nonthermal motions (on the order of 130 km/sec at most) are also observed in M as well as X flares, which are largest during the soft X-ray rise phase. Finally, it is shown that the method proposed by Gabriel and Phillips (1979) for detecting departures of electrons from Maxwellian velocity distributions is not sufficiently sensitive to give reliable results for the present data.

  2. Analysis of H-alpha flare spectra

    NASA Technical Reports Server (NTRS)

    Kulander, J. L.

    1977-01-01

    Spectrographs of the H-alpha line taken at 15 second intervals from the event of 5 Sept. 1973 were interpreted by comparison with synthetic profiles. A sequence of 27 high resolution H alpha profiles was obtained from the second brightest flare kernel. The profiles were generally self reversed with a maximum peak intensity of 1.16 x continuum and a maximum central intensity of .91 x continuum. The line characteristics such as red and violet peak intensities and positions, center shifts and wing intensities were tabulated. Synthetic H-alpha profiles were generated from a finite layer assuming simple parameteric forms for the source function and velocity field. The velocity chosen always decreased with optical depth and had the same sign. For absorption profiles, bisector shifts were calculated for a variety of velocities. The velocity field and source function were derived as a function of optical depth and time.

  3. Impulsive Phase He 10830 Spectra of a Large Solar Limb Flare of 16 August 1989*

    NASA Astrophysics Data System (ADS)

    You, Jianqi; Wang, Chuanjin; Fan, Zhongyu; Li, Hui

    1998-10-01

    We obtained simultaneously Hei 10830 Å spectra, Hα filtergrams and microwave data of a large limb flare (2N/X20) in 1989. In this paper we characterize Hei 10830 spectra in relation to the impulsive phase. All the Hei 10830 spectra, except those of the surge, show blue shift or blue asymmetry. The velocities inferred from the spectra range from a few to 160kms-1, implying that the horizontal motion is very likely present in the structure of this flare at different heights. The Hei 10830 profiles of a flare are relatively broad and cannot be simulated by the Doppler broadening mechanism with a uniform flare model atmosphere. It is most likely that these characteristics are related to rapid and localized heating in the low and middle chromosphere. Comparing the SXR and microwave data with the optical data leads to the following scenario: the corona was already heated to some extent before the flare onset, and in the first 2minutes of the impulsive phase, heat conduction was the main source or, at least, a competitive source, for chromospheric heating. However, the impulsive event, associated with the unusually broadened Hei 10830 line (Deltalambdaf>20Å) and temporally correlated with a microwave burst, is probably caused by electron-beam heating.

  4. Modeling solar flare hard X-ray images and spectra observed with RHESSI

    NASA Astrophysics Data System (ADS)

    Sui, Linhui

    2004-12-01

    predictions of the standard flare models: the downward motion of flare loops in the early impulsive phase of each flare, and an initially stationary coronal source above the loops. These features are believed to be related to the formation and development of a current sheet. In particular, the downward loop motion seems to be a common phenomenon in flares, suggesting the necessity for modifications to the existing standard flare models. Finally, thanks to the broad energy coverage of the RHESSI spectra, a low- energy cutoff of 28(+/-2) keV in the nonthermal electron distribution was determined for the April 15, 2002, flare. As a result, the energy carried by the nonthermal electrons is found to be comparable to the thermal energy of the flare, but one order of magnitude larger than the kinetic energy of the associated coronal mass ejection. The method used to deduce the electron low- energy cutoff will be useful in the analyses of similar events.

  5. Flat microwave spectra seen at X-class flares

    NASA Technical Reports Server (NTRS)

    Lee, Jeongwoo W.; Gary, Dale E.; Zirin, H.

    1994-01-01

    We report peculiar spectral activity of four large microwave bursts as obtained from the Solar Arrays at the Owens Valey Radio Observatory during observations of X-class flares on 24 May 1990 and 7, 8, 22 March 1991. Main observational points that we newly uncovered are: (1) flat flux spectra over 1-18 GHz in large amounts of flux ranging from 10(exp 2) to 10(exp 4) s.f.u. at the maximum phase, (2) a common evolutionary pattern in which the spectral region of dominant flux shifts from high frequencies at the initial rise to low frequencies at the decaying phase, and (3) unusual time profiles that are impulsive at high frequencies but more extended at lower frequencies. We carry out the model calculations of microwave spectra under assumptions of gyrosynchrotron mechanism and a dipole field configuration to reproduce the observational characteristics. Our results are summarized as follows. First, a flat microwave spectrum reaching up to 10(exp 2) - 10(exp 4) s.f.u. may occur in a case where a magnetic loop is extended to an angular size of approximately (0.7-7.0) x 10(exp -7) sterad and contains a huge number (N(E greater than 10 keV) approx. 10(exp 36) - 10(exp 38)) of nonthermal electrons with power-law index approx. 3-3.5 over the entire volume. Second, the observed spectral activity could adequately be accounted for by the shrinking of the region of nonthermal electrons to the loop top and by the softening of the power-law spectrum of electrons in a time scale ranging 3-45 min depending on the event. Third, the extended microwave activity at lower frequencies is probably due to electrons trapped in the loop top where magnetic fields are low. Finally, we clarify the physical distinction between these large, extended microwave bursts and the gradual/post-microwave bursts often seen in weak events, both of which are characterized by long-period activity and broadband spectra.

  6. Energetic electrons in impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Batchelor, D. A.

    1984-01-01

    A new analysis was made of a thermal flare model proposed by Brown, Melrose, and Spicer (1979) and Smith and Lilliequist (1979). They assumed the source of impulsive hard X-rays to be a plasma at a temperature of order 10 to the 8th power K, initially located at the apex of a coronal arch, and confined by ion-acoustic turbulence in a collisionless conduction front. Such a source would expand at approximately the ion-sound speed, C sub S = square root of (k T sub e/m sub i), until it filled the arch. Brown, Melrose, and Spicer and Smith and Brown (1980) argued that the source assumed in this model would not explain the simultaneous impulsive microwave emission. In contrast, the new results presented herein suggest that this model leads to the development of a quasi-Maxwellian distribution of electrons that explains both the hard X-ray and microwave emissions. This implies that the source sizes can be determined from observations of the optically-thick portions of microwave spectra and the temperatures obtained from associated hard X-ray observations. In this model, the burst emission would rise to a maximum in a time, t sub r, approximately equal to L/c sub s, where L is the half-length of the arch. New observations of these impulsive flare emissions were analyzed herein to test this prediction of the model. Observations made with the Solar Maximum Mission spacecraft and the Bern Radio Observatory are in good agreement with the model.

  7. Energetic electrons generated during solar flares

    NASA Astrophysics Data System (ADS)

    Mann, Gottfried

    2015-12-01

    > electrons are accelerated up to energies beyond 30 keV is one of the open questions in solar physics. A flare is considered as the manifestation of magnetic reconnection in the solar corona. Which mechanisms lead to the production of energetic electrons in the magnetic reconnection region is discussed in this paper. Two of them are described in more detail.

  8. EGRET High Energy Capability and Multiwavelength Flare Studies and Solar Flare Proton Spectra

    NASA Technical Reports Server (NTRS)

    Chupp, Edward L.

    1997-01-01

    UNH was assigned the responsibility to use their accelerator neutron measurements to verify the TASC response function and to modify the TASC fitting program to include a high energy neutron contribution. Direct accelerator-based measurements by UNH of the energy-dependent efficiencies for detecting neutrons with energies from 36 to 720 MeV in NaI were compared with Monte Carlo TASC calculations. The calculated TASC efficiencies are somewhat lower (by about 20%) than the accelerator results in the energy range 70-300 MeV. The measured energy-loss spectrum for 207 MeV neutron interactions in NaI were compared with the Monte Carlo response for 200 MeV neutrons in the TASC indicating good agreement. Based on this agreement, the simulation was considered to be sufficiently accurate to generate a neutron response library to be used by UNH in modifying the TASC fitting program to include a neutron component in the flare spectrum modeling. TASC energy-loss data on the 1991 June 11 flare was transferred to UNH. Also included appendix: Gamma-rays and neutrons as a probe of flare proton spectra: the solar flare of 11 June 1991.

  9. EGRET High Energy Capability and Multiwavelength Flare Studies and Solar Flare Proton Spectra

    NASA Technical Reports Server (NTRS)

    Chupp, Edward L.

    1998-01-01

    The accomplishments of the participation in the Compton Gamma Ray Observatory Guest investigator program is summarized in this report. The work involved the study of Energetic Gamma Ray Experiment Telescope (EGRET)/Total Absorption Shower Counter(TASC) flare data. The specific accomplishments were the use of the accelerator neutron measurements obtained at the University of New Hampshire to verify the TASC response function and to modify the TASC fitting program to include a high energy neutron contribution, and to determine a high energy neutron contribution to the emissions from the 1991 June 11, solar flare. The next step in the analysis of this event was doing fits to the TASC energy-loss spectra as a function of time. A significant hardening of the solar proton spectrum over time was found for the flare. Further data was obtained from the Yohkoh HXT time histories and images for the 1991 October 27 flare. The results to date demonstrate that the TASC spectral analysis contributes crucial information on the particle spectrum interacting at the Sun. The report includes a paper accepted for publication, a draft of a paper to be delivered at the 26th International Cosmic Ray Conference and an abstract of a paper to be presented at the Meeting of the American Physical Society.

  10. Fe XXI as an electron density diagnostic in solar flares

    NASA Technical Reports Server (NTRS)

    Mason, H. E.; Doschek, G. A.; Feldman, U.; Bhatia, A. K.

    1979-01-01

    Atomic data have been calculated for Fe XXI, and the theoretical intensity ratios for many transitions are tabulated. Fe XXI lines in wavelength regions 1-25 A, 90-200 A, and 300-2500 A are discussed with reference to presently available solar and laboratory spectra. It is found that Fe XXI is an excellent density diagnostic for solar-flare and tokamak plasmas, when densities are in the range from 10 to the 11th to 10 to the 15th per cu cm. The theoretical calculations are applied to flare spectra obtained from OSO 5, and an electron density of less than 10 to the 13th per cu cm is deduced for a temperature of 10,000,000 K. The results are somewhat ambiguous in several cases because of the limited spectral and temporal resolution of these earlier spectrometers. However, the calculations will be important for forthcoming solar projects, such as the Solar Maximum Mission.

  11. Energetic electrons and photospheric electric currents during solar flares

    NASA Astrophysics Data System (ADS)

    Musset, Sophie; Vilmer, Nicole; Bommier, Veronique

    2016-07-01

    It is currently admitted that solar flares are powered by magnetic energy previously stored in the coronal magnetic field. During magnetic reconnection processes, this energy is transferred to particle acceleration, plasma motion and plasma heating. Magnetic energy release is likely to occur on coronal currents sheets along regions of strong gradient of magnetic connectivity. These coronal current sheets can be traced by their footprints at the surface on the Sun, i.e. by photospheric current ribbons. We aim to study the relation between these current ribbons observed at the photospheric level, tracing the coronal current sheets, and the flare energetic electrons traced by their X-ray emissions. The photospheric magnetic field and vertical current density have been calculated from SDO/HMI spectropolarimetric data with the UNNOFIT inversion and Metcalf disambiguation codes, while the X-ray images and spectra have been reconstructed from RHESSI data. In a first case, the GOES X2.2 flare of February 15, 2011, a spatial correlation is observed between the photospheric current ribbons and the coronal X-ray emissions from energetic electrons. Moreover, a conjoint evolution of both the photospheric currents and the X-ray emission is observed during the course of the flare. Both results are interpreted as consequences of the magnetic reconnection in coronal current sheets, and propagation of the reconnection sites to new structures during the flare, leading to new X-ray emission and local increase of the photospheric currents (Musset et al., 2015). We shall discuss here similar results obtained for other X-class flares.

  12. Energy spectra of ions from impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Reames, D. V.; Richardson, I. G.; Wenzel, K.-P.

    1992-01-01

    A study of the energy spectra of ions from impulsive solar flares in the 0.1-100 MeV region is reported. Most of the events studied are dominated by He and these He spectra show a persistent steepening or break above about 10 MeV resulting in an increase in the power-law spectral indices from about 2 to about 3.5 or more. Spectra of H, He-3, O, and Fe have spectral indices that are consistent with a value of about 3.5 above about 2 MeV/amu. One event, dominated by protons, shows a clear maximum in the spectrum near 1 MeV. If the rollover in the spectrum below 1 MeV is interpreted as a consequence of matter traversal in the solar atmosphere, then the source of the acceleration would lie only about 800 km above the photosphere, well below the corona. Alternative interpretations are that trapping in the acceleration region directly causes a peak in the resulting ion spectrum or that low-energy particles encounter significant additional scattering during transport from the flare.

  13. Implications of X-Ray Observations for Electron Acceleration and Propagation in Solar Flares

    NASA Technical Reports Server (NTRS)

    Holman, G. D.; Aschwanden, M. J.; Aurass, H.; Battaglia, M.; Grigis, P. C.; Kontar, E. P.; Liu, W.; Saint-Hilaire, P.; Zharkova, V. V.

    2011-01-01

    High-energy X-rays and gamma-rays from solar flares were discovered just over fifty years ago. Since that time, the standard for the interpretation of spatially integrated flare X-ray spectra at energies above several tens of keV has been the collisional thick-target model. After the launch of the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in early 2002, X-ray spectra and images have been of sufficient quality to allow a greater focus on the energetic electrons responsible for the X-ray emission, including their origin and their interactions with the flare plasma and magnetic field. The result has been new insights into the flaring process, as well as more quantitative models for both electron acceleration and propagation, and for the flare environment with which the electrons interact. In this article we review our current understanding of electron acceleration, energy loss, and propagation in flares. Implications of these new results for the collisional thick-target model, for general flare models, and for future flare studies are discussed.

  14. Energy spectra of ions from impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Reames, D. V.; Richardson, I. G.; Wenzel, K.-P.

    1991-01-01

    A study of the energy spectra of ions from impulsive solar flares in the 0.1 to 100 MeV region is reported with data from the combined observations of experiments on the ISEE 3 and IMP 8 spacecraft. Most of the events studied are dominated by He, and these He spectra show a persistent steepening or break above about 10 MeV resulting in an increase in the power-law spectral indices from about 2 to about 3.5 or more. One event, dominated by protons, shows a clear maximum in the spectrum near 1 MeV. If the rollover in the spectrum below 1 MeV is interpreted as a consequence of matter traversal in the solar atmosphere, then the source of the acceleration would lie only about 800 km above the photosphere, well below the corona. An alternative interpretation is that trapping in the acceleration region directly causes a peak in the spectrum.

  15. The Effects of Low- and High-Energy Cutoffs on Solar Flare Microwave and Hard X-Ray Spectra

    NASA Technical Reports Server (NTRS)

    Holman, G. D.; Oegerle, William (Technical Monitor)

    2002-01-01

    Microwave and hard x-ray spectra provide crucial information about energetic electrons and their environment in solar flares. These spectra are becoming better determined with the Owens Valley Solar Array (OVSA) and the recent launch of the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The proposed Frequency Agile Solar Radiotelescope (FASR) promises even greater advances in radio observations of solar flares. Both microwave and hard x-ray spectra are sensitive to cutoffs in the electron distribution function. The determination of the high-energy cutoff from these spectra establishes the highest electron energies produced by the acceleration mechanism, while determination of the low-energy cutoff is crucial to establishing the total energy in accelerated electrons. This paper will show computations of the effects of both high- and low-energy cutoffs on microwave and hard x-ray spectra. The optically thick portion of a microwave spectrum is enhanced and smoothed by a low-energy cutoff, while a hard x-ray spectrum is flattened below the cutoff energy. A high-energy cutoff steepens the microwave spectrum and increases the wavelength at which the spectrum peaks, while the hard x-ray spectrum begins to steepen at photon energies roughly an order of magnitude below the electron cutoff energy. This work discusses how flare microwave and hard x-ray spectra can be analyzed together to determine these electron cutoff energies. This work is supported in part by the NASA Sun-Earth Connection Program.

  16. Acceleration of runaway electrons in solar flares

    NASA Technical Reports Server (NTRS)

    Moghaddam-Taaheri, E.; Goertz, C. K.

    1990-01-01

    The dc electric field acceleration of electrons out of a thermal plasma and the evolution of the runaway tail are studied numerically, using a relativistic quasi-linear code based on the Ritz-Galerkin method and finite elements. A small field-aligned electric field is turned on at a certain time. The resulting distribution function from the runaway process is used to calculate the synchrotron emission during the evolution of the runaway tail. It is found that, during the runaway tail formation, which lasts a few tens of seconds for typical solar flare conditions, the synchrotron emission level is low, almost ot the same order as the emission from the thermal plasma, at the high-frequency end of the spectrum. However, the emission is enhanced explosively in a few microseconds by several orders of magnitude at the time the runaway tail stops growing along the magnetic field and tends toward isotropy due to the pitch-angle scattering of the fast particles. Results indicate that, in order to account for the observed synchrotron emission spectrum of a typical solar flare, the electric field acceleration phase must be accompanied or preceded by a heating phase which yields an enhanced electron temperature of about 2-15 keV in the flare region if the electric field is 0.1-0.2 times the Dreicer field and cyclotron-to-plasma frequency ratios are of order 1-2.

  17. Acceleration of runaway electrons in solar flares

    SciTech Connect

    Moghaddam-taaheri, E.; Goertz, C.K. )

    1990-03-01

    The dc electric field acceleration of electrons out of a thermal plasma and the evolution of the runaway tail are studied numerically, using a relativistic quasi-linear code based on the Ritz-Galerkin method and finite elements. A small field-aligned electric field is turned on at a certain time. The resulting distribution function from the runaway process is used to calculate the synchrotron emission during the evolution of the runaway tail. It is found that, during the runaway tail formation, which lasts a few tens of seconds for typical solar flare conditions, the synchrotron emission level is low, almost ot the same order as the emission from the thermal plasma, at the high-frequency end of the spectrum. However, the emission is enhanced explosively in a few microseconds by several orders of magnitude at the time the runaway tail stops growing along the magnetic field and tends toward isotropy due to the pitch-angle scattering of the fast particles. Results indicate that, in order to account for the observed synchrotron emission spectrum of a typical solar flare, the electric field acceleration phase must be accompanied or preceded by a heating phase which yields an enhanced electron temperature of about 2-15 keV in the flare region if the electric field is 0.1-0.2 times the Dreicer field and cyclotron-to-plasma frequency ratios are of order 1-2. 23 refs.

  18. Inferring the Energy Distribution of Accelerated Electrons in Solar Flares from X-ray Observations

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.; Sui, Linhui; Su, Yang

    2008-01-01

    Knowledge of the energy distribution of electrons accelerated in solar flares is important for constraining possible acceleration mechanisms and for understanding the relationships between flare X-ray sources, radio sources, and particles observed in space. Solar flare hard X-rays are primarily emitted from dense, thick-target regions in the lower atmosphere, but the electrons are understood to be accelerated higher in the corona. Various processes can distort the X-ray spectrum or the energy distribution of electrons before they reach the thick-target region. After briefly reviewing the processes that affect the X-ray spectrum and the electron distribution, I will describe recent results from a study of flare spectra from RHESSI to determine the importance of these processes in inferring the energy distribution of accelerated electrons.

  19. Interstellar Electron Density Spectra

    NASA Astrophysics Data System (ADS)

    Lambert, Hendrick Clark

    This study concerns the investigation of the form of the wavenumber spectrum of the Galactic electron density fluctuations through an examination of the scattering of the radio pulses emitted by pulsars as they propagate through the diffuse ionized interstellar gas. A widely used model for the electron density spectrum is based on the simple power-law: Pne(q)∝ q-β, where β = 11/3 is usually assumed, corresponding to Kolmogorov's turbulence spectrum. The simple Kolmogorov model provides satisfactory agreement for observations along many lines of sight; however, major inconsistencies remain. The inconsistencies suggest that an increase in the ratio of the power between the high (10-8[ m]-1≤ q<=10-7[ m]-1) and low (10-13[ m]-1≤ q<=10-12[ m]-1) wavenumbers is needed. This enhancement in the ratio can in turn be achieved by either including an inner scale, corresponding to a dissipation scale for the turbulent cascade, in the Kolmogorov spectrum or by considering steeper spectra. Spectra with spectral exponents β > 4 have been in general rejected based on observations of pulsar refractive scintillations. The special case of β = 4 has been given little attention and is analyzed in detail. Physically, this 'β = 4' model corresponds to the random distribution, both in location and orientation, of discrete objects with relatively sharp boundaries across the line of sight. An outer scale is included in the model to account for the average size of such objects. We compare the predictions of the inner-scale and β = 4 models both with published observations and observations we made as part of this investigation. We conclude that the form of the wavenumber spectrum is dependent on the line of sight. We propose a composite spectrum featuring a uniform background turbulence in presence of randomly distributed discrete objects, as modeled by the β = model.

  20. Theoretical Model Images and Spectra for Comparison with HESSI and Microwave Observations of Solar Flares

    NASA Technical Reports Server (NTRS)

    Fisher, Richard R. (Technical Monitor); Holman, G. D.; Sui, L.; McTiernan, J. M.; Petrosian, V.

    2003-01-01

    We have computed bremsstrahlung and gyrosynchrotron images and spectra from a model flare loop. Electrons with a power-law energy distribution are continuously injected at the top of a semi-circular magnetic loop. The Fokker-Planck equation is integrated to obtain the steady-state electron distribution throughout the loop. Coulomb scattering and energy losses and magnetic mirroring are included in the model. The resulting electron distributions are used to compute the radiative emissions. Sample images and spectra are presented. We are developing these models for the interpretation of the High Energy Solar Spectroscopic Imager (HESSI) x-ray/gamma ray data and coordinated microwave observations. The Fokker-Planck and radiation codes are available on the Web at http://hesperia.gsfc.nasa.gov/hessi/modelware.htm This work is supported in part by the NASA Sun-Earth Connection Program.

  1. Solar flare composition and thermodynamics from RESIK X-ray spectra

    SciTech Connect

    Sylwester, B.; Sylwester, J.; Kępa, A.; Mrozek, T.; Phillips, K. J. H. E-mail: js@cbk.pan.wroc.pl E-mail: kennethjhphillips@yahoo.com

    2014-06-01

    Previous estimates of the solar flare abundances of Si, S, Cl, Ar, and K from the RESIK X-ray crystal spectrometer on board the CORONAS-F spacecraft were made on the assumption of isothermal X-ray emission. We investigate the effect on these estimates by relaxing this assumption and instead determining the differential emission measure (DEM) or thermal structure of the emitting plasma by re-analyzing RESIK data for a GOES class M1.0 flare on 2002 November 14 (SOL2002-11-14T22:26) for which there was good data coverage. The analysis method uses a maximum-likelihood (Withbroe-Sylwester) routine for evaluating the DEM. In a first step, called here AbuOpt, an optimized set of abundances of Si, S, Ar, and K is found that is consistent with the observed spectra. With these abundances, the DEM evolution during the flare is found. The abundance optimization leads to revised abundances of silicon and sulfur in the flare plasma: A(S) = 6.94 ± 0.06 and A(Si) = 7.56 ± 0.08 (on a logarithmic scale with A(H) = 12). Previously determined abundances of Ar, K, and Cl from an isothermal assumption are still the preferred values. During the flare's maximum phase, the X-ray-emitting plasma has a basically two-temperature structure, with the cooler plasma with approximately constant temperature (3-6 MK) and a hotter plasma with temperature 16-21 MK. Using imaging data from the RHESSI hard X-ray spacecraft, the emission volume of the hot plasma is deduced from which lower limits of the electron density N{sub e} and the thermal content of the plasma are given.

  2. High-resolution X-ray spectra of solar flares. III - General spectral properties of X1-X5 type flares

    NASA Technical Reports Server (NTRS)

    Doschek, G. A.; Feldman, U.; Kreplin, R. W.; Cohen, L.

    1980-01-01

    High-resolution X-ray spectra of six class X1-X5 solar flares are discussed. The spectra were recorded by spaceborne Bragg crystal spectrometers in the ranges 1.82-1.97, 2.98-3.07 and 3.14-3.24 A. Electron temperatures derived from dielectronic satellite line to resonance line ratios for Fe XXV and Ca XIX are found to remain fairly constant around 22,000,000 and 16,000,000 K respectively during the rise phase of the flares, then decrease by approximately 6,000,000 K during the decay phase. Nonthermal motions derived from line widths for the April 27, 1979 event are found to be greatest during the rise phase (approximately 130 km/sec) and decrease to about 60 km/sec during decay. Volume emission measures for Fe XXV, Ca XIX and Ca XX are derived from photon fluxes as a function of temperature, and examination of the intensity behavior of the Fe K alpha emission as a function of time indicates that it is a result of fluorescence. Differences between the present and previous observations of temperature variation are discussed, and it is concluded that the flare plasmas are close to ionization equilibrium for the flares investigated.

  3. On the 'fast electron hypothesis' for stellar flares

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.

    1990-01-01

    It is pointed out that Gurzadyan's (1988) fast-electron hypothesis for stellar flares encounters certain difficulties. The origin of the fast electrons is obscure. Negative flares and predicted ratios of X-ray to optical fluxes are not necessarily a proof of the fast-electron hypothesis. When the electrons thermalize, they will yield X-ray fluxes which are orders of magnitude too large to be consistent with observations.

  4. Acceleration of electrons during the flash phase of solar flares

    NASA Technical Reports Server (NTRS)

    Kane, S. R.

    1974-01-01

    The characteristics of the electron acceleration process operating during the flash phase of solar flares are deduced from the high time resolution observations of impulsive solar X rays greater than or equal to 10 keV and other flash phase emissions from small solar flares, and the implications of these findings are discussed.

  5. Onset of electron acceleration in a flare loop

    SciTech Connect

    Sharykin, Ivan; Liu, Siming; Fletcher, Lyndsay

    2014-09-20

    We carried out a detailed analysis of X-ray and radio observations of a simple flare loop that occurred on 2002 August 12, with the impulsive hard X-ray (HXR) light curves dominated by a single pulse. The emission spectra of the early impulsive phase are consistent with an isothermal model in the coronal loop with a temperature reaching several keV. A power-law high-energy spectral tail is evident near the HXR peak time, in accordance with the appearance of footpoints at high energies, and is well correlated with the radio emission. The energy content of the thermal component keeps increasing gradually after the disappearance of this nonthermal component. These results suggest that electron acceleration only covers the central period of a longer and more gradual energy dissipation process and that the electron transport within the loop plays a crucial role in the formation of the inferred power-law electron distribution. The spectral index of power-law photons shows a very gradual evolution, indicating that the electron accelerator is in a quasi-steady state, which is confirmed by radio observations. These results are consistent with the theory of stochastic electron acceleration from a thermal background. Advanced modeling with coupled electron acceleration and spatial transport processes is needed to explain these observations more quantitatively, which may reveal the dependence of the electron acceleration on the spatial structure of the acceleration region.

  6. Electron cyclotron maser emission from double footpoints in solar flares

    NASA Astrophysics Data System (ADS)

    Conway, A. J.; Willes, A. J.

    2000-03-01

    It is now known from Yohkoh Hard X-ray Telescope observations that double (or even multiple) hard X-ray sources in flares are a common occurrence. These sources, which are positioned at the feet of coronal soft X-ray loops, are synchronised to within 0.1s and have similar spectra, strongly suggesting that they are produced by a single population of electrons accelerated/injected at some point in the loop. As this electron population is reflected from the converging footpoint magnetic fields, it develops a loss cone and an electron-cyclotron maser instability may ensue. The frequency and intensity of such emission depends on the relative strengths and orientations of the footpoint magnetic fields. In this paper, we investigate the case of an almost symmetric loop to assess whether observable maser emission from both footpoints can result. In particular, we relate this theory to existing observations of solar microwave spike bursts which have two distinct frequency bands that are of non-integer ratio and comparable intensities. We conclude that differing footpoint magnetic field inclinations cannot explain the observations (specifically the comparable intensities), but that it is possible for slightly differing footpoint magnetic field strengths to explain the observations. The pros and cons of this `geometric' model are then compared with a previous model of these events, which explained them in terms of the growth and then coalescence of Bernstein waves. We conclude that both interpretations seem plausible given current observations, but present a list of observable features that might be used discriminate between them in flare observations of the next solar maximum.

  7. Narrowband Gyrosynchrotron Bursts: Probing Electron Acceleration in Solar Flares

    NASA Astrophysics Data System (ADS)

    Fleishman, Gregory D.; Nita, Gelu M.; Kontar, Eduard P.; Gary, Dale E.

    2016-07-01

    Recently, in a few case studies we demonstrated that gyrosynchrotron microwave emission can be detected directly from the acceleration region when the trapped electron component is insignificant. For the statistical study reported here, we have identified events with steep (narrowband) microwave spectra that do not show a significant trapped component and, at the same time, show evidence of source uniformity, which simplifies the data analysis greatly. Initially, we identified a subset of more than 20 radio bursts with such narrow spectra, having low- and high-frequency spectral indices larger than three in absolute value. A steep low-frequency spectrum implies that the emission is nonthermal (for optically thick thermal emission, the spectral index cannot be steeper than two), and the source is reasonably dense and uniform. A steep high-frequency spectrum implies that no significant electron trapping occurs, otherwise a progressive spectral flattening would be observed. Roughly half of these radio bursts have RHESSI data, which allow for detailed, joint diagnostics of the source parameters and evolution. Based on an analysis of radio-to-X-ray spatial relationships, timing, and spectral fits, we conclude that the microwave emission in these narrowband bursts originates directly from the acceleration regions, which have a relatively strong magnetic field, high density, and low temperature. In contrast, the thermal X-ray emission comes from a distinct loop with a smaller magnetic field, lower density, but higher temperature. Therefore, these flares likely occurred due to interaction between two (or more) magnetic loops.

  8. High resolution X-ray spectra of solar flares. V - Interpretation of inner-shell transitions in Fe XX-Fe XXIII

    NASA Technical Reports Server (NTRS)

    Doschek, G. A.; Feldman, U.; Cowan, R. D.

    1981-01-01

    The paper examines high-resolution solar flare iron line spectra recorded between 1.82 and 1.97 A by a spectrometer flown by the Naval Research Laboratory on an Air Force spacecraft launched on 1979 February 24. The emission line spectrum is due to inner-shell transitions in the ions Fe XX-Fe XXV. Using theoretical spectra and calculations of line intensities obtained by methods discussed by Merts, Cowan, and Magee (1976), electron temperatures as a function of time for two large class X flares are derived. These temperatures are deduced from intensities of lines of Fe XXII, Fe XXIII, and Fe XXIV. The determination of the differential emission measure between about 12-million and 20-million K using these temperatures is considered. The possibility of determining electron densities in flare and tokamak plasmas using the inner-shell spectra of Fe XXI and Fe XX is discussed.

  9. Signatures of Accelerated Electrons in Solar and Stellar Flares

    NASA Astrophysics Data System (ADS)

    Benz, Arnold O.

    2015-08-01

    Flares energize electrons (and ions) to supra-thermal energies. In most cases the final distribution in momentum or energy space is non-Maxwellian. The non-thermal part of the energy can be the source for various emissions, including hard X-rays, synchrotron radiation and coherent radio emission. Such non-thermal emissions may contain information on the acceleration process. Several acceleration scenarios have been proposed: electric DC field, stochastic, and shock acceleration. There is observational evidence for all three scenarios. The new data come from SDO, X-ray (RHESSI), radio observations (Nobeyama, VLA and e-Callisto). Solar energetic particles are an additional channel of information.Tiny solar microflares and huge stellar flares in binary systems (RS CVns) and dMe dwarfs differ by more than 10 orders of magnitude in released energy. Yet the relation between peak luminosity in thermal (soft) X-ray and non-thermal synchrotron (radio) emission is surprisingly constant. This observational fact indicates that flare acceleration scales with energy release over a large range. Electron acceleration in flares seems to be a universal process. The constraint on simultaneous thermal X-rays and non-thermal (radio) synchrotron emission seems to select on particular kind of flare. In this subset, there seems to be only one type of acceleration.Yet, small deviations are noted: Small solar flares are softer in hard X-rays. Solar nanoflares are relatively weak in synchrotron emission. The recently noted case of radio-poor preflares will also be presented. The deviations suggest that the acceleration is less efficient in small flares and in the early phase of flares. Larger deviations are reported occasionally for solar flares and more often from stellar flares, where either thermal or non-thermal emission seems to be missing completely.The location of the acceleration in solar flares remains disputed. Observations suggesting acceleration in the soft X-ray top-tops, above

  10. On helium-like 1s2l-1snl prime transitions in solar flare spectra

    NASA Technical Reports Server (NTRS)

    Kastner, S. O.; Neupert, W. M.; Swartz, M.

    1974-01-01

    Expected wavelengths and intensities are computed for 1s2l-1snl prime transitions in helium-like ions of the abundant elements from oxygen to iron under coronal conditions. Probable observations of some of these lines in the spectra of solar flares are discussed, and attention is called to a possible reversal of singlet and triplet intensities as compared to laboratory observations.

  11. Acceleration of runaway electrons and Joule heating in solar flares

    NASA Technical Reports Server (NTRS)

    Holman, G. D.

    1984-01-01

    The electric field acceleration of electrons out of a thermal plasma and the simultaneous Joule heating of the plasma are studied. Acceleration and heating timescales are derived and compared, and upper limits are obtained on the acceleration volume and the rate at which electrons can be accelerated. These upper limits, determined by the maximum magnetic field strength observed in flaring regions, place stringent restrictions upon the acceleration process. The role of the plasma resistivity in these processes is examined, and possible sources of anomalous resistivity are summarized. The implications of these results for the microwave and hard X-ray emission from solar flares are examined.

  12. Acceleration of runaway electrons and Joule heating in solar flares

    NASA Technical Reports Server (NTRS)

    Holman, G. D.

    1985-01-01

    The electric field acceleration of electrons out of a thermal plasma and the simultaneous Joule heating of the plasma are studied. Acceleration and heating timescales are derived and compared, and upper limits are obtained on the acceleration volume and the rate at which electrons can be accelerated. These upper limits, determined by the maximum magnetic field strength observed in flaring regions, place stringent restrictions upon the acceleration process. The role of the plasma resistivity in these processes is examined, and possible sources of anomalous resistivity are summarized. The implications of these results for the microwave and hard X-ray emission from solar flares are examined.

  13. The Energetic Importance of Accelerated Electrons in Solar Flares

    NASA Technical Reports Server (NTRS)

    Dennis, Brian R.; Oegerle, William (Technical Monitor)

    2002-01-01

    It has been claimed that a large fraction of the total energy released in a solar flare goes initially into accelerated electrons. These electrons generate the observed hard X-ray bremsstrahlung emission as they lose most of their energy by coulomb collisions in the lower corona and chromosphere to heat the plasma seen in soft X-rays. From several recent studies of the Neupert Effect - the empirical result that for many flares the time integral of the hard X-ray emission closely matches the temporal variation of the soft X-ray emission - it appears that the fraction of the released energy going into accelerated electrons is lower, on average, for smaller flares. Also, from relative timing differences, about 25% of all flares are inconsistent with the Neupert Effect. The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is uniquely capable of investigating the Neupert Effect since it covers soft X-rays down to 3 keV (when both attenuators are out of the field of view) and hard X-rays with keV energy resolution. It has arcsecond-class angular resolution and sub-second time resolution. Several M-class flares have already been detected by RHESSI and I will present their detailed time histories for different energy ranges. I will also present hard and soft X-ray images that reveal the spatial relation between the hot plasma and the accelerated electrons. The results are in general agreement with the Neupert Effect, but they also suggest that there must be other heating mechanisms besides the thermalization of accelerated electrons, even during the impulsive phase.

  14. Evidence for beamed electrons in a limb X-ray flare observed by Hard X-Ray Imaging Spectrometer (HXIS)

    NASA Technical Reports Server (NTRS)

    Haug, Eberhard; Elwert, Gerhard

    1986-01-01

    The limb flare of November 18, 1980, 14:51 UT, was investigated on the basis of X-ray images taken by the Hard X-ray Imaging Spectrometer (HXIS) and of X-ray spectra from the Hard X-Ray Burst Spectrometer (HXRBS) aboard the Solar Maximum Mission (SMM). The impulsive burst was also recorded at microwave frequencies between 2 and 20 GHz whereas no optical flare and no radio event at frequencies below 1 GHz were reported. The flare occurred directly at the SW limb of the solar disk. Taking advantage of the spatial resolution of HXIS images, the time evolution of the X-radiation originating from relatively small source regions can be studied. Using Monte Carlo computations of the energy distribution of energetic electrons traversing the solar plasma, the bremsstrahlung spectra produced by the electrons were derived.

  15. The energy spectrum of 20 keV-20 MeV electrons accelerated in large solar flares

    NASA Technical Reports Server (NTRS)

    Lin, R. P.; Mewaldt, R. A.; Van Hollebeke, M. A. I.

    1982-01-01

    IMP 6, 7, and 8 measurements of the energy spectrum of 20 keV to 20 MeV electrons observed from large solar flares are presented. To minimize propagation effects, only events from flares at W30 deg to W90 deg solar longitude are considered. The energy spectra are constructed using the maximum flux observed at each energy. It is shown that these spectra are representative of the spectra of the electrons escaping from the sun over this range of energies. It is found that every event shows the same spectral shape: a double power law with a smooth transition around 100-200 keV and power law exponents of 0.6-2.0 below and 2.4-4.3 above. The more intense the event, the harder the observed spectrum; in certain cases, the spectra are observed to steepen above 3 MeV.

  16. Differences between electron energy distributions in both steady and flare states of Mrk 501

    NASA Astrophysics Data System (ADS)

    Peng, Yaping; Yan, Dahai; Zhang, Li

    2014-08-01

    Possible electron energy distributions (EEDs) for Mrk 501 are studied through fitting multiband energy spectra in both steady and flare states with a one-zone synchrotron self-Compton model. Two kinds of the EEDs formed in different acceleration and cooling processes are assumed: a power law with an exponential cut-off (PLC) EED and a log-parabolic (LP) EED. The Markov Chain Monte Carlo method is used to estimate the model parameters in our fits. The results show that the LP model fits the spectral energy distributions better in both steady and flare states than PLC model, and the changes of model parameters from steady state to flare state can be explained reasonably. Therefore, it is concluded that the EEDs and the acceleration mechanisms in both steady and flare states would be the same for Mrk 501. Compared to Mrk 421 having different EEDs in different states, our analysis indicates that both acceleration and cooling processes are different in the jets of these two sources.

  17. The energy spectra of solar flare hydrogen, helium, oxygen, and iron - Evidence for stochastic acceleration

    NASA Technical Reports Server (NTRS)

    Mazur, J. E.; Mason, G. M.; Klecker, B.; Mcguire, R. E.

    1992-01-01

    The time-integrated differential energy spectra of H, He, O, and Fe measured in 10 large flare events observed at 1 AU over the energy range of 0.3-80 MeV/nucleon showed consistent patterns in their spectral shapes: particles with larger mean mass-to-charge ratios were generally less abundant at higher energies. A steady state model of stochastic particle acceleration with rigidity-dependent diffusion coefficients fit the spectra best; spectra representative of diffusive shock acceleration also described the spectra of some events with the same number of free parameters, but often fell off faster in energy above 30 MeV per nucleon than the observations. The two model predictions differed most at energies near 0.1 MeV per nucleon, below the lowest energies observed in this study. The stochastic model quantitatively described the observed spectral ordering with less efficient acceleration of species with larger mean mass-to-charge ratios.

  18. Coronal propagation of flare associated electrons and protons

    NASA Technical Reports Server (NTRS)

    Schellert, G.; Wibberenz, G.; Kunow, H.

    1985-01-01

    A statistical study of characteristic times and intensities of 36 solar particle events observed between 1977 and 1979 by the Kiel Cosmic Ray Experiment on board HELIOS-1 and -2 has been carried out. For approx. 0.5 MeV electrons we order the times of maximum and the absolute intensities with respect to angular distance from the parent flare. Discussion of coronal parameters in terms of Reid's model leads to typical time constants for coronal diffusion and escape.

  19. Quasi-periodic Pulsations in Solar and Stellar Flares: Re-evaluating their Nature in the Context of Power-law Flare Fourier Spectra

    NASA Astrophysics Data System (ADS)

    Inglis, A. R.; Ireland, J.; Dominique, M.

    2015-01-01

    The nature of quasi-periodic pulsations (QPPs) in solar and stellar flares remains debated. Recent work has shown that power-law-like Fourier power spectra are an intrinsic property of solar and stellar flare signals, a property that many previous studies of this phenomenon have not accounted for. Hence a re-evaluation of the existing interpretations and assumptions regarding QPPs is needed. We adopt a Bayesian method for investigating this phenomenon, fully considering the Fourier power-law properties of flare signals. Using data from the PROBA2/Large Yield Radiometer, Fermi/Gamma-ray Burst Monitor, Nobeyama Radioheliograph, and Yohkoh/HXT instruments, we study a selection of flares from the literature identified as QPP events. Additionally, we examine optical data from a recent stellar flare that appears to exhibit oscillatory properties. We find that, for all but one event tested, an explicit oscillation is not required to explain the observations. Instead, the flare signals are adequately described as a manifestation of a power law in the Fourier power spectrum. However, for the flare of 1998 May 8, strong evidence for an explicit oscillation with P ≈ 14-16 s is found in the 17 GHz radio data and the 13-23 keV Yohkoh/HXT data. We conclude that, most likely, many previously analyzed events in the literature may be similarly described by power laws in the flare Fourier power spectrum, without invoking a narrowband, oscillatory component. Hence the prevalence of oscillatory signatures in solar and stellar flares may be less than previously believed. The physical mechanism behind the appearance of the observed power laws is discussed.

  20. QUASI-PERIODIC PULSATIONS IN SOLAR AND STELLAR FLARES: RE-EVALUATING THEIR NATURE IN THE CONTEXT OF POWER-LAW FLARE FOURIER SPECTRA

    SciTech Connect

    Inglis, A. R.; Ireland, J.; Dominique, M.

    2015-01-10

    The nature of quasi-periodic pulsations (QPPs) in solar and stellar flares remains debated. Recent work has shown that power-law-like Fourier power spectra are an intrinsic property of solar and stellar flare signals, a property that many previous studies of this phenomenon have not accounted for. Hence a re-evaluation of the existing interpretations and assumptions regarding QPPs is needed. We adopt a Bayesian method for investigating this phenomenon, fully considering the Fourier power-law properties of flare signals. Using data from the PROBA2/Large Yield Radiometer, Fermi/Gamma-ray Burst Monitor, Nobeyama Radioheliograph, and Yohkoh/HXT instruments, we study a selection of flares from the literature identified as QPP events. Additionally, we examine optical data from a recent stellar flare that appears to exhibit oscillatory properties. We find that, for all but one event tested, an explicit oscillation is not required to explain the observations. Instead, the flare signals are adequately described as a manifestation of a power law in the Fourier power spectrum. However, for the flare of 1998 May 8, strong evidence for an explicit oscillation with P ≈ 14-16 s is found in the 17 GHz radio data and the 13-23 keV Yohkoh/HXT data. We conclude that, most likely, many previously analyzed events in the literature may be similarly described by power laws in the flare Fourier power spectrum, without invoking a narrowband, oscillatory component. Hence the prevalence of oscillatory signatures in solar and stellar flares may be less than previously believed. The physical mechanism behind the appearance of the observed power laws is discussed.

  1. IUE spectra of a flare in the RS Canum Venaticorum-type system UX Arietis

    NASA Technical Reports Server (NTRS)

    Simon, T.; Linsky, J. L.; Schiffer, F. H., III

    1980-01-01

    IUE spectra of UX Ari obtained during the large flare of 1979 January 1 exhibit chromospheric and transition-region emission-line fluxes about 2.5 and 5.5 times brighter than quiescent fluxes, respectively, and up to 1400 times brighter than the quiet sun. A high-dispersion spectrum of the 2000-3000 A region exhibits enhanced Fe II emission, which is probably associated mainly with the K0 IV star, and enhanced Mg II emission with asymmetric wings extending to +475 km/s. These line wings are interpreted as evidence for mass flow from the K0 IV star to the G5 V star. A speculative scenario of major long-lived RS CVn flares is proposed in which the component stars have very large corotating flux tubes, which occasionally interact. Magnetic reconnection results in flux tubes that temporarily connect the two stars.

  2. Possible evidence for beaming in flares from microwave and hard X-ray imaging and spectra

    NASA Technical Reports Server (NTRS)

    Schmahl, E. J.; Kundu, M. R.; Dennis, B. R.

    1986-01-01

    The magnetic field strength and number of burst-producing energetic electrons are presently deduced for the impulsive phase of a solar flare at microwave wavelengths, with the VLA, and hard X-rays, with the SMM Hard X-ray Burst Spectrometer. The combined data indicate that the number of microwave-emitting electrons is at least three orders of magnitude smaller than the number of thick target electrons producing the hard X-rays; this is suggested to be due to the high beaming and inefficient radiation of gyrosynchrotron emission by comparison with isotropically distributed electrons.

  3. Electron acceleration in a post-flare decimetric continuum source

    NASA Astrophysics Data System (ADS)

    Subramanian, P.; White, S. M.; Karlický, M.; Sych, R.; Sawant, H. S.; Ananthakrishnan, S.

    2007-06-01

    Aims:To calculate the power budget for electron acceleration and the efficiency of the plasma emission mechanism in a post-flare decimetric continuum source. Methods: We have imaged a high brightness temperature (˜ 109 K) post-flare source at 1060 MHz with the Giant Metrewave Radio Telescope (GMRT). We use information from these images and the dynamic spectrum from the Hiraiso spectrograph together with the theoretical method described in Subramanian & Becker (2006, Sol. Phys., 237, 185) to calculate the power input to the electron acceleration process. The method assumes that the electrons are accelerated via a second-order Fermi acceleration mechanism. Results: We find that the power input to the nonthermal electrons is in the range 3× 1025-1026 erg/s. The efficiency of the overall plasma emission process starting from electron acceleration and culminating in the observed emission could range from 2.87× 10-9 to 2.38 × 10-8.

  4. Degradation spectra of electrons in the ionosphere

    NASA Astrophysics Data System (ADS)

    Konovalov, V. P.; Son, E. E.

    2015-11-01

    Theory and numerical simulations of degradation spectra of electrons in gases are presented. Theory is based on the power spectra of degradation charged particles as the spectra with fluxes in energy space. Numerical calculations of the electron energy distribution function have been performed for ionospheric gas mixtures constituted of molecules N2, O2 and atom O under influence of high energy electron source with detailed elementary electron collision processes with molecules and atoms being taken into consideration. The energy expenses of electrons into ionization, dissociation and excitation of various levels have been obtained so that to determine the rates of electron collision processes. The dependence of the electron energy expenses into various inelastic electronic processes upon the energy of primary electron source has been revealed. The results are presented for the rates of numerous elementary processes of electron interaction with basic ionospheric components to be suitably determined.

  5. Ulysses-ARTEMIS radio observation of energetic flare electron

    NASA Technical Reports Server (NTRS)

    Hoang, S.; Moncuquet, M.; Poquerusse, M.

    1995-01-01

    Type 3 radio bursts allow us to follow energetic electrons ejected by solar flares into the interplanetary medium, even when the observer is far away from the electrons. The emission frequency f(sub p) is related to the ambient density n(sub e) by f(sub p) varies as the square root of n(sub e), and as a function of the distance r to the sun we have approximately n(sub e) varies as r(exp -2); as a consequence, on a 1/f - t dynamic spectrum type 3 bursts appear as nearly straight traces, whose slope gives an estimation of the source speed. We used the data of the URAP radio receiver on Ulysses (1-1000 kHz), observing sources in the solar wind, and the ground data of the ARTEMIS spectrograph (100-500 MHz), observing sources of the corona, over the years 1991-1994. We found a surprisingly large number of excellent high-frequency - low-frequency associations. A type 3 burst group on ARTEMIS (10 to 100 bursts over 1 to 10 minutes) typically gives rise to one isolated burst on Ulysses. As bursts often start in high frequencies during the maximum phase of flares, this demonstrates in a very convincing manner that some of the flare electrons themselves make it all the way to the interplanetary medium. We discuss decorrelation cases in the context of geometrical configuration between the active region and the two observing sites. We also study how apparent electron speeds vary with the distance to the sun.

  6. Electron Beam Return-Current Losses in Solar Flares: Initial Comparison of Analytical and Numerical Results

    NASA Technical Reports Server (NTRS)

    Holman, Gordon

    2010-01-01

    Accelerated electrons play an important role in the energetics of solar flares. Understanding the process or processes that accelerate these electrons to high, nonthermal energies also depends on understanding the evolution of these electrons between the acceleration region and the region where they are observed through their hard X-ray or radio emission. Energy losses in the co-spatial electric field that drives the current-neutralizing return current can flatten the electron distribution toward low energies. This in turn flattens the corresponding bremsstrahlung hard X-ray spectrum toward low energies. The lost electron beam energy also enhances heating in the coronal part of the flare loop. Extending earlier work by Knight & Sturrock (1977), Emslie (1980), Diakonov & Somov (1988), and Litvinenko & Somov (1991), I have derived analytical and semi-analytical results for the nonthermal electron distribution function and the self-consistent electric field strength in the presence of a steady-state return-current. I review these results, presented previously at the 2009 SPD Meeting in Boulder, CO, and compare them and computed X-ray spectra with numerical results obtained by Zharkova & Gordovskii (2005, 2006). The phYSical significance of similarities and differences in the results will be emphasized. This work is supported by NASA's Heliophysics Guest Investigator Program and the RHESSI Project.

  7. SUPPRESSION OF ENERGETIC ELECTRON TRANSPORT IN FLARES BY DOUBLE LAYERS

    SciTech Connect

    Li, T. C.; Drake, J. F.; Swisdak, M.

    2012-09-20

    During flares and coronal mass ejections, energetic electrons from coronal sources typically have very long lifetimes compared to the transit times across the systems, suggesting confinement in the source region. Particle-in-cell simulations are carried out to explore the mechanisms of energetic electron transport from the corona to the chromosphere and possible confinement. We set up an initial system of pre-accelerated hot electrons in contact with ambient cold electrons along the local magnetic field and let it evolve over time. Suppression of transport by a nonlinear, highly localized electrostatic electric field (in the form of a double layer) is observed after a short phase of free-streaming by hot electrons. The double layer (DL) emerges at the contact of the two electron populations. It is driven by an ion-electron streaming instability due to the drift of the back-streaming return current electrons interacting with the ions. The DL grows over time and supports a significant drop in temperature and hence reduces heat flux between the two regions that is sustained for the duration of the simulation. This study shows that transport suppression begins when the energetic electrons start to propagate away from a coronal acceleration site. It also implies confinement of energetic electrons with kinetic energies less than the electrostatic energy of the DL for the DL lifetime, which is much longer than the electron transit time through the source region.

  8. Observations of transitions of hydrogen-like Fe XXVI in solar flare spectra

    NASA Technical Reports Server (NTRS)

    Parmar, A. N.; Culhane, J. L.; Rapley, C. G.; Antonucci, E.; Gabriel, A. H.; Loulergue, M.

    1981-01-01

    Observations of solar flare spectra over the wavelength range 1.769-1.796 A with the Bent Crystal Spectrometer on the NASA Solar Maximum Mission satellite are presented. The 2P3/2, 2P1/2 and associated satellite transitions of Fe XXVI are identified, their intensities and widths estimated and the results compared with theoretical predictions. For two spectra, which include the isolated n = 2 satellite features, the observations can be reproduced by plasma temperatures of 24,000,000 and 28,400,000 K. Linewidth measurements show evidence for nonthermal velocities of up to 150 km/s. Emission measures derived from the Fe XXVI observations are compared with those from lower temperature Ca XIX and Fe XXV measurements and an emission measure decreasing with temperature is found.

  9. High-resolution X-ray spectra of solar flares. IX - Mass upflow in the long-duration flare of 1979 June 5

    NASA Technical Reports Server (NTRS)

    Doschek, G. A.; Feldman, U.; Seely, J. F.; Mckenzie, D. L.

    1989-01-01

    Blueshifted X-ray spectral line components in Fe and Ca spectra of a large long-duration flare observed on June 5, 1979. It is found that blueshifted emission exists for a time interval of at least 28 minutes indicating upflowing plasma at about 250 km/s. Emission measures for both the blueshifted and stationary plasma are derived and the results are interpreted in terms of chromospheric evaporation. The total amount of hot upflowing plasma during the flare rise time exceeds the amount of stationary plasma contained in the loop close to the time of the peak of the flare. This result contradicts the simplest version of the evaporation model. Evaporation can account for the observations only if some of the upflowing plasma cools on time scales much shorter than the rise time of the event, which was about 40 minutes.

  10. CORONAL ELECTRON DISTRIBUTION IN SOLAR FLARES: DRIFT-KINETIC MODEL

    SciTech Connect

    Minoshima, Takashi; Kusano, Kanya; Masuda, Satoshi; Miyoshi, Yoshizumi

    2011-05-10

    Using a model of particle acceleration and transport in solar flares, we investigate the height distribution of coronal electrons by focusing on the energy-dependent pitch-angle scattering. When pitch-angle scattering is not included, the peak heights of loop-top electrons are constant, regardless of their energy, owing to the continuous acceleration and compression of the electrons via shrinkage of magnetic loops. On the other hand, under pitch-angle scattering, the electron heights are energy-dependent: intermediate-energy electrons are at a higher altitude, whereas lower and higher energy electrons are at lower altitudes. This implies that the intermediate-energy electrons are inhibited from following the shrinking field lines to lower altitudes because pitch-angle scattering causes efficient precipitation of these electrons into the footpoint and their subsequent loss from the loop. This result is qualitatively consistent with the position of the above-the-loop-top hard X-ray (HXR) source that is located above coronal HXR loops emitted by lower energy electrons and microwaves emitted by higher energy electrons. Quantitative agreement with observations might be achieved by considering primary acceleration before the onset of loop shrinkage and additional pitch-angle scattering via wave-particle interactions.

  11. Magnetic Structure and Nonthermal Electrons in the X6.9 Flare on 2011 August 9

    NASA Astrophysics Data System (ADS)

    Hwangbo, Jung-Eun; Lee, Jeongwoo; Park, Sung-Hong; Kim, Sujin; Lee, Dae-Young; Bong, Su-Chan; Kim, Yeon-Han; Cho, Kyung-Suk; Park, Young-Deuk

    2014-12-01

    The 2011 August 9 flare is one of the largest X-ray flares of sunspot cycle 24, but spatial information is rather limited due to its position close to the western limb. This paper presents information about the location of high-energy electrons derived from hard X-ray and microwave spectra obtained with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and the Korean Solar Radio Burst Locator (KSRBL), respectively. The KSRBL microwave spectrum shows significant fluxes at low frequencies, implying that the high-energy electrons reside in a coronal volume highly concentrated at strong magnetic fields, and rapidly expanding with decreasing magnetic fields. After a simple modeling of the microwave spectrum, we found that the microwave source should be located above the inner pair of magnetic poles in a large quadrupolar configuration. The time-dependent evolution of the magnetic field distribution and total nonthermal energy derived from the microwave spectra is also consistent with the standard picture of multiple magnetic reconnections recurring at a magnetic null point that forms above the magnetic quadrupoles and moves up with time.

  12. Magnetic Structure and Nonthermal Electrons in the X6.9 Flare on 2011 August 09

    NASA Astrophysics Data System (ADS)

    Hwangbo, J. E.; Lee, J.; Park, S. H.; Bong, S. C.; Lee, D. Y.; Kim, Y. H.; Cho, K. S. F.; Park, Y. D.

    2014-12-01

    The 2011 August 09 Flare is one of the largest X-ray flares of Sunspot Cycle 24, but the spatial information is rather limited due to its position close to the western limb. This paper presents the information on the location of high energy electrons derived from the hard X-ray and microwave spectra obtained with the Reuven Ramaty High-Energy Solar Spectroscopic Imager(RHESSI) and the Korean Solar Radio Burst Locator (KSRBL), respectively. The KSRBL microwave spectrum shows significant fluxes at low frequencies, implying that the high energy electrons reside in a coronal volume highly concentrated at strong magnetic fields, and rapidly expanding with decreasing magnetic fields. After a simple modeling of the microwave spectrum, we found that the microwave source should be located above the inner pair of magnetic poles in a large quadrupolar configuration. The time-dependent evolution of magnetic field distribution and total nonthermal energy derived from the microwave spectra is also consistent with the standard picture of multiple magnetic reconnections recurring at a magnetic null point that forms above the magnetic quadrupoles and moves up with time.

  13. Magnetic structure and nonthermal electrons in the X6.9 flare on 2011 August 9

    SciTech Connect

    Hwangbo, Jung-Eun; Lee, Dae-Young; Lee, Jeongwoo; Park, Sung-Hong; Kim, Sujin; Bong, Su-Chan; Kim, Yeon-Han; Cho, Kyung-Suk; Park, Young-Deuk

    2014-12-01

    The 2011 August 9 flare is one of the largest X-ray flares of sunspot cycle 24, but spatial information is rather limited due to its position close to the western limb. This paper presents information about the location of high-energy electrons derived from hard X-ray and microwave spectra obtained with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and the Korean Solar Radio Burst Locator (KSRBL), respectively. The KSRBL microwave spectrum shows significant fluxes at low frequencies, implying that the high-energy electrons reside in a coronal volume highly concentrated at strong magnetic fields, and rapidly expanding with decreasing magnetic fields. After a simple modeling of the microwave spectrum, we found that the microwave source should be located above the inner pair of magnetic poles in a large quadrupolar configuration. The time-dependent evolution of the magnetic field distribution and total nonthermal energy derived from the microwave spectra is also consistent with the standard picture of multiple magnetic reconnections recurring at a magnetic null point that forms above the magnetic quadrupoles and moves up with time.

  14. Spatially Resolved Energetic Electron Properties for the 21 May 2004 Flare from Radio Observations and 3D Simulations

    NASA Astrophysics Data System (ADS)

    Kuznetsov, A. A.; Kontar, E. P.

    2015-01-01

    We investigated in detail the 21 May 2004 flare using simultaneous observations of the Nobeyama Radioheliograph, the Nobeyama Radiopolarimeters, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and the Solar and Heliospheric Observatory (SOHO). The flare images in different spectral ranges reveal a well-defined single flaring loop in this event. We simulated the gyrosynchrotron microwave emission using the recently developed interactive IDL tool GX Simulator. By comparing the simulation results with the observations, we deduced the spatial and spectral properties of the non-thermal electron distribution. The microwave emission has been found to be produced by the high-energy electrons (> 100 keV) with a relatively hard spectrum ( δ≃2); the electrons were strongly concentrated near the loop top. At the same time, the number of high-energy electrons near the footpoints was too low to be detected in the RHESSI images and spatially unresolved data. The SOHO Extreme-ultraviolet Imaging Telescope images and the low-frequency microwave spectra suggest the presence of an extended "envelope" of the loop with lower magnetic field. Most likely, the energetic electron distribution in the considered flare reflects the localized (near the loop top) particle acceleration (injection) process accompanied by trapping and scattering.

  15. Modeling Flare Hard X-ray Emission from Electrons in Contracting Magnetic Islands

    NASA Astrophysics Data System (ADS)

    Guidoni, Silvina E.; Allred, Joel C.; Alaoui, Meriem; Holman, Gordon D.; DeVore, C. Richard; Karpen, Judith T.

    2016-05-01

    The mechanism that accelerates particles to the energies required to produce the observed impulsive hard X-ray emission in solar flares is not well understood. It is generally accepted that this emission is produced by a non-thermal beam of electrons that collides with the ambient ions as the beam propagates from the top of a flare loop to its footpoints. Most current models that investigate this transport assume an injected beam with an initial energy spectrum inferred from observed hard X-ray spectra, usually a power law with a low-energy cutoff. In our previous work (Guidoni et al. 2016), we proposed an analytical method to estimate particle energy gain in contracting, large-scale, 2.5-dimensional magnetic islands, based on a kinetic model by Drake et al. (2010). We applied this method to sunward-moving islands formed high in the corona during fast reconnection in a simulated eruptive flare. The overarching purpose of the present work is to test this proposed acceleration model by estimating the hard X-ray flux resulting from its predicted accelerated-particle distribution functions. To do so, we have coupled our model to a unified computational framework that simulates the propagation of an injected beam as it deposits energy and momentum along its way (Allred et al. 2015). This framework includes the effects of radiative transfer and return currents, necessary to estimate flare emission that can be compared directly to observations. We will present preliminary results of the coupling between these models.

  16. Electronic spectra of semiconductor nanocrystals

    SciTech Connect

    Alivisatos, A.P.

    1993-12-31

    Semiconductor nanocrystals smaller than the bulk exciton show substantial quantum confinement effects. Recent experiments including Stark effect, resonance Raman, valence band photoemission, and near edge X-ray adsorption will be used to put together a picture of the nanocrystal electronic states.

  17. THE SOLAR FLARE CHLORINE ABUNDANCE FROM RESIK X-RAY SPECTRA

    SciTech Connect

    Sylwester, B.; Sylwester, J.; Phillips, K. J. H.; Kuznetsov, V. D. E-mail: js@cbk.pan.wroc.pl E-mail: kvd@izmiran.ru

    2011-09-01

    The abundance of chlorine is determined from X-ray spectra obtained with the RESIK instrument on CORONAS-F during solar flares between 2002 and 2003. Using weak lines of He-like Cl, Cl XVI, between 4.44 and 4.50 A, and with temperatures and emission measures from GOES on an isothermal assumption, we obtained A(Cl) = 5.75 {+-} 0.26 on a scale A(H) = 12. The uncertainty reflects an approximately a factor of two scatter in measured line fluxes. Nevertheless, our value represents what is probably the best solar determination yet obtained. It is higher by factors of 1.8 and 2.7 than Cl abundance estimates from an infrared sunspot spectrum and nearby H II regions. The constancy of the RESIK abundance values over a large range of flares (GOES class from below C1 to X1) argues for any fractionation that may be present in the low solar atmosphere to be independent of the degree of solar activity.

  18. Relativistic Electrons Produced by Reconnecting Electric Fields in a Laser-driven Bench-top Solar Flare

    NASA Astrophysics Data System (ADS)

    Zhong, J. Y.; Lin, J.; Li, Y. T.; Wang, X.; Li, Y.; Zhang, K.; Yuan, D. W.; Ping, Y. L.; Wei, H. G.; Wang, J. Q.; Su, L. N.; Li, F.; Han, B.; Liao, G. Q.; Yin, C. L.; Fang, Y.; Yuan, X.; Wang, C.; Sun, J. R.; Liang, G. Y.; Wang, F. L.; Ding, Y. K.; He, X. T.; Zhu, J. Q.; Sheng, Z. M.; Li, G.; Zhao, G.; Zhang, J.

    2016-08-01

    Laboratory experiments have been carried out to model the magnetic reconnection process in a solar flare with powerful lasers. Relativistic electrons with energy up to megaelectronvolts are detected along the magnetic separatrices bounding the reconnection outflow, which exhibit a kappa-like distribution with an effective temperature of ∼109 K. The acceleration of non-thermal electrons is found to be more efficient in the case with a guide magnetic field (a component of a magnetic field along the reconnection-induced electric field) than in the case without a guide field. Hardening of the spectrum at energies ≥500 keV is observed in both cases, which remarkably resembles the hardening of hard X-ray and γ-ray spectra observed in many solar flares. This supports a recent proposal that the hardening in the hard X-ray and γ-ray emissions of solar flares is due to a hardening of the source-electron spectrum. We also performed numerical simulations that help examine behaviors of electrons in the reconnection process with the electromagnetic field configurations occurring in the experiments. The trajectories of non-thermal electrons observed in the experiments were well duplicated in the simulations. Our numerical simulations generally reproduce the electron energy spectrum as well, except for the hardening of the electron spectrum. This suggests that other mechanisms such as shock or turbulence may play an important role in the production of the observed energetic electrons.

  19. Relativistic Electrons Produced by Reconnecting Electric Fields in a Laser-driven Bench-top Solar Flare

    NASA Astrophysics Data System (ADS)

    Zhong, J. Y.; Lin, J.; Li, Y. T.; Wang, X.; Li, Y.; Zhang, K.; Yuan, D. W.; Ping, Y. L.; Wei, H. G.; Wang, J. Q.; Su, L. N.; Li, F.; Han, B.; Liao, G. Q.; Yin, C. L.; Fang, Y.; Yuan, X.; Wang, C.; Sun, J. R.; Liang, G. Y.; Wang, F. L.; Ding, Y. K.; He, X. T.; Zhu, J. Q.; Sheng, Z. M.; Li, G.; Zhao, G.; Zhang, J.

    2016-08-01

    Laboratory experiments have been carried out to model the magnetic reconnection process in a solar flare with powerful lasers. Relativistic electrons with energy up to megaelectronvolts are detected along the magnetic separatrices bounding the reconnection outflow, which exhibit a kappa-like distribution with an effective temperature of ˜109 K. The acceleration of non-thermal electrons is found to be more efficient in the case with a guide magnetic field (a component of a magnetic field along the reconnection-induced electric field) than in the case without a guide field. Hardening of the spectrum at energies ≥500 keV is observed in both cases, which remarkably resembles the hardening of hard X-ray and γ-ray spectra observed in many solar flares. This supports a recent proposal that the hardening in the hard X-ray and γ-ray emissions of solar flares is due to a hardening of the source-electron spectrum. We also performed numerical simulations that help examine behaviors of electrons in the reconnection process with the electromagnetic field configurations occurring in the experiments. The trajectories of non-thermal electrons observed in the experiments were well duplicated in the simulations. Our numerical simulations generally reproduce the electron energy spectrum as well, except for the hardening of the electron spectrum. This suggests that other mechanisms such as shock or turbulence may play an important role in the production of the observed energetic electrons.

  20. Electron spectra derived from depth dose distributions.

    PubMed

    Faddegon, B A; Blevis, I

    2000-03-01

    The technique of extracting electron energy spectra from measured distributions of dose along the central axis of clinical electron beams is explored in detail. Clinical spectra measured with this simple spectroscopy tool are shown to be sufficient in accuracy and resolution for use in Monte Carlo treatment planning. A set of monoenergetic depth dose curves of appropriate energy spacing, precalculated with Monte Carlo for a simple beam model, are unfolded from the measured depth dose curve. The beam model is comprised of a point electron and photon source placed in vacuum with a source-to-surface distance of 100 cm. Systematic error introduced by this model affects the calculated depth dose curve by no more than 2%/2 mm. The component of the dose due to treatment head bremsstrahlung, subtracted prior to unfolding, is estimated from the thin-target Schiff spectrum within 0.3% of the maximum total dose (from electrons and photons) on the beam axis. Optimal unfolding parameters are chosen, based on physical principles. Unfolding is done with the public-domain code FERDO. Comparisons were made to previously published spectra measured with magnetic spectroscopy and to spectra we calculated with Monte Carlo treatment head simulation. The approach gives smooth spectra with an average resolution for the 27 beams studied of 16+/-3% of the mean peak energy. The mean peak energy of the magnetic spectrometer spectra was calculated within 2% for the AECL T20 scanning beam accelerators, 3% for the Philips SL25 scattering foil based machine. The number of low energy electrons in Monte Carlo spectra is estimated by unfolding with an accuracy of 2%, relative to the total number of electrons in the beam. Central axis depth dose curves calculated from unfolded spectra are within 0.5%/0.5 mm of measured and simulated depth dose curves, except near the practical range, where 1%/1 mm errors are evident. PMID:10757603

  1. TIME-RESOLVED PROPERTIES AND GLOBAL TRENDS IN dMe FLARES FROM SIMULTANEOUS PHOTOMETRY AND SPECTRA

    SciTech Connect

    Kowalski, Adam F.; Hawley, Suzanne L.; Davenport, James R. A.; Wisniewski, John P.; Osten, Rachel A.; Hilton, Eric J.; Holtzman, Jon A.; Schmidt, Sarah J.

    2013-07-15

    We present a homogeneous analysis of line and continuum emission from simultaneous high-cadence spectra and photometry covering near-ultraviolet and optical wavelengths for 20 M dwarf flares. These data were obtained to study the white-light continuum components at bluer and redder wavelengths than the Balmer jump. Our goals were to break the degeneracy between emission mechanisms that have been fit to broadband colors of flares and to provide constraints for radiative-hydrodynamic (RHD) flare models that seek to reproduce the white-light flare emission. The main results from the analysis are the following: (1) the detection of Balmer continuum (in emission) that is present during all flares and with a wide range of relative contributions to the continuum flux at bluer wavelengths than the Balmer jump; (2) a blue continuum at flare maximum that is linearly decreasing with wavelength from {lambda} = 4000-4800 A, indicative of hot, blackbody emission with typical temperatures of T{sub BB} {approx} 9000-14, 000 K; (3) a redder continuum apparent at wavelengths longer than H{beta} ({lambda} {approx}> 4900 A) which becomes relatively more important to the energy budget during the late gradual phase. The hot blackbody component and redder continuum component have been detected in previous studies of flares. However, we have found that although the hot blackbody emission component is relatively well-represented by a featureless, single-temperature Planck function, this component includes absorption features and has a continuum shape strikingly similar to the spectrum of an A-type star as directly observed in our flare spectra. New model constraints are presented for the time evolution among the hydrogen Balmer lines and between Ca II K and the blackbody continuum emission. We calculate Balmer jump flux ratios and compare to the solar-type flare heating predictions from RHD models. The model ratios are too large and the blue-optical ({lambda} = 4000-4800 A) slopes are too

  2. Comparing Solar-Flare Acceleration of >-20 MeV Protons and Electrons Above Various Energies

    NASA Technical Reports Server (NTRS)

    Shih, Albert Y.

    2010-01-01

    A large fraction (up to tens of percent) of the energy released in solar flares goes into accelerated ions and electrons, and studies indicate that these two populations have comparable energy content. RHESSI observations have shown a striking close linear correlation between the 2.223 MeV neutron-capture gamma-ray line and electron bremsstrahlung emission >300 keV, indicating that the flare acceleration of >^20 MeV protons and >300 keV electrons is roughly proportional over >3 orders of magnitude in fluence. We show that the correlations of neutron-capture line fluence with GOES class or with bremsstrahlung emission at lower energies show deviations from proportionality, primarily for flares with lower fluences. From analyzing thirteen flares, we demonstrate that there appear to be two classes of flares with high-energy acceleration: flares that exhibit only proportional acceleration of ions and electrons down to 50 keV and flares that have an additional soft, low-energy bremsstrahlung component, suggesting two separate populations of accelerated electrons. We use RHESSI spectroscopy and imaging to investigate a number of these flares in detail.

  3. Extreme Ultraviolet Spectra of Solar Flares from the Extreme Ultraviolet Spectroheliograph SPIRIT Onboard the CORONAS-F Satellite

    NASA Astrophysics Data System (ADS)

    Shestov, S.; Reva, A.; Kuzin, S.

    2014-01-01

    We present detailed extreme ultraviolet (EUV) spectra of four large solar flares: M5.6, X1.3, X3.4, and X17 classes in the spectral ranges 176-207 Å and 280-330 Å. These spectra were obtained by the slitless spectroheliograph SPIRIT onboard the CORONAS-F satellite. To our knowledge, these are the first detailed EUV spectra of large flares obtained with a spectral resolution of ~0.1 Å. We performed a comprehensive analysis of the obtained spectra and provide identification of the observed spectral lines. The identification was performed based on the calculation of synthetic spectra (the CHIANTI database was used), with simultaneous calculations of the differential emission measure (DEM) and density of the emitting plasma. More than 50 intense lines are present in the spectra that correspond to a temperature range of T = 0.5-16 MK most of the lines belong to Fe, Ni, Ca, Mg, and Si ions. In all the considered flares, intense hot lines from Ca XVII, Ca XVIII, Fe XX, Fe XXII, and Fe XXIV are observed. The calculated DEMs have a peak at T ~ 10 MK. The densities were determined using Fe XI-Fe XIII lines and averaged 6.5 × 109 cm-3. We also discuss the identification, accuracy, and major discrepancies of the spectral line intensity prediction.

  4. Extreme ultraviolet spectra of solar flares from the extreme ultraviolet spectroheliograph SPIRIT onboard the CORONAS-F satellite

    SciTech Connect

    Shestov, S.; Kuzin, S.; Reva, A.

    2014-01-01

    We present detailed extreme ultraviolet (EUV) spectra of four large solar flares: M5.6, X1.3, X3.4, and X17 classes in the spectral ranges 176-207 Å and 280-330 Å. These spectra were obtained by the slitless spectroheliograph SPIRIT onboard the CORONAS-F satellite. To our knowledge, these are the first detailed EUV spectra of large flares obtained with a spectral resolution of ∼0.1 Å. We performed a comprehensive analysis of the obtained spectra and provide identification of the observed spectral lines. The identification was performed based on the calculation of synthetic spectra (the CHIANTI database was used), with simultaneous calculations of the differential emission measure (DEM) and density of the emitting plasma. More than 50 intense lines are present in the spectra that correspond to a temperature range of T = 0.5-16 MK; most of the lines belong to Fe, Ni, Ca, Mg, and Si ions. In all the considered flares, intense hot lines from Ca XVII, Ca XVIII, Fe XX, Fe XXII, and Fe XXIV are observed. The calculated DEMs have a peak at T ∼ 10 MK. The densities were determined using Fe XI-Fe XIII lines and averaged 6.5 × 10{sup 9} cm{sup –3}. We also discuss the identification, accuracy, and major discrepancies of the spectral line intensity prediction.

  5. A Test of Thick-Target Nonuniform Ionization as an Explanation for Breaks in Solar Flare Hard X-Ray Spectra

    NASA Technical Reports Server (NTRS)

    Holman, gordon; Dennis Brian R.; Tolbert, Anne K.; Schwartz, Richard

    2010-01-01

    Solar nonthermal hard X-ray (HXR) flare spectra often cannot be fitted by a single power law, but rather require a downward break in the photon spectrum. A possible explanation for this spectral break is nonuniform ionization in the emission region. We have developed a computer code to calculate the photon spectrum from electrons with a power-law distribution injected into a thick-target in which the ionization decreases linearly from 100% to zero. We use the bremsstrahlung cross-section from Haug (1997), which closely approximates the full relativistic Bethe-Heitler cross-section, and compare photon spectra computed from this model with those obtained by Kontar, Brown and McArthur (2002), who used a step-function ionization model and the Kramers approximation to the cross-section. We find that for HXR spectra from a target with nonuniform ionization, the difference (Delta-gamma) between the power-law indexes above and below the break has an upper limit between approx.0.2 and 0.7 that depends on the power-law index delta of the injected electron distribution. A broken power-law spectrum with a. higher value of Delta-gamma cannot result from nonuniform ionization alone. The model is applied to spectra obtained around the peak times of 20 flares observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI from 2002 to 2004 to determine whether thick-target nonuniform ionization can explain the measured spectral breaks. A Monte Carlo method is used to determine the uncertainties of the best-fit parameters, especially on Delta-gamma. We find that 15 of the 20 flare spectra require a downward spectral break and that at least 6 of these could not be explained by nonuniform ionization alone because they had values of Delta-gamma with less than a 2.5% probability of being consistent with the computed upper limits from the model. The remaining 9 flare spectra, based on this criterion, are consistent with the nonuniform ionization model.

  6. Characteristics of hard X-ray spectra of impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Dulk, G. A.; Kiplinger, A. L.; Winglee, R. M.

    1992-01-01

    The typical characteristics of the hard X-ray emission of impulsive solar flares are examined. At times of hard X-ray peaks, spectra that break downward are the rule rather than the exception. The break energy is typically at about 100 keV and rarely exceed 150 keV. There is little or no dependence of spectral slopes or of the break energy on the hard X-ray fluxes. During the burst decay phases, there is a strong tendency for the spectra to evolve to either a single power law or to cross over to one that breaks upward. The break energy is usually lower after the crossover, but in about 30 percent of the cases it is higher. During the rise phase of many fast bursts, the rise in flux at high energies occurs later than that at lower energies. In most cases the high-energy flux catches up by the time of the burst peak and the lag is rarely or never observed in bursts whose rise time is more than about 10 s.

  7. Spectra of electron oscillations in magnetoplasmadynamic thruster

    NASA Astrophysics Data System (ADS)

    Kirdyashev, K. P.; Kubarev, Yu. V.

    2012-03-01

    The intensity and spectra of electron oscillations in magnetoplasmadynamic (MPD) thruster have been experimentally studied. Oscillatory regimes corresponding to various relations between the relative gradients of magnetic field, electron concentration, and residual gas pressure in the vacuum chamber of the experimental setup have been determined. Relationship between the regimes of excitation of electron oscillations, the formation of an azimuthal current, and a change in the plasma flow potential is revealed. Model notions about the instability of plasma flow on low- and high-frequency branches of electron oscillations are developed.

  8. Origin of electron spectra and its characteristics

    NASA Astrophysics Data System (ADS)

    Mineev, Yu. V.

    This work presents the data on differential energy spectra of cosmic electrons with energies 0.1-6.0 MeV from the Pioneer-8-11, Prognoz-4-10, IMP-6,7,8, and Intercosmos-19 (polar cap measurements) spacecraft during 1975-1998. Some different sources of energetic electron are discussed. Analysis of the spectra permits a conclusion about a preferential contribution of galactic, solar and Jupiterian sources, depending on energies and on time of measurements. The dependencies of the sign and values of north-south asymmetry on the sector structure of the interplanetary magnetic field are obtained. The asymmetry sign and the size of cosmic electron fluxes for the above energies are compared with the earlier data in the high and low electron energy ranges for solar cycles 21-22.

  9. Soft X-ray diagnostics of electron-heated solar flare atmospheres

    NASA Technical Reports Server (NTRS)

    Li, Peng; Emslie, A. Gordon; Mariska, John T.

    1989-01-01

    The dependence of the impulsive-phase Ca XIX w line profile on the form of the flare energy input (assumed to be due to the collisional degradation of a beam of high-energy electrons) is considered. The injected flux spectrum has the form of a power law with a low-energy 'knee', and the effects of varying the total energy flux, spectral index, and knee energy on the w line profile during the impulsive phase have been evaluated. Early in the burst, blueshifts of order 400 km/s are noted, and the peak intensity of the blueshifted component together with spatially unresolved hard X-ray burst spectra can be used to determine the beam filling factor.

  10. An investigation of solar flares and associated solar radio bursts on ionospheric total electron content

    NASA Astrophysics Data System (ADS)

    Uwamahoro, Jean

    2016-07-01

    Solar transients events such as Coronal Mass Ejections (CMEs) and solar flares represent are the cause of various aspects of space weather and can impact the modern man made technological system. Such solar transients are often associated with solar radio bursts (SRBs), particularly of type II and III that , at ground level can be detected by the CALLISTO (Compact Astronomical Low-frequency Low-cost Instrument for Spectroscopy and Transportable Observatories) solar spectrometer. The present study aims at investigating solar flares and associated SRBs impact on the ionospheric total electron content (TEC). SRBs data used are dynamic spectra covering the 2014-2015 period and detected by the CALLISTO instrument that is installed at the university of Rwanda, Kigali. To investigate ionospheric impact, we use TEC data from IGS stations located at almost the same universal time zone, and correlate the observed TEC changes to the corresponding observed solar bursts events. Preliminary observations resulting from this study indicate a slight enhancement in TEC during the burst event days. The observed TEC enhancement on the burst day can be associated to increased UV and X-rays radiations and particle acceleration that are associated with SRBs events. This work is a contribution to more understanding of the geo-space impact of solar transients phenomena for modeling and prediction.

  11. An investigation of solar flares and associated solar radio bursts impact on ionospheric total electron content

    NASA Astrophysics Data System (ADS)

    Tuyizere, Sarathiel

    2016-07-01

    Solar transients events such as Coronal Mass Ejections (CMEs) and solar flares represent the cause of various aspects of space weather and can impact the modern man made technological system. Such solar transients are often associated with solar radio bursts (SRBs), particularly of type II and III that , at ground level can be detected by the CALLISTO (Compact Astronomical Low-frequency Low-cost Instrument for Spectroscopy and Transportable Observatories) solar spectrometer. The present study aims at investigating solar flares and associated SRBs impact on the ionospheric total electron content (TEC). SRBs data used are dynamic spectra covering the 2014-2015 period and detected by the CALLISTO instrument that is installed at the university of Rwanda, Kigali. To investigate ionospheric impact, we use TEC data from IGS stations located at almost the same universal time zone, and correlate the observed TEC changes to the corresponding observed solar bursts events. Preliminary observations resulting from this study indicate a slight enhancement in TEC during the burst event days. The observed TEC enhancement on the burst day can be associated to increased UV and X-rays radiations and particle acceleration that are associated with SRBs events. This work is a contribution to more understanding of the geo-space impact of solar transients phenomena for modeling and prediction.

  12. Inner-shell transitions in Fe XIX-XXII in the X-ray spectra of solar flares and Tokamaks

    NASA Technical Reports Server (NTRS)

    Phillips, K. J. H.; Lemen, J. R.; Cowan, R. D.; Doschek, G. A.; Leibacher, J. W.

    1983-01-01

    Calculated spectra of the ions Fe XIX-XXII for various densities and temperatures are presented, thereby extending the work begun by Doschek, Feldman, and Cowan (1981). The calculations are based on a code (the Cowan code) that computes both the level structure of an ion and intensity factors for the 1s-2p satellite lines. A comparison is made between the calculated spectra and those observed in solar flares by the P78-1 and SMM instruments. The observed intensities of Fe XX lines, which are the most sensitive to density, are found to agree well with those calculated in the low-density limit. The agreement for lines arising from other ions is also very good. It is also seen that the predicted density variations in Fe XX are confirmed by the higher density Princeton Large Torus plasmas. Thus a possible useful density diagnostic is indicated for tokamak and high-density astrophysical plasmas, perhaps including some solar flares.

  13. Extreme Ultraviolet Radiation Flux Changes and Total Electron Content Enhancement During Solar Flares

    NASA Astrophysics Data System (ADS)

    Kelley, T. P.; Zhang, S.; Coster, A. J.

    2011-12-01

    Solar flares induce sudden changes in X-ray irradiance and EUV flux. The possibility of a correlation between these changes and the daytime global value of total electron content (TEC) is investigated through the use of data from the GPS, SOHO, and GOES satellites. The Millstone Hill Incoherent Scatter Radar (ISR) is used to investigate the altitude stratification of the flare induced TEC enhancement. A study is conducted for the months of October 2002 and September 2005 as they had 329 and 114 flares, respectively. The amount of TEC enhancement due to a solar flare is found to be dependent on solar activity, solar flare strength, and the background TEC. On average, October 2002 had solar flares of less strength and higher solar activity. Flare effects were more evident in September 2005 which had on average, a small background TEC (10-15 TECu) and prominent (~2 TECu) TEC enhancements. In addition, a high and positive correlation between X-ray irradiance and EUV flux was seen during solar flare events. Through the comparison of the different data sets, it is found that the majority of the TEC enhancement is in the E and F regions (100-150 km) which corresponds to the portion of the ionosphere ionized by EUV radiation.

  14. HF Accelerated Electron Fluxes, Spectra, and Ionization

    NASA Astrophysics Data System (ADS)

    Carlson, Herbert C.; Jensen, Joseph B.

    2015-10-01

    Wave particle interactions, an essential aspect of laboratory, terrestrial, and astrophysical plasmas, have been studied for decades by transmitting high power HF radio waves into Earth's weakly ionized space plasma, to use it as a laboratory without walls. Application to HF electron acceleration remains an active area of research (Gurevich in Usp Fizicheskikh Nauk 177(11):1145-1177, 2007) today. HF electron acceleration studies began when plasma line observations proved (Carlson et al. in J Atmos Terr Phys 44:1089-1100, 1982) that high power HF radio wave-excited processes accelerated electrons not to ~eV, but instead to -100 times thermal energy (10 s of eV), as a consequence of inelastic collision effects on electron transport. Gurevich et al (J Atmos Terr Phys 47:1057-1070, 1985) quantified the theory of this transport effect. Merging experiment with theory in plasma physics and aeronomy, enabled prediction (Carlson in Adv Space Res 13:1015-1024, 1993) of creating artificial ionospheres once ~GW HF effective radiated power could be achieved. Eventual confirmation of this prediction (Pedersen et al. in Geophys Res Lett 36:L18107, 2009; Pedersen et al. in Geophys Res Lett 37:L02106, 2010; Blagoveshchenskaya et al. in Ann Geophys 27:131-145, 2009) sparked renewed interest in optical inversion to estimate electron spectra in terrestrial (Hysell et al. in J Geophys Res Space Phys 119:2038-2045, 2014) and planetary (Simon et al. in Ann Geophys 29:187-195, 2011) atmospheres. Here we present our unpublished optical data, which combined with our modeling, lead to conclusions that should meaningfully improve future estimates of the spectrum of HF accelerated electron fluxes. Photometric imaging data can significantly improve detection of emissions near ionization threshold, and confirm depth of penetration of accelerated electrons many km below the excitation altitude. Comparing observed to modeled emission altitude shows future experiments need electron density profiles

  15. Stochastic acceleration of electrons by fast magnetosonic waves in solar flares: the effects of anisotropy in velocity and wavenumber space

    SciTech Connect

    Pongkitiwanichakul, Peera; Chandran, Benjamin D. G.

    2014-11-20

    We develop a model for stochastic acceleration of electrons in solar flares. As in several previous models, the electrons are accelerated by turbulent fast magnetosonic waves ({sup f}ast waves{sup )} via transit-time-damping (TTD) interactions. (In TTD interactions, fast waves act like moving magnetic mirrors that push the electrons parallel or anti-parallel to the magnetic field). We also include the effects of Coulomb collisions and the waves' parallel electric fields. Unlike previous models, our model is two-dimensional in both momentum space and wavenumber space and takes into account the anisotropy of the wave power spectrum F{sub k} and electron distribution function f {sub e}. We use weak turbulence theory and quasilinear theory to obtain a set of equations that describes the coupled evolution of F{sub k} and f {sub e}. We solve these equations numerically and find that the electron distribution function develops a power-law-like non-thermal tail within a restricted range of energies E in (E {sub nt}, E {sub max}). We obtain approximate analytic expressions for E {sub nt} and E {sub max}, which describe how these minimum and maximum energies depend upon parameters such as the electron number density and the rate at which fast-wave energy is injected into the acceleration region at large scales. We contrast our results with previous studies that assume that F{sub k} and f {sub e} are isotropic, and we compare one of our numerical calculations with the time-dependent hard-X-ray spectrum observed during the 1980 June 27 flare. In our numerical calculations, the electron energy spectra are softer (steeper) than in models with isotropic F{sub k} and f {sub e} and closer to the values inferred from observations of solar flares.

  16. OBSERVATION OF HEATING BY FLARE-ACCELERATED ELECTRONS IN A SOLAR CORONAL MASS EJECTION

    SciTech Connect

    Glesener, Lindsay; Bain, Hazel M.; Krucker, Säm; Lin, Robert P.

    2013-12-20

    We report a Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observation of flare-accelerated electrons in the core of a coronal mass ejection (CME) and examine their role in heating the CME. Previous CME observations have revealed remarkably high thermal energies that can far surpass the CME's kinetic energy. A joint observation by RHESSI and the Atmospheric Imaging Assembly of a partly occulted flare on 2010 November 3 allows us to test the hypothesis that this excess energy is collisionally deposited by flare-accelerated electrons. Extreme ultraviolet (EUV) images show an ejection forming the CME core and sheath, with isothermal multifilter analysis revealing temperatures of ∼11 MK in the core. RHESSI images reveal a large (∼100 × 50 arcsec{sup 2}) hard X-ray (HXR) source matching the location, shape, and evolution of the EUV plasma, indicating that the emerging CME is filled with flare-accelerated electrons. The time derivative of the EUV emission matches the HXR light curve (similar to the Neupert effect observed in soft and HXR time profiles), directly linking the CME temperature increase with the nonthermal electron energy loss, while HXR spectroscopy demonstrates that the nonthermal electrons contain enough energy to heat the CME. This is the most direct observation to date of flare-accelerated electrons heating a CME, emphasizing the close relationship of the two in solar eruptive events.

  17. Statistical analysis of the dynamics of secondary electrons in the flare of a high-voltage beam-type discharge

    SciTech Connect

    Demkin, V. P.; Mel'nichuk, S. V.

    2014-09-15

    In the present work, results of investigations into the dynamics of secondary electrons with helium atoms in the presence of the reverse electric field arising in the flare of a high-voltage pulsed beam-type discharge and leading to degradation of the primary electron beam are presented. The electric field in the discharge of this type at moderate pressures can reach several hundred V/cm and leads to considerable changes in the kinetics of secondary electrons created in the process of propagation of the electron beam generated in the accelerating gap with a grid anode. Moving in the accelerating electric field toward the anode, secondary electrons create the so-called compensating current to the anode. The character of electron motion and the compensating current itself are determined by the ratio of the field strength to the concentration of atoms (E/n). The energy and angular spectra of secondary electrons are calculated by the Monte Carlo method for different ratios E/n of the electric field strength to the helium atom concentration. The motion of secondary electrons with threshold energy is studied for inelastic collisions of helium atoms and differential analysis is carried out of the collisional processes causing energy losses of electrons in helium for different E/n values. The mechanism of creation and accumulation of slow electrons as a result of inelastic collisions of secondary electrons with helium atoms and selective population of metastable states of helium atoms is considered. It is demonstrated that in a wide range of E/n values the motion of secondary electrons in the beam-type discharge flare has the character of drift. At E/n values characteristic for the discharge of the given type, the drift velocity of these electrons is calculated and compared with the available experimental data.

  18. Statistical analysis of the dynamics of secondary electrons in the flare of a high-voltage beam-type discharge

    NASA Astrophysics Data System (ADS)

    Demkin, V. P.; Mel'nichuk, S. V.

    2014-09-01

    In the present work, results of investigations into the dynamics of secondary electrons with helium atoms in the presence of the reverse electric field arising in the flare of a high-voltage pulsed beam-type discharge and leading to degradation of the primary electron beam are presented. The electric field in the discharge of this type at moderate pressures can reach several hundred V/cm and leads to considerable changes in the kinetics of secondary electrons created in the process of propagation of the electron beam generated in the accelerating gap with a grid anode. Moving in the accelerating electric field toward the anode, secondary electrons create the so-called compensating current to the anode. The character of electron motion and the compensating current itself are determined by the ratio of the field strength to the concentration of atoms (Е/n). The energy and angular spectra of secondary electrons are calculated by the Monte Carlo method for different ratios E/n of the electric field strength to the helium atom concentration. The motion of secondary electrons with threshold energy is studied for inelastic collisions of helium atoms and differential analysis is carried out of the collisional processes causing energy losses of electrons in helium for different E/n values. The mechanism of creation and accumulation of slow electrons as a result of inelastic collisions of secondary electrons with helium atoms and selective population of metastable states of helium atoms is considered. It is demonstrated that in a wide range of E/n values the motion of secondary electrons in the beam-type discharge flare has the character of drift. At E/n values characteristic for the discharge of the given type, the drift velocity of these electrons is calculated and compared with the available experimental data.

  19. Impact of X-class solar flares on the ionospheric Total Electron Content over low latitude stations in India

    NASA Astrophysics Data System (ADS)

    Chakraborty, Monti; Kumar, Sanjay; Guha, Anirban; De, Barin Kumar

    X-rays, UV radiation and Coronal mass emitted during solar flares can affect the Earth's ionosphere and disrupt long-range radio communications. The present study investigates the effects of solar flares on the ionospheric Total Electron Content (TEC) with the help of global positioning system (GPS) data from low latitude stations in India located within the EIA region. Two X-class solar flares on 05th and 08th November 2013 have been selected for the present study. A significant enhancement in TEC is observed at regions around the EIA crest region during the flare and this enhancement is attributed to (a) the flare related EUV flux enhancement and consequent increased production of ionization, and (b) flare induced changes in the equatorial electrodynamics which in turn modifies ionospheric altitude profile of plasma via E × B drift mechanism. The supporting data from COSMIC electron density profile is also used to confirm the flare time enhancement.

  20. Electron precipitation and mass motion in the 1991 June 9 white-light flare

    NASA Technical Reports Server (NTRS)

    Dela Beaujardiere, J. -F.; Canfield, R. C.; Metcalf, T. R.; Hiei, E.; Sakurai, T.; Ichimoto, K.

    1994-01-01

    We use H alpha line profiles as a diagnostic of mass motion and nonthermal electron precipitation in the white-light flare (WLF) of 1991 June 9 01:34 UT. We find only weak downflow velocities (approximately equals 10km/s) at the site of white-light emission, and comparable velocities elsewhere. We also find that electron precipitation is strongest at the WLF site. We conclude that continuum emission in this flare was probably caused by nonthermal electrons and not by dynamical energy transport via a chromospheric condensation.

  1. A comparison of helium and heavy ion spectra in He/3/ rich solar flares with a model calculation

    NASA Technical Reports Server (NTRS)

    Mobius, E.; Hovestadt, D.; Klecker, B.; Scholer, M.; Gloeckler, G.

    1981-01-01

    He isotopes, O and Fe in He(3) rich solar flares are studied during the 1977 to 1979 period with the MPI/UoMd particle experiment on ISEE-1 and ISEE-3. The study revealed that the He(3) spectrum is generally harder than that of He(4), and the O spectrum is harder than that of Fe. The spectra are compared with a stationary model based on stochastic Fermi acceleration in Alfven turbulence including a rigidity dependent particle loss. Model calculations fit the He(3) and He(4) spectra between 0.4 and 4.0 MeV/nucleon, with discrepancies at lower and higher energies, and the O and Fe spectra cannot be fitted simultaneously.

  2. Electron acceleration at slow-mode shocks in the magnetic reconnection region in solar flares

    NASA Astrophysics Data System (ADS)

    Mann, Gottfried; Aurass, Henry; Onel, Hakan; Warmuth, Alexander

    2016-04-01

    A solar flare appears as an sudden enhancement of the emission of electromagnetic radiation of the Sun covering a broad range of the spectrum from the radio up to the gamma-ray range. That indicates the generation of energetic electrons during flares, which are considered as the manifestation of magnetic reconnection in the solar corona. Spacecraft observations in the Earth's magnetosphere, as for instance by NASA's MMS mission, have shown that electrons can efficiently accelerated at the slow-mode shocks occuring in the magnetic reconnection region. This mechanism is applied to solar flares. The electrons are accelerated by the cross-shock potential at slow-mode shocks resulting in magnetic field aligned beams of energetic electrons in the downstream region. The interaction of this electron beam with the plasma leads to the excitation of whistler waves and, subsequently, to a strong heating of the electrons in the downstream region. Considering this process under coronal circumstances, enough electrons with energies >30keV are generated in the magnetic reconnection region as required for the hard X-ray radiation during solar flares as observed by NASA's RHESSI mission.

  3. Electron Densities in Solar Flare Loops, Chromospheric Evaporation Upflows, and Acceleration Sites

    NASA Technical Reports Server (NTRS)

    Aschwanden, Markus J.; Benz, Arnold O.

    1996-01-01

    We compare electron densities measured at three different locations in solar flares: (1) in Soft X-Ray (SXR) loops, determined from SXR emission measures and loop diameters from Yohkoh Soft X-Ray Telescope maps (n(sub e, sup SXR) = (0.2-2.5) x 10(exp 11)/ cu cm); (2) in chromospheric evaporation upflows, inferred from plasma frequency cutoffs of decimetric radio bursts detected with the 0.1-3 GHz spectrometer Phoenix of ETH Zuerich (n(sub e, sup upflow) = (0.3-11) x 10(exp 10)/cu cm; and (3) in acceleration sites, inferred from the plasma frequency at the separatrix between upward-accelerated (type III bursts) and downward-accelerated (reverse-drift bursts) electron beams [n(sub e, sup acc) = (0.6-10) x 10(exp 9)/cu cm]. The comparison of these density measurements, obtained from 44 flare episodes (during 14 different flares), demonstrates the compatibility of flare plasma density diagnostics with SXR and radio methods. The density in the upflowing plasma is found to be somewhat lower than in the filled loops, having ratios in a range n(sub e, sup upflow)/n(sub e, sup SXR) = 0.02-1.3, and a factor of 3.6 higher behind the upflow front. The acceleration sites are found to have a much lower density than the SXR-bright flare loops, i.e., n(sub e, sup acc)/n(sub e, sup SXR) = 0.005- 0.13, and thus must be physically displaced from the SXR-bright flare loops. The scaling law between electron time-of-flight distances l' and loop half-lengths s, l'/s = 1.4 +/- 0.3, recently established by Aschwanden et al. suggests that the centroid of the acceleration region is located above the SXR-bright flare loop, as envisioned in cusp geometries (e.g., in magnetic reconnection models).

  4. The smallest hard X-ray flare?

    NASA Astrophysics Data System (ADS)

    Glesener, Lindsay; Krucker, Sam; Hannah, Iain; Smith, David M.; Grefenstette, Brian; Marsh, Andrew; Hudson, Hugh S.; White, Stephen M.; Chen, Bin

    2016-05-01

    We report a NuSTAR observation of a small solar flare on 2015 September 1, estimated to be on the order of a GOES class A.05 flare in brightness. This flare is fainter than any hard X-ray (HXR) flares in the existing literature, and with a peak rate of only ∼5 counts s‑1 detector‑1 observed by RHESSI, is effectively the smallest that can just barely be detected by the current standard (indirectly imaging) solar HXR instrumentation, though we expect that smaller flares will continue to be discovered as instrumental and observational techniques progress. The flare occurred during a solar observation by the highly sensitive NuSTAR astrophysical HXR spacecraft, which used its direct focusing optics to produce detailed flare spectra and images. The flare exhibits properties commonly observed in larger flares, including a fast rise and more gradual decay, and similar spatial dimensions to the RHESSI microflares. We will discuss the presence of non-thermal (flare-accelerated) electrons during the impulsive phase. The flare is small in emission measure, temperature, and energy, though not in physical dimensions. Its presence is an indication that flares do indeed scale down to smaller energies and retain what we customarily think of as “flarelike” properties.

  5. The collisional relaxation of electrons in hot flaring plasma and inferring the properties of solar flare accelerated electrons from X-ray observations.

    NASA Astrophysics Data System (ADS)

    Jeffrey, N. L. S.; Kontar, E. P.; Emslie, A. G.; Bian, N. H.

    2015-09-01

    X-ray observations are a direct diagnostic of fast electrons produced in solar flares, energized during the energy release process and directed towards the Sun. Since the properties of accelerated electrons can be substantially changed during their transport and interaction with the background plasma, a model must ultimately be applied to X-ray observations in order to understand the mechanism responsible for their acceleration. A cold thick target model is ubiquitously used for this task, since it provides a simple analytic relationship between the accelerated electron spectrum and the emitting electron spectrum in the X-ray source, with the latter quantity readily obtained from X-ray observations. However, such a model is inappropriate for the majority of solar flares in which the electrons propagate in a hot megaKelvin plasma, because it does not take into account the physics of thermalization of fast electrons. The use of a more realistic model, properly accounting for the properties of the background plasma, and the collisional diffusion and thermalization of electrons, can alleviate or even remove many of the traditional problems associated with the cold thick target model and the deduction of the accelerated electron spectrum from X-ray spectroscopy, such as the number problem and the need to impose an ad hoc low energy cut-off.

  6. TEMPERATURE AND ELECTRON DENSITY DIAGNOSTICS OF A CANDLE-FLAME-SHAPED FLARE

    SciTech Connect

    Guidoni, S. E.; Plowman, J. E.

    2015-02-10

    Candle-flame-shaped flares are archetypical structures that provide indirect evidence of magnetic reconnection. A flare resembling Tsuneta's famous 1992 candle-flame flare occurred on 2011 January 28; we present its temperature and electron density diagnostics. This flare was observed with Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), Hinode/X-Ray Telescope (XRT), and Solar Terrestrial Relations Observatory Ahead (STEREO-A)/Extreme Ultraviolet Imager, resulting in high-resolution, broad temperature coverage, and stereoscopic views of this iconic structure. The high-temperature images reveal a brightening that grows in size to form a tower-like structure at the top of the posteruption flare arcade, a feature that has been observed in other long-duration events. Despite the extensive work on the standard reconnection scenario, there is no complete agreement among models regarding the nature of this high-intensity elongated structure. Electron density maps reveal that reconnected loops that are successively connected at their tops to the tower develop a density asymmetry of about a factor of two between the two legs, giving the appearance of ''half-loops''. We calculate average temperatures with a new fast differential emission measure (DEM) method that uses SDO/AIA data and analyze the heating and cooling of salient features of the flare. Using STEREO observations, we show that the tower and the half-loop brightenings are not a line-of-sight projection effect of the type studied by Forbes and Acton. This conclusion opens the door for physics-based explanations of these puzzling, recurrent solar flare features, previously attributed to projection effects. We corroborate the results of our DEM analysis by comparing them with temperature analyses from Hinode/XRT.

  7. Temperature and Electron Density Diagnostics of a Candle-flame-shaped Flare

    NASA Astrophysics Data System (ADS)

    Guidoni, S. E.; McKenzie, D. E.; Longcope, D. W.; Plowman, J. E.; Yoshimura, K.

    2015-02-01

    Candle-flame-shaped flares are archetypical structures that provide indirect evidence of magnetic reconnection. A flare resembling Tsuneta's famous 1992 candle-flame flare occurred on 2011 January 28; we present its temperature and electron density diagnostics. This flare was observed with Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), Hinode/X-Ray Telescope (XRT), and Solar Terrestrial Relations Observatory Ahead (STEREO-A)/Extreme Ultraviolet Imager, resulting in high-resolution, broad temperature coverage, and stereoscopic views of this iconic structure. The high-temperature images reveal a brightening that grows in size to form a tower-like structure at the top of the posteruption flare arcade, a feature that has been observed in other long-duration events. Despite the extensive work on the standard reconnection scenario, there is no complete agreement among models regarding the nature of this high-intensity elongated structure. Electron density maps reveal that reconnected loops that are successively connected at their tops to the tower develop a density asymmetry of about a factor of two between the two legs, giving the appearance of "half-loops." We calculate average temperatures with a new fast differential emission measure (DEM) method that uses SDO/AIA data and analyze the heating and cooling of salient features of the flare. Using STEREO observations, we show that the tower and the half-loop brightenings are not a line-of-sight projection effect of the type studied by Forbes & Acton. This conclusion opens the door for physics-based explanations of these puzzling, recurrent solar flare features, previously attributed to projection effects. We corroborate the results of our DEM analysis by comparing them with temperature analyses from Hinode/XRT.

  8. An improved parameterization of electron heating, with application to an X17 flare

    NASA Astrophysics Data System (ADS)

    Smithtro, C. G.; Solomon, S. C.

    2007-12-01

    Ionospheric models typically rely on parameterizations to account for the effects of secondary ionization and heating by photoelectrons. These parameterizations rely on an assumed form for the input solar irradiance; however, during solar flares the shape of the ionizing spectrum can change dramatically. Solomon and Qian [2005] recently updated the parameterization of secondary ionization to account for spectral changes. In this work, we describe a similar improvement to the parameterization of electron heating. The new algorithm is included in a simple ionospheric model and applied to the X17 flare of 28 Oct 2003. With these changes the modeled electron temperature and neutral gas heating rate are shown to increase significantly over previous results. This has particular relevance to the calculation of flare-induced satellite drag.

  9. Quantum synchrotron spectra from semirelativistic electrons in teragauss magnetic fields

    NASA Technical Reports Server (NTRS)

    Brainerd, J. J.

    1987-01-01

    Synchrotron spectra are calculated from quantum electrodynamic transition rates for thermal and power-law electron distributions. It is shown that quantum effects appear in thermal spectra when the photon energy is greater than the electron temperature, and in power-law spectra when the electron energy in units of the electron rest mass times the magnetic field strength in units of the critical field strength is of order unity. These spectra are compared with spectra calculated from the ultrarelativistic approximation for synchrotron emission. It is found that the approximation for the power-law spectra is good, and the approximation for thermal spectra produces the shape of the spectrum accurately but fails to give the correct normalization. Single photon pair creation masks the quantum effects for power-law distributions, so only modifications to thermal spectra are important for gamma-ray bursts.

  10. Diffusive transport of energetic electrons in the 2004, May 21 solar flare

    NASA Astrophysics Data System (ADS)

    Musset, Sophie; Kontar, Eduard; Vilmer, Nicole

    2016-07-01

    Solar flares are associated with efficient particle acceleration, in particular with the production of energetic electrons which are diagnosed through the X-ray and radio emissions that they produce when interacting with the solar atmosphere. Particle transport from the acceleration sites to the radiation sites remains of the challenging topic in the field of high energy solar physics and has an important impact on the interpretation of the particle emissions in the context of acceleration models. In order to address the transport of flare associated energetic electrons in the low corona, we use imaging spectroscopic observations from RHESSI of the 2004 May 21 solar flare which presents together with the usually observed HXR footpoints a well observed coronal non-thermal X-ray source. The number of X-ray emitting energetic electrons in the coronal source is compared to the number of electrons needed to produce the hard X-ray emission in the footpoints and is found twice as large. Such an excess of the number of electrons in the coronal source cannot be explained in the context of the standard model of X-ray emissions in which the dominant electron transport is collisional. In the present flare, an additional process is needed to explain how energetic electrons can be efficiently trapped in the corona. In the hypothesis of turbulent pitch-angle scattering of hard X-ray producing energetic electrons (Kontar et al, 2014), diffusive transport can indeed lead to a confinement of energetic electrons in the coronal source. Based on this assumption, we estimated for the present event the mean-free path of energetic electrons and found a value of 10^8 - 10^9 meters, much smaller than the size of the observed flaring loop itself. This implies that a diffusive transport of energetic electrons is dominant in this flare which is in good agreement with the results of a previous study based on the gyrosynchrotron emissions from the energetic electrons (Kuznetsov & Kontar, 2015).

  11. Radial Distribution of Electron Spectra from High-Energy Ions

    NASA Technical Reports Server (NTRS)

    Cucinotta, Francis A.; Katz, Robert; Wilson, John W.

    1998-01-01

    The average track model describes the response of physical and biological systems using radial dose distribution as the key physical descriptor. We report on an extension of this model to describe the average distribution of electron spectra as a function of radial distance from an ion. We present calculations of these spectra for ions of identical linear energy transfer (LET), but dissimilar charge and velocity to evaluate the differences in electron spectra from these ions. To illustrate the usefulness of the radial electron spectra for describing effects that are not described by electron dose, we consider the evaluation of the indirect events in microdosimetric distributions for ions. We show that folding our average electron spectra model with experimentally determined frequency distributions for photons or electrons provides a good representation of radial event spectra from high-energy ions in 0.5-2 micrometer sites.

  12. THE n-DISTRIBUTION OF ELECTRONS AND DOUBLE LAYERS IN THE ELECTRON-BEAM-RETURN-CURRENT SYSTEM OF SOLAR FLARES

    SciTech Connect

    Karlicky, Marian

    2012-05-01

    We investigate processes in the electron-beam-return-current system in the impulsive phase of solar flares to answer a question about the formation of the n-electron distribution detected in this phase of solar flares. An evolution of the electron-beam-return-current system with an initial local density depression is studied using a three-dimensional electromagnetic particle-in-cell model. In the system the strong double layer is formed. Its electric field potential increases with the electron beam flux. In this electric field potential, the electrons of background plasma are strongly accelerated and propagate in the return-current direction. The high-energy part of their distribution at the high-potential side of the strong double layer resembles that of the n-distribution. Thus, the detection of the n-distributions, where a form of the high-energy part of the distribution is the most important, can indicate the presence of strong double layers in solar flares. The similarity between processes in solar flare loops and those in the downward current region of the terrestrial aurora, where the double layers were observed by FAST satellite, supports this idea.

  13. Evidence of Electron Acceleration around the Reconnection X-point in a Solar Flare

    NASA Astrophysics Data System (ADS)

    Narukage, Noriyuki; Shimojo, Masumi; Sakao, Taro

    2016-05-01

    Particle acceleration is one of the most significant features that are ubiquitous among space and cosmic plasmas. It is most prominent during flares in the case of the Sun, with which huge amounts of electromagnetic radiation and high-energy particles are expelled into the interplanetary space through acceleration of plasma particles in the corona. Though it has been well understood that energies of flares are supplied by the mechanism called magnetic reconnection based on the observations in X-rays and EUV with space telescopes, where and how in the flaring magnetic field plasmas are accelerated has remained unknown due to the low plasma density in the flaring corona. We here report the first observational identification of the energetic non-thermal electrons around the point of the ongoing magnetic reconnection (X-point), with the location of the X-point identified by soft X-ray imagery and the localized presence of non-thermal electrons identified from imaging-spectroscopic data at two microwave frequencies. Considering the existence of the reconnection outflows that carries both plasma particles and magnetic fields out from the X-point, our identified non-thermal microwave emissions around the X-point indicate that the electrons are accelerated around the reconnection X-point.

  14. Evidence of electron acceleration around the reconnection X-point in a solar flare

    SciTech Connect

    Narukage, Noriyuki; Shimojo, Masumi; Sakao, Taro

    2014-06-01

    Particle acceleration is one of the most significant features that are ubiquitous among space and cosmic plasmas. It is most prominent during flares in the case of the Sun, with which huge amounts of electromagnetic radiation and high-energy particles are expelled into the interplanetary space through acceleration of plasma particles in the corona. Though it has been well understood that energies of flares are supplied by the mechanism called magnetic reconnection based on the observations in X-rays and EUV with space telescopes, where and how in the flaring magnetic field plasmas are accelerated has remained unknown due to the low plasma density in the flaring corona. We here report the first observational identification of the energetic non-thermal electrons around the point of the ongoing magnetic reconnection (X-point), with the location of the X-point identified by soft X-ray imagery and the localized presence of non-thermal electrons identified from imaging-spectroscopic data at two microwave frequencies. Considering the existence of the reconnection outflows that carries both plasma particles and magnetic fields out from the X-point, our identified non-thermal microwave emissions around the X-point indicate that the electrons are accelerated around the reconnection X-point. Additionally, the plasma around the X-point was also thermally heated up to 10 MK. The estimated reconnection rate of this event is ∼0.017.

  15. Solar Flares

    NASA Technical Reports Server (NTRS)

    Shih, Albert

    2011-01-01

    Solar flares accelerate both ions and electrons to high energies, and their X-ray and gamma-ray signatures not only probe the relationship between their respective acceleration, but also allow for the measurement of accelerated and ambient abundances. RHESSI observations have shown a striking close linear correlation of gamma-ray line fluence from accelerated ions > approx.20 MeV and bremsstrahlung emission from relativistic accelerated electrons >300 keV, when integrated over complete flares, suggesting a common acceleration mechanism. SMM/GRS observations, however, show a weaker correlation, and this discrepancy might be associated with previously observed electron-rich episodes within flares and/or temporal variability of gamma-ray line fluxes over the course of flares. We use the latest RHESSI gamma-ray analysis techniques to study the temporal behavior of the RHESSI flares, and determine what changes can be attributed to an evolving acceleration mechanism or to evolving abundances.

  16. Electronic spectra of structurally deformed lutein.

    PubMed

    Macernis, Mindaugas; Sulskus, Juozas; Duffy, Christopher D P; Ruban, Alexander V; Valkunas, Leonas

    2012-10-11

    Quantum chemical calculations have been employed for the investigation of the lowest excited electronic states of lutein, with particular reference to its function within light harvesting antenna complexes of higher plants. Through comparative analysis obtained by using different methods based on gas-phase calculations of the spectra, it was determined that variations in the lengths of the long C-C valence bonds and the dihedral angles of the polyene chain are the dominant factors in determining the spectral properties of Lut 1 and Lut 2 corresponding to the deformed lutein molecules taken from crystallographic data of the major pigment-protein complex of photosystem II. By MNDO-CAS-CI method, it was determined that the two singlet B(u) states of lutein (nominally 1B(u)(-)* and 1B(u)(+)) arise as a result of mixing of the canonical 1B(u)(-) and 1B(u)(+) states of the all-trans polyene due to the presence of the ending rings in lutein. The 1B(u)(-)* state of lutein is optically allowed, while the 1B(u)(-) of a pure all-trans polyene chain is optically forbidden. As demonstrated, the B(u) states are much more sensitive to minor distortions of the conjugated chain due to mixing of the canonical states, resulting in states of poorly defined particle-hole symmetry. Conversely, the A(g) states are relatively robust with respect to geometric distortion, and their respective inversion and particle-hole symmetries remain relatively well-defined. PMID:22974387

  17. The acceleration and propagation of solar flare energetic particles

    NASA Technical Reports Server (NTRS)

    Forman, M. A.; Ramaty, R.; Zweibel, E. G.

    1986-01-01

    A review of the most pertinent data on solar energetic particles is presented, and the implications of the data are discussed, taking into account radio emissions, hard X-rays, gamma rays, energy spectra and electron-proton correlations, chemical compositions, and isotopic and ionic compositions. The mechanisms of solar flare particle acceleration are considered along with solar flare particle spectra in interplanetary space. Attention is given to stochastic acceleration, shock acceleration, acceleration in direct electric fields, the mean free paths of solar electrons and protons in interplanetary space, and an illustration of the probable effect of adiabatic deceleration on the spectra of solar flare ions at the time of maximum.

  18. Energetic electrons from solar flares and associated type 3 radio bursts from metric to hectometric wave frequencies

    NASA Technical Reports Server (NTRS)

    Sakurai, K.

    1972-01-01

    Distinct Kev electron events as observed by satellites near the earth are, in general, associated with solar flares which are accompained by the emission of both metric and hectometric type 3 radio bursts. The positions of these flares are mainly on the western hemisphere of the sun. These results show that Kev electrons propagate under the control of the magnetic field in the interplanetary space and that, while propagating through this space, these electrons excite type 3 radio bursts from metric to hectometric wave frequencies. Emission characteristics of hectometric type 3 bursts are briefly considered in relation to the positions of associated flares.

  19. Impulsive phase of solar flares. I - Characteristics of high energy electrons

    NASA Technical Reports Server (NTRS)

    Leach, J.; Petrosian, V.

    1981-01-01

    The models describing the operative physical processes occurring during the impulsive phase of a solar flare can be broadly classified as thermal or nonthermal models. The current investigation is part of a series of studies which analyze the general characteristics of the 'nonthermal' models. The results are presented of an analysis regarding the steady state distribution of energetic electrons within the flare plasma. The time independent Fokker-Planck equation is used to determine the steady state distribution of the electrons in the ambient plasma. The model investigated encompasses thick-target, thin-target, and trap aspects of nonthermal hard X-ray models. High energy electrons with some initial energy spectrum and pitch angle distribution are injected at a height above the photosphere either into a closed magnetic loop structure or into an open field structure. Some approximate analytic solutions are discussed and the results of a numerical analysis are presented.

  20. Faint Coronal Hard X-rays From Accelerated Electrons in Solar Flares

    NASA Astrophysics Data System (ADS)

    Glesener, Lindsay Erin

    Solar flares are huge explosions on the Sun that release a tremendous amount of energy from the coronal magnetic field, up to 1033 ergs, in a short time (100--1000 seconds), with much of the energy going into accelerated electrons and ions. An efficient acceleration mechanism is needed, but the details of this mechanism remain relatively unknown. A fraction of this explosive energy reaches the Earth in the form of energetic particles, producing geomagnetic storms and posing dangers to spaceborne instruments, astronauts, and Earthbound power grids. There are thus practical reasons, as well as intellectual ones, for wishing to understand this extraordinary form of energy release. Through imaging spectroscopy of the hard X-ray (HXR) emission from solar flares, the behavior of flare-accelerated electrons can be studied. The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI ) spacecraft launched in 2002 with the goal of better understanding flare particle acceleration. Using rotation modulation collimators, RHESSI is able to cover a wide energy range (3 keV--17 MeV) with fine angular and energy resolutions. RHESSI's success in the last 10 years in investigating the relationship between energetic electrons and ions, the nature of faint sources in the corona, the energy distribution of flares, and several other topics have significantly advanced the understanding of flares. But along with the wealth of information revealed by RHESSI come some clear observational challenges. Very few, if any, RHESSI observations have come close to imaging the electron acceleration region itself. This is undoubtedly due to a lack of both sensitivity (HXRs from electron beams in the tenuous corona are faint) and dynamic range (HXR sources at chromospheric flare footpoints are much brighter and tend to obscure faint coronal sources). Greater sensitivity is also required to investigate the role that small flares in the quiet Sun could play in heating the corona. The Focusing Optics

  1. Energetic electron propagation in the decay phase of non-thermal flare emission

    SciTech Connect

    Huang, Jing; Yan, Yihua; Tsap, Yuri T.

    2014-06-01

    On the basis of the trap-plus-precipitation model, the peculiarities of non-thermal emission in the decay phase of solar flares have been considered. The calculation formulas for the escape rate of trapped electrons into the loss cone in terms of time profiles of hard X-ray (HXR) and microwave (MW) emission have been obtained. It has been found that the evolution of the spectral indices of non-thermal emission depend on the regimes of the pitch angle diffusion of trapped particles into the loss cone. The properties of non-thermal electrons related to the HXR and MW emission of the solar flare on 2004 November 3 are studied with Nobeyama Radioheliograph, Nobeyama Radio Polarimeters, RHESSI, and Geostationary Operational Environmental Satellite observations. The spectral indices of non-thermal electrons related to MW and HXR emission remained constant or decreased, while the MW escape rate as distinguished from that of the HXRs increased. This may be associated with different diffusion regimes of trapped electrons into the loss cone. New arguments in favor of an important role of the superstrong diffusion for high-energy electrons in flare coronal loops have been obtained.

  2. Electron distribution functions in solar flares from combined X-ray and extreme-ultraviolet observations

    SciTech Connect

    Battaglia, M.; Kontar, E. P.

    2013-12-20

    Simultaneous solar flare observations with SDO and RHESSI provide spatially resolved information about hot plasma and energetic particles in flares. RHESSI allows the properties of both hot (≳8 MK) thermal plasma and non-thermal electron distributions to be inferred, while SDO/AIA is more sensitive to lower temperatures. We present and implement a new method to reconstruct electron distribution functions from SDO/AIA data. The combined analysis of RHESSI and AIA data allows the electron distribution function to be inferred over the broad energy range from 0.1 keV up to a few tens of keV. The analysis of two well-observed flares suggests that the distributions in general agree to within a factor of three when the RHESSI values are extrapolated into the intermediate range 1-3 keV, with AIA systematically predicting lower electron fluxes. Possible instrumental and numerical effects, as well as potential physical origins for this discrepancy, are discussed. The inferred electron distribution functions in general show one or two nearly Maxwellian components at energies below ∼15 keV and a non-thermal tail above.

  3. Radio Spectroscopic Imaging of Bi-directional Electron Beam Pairs in a Solar Flare

    NASA Astrophysics Data System (ADS)

    Chen, Bin; Wang, Zhitao; Gary, Dale E.

    2016-05-01

    In solar flares, energetic electrons are believed to be accelerated at or near the magnetic reconnection site. They propagate outward along newly reconnected field lines usually in the form of electron beams. These beams can emit radio waves commonly known as type III radio bursts. An important feature of these bursts is that they are emitted near the local plasma frequency or its harmonic, which is only a function of the ambient plasma density. In particular, an electron beam propagating upward in the corona encounters plasma with lower and lower density, producing a radio burst with a “normal” frequency slope (whose frequency decreases in time). Similarly, a downward propagating beam produces a reverse-slope burst. Sometimes both the normal- and reverse-slope type III bursts are observed simultaneously. These type III burst with opposite slopes have been considered to be the signature of a pair of bi-directional electron beams emerging from a common acceleration site. However, previous studies had no imaging capability to locate these bursts and put them in the flare context. Here we report observations of decimetric type III burst pairs by the Karl G. Jansky Very Large Array (VLA) during the impulsive phase of a C5.6 flare. Using VLA’s unprecedented ultra-high-cadence spectroscopic imaging capability, we demonstrate that the type III burst pairs indeed correspond to high speed (~0.1c), bi-directional electron beams emerging from a common site in the corona where post-flare loops appeared later on. Implications of our results on magnetic reconnection and particle acceleration will be briefly discussed.

  4. Coherent-phase or random-phase acceleration of electron beams in solar flares

    NASA Technical Reports Server (NTRS)

    Aschwanden, Markus J.; Benz, Arnold O.; Montello, Maria L.

    1994-01-01

    Time structures of electron beam signatures at radio wavelengths are investigated to probe correlated versus random behavior in solar flares. In particular we address the issue whether acceleration and injection of electron beams is coherently modulated by a single source, or whether the injection is driven by a stochastic (possibly spatially fragmented) process. We analyze a total of approximately = 6000 type III bursts observed by Ikarus (Zurich) in the frequency range of 100-500 MHz, during 359 solar flares with simultaneous greater than or = 25 keV hard X-ray emission, in the years 1890-1983. In 155 flares we find a total of 260 continuous type III groups, with an average number of 13 +/- 9 bursts per group, a mean duration of D = 12 +/- 14 s, a mean period of P = 2.0 +/- 1.2 s, with the highest burst rate at a frequency of nu = 310 +/- 120 MHz. Pulse periods have been measured between 0.5 and 10 s, and can be described by an exponential distribution, i.e., N(P) varies as e (exp -P/1.0s). The period shows a frequency dependence of P(nu)=46(exp-0.6)(sub MHz)s for different flares, but is invariant during a particular flare. We measure the mean period P and its standard deviation sigma (sub p) in each type III group, and quantify the degree of periodicity (or phase-coherence) by the dimensionless parameter sigma (sub p)P. The representative sample of 260 type III burst groups shows a mean periodicity of sigma (sub p/P) = 0.37 +/- 0.12, while Monte Carlo simulations of an equivalent set of truly random time series show a distinctly different value of sigma (sub p)P = 0.93 +/- 0.26. This result indicates that the injection of electron beams is coherently modulated by a particle acceleration source which is either compact or has a global organization on a timescale of seconds, in contrast to an incoherent acceleration source, which is stochastic either in time or space. We discuss the constraints on the size of the acceleration region resulting from electron beam

  5. BAYESIAN CONFIDENCE LIMITS OF ELECTRON SPECTRA OBTAINED THROUGH REGULARIZED INVERSION OF SOLAR HARD X-RAY SPECTRA

    SciTech Connect

    Emslie, A. Gordon; Massone, Anna Maria E-mail: annamaria.massone@cnr.it

    2012-11-10

    Many astrophysical observations are characterized by a single, non-repeatable measurement of a source brightness or intensity, from which we are to construct estimates for the true intensity and its uncertainty. For example, the hard X-ray count spectrum from transient events such as solar flares can be observed only once, and from this single spectrum one must determine the best estimate of the underlying source spectrum I({epsilon}), and hence the form of the responsible electron spectrum F(E). Including statistical uncertainties on the measured count spectrum yields a 'confidence strip' that delineates the boundaries of electron spectra that are consistent with the observed photon spectrum. In this short article, we point out that the expectation values of the source brightness and its variance in a given photon energy bin are in general not (as has been assumed in prior works) equal to n, the number of counts observed in that energy bin. Rather, they depend both on n and on prior knowledge of the overall photon spectrum. Using Bayesian statistics, we provide an explicit procedure and formulas for determining the 'confidence strip' (Bayesian credible region) for F(E), thus providing rigorous bounds on the intensity and shape of the accelerated electron spectrum.

  6. Energy transport by energetic electrons released during solar flares. II - Current filamentation and plasma heating

    NASA Technical Reports Server (NTRS)

    Winglee, R. M.; Dulk, G. A.; Pritchett, P. L.

    1988-01-01

    Two-dimensional electrostatic particle simulations are performed in order to investigate energy transport associated with the propagation of energetic electrons through a flaring flux tube. Results indicate that as the energetic electrons flow outward, a return current of ambient plasma electrons is drawn inward (to maintain quasi-neutrality) which can be spatially separate from the primary current carried by the energetic electrons. Return current electrons are shown to accumulate on either side of the acceleration region of the energetic electrons, and depletions of ambient plasma electrons develop in the return current regions. Plasma ions accelerate across the field lines to produce current closure or charge neutralization, achieving energies comparable to those of the energetic electrons.

  7. On the importance of reverse current ohmic losses in electron-heated solar flare atmospheres

    NASA Technical Reports Server (NTRS)

    Emslie, A. G.

    1980-01-01

    The passage of a beam of nonthermal electrons through the flaring solar atmosphere is considered, paying particular attention to the requirement that the beam be stable to the generation of plasma turbulence. The ratio is computed of energy losses due to reverse current ohmic heating, and heating by Coulomb collisions, respectively, for the greatest flux which can pass stably through the atmosphere. It is demonstrated that this ratio is determined by the low energy cutoff of the beam, by the electron temperature of the ambient atmosphere, and by the electron to ion temperature ratio. It is also independent of the atmospheric density.

  8. On the filamentary structure of energetic electrons during flares

    NASA Astrophysics Data System (ADS)

    Drake, J.; Swisdak, M.; Shay, M.

    2007-12-01

    Simulations and analytic arguments are presented that demonstrate that magnetic reconnection in the tenuous high temperature corona does not occur as a single large-scale x-line. Rather the narrow current layers that form at x-lines form secondary magnetic islands at small spatial scales. An electron acceleration model based on the interaction of particles with many contracting islands has been developed. A consequence of particle acceleration in any multi-island system is that energetic particles are released in narrow streams with characteristic widths of the order of the electron skin depth. This is because electrons are released from islands as they reconnect with the macro-scale field of the corona or magnetosphere. The characteristic width of the released energetic electron streams correspond to the width of the reconnection dissipation region. Thus, energetic electrons do not propagate away from the reconnection site in the corona as a single large-scale front but as a filamentary web. As a result, the return current problem is transformed: the narrow filaments of energetic particles propagate parallel to the magnetic field as kinetic Alfven waves with propagation speeds comparable to the thermal velocity of the energetic particles. Simple estimates suggest that the conversion of particle to kinetic Alfven wave energy is efficient so that the wave and particle energy propagates together as a radiation front from the corona toward the solar surface. The structure and dynamics of this radiation front are being explored.

  9. Surface Electronic Spectra Detected by Atomic Desorption

    SciTech Connect

    Joly, Alan G.; Beck, Kenneth M.; Henyk, Matthias; Hess, Wayne P.; Sushko, Petr V.; Shluger, Alexander L.

    2003-10-10

    Using continuously tunable laser excitation of KI we measure the velocity profiles and the yield of desorbing hyperthermal iodine atoms as a function of photon energy. Based on the theoretical model of desorption we demonstrate that these spectra display a signature of a surface exciton and constitute a new sensitive method of surface specific desorption spectroscopy. Our results demonstrate that creation of surface excitions can be a much more general phenomenon than was previously thought based on extant spectroscopic measurements.

  10. Electron energy-loss spectra in molecular fluorine

    NASA Technical Reports Server (NTRS)

    Nishimura, H.; Cartwright, D. C.; Trajmar, S.

    1979-01-01

    Electron energy-loss spectra in molecular fluorine, for energy losses from 0 to 17.0 eV, have been taken at incident electron energies of 30, 50, and 90 eV and scattering angles from 5 to 140 deg. Features in the spectra above 11.5 eV energy loss agree well with the assignments recently made from optical spectroscopy. Excitations of many of the eleven repulsive valence excited electronic states are observed and their location correlates reasonably well with recent theoretical results. Several of these excitations have been observed for the first time and four features, for which there are no identifications, appear in the spectra.

  11. Electron acceleration in the turbulent reconnecting current sheets in solar flares

    NASA Astrophysics Data System (ADS)

    Wu, G. P.; Huang, G. L.

    2009-07-01

    Context: We investigate the nonlinear evolution of the electron distribution in the presence of the strong inductive electric field in the reconnecting current sheets (RCS) of solar flares. Aims: We aim to study the characteristics of nonthermal electron-beam plasma instability and its influence on electron acceleration in RCS. Methods: Including the external inductive field, the one-dimensional Vlasov simulation is performed with a realistic mass ratio for the first time. Results: Our principal findings are as follows: 1) the Buneman instability can be quickly excited on the timescale of 10-7 s for the typical parameters of solar flares. After saturation, the beam-plasma instabilities are excited due to the non-Maxwellian electron distribution; 2) the final velocity of the electrons trapped by these waves is of the same order as the phase speed of the waves, while the untrapped electrons continue to be accelerated; 3) the inferred anomalous resistance of the current sheet and the energy conversion rate are basically of the same order as those previously estimated, e.g., “the analysis of Martens”. Conclusions: The Buneman instability is excited on the timescale of 10-7 s and the wave-particle resonant interaction limits the low-energy electrons to be further accelerated in RCS.

  12. Microwave imaging of a solar limb flare - Comparison of spectra and spatial geometry with hard X-rays

    NASA Technical Reports Server (NTRS)

    Schmahl, E. J.; Kundu, M. R.; Dennis, B. R.

    1985-01-01

    A solar limb flare was mapped using the Very Large Array (VLA) together with hard X-ray (HXR) spectral and spatial observations of the Solar Maximum Mission satellite. Microwave flux records from 2.8 to 19.6 GHz were instrumental in determining the burst spectrum, which has a maximum at 10 GHz. The flux spectrum and area of the burst sources were used to determine the number of electrons producing gyrosynchrotron emission, magnetic field strength, and the energy distribution of gyrosynchrotron-emitting electrons. Applying the thick target model to the HXR spectrum, the number of high energy electrons responsible for the X-ray bursts was found to be 10 to the 36th, and the electron energy distribution was approximately E exp -5, significantly different from the parameters derived from the microwave observations. The HXR imaging observations exhibit some similiarities in size and structure o the first two burst sources mapped with the VLA. However, during the initial burst, the HXR source was single and lower in the corona than the double 6 cm source. The observations are explained in terms of a single loop with an isotropic high-energy electron distribution which produced the microwaves, and a larger beamed component which produced the HXR at the feet of the loop.

  13. Solar Flare Track Exposure Ages in Regolith Particles: A Calibration for Transmission Electron Microscope Measurements

    NASA Technical Reports Server (NTRS)

    Berger, Eve L.; Keller, Lindsay P.

    2015-01-01

    Mineral grains in lunar and asteroidal regolith samples provide a unique record of their interaction with the space environment. Space weathering effects result from multiple processes including: exposure to the solar wind, which results in ion damage and implantation effects that are preserved in the rims of grains (typically the outermost 100 nm); cosmic ray and solar flare activity, which result in track formation; and impact processes that result in the accumulation of vapor-deposited elements, impact melts and adhering grains on particle surfaces. Determining the rate at which these effects accumulate in the grains during their space exposure is critical to studies of the surface evolution of airless bodies. Solar flare energetic particles (mainly Fe-group nuclei) have a penetration depth of a few millimeters and leave a trail of ionization damage in insulating materials that is readily observable by transmission electron microscope (TEM) imaging. The density of solar flare particle tracks is used to infer the length of time an object was at or near the regolith surface (i.e., its exposure age). Track measurements by TEM methods are routine, yet track production rate calibrations have only been determined using chemical etching techniques [e.g., 1, and references therein]. We used focused ion beam-scanning electron microscope (FIB-SEM) sample preparation techniques combined with TEM imaging to determine the track density/exposure age relations for lunar rock 64455. The 64455 sample was used earlier by [2] to determine a track production rate by chemical etching of tracks in anorthite. Here, we show that combined FIB/TEM techniques provide a more accurate determination of a track production rate and also allow us to extend the calibration to solar flare tracks in olivine.

  14. Using Gamma-Ray and Neutron Emission to Determine Solar Flare Accelerated Particle Spectra and Composition and the Conditions within the Flare Magnetic Loop

    NASA Astrophysics Data System (ADS)

    Murphy, R. J.; Kozlovsky, Benzion; Share, G. H.; Hua, X.-M.; Lingenfelter, R. E.

    2007-01-01

    The measurable quantities associated with γ-ray and neutron observations of solar flares are nuclear-deexcitation line shapes, shifts, fluences, and time histories; neutron capture and annihilation line fluences and time histories; and energy-dependent escaping neutron fluence and time history. A comprehensive understanding of these quantities requires a model for ion acceleration, transport, and interaction. In this paper we address transport and interaction using a magnetic loop model that includes energy losses due to Coulomb collisions, removal by nuclear reactions, magnetic mirroring in the convergent flux tube, and MHD pitch-angle scattering in the corona. The accelerated ions are assumed to have a given kinetic energy spectrum and composition. Each measurable quantity depends to varying degree on the parameters of the loop model and of the accelerated ions. We explore these dependences in detail and construct a self-consistent approach to the analysis of high-energy flare data that provides an optimum set of parameters with meaningful uncertainties. To illustrate this approach, the calculations are applied in a comprehensive analysis of the γ-ray and neutron observations of the 1991 June 4 solar flare obtained with OSSE on CGRO. We find that the loop model can account for these observations with physically reasonable values for the parameters. In addition, our analysis of the neutron data shows that the accelerated ion spectrum for this flare was not an unbroken power law but had to steepen sharply above ~125 MeV nucleon-1. The paper also provides yields and yield ratios calculated with assumed abundances and spectral forms currently considered appropriate for solar flares. They can be used by other researchers analyzing high-energy solar flare data.

  15. Electron trapping and acceleration by kinetic Alfvén waves in solar flares

    NASA Astrophysics Data System (ADS)

    Artemyev, A. V.; Zimovets, I. V.; Rankin, R.

    2016-05-01

    Context. Theoretical models and spacecraft observations of solar flares highlight the role of wave-particle interaction for non-local electron acceleration. In one scenario, the acceleration of a large electron population up to high energies is due to the transport of electromagnetic energy from the loop-top region down to the footpoints, which is then followed by the energy being released in dense plasma in the lower atmosphere. Aims: We consider one particular mechanism of non-linear electron acceleration by kinetic Alfvén waves. Here, waves are generated by plasma flows in the energy release region near the loop top. We estimate the efficiency of this mechanism and the energies of accelerated electrons. Methods: We use analytical estimates and test-particle modelling to investigate the effects of electron trapping and acceleration by kinetic Alfvén waves in the inhomogeneous plasma of the solar corona. Results: We demonstrate that, for realistic wave amplitudes, electrons can be accelerated up to 10-1000 keV during their propagation along magnetic field lines. Here the electric field that is parallel to the direction of the background magnetic field is about 10 to 103 times the amplitude of the Dreicer electric field. The acceleration mechanism strongly depends on electron scattering which is due to collisions that only take place near the loop footpoints. Conclusions: The non-linear wave-particle interaction can play an important role in the generation of relativistic electrons within flare loops. Electron trapping and coherent acceleration by kinetic Alfvén waves represent the energy cascade from large-scale plasma flows that originate at the loop-top region down to the electron scale. The non-diffusive character of the non-linear electron acceleration may be responsible for the fast generation of high-energy particles.

  16. Copper(II) phthalocyanine: Electronic and vibrational tunneling spectra

    SciTech Connect

    Hipps, K.W. )

    1989-08-10

    Inelastic electron tunneling spectra (IETS) obtained from Al-AlO{sub x}-CuPc-M junctions (M = Pb or Tl) are presented and compared with previous reports. Improved experimental methods allow them to report the entire spectrum in the region below 16,000 cm{sup {minus}1} in both bias directions. In contrast to previous studies, they will show that (a) tunneling spectra are very dependent upon the AlO{sub x}/CuPc and CuPc/M imbedded interfaces, (b) spectra contain both temperature-dependent and temperature-independent features, and (c) certain electronic and the vibrational features depend on junction bias.

  17. Behaviour of Electron Content in the Ionospheric D-Region During Solar X-Ray Flares

    NASA Astrophysics Data System (ADS)

    Todorović Drakul, M.; Čadež, V. M.; Bajčetić, J.; Popović, L. Č.; Blagojević, D.; Nina, A.

    2016-08-01

    One of the most important parameters in ionospheric plasma research, also having a wide practical application in wireless satellite telecommunications, is the total electron content (TEC) representing the columnal electron number density. The F-region with high electron density provides the biggest contribution to TEC while the relatively weakly ionized plasma of the D-region (60 km - 90 km above Earth's surface) is often considered as a negligible cause of satellite signal disturbances. However, sudden intensive ionization processes, like those induced by solar X-ray flares, can cause relative increases of electron density that are significantly larger in the D-region than in regions at higher altitudes. Therefore, one cannot exclude a priori the D-region from investigations of ionospheric influences on propagation of electromagnetic signals emitted by satellites. We discuss here this problem which has not been sufficiently treated in literature so far. The obtained results are based on data collected from the D-region monitoring by very low frequency radio waves and on vertical TEC calculations from the Global Navigation Satellite System (GNSS) signal analyses, and they show noticeable variations in the D-region's electron content (TEC_{D}) during activity of a solar X-ray flare (it rises by a factor of 136 in the considered case) when TEC_{D} contribution to TEC can reach several percent and which cannot be neglected in practical applications like global positioning procedures by satellites.

  18. X-class Solar Flare Energy Partition into Radiative, Non-Thermal Acceleration of Electrons and Peak Thermal Plasma Components - Methodology and Results

    NASA Astrophysics Data System (ADS)

    Moore, Christopher S.; Chamberlin, Phillip; Dennis, Brian R.; Hock, Rachel

    2015-08-01

    Solar flares are among the most energetic processes in the solar system. X-class flares are the largest and can convert up to 1033 ergs of magnetic energy into the acceleration of charged particles and the heating of plasma. They are often accompanied by coronal mass ejections (CMEs). We discuss the methodology and results of the energy partition into three main components: (1) radiative energy, (2) non-thermal acceleration of electrons, and (3) the peak thermal energy content, for a subset of the largest eruptive events from Solar Cycle 23, as derived from satellite observations and empirical models. The bolometric energy content is on the order of 1031 - 1032 ergs and is extracted from Total Solar Irradiance (TSI) measurements by the Total Irradiance Monitor (TIM) onboard the SOlar Radiation and Climate Experiment (SORCE). The Vacuum Ultraviolet (VUV) contribution of the total radiative output is obtained by implementing the Flare Irradiance Spectral Model (FISM). Furthermore, we partition the radiative release into impulsive and gradual phases. X-ray spectra from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) are used to deduce the energy in the non-thermal accelerated electrons, generally found to be 1031 -1032 ergs, and the peak thermal energy content of around 1030 - 1031 ergs. Aside from the CME kinetic energy, these three components contain a substantial amount of the initial available magnetic energy.

  19. Secondary electron spectra: a semiempirical model

    SciTech Connect

    Miller, J.H.; Wilson, W.E.; Manson, S.T.

    1985-05-01

    A model based on evaluation of coefficients in Bethe's asymptotic expansion of the first Born approximation has been developed to extend the data base of differential ionization cross sections needed in track structure calculations. The coefficient of the lowest-order term in this expansion is related to the photoionization cross section of the target, but optical data alone are generally not sufficient to determine differential cross sections for ionization by charged particles. We have used proton-impact, differential ionization data to evaluate the coefficient of the next higher-order term in the expansion. Since these coefficients are independent of the projectile, the experimentally derived coefficients can be used to predict differential cross sections for ionization of the target by bare ions and electrons that are sufficiently energetic to make the Bethe theory valid. This paper compares model calculations with recent experimental data on ionization of water vapor by high-energy electrons and protons. 20 refs., 2 figs.

  20. TEMPORAL VARIATIONS OF X-RAY SOLAR FLARE LOOPS: LENGTH, CORPULENCE, POSITION, TEMPERATURE, PLASMA PRESSURE, AND SPECTRA

    SciTech Connect

    Jeffrey, Natasha L. S.; Kontar, Eduard P.

    2013-04-01

    The spatial and spectral properties of three solar flare coronal X-ray loops are studied before, during, and after the peak X-ray emission. Using observations from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we deduce the temporal changes in emitting X-ray length, corpulence, volume, position, number density, and thermal pressure. We observe a decrease in the loop length, width, and volume before the X-ray peak, and an increasing number density and thermal pressure. After the X-ray peak, volume increases and loop corpulence grows due to increasing width. The volume variations are more pronounced than the position variations, often known as magnetic field line contraction. We believe this is the first dedicated study examining the temporal evolution of X-ray loop lengths and widths. Collectively, the observations also show for the first time three temporal phases given by peaks in temperature, X-ray emission, and thermal pressure, with the minimum volume coinciding with the X-ray peak. Although the volume of the flaring plasma decreases before the peak in X-ray emission, the relationship between temperature and volume does not support simple compressive heating in a collapsing magnetic trap model. Within a low {beta} plasma, shrinking loop widths perpendicular to the guiding field can be explained by squeezing the magnetic field threading the region. Plasma heating leads to chromospheric evaporation and growing number density. This produces increasing thermal pressure and decreasing loop lengths as electrons interact at shorter distances and we believe after the X-ray peak, the increasing loop corpulence.

  1. Electronic and vibrational circular dichroism spectra of (R)-(-)-apomorphine

    NASA Astrophysics Data System (ADS)

    Abbate, Sergio; Longhi, Giovanna; Lebon, France; Tommasini, Matteo

    2012-09-01

    Apomorphine is a chiral drug molecule; notwithstanding its extraordinary importance, little attention has been paid to the characterization of its chiroptical properties. Here we report on its electronic circular dichroism (ECD) spectra, recorded in methanol and water, and vibrational circular dichroism (VCD) in methanol and dimethyl sulfoxide (DMSO) solutions. Density functional theory (DFT) calculations have allowed us to interpret the spectra and to evaluate the role of possible conformations, charge-states and interactions with counter ions.

  2. Lower hybrid resonance acceleration of electrons and ions in solar flares and the associated microwave emission

    NASA Technical Reports Server (NTRS)

    Mcclements, K. G.; Bingham, R.; Su, J. J.; Dawson, J. M.; Spicer, D. S.

    1993-01-01

    The particle acceleration processes here studied are driven by the relaxation of unstable ion ring distributions; these produce strong wave activity at the lower hybrid resonance frequency which collapses, and forms energetic electron and ion tails. The results obtained are applied to the problem posed by the production of energetic particles by solar flares. The numerical simulation results thus obtained by a 2 1/2-dimensional particle-in-cell code show a simultaneous acceleration of electrons to 10-500 keV energies, and of ions to as much as the 1 MeV range; the energy of the latter is still insufficient to account for gamma-ray emission in the 4-6 MeV range, but furnish a seed population for further acceleration.

  3. Positron fraction, electron and positron spectra measured by AMS-02

    NASA Astrophysics Data System (ADS)

    Pizzolotto, Cecilia

    2016-07-01

    A precise measurement by AMS-02 of the electron spectrum up to 700 GeV and of the positron spectrum and positron fraction in primary cosmic rays up 500 GeV are presented. The combined measurement of the cosmic-ray electron and positron energy spectra and fraction provide a unique tool to improve our understanding of the production, acceleration and propagation mechanism of cosmic rays.

  4. Using Supra-Arcade Downflows as Probes of Electron Acceleration During Solar Flares

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina L.

    2011-01-01

    Extracting information from coronal features above flares has become more reliable with the availability of increasingly higher spatial and temporal-resolution data in recent decades. We are now able to sufficiently probe the region high above long-duration flaring active regions where reconnection is expected to be continually occurring. Flows in the supra-arcade region, first observed with Yohkoh/SXT, have been theorized to be associated with newly-reconnected outflowing loops. High resolution data appears to confirm these assertions. Assuming that these flows are indeed reconnection outflows, then the detection of those directed toward the solar surface (i.e. downflowing) should be associated with particle acceleration between the current sheet and the loop footpoints rooted in the chromosphere. RHESSI observations of highly energetic particles with respect to downflow detections could potentially constrain electron acceleration models. I will discuss measurements of these supra-arcade downflows (SADs) in relation to reconnection model parameters and present preliminary findings comparing the downflow timings with high-energy RHESSI lightcurves.

  5. Multiple-wavelength analysis of energy release during a solar flare - Thermal and nonthermal electron populations

    NASA Technical Reports Server (NTRS)

    Willson, Robert F.; Lang, Kenneth R.; Klein, Karl-Ludwig; Kerdraon, Alain; Trottet, Gerard

    1990-01-01

    Collaborative solar investigations by Tufts University and the Observatoire de Paris have resulted in simultaneous radio observations with the Very Large Array (VLA) and the Nancay Radioheliograph (NR), comparisons of this radio data with X-ray observations, and theoretical interpretations of the dominant radiation mechanisms during a weak impulsive solar flare observed on May 28, 1988. The VLA has mapped the flaring structures at time intervals of 3.3 s, showing that the preflash and flash-phase components of the impulsive emission originate in spatially separated sources. The 20.7 cm preflash source is ascribed to thermal gyroresonance emission from coronal loops with typical magnetic field strengths of up to 270 G; this emission is associated with heating and exhibits no detectable hard X-ray radiation above 30 keV. The flash-phase 20.7 cm source and the hard X-ray emission are attributed to nonthermal electrons in the coronal and chromospheric portions of a magnetic loop. The combination of imaging observations at 20.7 and 91.6 cm excludes emission from a confined hot plasma during the flash phase.

  6. Multispectral elastic scanning lidar for industrial flare research: characterizing the electronic subsystem and application.

    PubMed

    Guerrero-Rascado, Juan Luis; Facundes da Costa, Renata; Bedoya, Andrés Esteban; Guardani, Roberto; Alados-Arboledas, Lucas; Bastidas, Álvaro Efrain; Landulfo, Eduardo

    2014-12-15

    This work deals with the analysis of the electronic subsystem of a multiwavelength elastic scanning lidar. Several calibration tests are applied to the Cubatão scanning lidar placed at the industrial area of Cubatão in the State of São Paulo (Brazil), in order to improve the knowledge of its performing itself and to design protocols for correcting lidar signal for undesirable instrumental effects. In particular, the trigger delay is assessed by means of zero-bin and bin-shift tests for analog (AN) and photo-counting (PC) signals, respectively. Dark current test is also performed to detect potential range-dependency that could affect lidar products. All tests were performed at different spatial resolutions. These instrumental corrections were applied to a case study of data acquired for characterizing the optical and microphysical properties of particles in an industrial flare. To that aim, a graphical method based on the space defined by the extinction-related Angström exponent versus its spectral curvature is used to derive the contribution of fine aerosol to extinction and the size of the fine aerosols in the industrial flare, therefore revealing features of the processes occurring inside the flame. Our study demonstrates the potential of this new technique for the study and measurement of industrial emissions. PMID:25607056

  7. The formation of kappa-distribution accelerated electron populations in solar flares

    SciTech Connect

    Bian, Nicolas H.; Stackhouse, Duncan J.; Kontar, Eduard P.; Emslie, A. Gordon E-mail: d.stackhouse.1@research.gla.ac.uk E-mail: emslieg@wku.edu

    2014-12-01

    Driven by recent RHESSI observations of confined loop-top hard X-ray sources in solar flares, we consider stochastic acceleration of electrons in the presence of Coulomb collisions. If electron escape from the acceleration region can be neglected, the electron distribution function is determined by a balance between diffusive acceleration and collisions. Such a scenario admits a stationary solution for the electron distribution function that takes the form of a kappa distribution. We show that the evolution toward this kappa distribution involves a 'wave front' propagating forward in velocity space, so that electrons of higher energy are accelerated later; the acceleration timescales with energy according to τ{sub acc} ∼ E {sup 3/2}. At sufficiently high energies escape from the finite-length acceleration region will eventually dominate. For such energies, the electron velocity distribution function is obtained by solving a time-dependent Fokker-Planck equation in the 'leaky-box' approximation. Solutions are obtained in the limit of a small escape rate from an acceleration region that can effectively be considered a thick target.

  8. The Formation of Kappa-distribution Accelerated Electron Populations in Solar Flares

    NASA Astrophysics Data System (ADS)

    Bian, Nicolas H.; Emslie, A. Gordon; Stackhouse, Duncan J.; Kontar, Eduard P.

    2014-12-01

    Driven by recent RHESSI observations of confined loop-top hard X-ray sources in solar flares, we consider stochastic acceleration of electrons in the presence of Coulomb collisions. If electron escape from the acceleration region can be neglected, the electron distribution function is determined by a balance between diffusive acceleration and collisions. Such a scenario admits a stationary solution for the electron distribution function that takes the form of a kappa distribution. We show that the evolution toward this kappa distribution involves a "wave front" propagating forward in velocity space, so that electrons of higher energy are accelerated later; the acceleration timescales with energy according to τacc ~ E 3/2. At sufficiently high energies escape from the finite-length acceleration region will eventually dominate. For such energies, the electron velocity distribution function is obtained by solving a time-dependent Fokker-Planck equation in the "leaky-box" approximation. Solutions are obtained in the limit of a small escape rate from an acceleration region that can effectively be considered a thick target.

  9. HARD X-RAY FOOTPOINT SIZES AND POSITIONS AS DIAGNOSTICS OF FLARE ACCELERATED ENERGETIC ELECTRONS IN THE LOW SOLAR ATMOSPHERE

    SciTech Connect

    Battaglia, M.; Kontar, E. P.

    2011-07-01

    The hard X-ray (HXR) emission in solar flares comes almost exclusively from a very small part of the flaring region, the footpoints of magnetic loops. Using RHESSI observations of solar flare footpoints, we determine the radial positions and sizes of footpoints as a function of energy in six near-limb events to investigate the transport of flare accelerated electrons and the properties of the chromosphere. HXR visibility forward fitting allows us to find the positions/heights and the sizes of HXR footpoints along and perpendicular to the magnetic field of the flaring loop at different energies in the HXR range. We show that in half of the analyzed events, a clear trend of decreasing height of the sources with energy is found. Assuming collisional thick-target transport, HXR sources are located between 600 and 1200 km above the photosphere for photon energies between 120 and 25 keV, respectively. In the other events, the position as a function of energy is constant within the uncertainties. The vertical sizes (along the path of electron propagation) range from 1.3 to 8 arcsec which is up to a factor four larger than predicted by the thick-target model even in events where the positions/heights of HXR sources are consistent with the collisional thick-target model. Magnetic mirroring, collisional pitch-angle scattering, and X-ray albedo are discussed as potential explanations of the findings.

  10. Complex Study of Electronic States and Spectra of 3-Nitroformazans

    NASA Astrophysics Data System (ADS)

    Valiev, R. R.; Drozdova, A. K.; Petunin, P. V.; Postnikov, P. S.; Trusova, M. E.; Cherepanov, V. N.

    2016-06-01

    A theoretical and experimental study of electronic states and the absorption spectra of 3-nitroformazan molecules was conducted. The results of the study show that the first electron transition is σ→π-transition, and the second one is π→π-transition. The energies of the transitions calculated using methods RI-CC2 and TDDFT correlate well with the experimental measurements. The dependence of the first electron transition wavenumber on the degree of electron donating and accepting of substitutituents was studied using empirical constants. High correlation between the constants of Hammett, Braun, and wavenumbers (TDDFT) of the first electron transition shows that the description of electronic states of the studied 3-nitroformazans is correct.

  11. Electronic absorption spectra of some arylidene pyrazolone derivatives

    NASA Astrophysics Data System (ADS)

    Mahmoud, M. R.; El-Kashef, H. S.; El-Hamide, R. Abd

    The u.v. and visible spectra of some 1 - phenyl - 3 - methyl - 4 - arylidene - 2 - pyrazolin - 5 - one derivatives are investigated in pure and mixed organic solvents as well as in aqueous buffer solutions. Electronic transitions have been identified as either locally excited or predominantly charge transfer states. Moreover, the spectra of the hydroxy derivatives in proton acceptor solvents (DMF, DMSO, ethanol) are characterized by an extra band located at longer wavelengths, which is ascribed to an intermolecular CT transition. This involves an electron transfer from the lone pair of electrons of the oxygen atom of the solvent molecules (ψ ol) to the antibonding orbital of the substituent OH group. The spectral shifts are discussed in terms of medium effects and in relation to molecular structure. The variation of absorbance with pH is utilized for the determination of p K a for the dimethylamino and hydroxy derivatives.

  12. Acceleration of electrons and ions by strong lower-hybrid turbulence in solar flares

    NASA Technical Reports Server (NTRS)

    Spicer, D. S.; Bingham, R.; Su, J. J.; Shapiro, V. D.; Shevchenko, V.; Ma, S.; Dawson, J. M.; Mcclements, K. G.

    1994-01-01

    One of the outstanding problems in solar flare theory is how to explain the 10-20 keV and greater hard x-ray emissions by a thick target bremsstrahlung model. The model requires the acceleration mechanism to accelerate approximately 10(exp 35) electrons sec(exp -l) with comparable energies, without producing a large return current which persists for long time scales after the beam ceases to exist due to Lenz's law, thereby, producing a self-magnetic field of order a few mega-Gauss. In this paper, we investigate particle acceleration resulting from the relaxation of unstable ion ring distributions, producing strong wave activity at the lower hybrid frequency. It is shown that strong lower hybrid wave turbulence collapses in configuration space producing density cavities containing intense electrostatic lower hybrid wave activity. The collapse of these intense nonlinear wave packets saturate by particle acceleration producing energetic electron and ion tails. There are several mechanisms whereby unstable ion distributions could be formed in the solar atmosphere, including reflection at perpendicular shocks, tearing modes, and loss cone depletion. Numerical simulations of ion ring relaxation processes, obtained using a 2 1/2-D fully electromagnetic, relativistic particle in cell code are discussed. We apply the results to the problem of explaining energetic particle production in solar flares. The results show the simultaneous acceleration of both electrons and ions to very high energies: electrons are accelerated to energies in the range 10-500 keV, while ions are accelerated to energies of the order of MeVs, giving rise to x-ray emission and gamma-ray emission respectively. Our simulations also show wave generation at the electron cyclotron frequency. We suggest that these waves are the solar millisecond radio spikes. The strong turbulence collapse process leads to a highly filamented plasma producing many localized regions for particle acceleration and resulting in

  13. Electron precipitation spectra; a global view using DEMETER and POES

    NASA Astrophysics Data System (ADS)

    Whittaker, Ian; Rodger, Craig; Clilverd, Mark; Gamble, Rory; Sauvaud, Jean-Andre

    2014-05-01

    The Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) microsatellite electron flux instrument is comparatively unusual in that it has very high energy resolution (128 channels with 17.9 keV widths in normal survey mode), which lends itself to spectral analysis of electron precipitation from the Earth's radiation belts. Here electron spectra from DEMETER have been analyzed from all 6 years of its operation. Global electron flux maps are produced and average spectral fit values are taken during geomagnetic storm and quiet times. The flux behaviour and spectral variation during geomagnetic storm time and the recovery period are also examined, showing differences between the two radiation belts and the slot region. The high energy resolution of the DEMETER satellite also allows insightful comparisons with electron flux measurements from MEPED (Medium Energy Proton and Electron Detector) instrument onboard the POES constellation of satellites. Unlike the high-resolution observations, POES/MEPED provide only 3 integral electron telescopes. Our comparison allows a test of the MEPED geometric factor equations given by Yando et al., [JGR (116, A10231), 2011] which characterized proton contamination of the electron telescopes as well as a variation in detector efficiency with energy. Electron fluxes are compared when the MetOp-02 POES satellite is in similar locations to DEMETER (ΔL < 0.5, Δlongitude < 4 degrees) using the MEPED 90 degree telescope as both instruments observe essentially the same particle populations (drift loss cone or trapped particles depending on the L shell). Simplified equations are calculated to reverse the geomagnetic factor (for SEM-2 electron instruments only) and then tested, these equations allow the MEPED electron fluxes to be corrected quickly and easily based on the values from Yando et al. Differential fluxes from the integral POES data are also calculated in the comparison. This process is shown to work

  14. Stochastic gyroresonant electron acceleration on a low-beta plasma. II - Implications of thermal effects in a solar flare plasma

    NASA Technical Reports Server (NTRS)

    Miller, James A.; Steinacker, Juergen

    1992-01-01

    We consider the thermal damping of R and L waves under typical solar flare conditions. We find that the thermal particles cause rapid dissipation of the cyclotron waves, but do not affect whistlers and Alfven waves. The dissipation of electron cyclotron waves in particular leads to a threshold energy for acceleration which is about 10 times the thermal energy. Therefore, in the absence of an instability that excites these HF waves, a second mechanism is required in order to inject a sufficient number of electrons above the threshold energy and account for solar flare gamma-ray bremsstrahlung emission. We also find that the comoving gyroresonance, which occurs when the electron is in gyroresonance with an R wave whose group velocity equals the parallel electron velocity, can be realized by relativistic electrons if the plasma temperature is less than or approximately equal to 5,000,000 K.

  15. The electronic spectra of mu-peroxodicobalt(III) complexes

    NASA Technical Reports Server (NTRS)

    Miskowski, Vincent M.

    1987-01-01

    Problems found in the determination of the electronic spectra of mu-peroxodicobalt(III) complexes are considered, and the common formation of different mu-peroxocomplexes upon oxygenation of Co(II)-ligand solutions is discussed. Three classes of spectra have been identified: (1) planar single bridged complexes; (2) nonplanar single-bridged complexes with a dihedral angle near 145 deg; and (3) dibridged mu-OH(-),O2(2-) complexes with a dihedral angle near 60 deg. All of the peroxide ligand-to-metal charge-transfer spectra are found to be consistent with a simple model that assumes a sinusoidal dependence of pi-asterisk O2(2-) energies and sigma-overlaps upon the dihedral angle.

  16. Electronic spectra and structures of some biologically important xanthines

    NASA Astrophysics Data System (ADS)

    Shukla, M. K.; Mishra, P. C.

    1994-08-01

    Electronic absorption and fluorescence spectra of aqueous solutions of xanthine, caffeine, theophylline and theobromine have been studied at different pH. The observed spectra have been interpreted in terms of neutral and ionic forms of the molecules with the help of molecular orbital calculations. At neutral and acidic pH, the spectra can be assigned to the corresponding most stable neutral forms, with the exception that the fluorescence of xanthine at acidic pH appears to originate from the lowest singlet excited state of a cation of the molecule. At alkaline pH, xanthine and theophylline exist mainly as their monoanions. In xanthine and theophylline at alkaline pH, fluorescence originates from the lowest singlet excited state of the corresponding anion. However, in caffeine and theobromine, even at alkaline pH, fluorescence belongs to the neutral species. On the whole, the properties of xanthine are quite different from those of the methyl xanthines.

  17. The X-ray spectra of the flaring and quiescent states of AT Microscopii observed by XMM-Newton

    NASA Astrophysics Data System (ADS)

    Raassen, A. J. J.; Mewe, R.; Audard, M.; Güdel, M.

    2003-12-01

    The X-ray spectrum of the late-type M-dwarf binary AT Mic (dM4.5e+dM4.5e) is observed in the wavelength range 1-40 Å by means of RGS and EPIC-MOS on board XMM-Newton. During the exposure a flare occured. We have performed a 3-temperature fit and a DEM-modeling to the flaring and quiescent part of the spectrum. We report the coronal temperature distribution, emission measures, and abundances of the flaring and quiescent state of this bright X-ray source. The temperature range stretches from about 1 to 60 MK. The total volume emission measure in this temperature interval is ~ 12.2 x 1051 cm-3 for the quiescent state and ~ 19.5 x 1051 cm-3 for the flare state. This difference is due to the contribution of the hot temperature component. The high-resolution spectrum of AT Mic, obtained by RGS, is dominated by the H- and He-like transitions of C, N, O, and Ne and by Fe XVII lines, produced by the plasma with temperatures from 1 to 10 MK. The EPIC-MOS spectrum below 10 Å shows H- and He-like Ne, Si and the iron K-shell transitions. They are produced by the hot component (30 MK). The iron K-shell is more prominent in the flare state. The abundance pattern in the quiescent state of AT Mic shows the depletion of low-FIP elements relative to high-FIP elements, indicating the presence of an I(nverse)FIP effect in this active star. In the flare state, however, some flattening of this IFIP effect is present. Based on observations obtained with XMM-Newton, an ESA scienc mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).

  18. Rapid temporal evolution of radiation from non-thermal electrons in solar flares

    NASA Technical Reports Server (NTRS)

    Lu, Edward T.; Petrosian, Vahe

    1987-01-01

    Solutions of the time dependent Fokker-Planck equation was found for accelerated electrons undergoing Coulomb collisions in a magnetized, fully ionized plasma. An exact solution was found for arbitrary pitch angle and energy distribution in a uniform background plasma. Then, for an inhomogeneous plasma, a solution was found for particles with small pitch angles. These solutions were used to calculate the temporal evolution of bremsstrahlung x-rays from short bursts of nonthermal electron beams, and these spectra were compared with observed high time resolution spectra of short timescale solar hard x-ray bursts. It is shown that the observed softening in time of the spectra rules out a homogeneous background and therefore the possibility of electrons being confined to the corona either because of converging magnetic field or high densities. The inhomogeneous solution was also applied to a model with constant coronal density and exponentially rising chromospheric density. The spectra are shown to be consistent with that produced by a collimated beam of electrons accelerated in the corona with certain given conditions. These conditions could be violated if large pitch angle electrons are present.

  19. Constraining and validating the Oct/Nov 2003 X-class EUV flare enhancements with observations of FUV dayglow and E-region electron densities

    NASA Astrophysics Data System (ADS)

    Strickland, D. J.; Lean, J. L.; Daniell, R. E.; Knight, H. K.; Woo, W. K.; Meier, R. R.; Straus, P. R.; Woods, T. N.; Eparvier, F. G.; McMullin, D. R.; Christensen, A. B.; Morrison, D.; Paxton, L. J.

    2007-06-01

    Near peak activity of two X-class solar flares, on 28 October and 4 November 2003, the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/Solar EUV Experiment (SEE) instrument recorded order of magnitude increases in solar EUV irradiance, the TIMED/Global Ultraviolet Imager (GUVI) observed simultaneous increases in upper atmosphere far ultraviolet (FUV) dayglow, and the European Incoherent Scatter Scientific Association (EISCAT) radar and the Ionospheric Occultation Experiment onboard the PICOSat spacecraft recorded corresponding changes in E-region electron densities. Calculations of the FUV dayglow and electron density profiles using Version 8 SEE flare spectra overestimate the actual observed increases by more than a factor of 2.0. This prompted the development of an alternative approach that uses the FUV dayglow and associated E-layer electron density profiles to derive and validate, respectively, the increases in the solar EUV irradiance spectrum. The solar EUV spectrum required to produce the FUV dayglow is specified between 45 and 27 nm by SEE's EGS measurements, between 27 and 5 nm by GUVI dayglow measurements, and between 5 and 1 nm using a combination of the GOES X-ray data and the NRLEUV model. The energy fluxes in the 5- to 27-nm bands (at 5-10, 10-15, 15-20, and 20-27 nm) are randomly varied in search of combinations such that the full spectrum (λ < 45 nm) replicates the GUVI dayglow observations. In contrast to the Version 8 SEE XPS observations, solar EUV spectra derived using the multiband yield approach produce electron densities that are consistent with those observed independently. The new multiband yield algorithm thus provides a unique tool for independent validation of solar EUV spectral irradiance measurements using FUV dayglow observations.

  20. Measurement of wavelengths and lamb shifts for inner-shell transitions in Fe XVIII-XXIV. [from solar flare X-ray spectra

    NASA Technical Reports Server (NTRS)

    Seely, J. F.; Feldman, U.; Safronova, U. I.

    1986-01-01

    The wavelengths of inner-shell 1s-2p transitions in the ions Fe XVIII-XXIV have been measured in solar flare spectra recorded by the Naval Research Laboratory crystal spectrometer (SOLFLEX) on the Air Force P78-1 spacecraft. The measurements are compared with previous measurements and with recently calculated wavelengths. It is found that the measured wavelengths are systematically larger than the wavelengths calculated using the Z-expansion method by up to 0.65 mA. For the more highly charged ions, these differences can be attributed to the QED contributions to the transition energies that are not included in the Z-expansion calculations.

  1. Gamma-ray lines and neutrons from solar flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Murphy, R. J.; Kozlovsky, B.; Lingenfelter, R. E.

    1983-01-01

    The energy spectrum of accelerated protons and nuclei at the site of a limb flare was derived by a technique, using observations of the time dependent flux of high energy neutrons at the Earth. This energy spectrum is very similar to the energy spectra of 7 disk flares for which the accelerated particle spectra was previously derived using observations of 4 to 7 MeV to 2.223 MeV fluence ratios. The implied spectra for all of these flares are too steep to produce any significant amount of radiation from pi meson decay. It is suggested that the observed 10 MeV gamma rays from the flare are bremsstrahlung of relativistic electrons.

  2. Gamma-ray lines and neutrons from solar flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Murphy, R. J.; Kozlovsky, B.; Lingenfelter, R. E.

    1983-01-01

    The energy spectrum of accelerated protons and nuclei at the site of a limb flare was derived by a technique, using observations of the time dependent flux of high energy neutrons at the earth. This energy spectrum is very similar to the energy spectra of 7 disk flares for which the accelerated particle spectra was previously derived using observations of 4 to 7 MeV to 2.223 MeV fluence ratios. The implied spectra for all of these flares are too steep to produce any significant amount of radiation from pi meson decay. It is suggested that the observed 10 MeV gamma rays from the flare are bremsstrahlung of relativistic electrons. Previously announced in STAR as N83-19695

  3. Electronic spectra from TDDFT and machine learning in chemical space

    SciTech Connect

    Ramakrishnan, Raghunathan; Hartmann, Mia; Tapavicza, Enrico; Lilienfeld, O. Anatole von

    2015-08-28

    Due to its favorable computational efficiency, time-dependent (TD) density functional theory (DFT) enables the prediction of electronic spectra in a high-throughput manner across chemical space. Its predictions, however, can be quite inaccurate. We resolve this issue with machine learning models trained on deviations of reference second-order approximate coupled-cluster (CC2) singles and doubles spectra from TDDFT counterparts, or even from DFT gap. We applied this approach to low-lying singlet-singlet vertical electronic spectra of over 20 000 synthetically feasible small organic molecules with up to eight CONF atoms. The prediction errors decay monotonously as a function of training set size. For a training set of 10 000 molecules, CC2 excitation energies can be reproduced to within ±0.1 eV for the remaining molecules. Analysis of our spectral database via chromophore counting suggests that even higher accuracies can be achieved. Based on the evidence collected, we discuss open challenges associated with data-driven modeling of high-lying spectra and transition intensities.

  4. Electronic spectra from TDDFT and machine learning in chemical space

    NASA Astrophysics Data System (ADS)

    Ramakrishnan, Raghunathan; Hartmann, Mia; Tapavicza, Enrico; von Lilienfeld, O. Anatole

    2015-08-01

    Due to its favorable computational efficiency, time-dependent (TD) density functional theory (DFT) enables the prediction of electronic spectra in a high-throughput manner across chemical space. Its predictions, however, can be quite inaccurate. We resolve this issue with machine learning models trained on deviations of reference second-order approximate coupled-cluster (CC2) singles and doubles spectra from TDDFT counterparts, or even from DFT gap. We applied this approach to low-lying singlet-singlet vertical electronic spectra of over 20 000 synthetically feasible small organic molecules with up to eight CONF atoms. The prediction errors decay monotonously as a function of training set size. For a training set of 10 000 molecules, CC2 excitation energies can be reproduced to within ±0.1 eV for the remaining molecules. Analysis of our spectral database via chromophore counting suggests that even higher accuracies can be achieved. Based on the evidence collected, we discuss open challenges associated with data-driven modeling of high-lying spectra and transition intensities.

  5. Electronic spectra from TDDFT and machine learning in chemical space.

    PubMed

    Ramakrishnan, Raghunathan; Hartmann, Mia; Tapavicza, Enrico; von Lilienfeld, O Anatole

    2015-08-28

    Due to its favorable computational efficiency, time-dependent (TD) density functional theory (DFT) enables the prediction of electronic spectra in a high-throughput manner across chemical space. Its predictions, however, can be quite inaccurate. We resolve this issue with machine learning models trained on deviations of reference second-order approximate coupled-cluster (CC2) singles and doubles spectra from TDDFT counterparts, or even from DFT gap. We applied this approach to low-lying singlet-singlet vertical electronic spectra of over 20 000 synthetically feasible small organic molecules with up to eight CONF atoms. The prediction errors decay monotonously as a function of training set size. For a training set of 10 000 molecules, CC2 excitation energies can be reproduced to within ±0.1 eV for the remaining molecules. Analysis of our spectral database via chromophore counting suggests that even higher accuracies can be achieved. Based on the evidence collected, we discuss open challenges associated with data-driven modeling of high-lying spectra and transition intensities. PMID:26328822

  6. On the solution of the continuity equation for precipitating electrons in solar flares

    SciTech Connect

    Emslie, A. Gordon; Holman, Gordon D.; Litvinenko, Yuri E. E-mail: gordon.d.holman@nasa.gov

    2014-09-01

    Electrons accelerated in solar flares are injected into the surrounding plasma, where they are subjected to the influence of collisional (Coulomb) energy losses. Their evolution is modeled by a partial differential equation describing continuity of electron number. In a recent paper, Dobranskis and Zharkova claim to have found an 'updated exact analytical solution' to this continuity equation. Their solution contains an additional term that drives an exponential decrease in electron density with depth, leading them to assert that the well-known solution derived by Brown, Syrovatskii and Shmeleva, and many others is invalid. We show that the solution of Dobranskis and Zharkova results from a fundamental error in the application of the method of characteristics and is hence incorrect. Further, their comparison of the 'new' analytical solution with numerical solutions of the Fokker-Planck equation fails to lend support to their result. We conclude that Dobranskis and Zharkova's solution of the universally accepted and well-established continuity equation is incorrect, and that their criticism of the correct solution is unfounded. We also demonstrate the formal equivalence of the approaches of Syrovatskii and Shmeleva and Brown, with particular reference to the evolution of the electron flux and number density (both differential in energy) in a collisional thick target. We strongly urge use of these long-established, correct solutions in future works.

  7. Impulsive phase of solar flares. 1: Characteristics of high energy electrons

    NASA Technical Reports Server (NTRS)

    Leach, J.; Petrosian, V.

    1981-01-01

    The variation along a magnetic field line of the energy and pitch angle distribution of high energy electrons injected into a cold hydrogen plasma containing either an open or closed magnetic field structure was investigated. The problem is formulated as a time independent Fokker-Planck Equation for the electron number distribution as a function of the electron energy, electron pitch angle, and the structure of the global magnetic field. Simple analytic solution valid in the small pitch angle regime and for slowly varying magnetic field is presented. For the more general situation a numerical code for solving the Fokker-Planck Equation was used and it was found that the analytic expression agrees well with the numerical results to values of the pitch angle much larger than expected. For most practical applications, one many confidently use the analytic expression instead of having to resort to lengthy numerical computations. These results are useful in the study of the nonthermal models of the impulsive phase of solar flares.

  8. On the Solution of the Continuity Equation for Precipitating Electrons in Solar Flares

    NASA Technical Reports Server (NTRS)

    Emslie, A. Gordon; Holman, Gordon D.; Litvinenko, Yuri E.

    2014-01-01

    Electrons accelerated in solar flares are injected into the surrounding plasma, where they are subjected to the influence of collisional (Coulomb) energy losses. Their evolution is modeled by a partial differential equation describing continuity of electron number. In a recent paper, Dobranskis & Zharkova claim to have found an "updated exact analytical solution" to this continuity equation. Their solution contains an additional term that drives an exponential decrease in electron density with depth, leading them to assert that the well-known solution derived by Brown, Syrovatskii & Shmeleva, and many others is invalid. We show that the solution of Dobranskis & Zharkova results from a fundamental error in the application of the method of characteristics and is hence incorrect. Further, their comparison of the "new" analytical solution with numerical solutions of the Fokker-Planck equation fails to lend support to their result.We conclude that Dobranskis & Zharkova's solution of the universally accepted and well-established continuity equation is incorrect, and that their criticism of the correct solution is unfounded. We also demonstrate the formal equivalence of the approaches of Syrovatskii & Shmeleva and Brown, with particular reference to the evolution of the electron flux and number density (both differential in energy) in a collisional thick target. We strongly urge use of these long-established, correct solutions in future works.

  9. Background fitting for electron energy-loss spectra

    SciTech Connect

    Bentley, J.; Lehman, G.L.; Sklad, P.S.

    1981-01-01

    Microanalysis using electron energy loss spectroscopy is now well established. In order to assess true edge profiles and obtain integrated intensities of the inner shell ionization edges of interest, it is first necessary to subtract the background. Usually a simple inverse power law is used, but for some spectra this form does not fit well. An alternative form which results in superior fits is described.

  10. Comparison of optical and electron spectra in an infra-red free electron laser

    SciTech Connect

    MacLeod, A.M.; Gillespie, W.A.; Martin, P.F.

    1995-12-31

    Time-resolved electron and optical spectra recently acquired at the FELIX facility are presented, showing the evolution of the respective macropulses. A comparison is made between the optical power output during the macropulse and the measured power extracted from the electron beam using a simple model of the cavity losses. Data are available for a wide range of operating conditions: the wavelength range is from 9 {mu}m to 28 {mu}m and detuning are between 1/4{lambda} and 2{lambda}. The effect of rapid electron beam energy changes on the optical and electron spectra will also be discussed.

  11. Toward the Accurate Simulation of Two-Dimensional Electronic Spectra

    NASA Astrophysics Data System (ADS)

    Giussani, Angelo; Nenov, Artur; Segarra-Martí, Javier; Jaiswal, Vishal K.; Rivalta, Ivan; Dumont, Elise; Mukamel, Shaul; Garavelli, Marco

    2015-06-01

    Two-dimensional pump-probe electronic spectroscopy is a powerful technique able to provide both high spectral and temporal resolution, allowing the analysis of ultrafast complex reactions occurring via complementary pathways by the identification of decay-specific fingerprints. [1-2] The understanding of the origin of the experimentally recorded signals in a two-dimensional electronic spectrum requires the characterization of the electronic states involved in the electronic transitions photoinduced by the pump/probe pulses in the experiment. Such a goal constitutes a considerable computational challenge, since up to 100 states need to be described, for which state-of-the-art methods as RASSCF and RASPT2 have to be wisely employed. [3] With the present contribution, the main features and potentialities of two-dimensional electronic spectroscopy are presented, together with the machinery in continuous development in our groups in order to compute two-dimensional electronic spectra. The results obtained using different level of theory and simulations are shown, bringing as examples the computed two-dimensional electronic spectra for some specific cases studied. [2-4] [1] Rivalta I, Nenov A, Cerullo G, Mukamel S, Garavelli M, Int. J. Quantum Chem., 2014, 114, 85 [2] Nenov A, Segarra-Martí J, Giussani A, Conti I, Rivalta I, Dumont E, Jaiswal V K, Altavilla S, Mukamel S, Garavelli M, Faraday Discuss. 2015, DOI: 10.1039/C4FD00175C [3] Nenov A, Giussani A, Segarra-Martí J, Jaiswal V K, Rivalta I, Cerullo G, Mukamel S, Garavelli M, J. Chem. Phys. submitted [4] Nenov A, Giussani A, Fingerhut B P, Rivalta I, Dumont E, Mukamel S, Garavelli M, Phys. Chem. Chem. Phys. Submitted [5] Krebs N, Pugliesi I, Hauer J, Riedle E, New J. Phys., 2013,15, 08501

  12. THE SPECIFIC ACCELERATION RATE IN LOOP-STRUCTURED SOLAR FLARES-IMPLICATIONS FOR ELECTRON ACCELERATION MODELS

    SciTech Connect

    Guo, Jingnan; Emslie, A. Gordon; Piana, Michele E-mail: piana@dima.unige.it

    2013-03-20

    We analyze electron flux maps based on RHESSI hard X-ray imaging spectroscopy data for a number of extended coronal-loop flare events. For each event, we determine the variation of the characteristic loop length L with electron energy E, and we fit this observed behavior with models that incorporate an extended acceleration region and an exterior 'propagation' region, and which may include collisional modification of the accelerated electron spectrum inside the acceleration region. The models are characterized by two parameters: the plasma density n in, and the longitudinal extent L{sub 0} of, the acceleration region. Determination of the best-fit values of these parameters permits inference of the volume that encompasses the acceleration region and of the total number of particles within it. It is then straightforward to compute values for the emission filling factor and for the specific acceleration rate (electrons s{sup -1} per ambient electron above a chosen reference energy). For the 24 events studied, the range of inferred filling factors is consistent with a value of unity. The inferred mean value of the specific acceleration rate above E{sub 0} = 20 keV is {approx}10{sup -2} s{sup -1}, with a 1{sigma} spread of about a half-order-of-magnitude above and below this value. We compare these values with the predictions of several models, including acceleration by large-scale, weak (sub-Dreicer) fields, by strong (super-Dreicer) electric fields in a reconnecting current sheet, and by stochastic acceleration processes.

  13. Electronic and vibrational spectra of some rare earth trifluoromethanesulfonates crystals.

    PubMed

    Paul, P; Ghosh, M; Neogy, D; Mallick, P K

    2011-01-01

    The Raman and infrared spectra of some rare earth (dysprosium and terbium) trifluoromethanesulfonates crystals have been analyzed. Different vibrational frequencies of trifluoromethanesulfonate ions (CF3SO3-) are identified and assigned to different vibrations of the SO3 and CF3 groups. Electronic transitions of R3+ ions (R=Dy, Tb) in these salts have been assigned to transitions from the ground to different energy levels of the ground multiplet. The electronic energy levels of the rare earth ions are also determined theoretically with the help of single electron crystal field theory. They are found to yield results not only in good agreement with the observed spectral data but also in good conformity with those obtained previously from magnetic measurements. PMID:20934907

  14. EPR and electronic absorption spectra of copper bearing turquoise mineral

    NASA Astrophysics Data System (ADS)

    Sharma, K. B. N.; Moorthy, L. R.; Reddy, B. J.; Vedanand, S.

    1988-10-01

    Electron paramagnetic resonance and optical absorption spectra of turquoise have been studied both at room and low temperatures. It is concluded from the EPR spectra that the ground state of Cu 2+ ion in turquoise is 2A g(d x2- y2) and it is sited in an elongated rhombic octahedron (D 2π). The observed absorption bands at 14970 and 18354 cm -1 are assigned at 2A g→ 2B 1 g( dx2- y2→ xy) and 2A g→[ su2B 3g(d x 2-y 2→d yz) respectively assuming D 2π symmetry which are inconsistent with EPR studies. The three bands in the NIR region are attributed to combinations of fundamental modes of the H 2O molecule present in the sample.

  15. Ionisation Equilibrium for the Non-Maxwellian Electron n-Distributions in Solar Flares: Updated Calculations

    NASA Astrophysics Data System (ADS)

    Dzifčáková, Elena; Dudík, Jaroslav

    2015-12-01

    We use the latest available atomic data to calculate the ionisation and recombination rates for the non-Maxwellian n-distributions, which were shown previously to provide a good fit to the enhanced intensities of dielectronic satellite lines during solar flares. The ionisation and recombination coefficients are subsequently used to derive the ionisation equilibrium. To do so, we consider odd values of n ranging from 1 to 19, i.e., from Maxwellian to strongly non-Maxwellian cases. These calculations involve all elements with proton number up to 30, i.e., H to Zn. The n-distributions modify both the ionisation and the recombination rates. The ionisation rates decrease more steeply at lower pseudo-temperatures, while the radiative recombination rate is reduced due to a lower number of low-energy electrons. The peaks of the dielectronic recombination rates become narrower. These changes are reflected in the ionisation equilibrium. Ion abundance peaks become narrower and can also be shifted, mostly towards higher temperatures. The He-like ions are an important exception, as they are formed in a larger temperature range than that for the Maxwellian distribution. The ions Si xiii - xiv used previously for the diagnostics of the n-distributions are affected only weakly, confirming the determination of n. The ionisation equilibria are available as the electronic supplementary material in a format compatible with the CHIANTI database.

  16. Absolute Abundance Measurements in Solar Flares

    NASA Astrophysics Data System (ADS)

    Warren, Harry

    2014-06-01

    We present measurements of elemental abundances in solar flares with EVE/SDO and EIS/Hinode. EVE observes both high temperature Fe emission lines Fe XV-XXIV and continuum emission from thermal bremsstrahlung that is proportional to the abundance of H. By comparing the relative intensities of line and continuum emission it is possible to determine the enrichment of the flare plasma relative to the composition of the photosphere. This is the first ionization potential or FIP bias (F). Since thermal bremsstrahlung at EUV wavelengths is relatively insensitive to the electron temperature it is important to account for the distribution of electron temperatures in the emitting plasma. We accomplish this by using the observed spectra to infer the differential emission measure distribution and FIP bias simultaneously. In each of the 21 flares that we analyze we find that the observed composition is close to photospheric. The mean FIP bias in our sample is F=1.17+-0.22. Furthermore, we have compared the EVE measurements with corresponding flare observations of intermediate temperature S, Ar, Ca, and Fe emission lines taken with EIS. Our initial calculations also indicate a photospheric composition for these observations. This analysis suggests that the bulk of the plasma evaporated during a flare comes from deep in the chromosphere, below the region where elemental fractionation in the non-flaring corona occurs.

  17. Multiple scattering calculations of relativistic electron energy loss spectra

    NASA Astrophysics Data System (ADS)

    Jorissen, K.; Rehr, J. J.; Verbeeck, J.

    2010-04-01

    A generalization of the real-space Green’s-function approach is presented for ab initio calculations of relativistic electron energy loss spectra (EELS) which are particularly important in anisotropic materials. The approach incorporates relativistic effects in terms of the transition tensor within the dipole-selection rule. In particular, the method accounts for relativistic corrections to the magic angle in orientation resolved EELS experiments. The approach is validated by a study of the graphite CK edge, for which we present an accurate magic angle measurement consistent with the predicted value.

  18. Proportionality law between the flare SXR intensity and the number of released solar near-relativistic electrons

    NASA Astrophysics Data System (ADS)

    Agueda, N.; Klein, K.-L.; SEPServer Consortium

    2015-05-01

    We study a set of solar near-relativistic (NR; >50 keV) electron events observed by the Wind and the ACE spacecraft near the Earth orbit. Interplanetary transport simulations are used to take into account the propagation effects from the source to the spacecraft. Inversion methods developed within the EU/FP7 SEPServer project are then used to extract, from directional intensities observed near the Earth orbit, the electron release history in the low solar corona. We compare the release time histories with context electromagnetic observations of solar eruptions, in soft X-rays, radio, hard X-rays and white light. The distribution of release profiles is bimodal. NR electrons are released during either short (<30 min) or long (>2 h) periods. Short release episodes appear to originate in solar flares, in coincidence with the timing of type III radio bursts reaching the local plasma line measured at 1 AU. The origin of long release episodes seems to be more intricate. They are associated with signatures of long acceleration processes in the low corona (long decay of the soft X-ray emission, type IV radio bursts, and time-extended microwave emission). We present a proportionality empirical law between the intensity of the SXR flare and the number of electrons released during flare-accelerated events.

  19. Unsaturated Comptonization of isotropic photon spectra by relativistic electrons

    NASA Technical Reports Server (NTRS)

    Loeb, Abraham; Mckee, Christopher F.; Lahav, Ofer

    1991-01-01

    The multiple scattering approach for evaluating the transformation of an arbitrary soft photon spectrum as a result of unsaturated Compton scatterings in a medium of relativistic electrons is explored. The medium is assumed to be infinite and spatially homogeneous but may be time-dependent, and the photons are isotropic. It is shown that the distortion of a radiation spectrum can be described analytically in a compact form using the Fourier transform of the single-scattering probability. In the nonrelativistic case, the validity of the known analytical results derived from the Kompaneets (1957) equation is extended to arbitrary electron distribution functions and photon spectra. For relativistic electrons, simple expressions are obtained for the total energy that is transferred from the electrons to the photons and for the distortion in the Rayleigh-Jeans regime of a blackbody spectrum. It is demonstrated that the treatment applies to Comptonization in a relativistic jet and that Comptonization of very soft trapped photons by semirelativistic electrons in an expanding medium leads naturally to a log Gaussian spectrum, of the form observed in blazars.

  20. A FAST FLARE AND DIRECT REDSHIFT CONSTRAINT IN FAR-ULTRAVIOLET SPECTRA OF THE BLAZAR S5 0716+714

    SciTech Connect

    Danforth, Charles W.; Nalewajko, Krzysztof; France, Kevin; Keeney, Brian A.

    2013-02-10

    The BL Lacertae object S5 0716+714 is one of the most studied blazars on the sky due to its active variability and brightness in many bands, including very-high-energy gamma rays. We present here two serendipitous results from recent far-ultraviolet spectroscopic observations by the Cosmic Origins Spectrograph onboard the Hubble Space Telescope (HST). First, during the course of our 7.3 hr HST observations, the blazar increased in flux rapidly by {approx}40% (-0.45 mag hr{sup -1}) followed by a slower decline (+0.36 mag hr{sup -1}) to previous FUV flux levels. We model this flare using asymmetric flare templates and constrain the physical size and energetics of the emitting region. Furthermore, the spectral index of the object softens considerably during the course of the flare from {alpha}{sub {nu}} Almost-Equal-To -1.0 to {alpha}{sub {nu}} Almost-Equal-To -1.4. Second, we constrain the source redshift directly using the {approx}30 intervening absorption systems. A system at z = 0.2315 is detected in Ly{alpha}, Ly{beta}, O VI, and N V and defines the lower bound on the source redshift. No absorbers are seen in the remaining spectral coverage (0.2315 < z {sub Ly{alpha}} {approx}< 0.47) and we set a statistical upper bound of z < 0.322 (95% confidence) on the blazar. This is the first direct redshift limit for this object and is consistent with literature estimates of z = 0.31 {+-} 0.08 based on the detection of a host galaxy.

  1. A Fast Flare and Direct Redshift Constraint in Far-ultraviolet Spectra of the Blazar S5 0716+714

    NASA Astrophysics Data System (ADS)

    Danforth, Charles W.; Nalewajko, Krzysztof; France, Kevin; Keeney, Brian A.

    2013-02-01

    The BL Lacertae object S5 0716+714 is one of the most studied blazars on the sky due to its active variability and brightness in many bands, including very-high-energy gamma rays. We present here two serendipitous results from recent far-ultraviolet spectroscopic observations by the Cosmic Origins Spectrograph onboard the Hubble Space Telescope (HST). First, during the course of our 7.3 hr HST observations, the blazar increased in flux rapidly by ~40% (-0.45 mag hr-1) followed by a slower decline (+0.36 mag hr-1) to previous FUV flux levels. We model this flare using asymmetric flare templates and constrain the physical size and energetics of the emitting region. Furthermore, the spectral index of the object softens considerably during the course of the flare from αν ≈ -1.0 to αν ≈ -1.4. Second, we constrain the source redshift directly using the ~30 intervening absorption systems. A system at z = 0.2315 is detected in Lyα, Lyβ, O VI, and N V and defines the lower bound on the source redshift. No absorbers are seen in the remaining spectral coverage (0.2315 < z Lyα <~ 0.47) and we set a statistical upper bound of z < 0.322 (95% confidence) on the blazar. This is the first direct redshift limit for this object and is consistent with literature estimates of z = 0.31 ± 0.08 based on the detection of a host galaxy. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

  2. Electronic spectra of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation and radical

    DOE PAGESBeta

    Peter R. Craig; Miller, John R.; Havlas, Zdenek; Trujillo, Marianela; Rempala, Pawel; Kirby, James P.; Noll, Bruce C.; Michl, Josef

    2016-05-02

    In this study, properties of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation 1 and its tetra-o-fluoro derivative 1a have been measured and calculated. The B3LYP/TZP optimized geometry of the free cation 1 agrees with a single-crystal X-ray diffraction structure except that in the crystal one of the phenyl substituents is strongly twisted to permit a close-packing interaction of two of its hydrogens with a nearby BF–4 anion. The low-energy parts of the solution electronic absorption and magnetic circular dichroism (MCD) spectra of 1 and 1a have been interpreted by comparison with TD-DFT (B3LYP/TZP) results. Reduction or pulse radiolysis lead to a neutral 19-electron radical,more » whose visible absorption and MCD spectra have been recorded and interpreted as well. The reduction is facilitated by ~0.1 V upon going from 1 to 1a« less

  3. Electronic Spectra of the Tetraphenylcyclobutadienecyclopentadienylnickel(II) Cation and Radical.

    PubMed

    Craig, Peter R; Havlas, Zdeněk; Trujillo, Marianela; Rempala, Pawel; Kirby, James P; Miller, John R; Noll, Bruce C; Michl, Josef

    2016-05-26

    Properties of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation 1 and its tetra-o-fluoro derivative 1a have been measured and calculated. The B3LYP/TZP optimized geometry of the free cation 1 agrees with a single-crystal X-ray diffraction structure except that in the crystal one of the phenyl substituents is strongly twisted to permit a close-packing interaction of two of its hydrogens with a nearby BF4(-) anion. The low-energy parts of the solution electronic absorption and magnetic circular dichroism (MCD) spectra of 1 and 1a have been interpreted by comparison with TD-DFT (B3LYP/TZP) results. Reduction or pulse radiolysis lead to a neutral 19-electron radical, whose visible absorption and MCD spectra have been recorded and interpreted as well. The reduction is facilitated by ∼0.1 V upon going from 1 to 1a. Unsuccessful attempts to prepare several other aryl substituted derivatives of 1 by the classical synthetic route are described in the Supporting Information . PMID:27136127

  4. Site-specific Auger electron spectra of ethyl trifluoroacelate molecules studied by magnetic bottle electron spectrometer

    NASA Astrophysics Data System (ADS)

    Iwayama, Hiroshi; Shigemasa, Eiji; Hikosaka, Yasumasa; Nakano, Motoyoshi; Ito, Kenji; Lablanquie, Pascal; Penet, Francis; Andric, Lidija; Selles, Patricia

    2012-11-01

    We performed multielectron coincidence measurements for inner-shell photoionizations of ethyl trifluoroacelate molecules (C4H5F3O2) using a magnetic bottle electron spectrometer. From a two dimensional coincidence map between a photoelectron and Auger electron for C 1s ionizations, we extracted site-specific Auger electron spectra for each carbon site and corresponding binding energy of doubly charged states.

  5. Impulsive H-alpha diagnostics of electron-beam-heated solar flare model chromospheres

    NASA Technical Reports Server (NTRS)

    Canfield, Richard C.; Gayley, Kenneth G.

    1987-01-01

    Time-dependent H-alpha profiles were computed for the dynamic model atmospheres of Fisher, Canfield, and McClymont (1985) simulating the effects of an intense impulsively initiated power-law beam of electrons incident on the chromosphere. The temporal response of H-alpha arises from three separate physical mechanisms, whose relative importance varies over the line profile. The fastest variations (typically less than 0.1 s for the explosive heating discussed here) arise from energy imbalance; these are apparent on chromospheric heating and cooling time scales and have their greatest amplitude at line center. Slower variations arise from ionization imbalance and are most apparent in the blue wing. The slowest variations arise from hydrodynamic effects and are related to the formation of a chromospheric condensation; these are most apparent in the red wing. These results provide a basis for the design and analysis of observations of H-alpha, in coordination with hard X-rays or microwaves, to test mechanisms of energy transport in solar flares.

  6. On the sensitivity of the goes flare classification to properties of the electron beam in the thick-target model

    SciTech Connect

    Reep, J. W.; Bradshaw, S. J.; McAteer, R. T. J. E-mail: stephen.bradshaw@rice.edu

    2013-11-20

    The collisional thick-target model, wherein a large number of electrons are accelerated down a flaring loop, can be used to explain many observed properties of solar flares. In this study, we focus on the sensitivity of (GOES) flare classification to the properties of the thick-target model. Using a hydrodynamic model with RHESSI-derived electron beam parameters, we explore the effects of the beam energy flux (or total non-thermal energy), the cut-off energy, and the spectral index of the electron distribution on the soft X-rays observed by GOES. We conclude that (1) the GOES class is proportional to the non-thermal energy E {sup α} for α ≈ 1.7 in the low-energy passband (1-8 Å) and ≈1.6 in the high-energy passband (0.5-4 Å); (2) the GOES class is only weakly dependent on the spectral index in both passbands; (3) increases in the cut-off will increase the flux in the 0.5-4 Å passband but decrease the flux in the 1-8 Å passband, while decreases in the cut-off will cause a decrease in the 0.5-4 Å passband and a slight increase in the 1-8 Å passband.

  7. High-resolution X-ray spectra of solar flares. VII - A long-duration X-ray flare associated with a coronal mass ejection

    NASA Technical Reports Server (NTRS)

    Kreplin, R. W.; Doschek, G. A.; Feldman, U.; Sheeley, N. R., Jr.; Seely, J. F.

    1985-01-01

    It has been recognized that very long duration X-ray events (lasting several hours) are frequently associated with coronal mass ejection. Thus, Sheeley et al. (1983) found that the probability of the occurrence of a coronal mass ejection (CME) increases monotonically with the X-ray event duration time. It is pointed out that the association of long-duration, or long-decay, X-ray events (LDEs) with CMEs was first recognized from analysis of solar images obtained by the X-ray telescopes on Skylab and the Naval Research Laboratory (NRL) slitless spectroheliograph. Recently high-resolution Bragg crystal X-ray spectrometers have been flown on three spacecraft, including the Department of Defense P78-1 spacecraft, the NASA Solar Maximum Mission (SMM), and the Japanese Hinotori spacecraft. In the present paper, P78-1 X-ray spectra of an LDE which had its origin behind the solar west limb on November 14, 1980 is presented. The obtained data make it possible to estimate temperatures of the hottest portion of the magnetic loops in which the emission arises.

  8. Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA)

    National Institute of Standards and Technology Data Gateway

    SRD 100 Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA) (PC database for purchase)   This database has been designed to facilitate quantitative interpretation of Auger-electron and X-ray photoelectron spectra and to improve the accuracy of quantitation in routine analysis. The database contains all physical data needed to perform quantitative interpretation of an electron spectrum for a thin-film specimen of given composition. A simulation module provides an estimate of peak intensities as well as the energy and angular distributions of the emitted electron flux.

  9. The great flare of 1982 June 6

    NASA Technical Reports Server (NTRS)

    Tanaka, K.; Zirin, H.

    1985-01-01

    The great soft X-ray (SXR) flare (X12) of the past solar maximum was observed by Hinotori and by Big Bear Solar Observatory (BBSO) on June 6, 1982. Hinotori data consist of hard X-ray (HXR) and SXR images in the rise and decay of the flare, high-resolution soft X-ray spectra throughout the flare, and HXR and gamma-ray data. The BBSO data include films of H-alpha, H-alpha blue wing, D3 and longitudinal magnetic field, as well as video tapes of continuum. Images in HXR, SXR, H-alpha, D3 and the continuum are compared and SXR spectra analyzed. The flare resulted from extended motion of a large spot shearing the magnetic field. D3 and white-light images exhibit a progression from fast flashes to two ribbons, while both HXR and SXR are centered on the optical kernels. The continuum emission shows the same temporal behavior as the HXR at 160 keV. In its early phases, the Fe XXV line was double-peaked, and a decreasing blueshifted (up to 400 km/sec) component was observed, from which the evaporation rate of chromospheric material was estimated. It is suggested that this upflow is adequate to supply the coronal cloud. Flare energetics are discussed in detail, and it is concluded that a significant amount of energy was deposited in the corona, and that nonthermal electrons are the major energy input.

  10. Particle kinematics in solar flares: observations and theory

    NASA Astrophysics Data System (ADS)

    Battaglia, Marina

    2008-12-01

    This thesis is devoted to the study of particle acceleration and propagation processes in solar flares. Solar flares are amongst the most powerful and energetic activity phenomena our Sun exhibits. They release energy of the order of 10(32) erg in seconds to minutes. In the process, electrons and protons are accelerated to relativistic energies, making flares very efficient particle accelerators. The most compelling observational signatures of flares can be found in X-rays and extreme ultra-violet wavelengths. Due to atmospheric absorption, those wavelengths can only be studied from space. Since the beginning of the space age, countless flares have been observed by satellites. The present work is largely based on observations by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), an X-ray satellite which has been observing the Sun since February 2002. It is a NASA mission with substantial Swiss hardware and software contribution. Using RHESSI observations of flares of different intensity, a deeper understanding of the particle transport and energy transport processes in flare loops, as well as the acceleration site and acceleration mechanism is sought. The time evolution of images and spectra is studied along with the quantitative relations between X-ray sources observed in the corona (coronal sources) and from the chromosphere (footpoints). The spectral relations found between coronal sources and footpoints are compared to the so-called ``intermediate thin-thick target model'', which was based on observations by the satellite Yohkoh. We show that the spectral relations between coronal sources and footpoints observed with RHESSI cannot be explained by the intermediate thin-thick target model. In a next step, return currents in the flare loop were considered. With this extension to the existing model, the spectra of the coronal source and the footpoints, as well as the relations between them can be explained, indicating the importance of return currents in

  11. Electron-impact mass spectra of carbomethoxyl derivatives of cyclopropylthiophenes

    SciTech Connect

    Kadentsev, V.I.; Kolotyrkina, N.G.; Chizhov, O.S.; Shostakovskii, V.M.; Vasil'vitskii, A.A.; Zlatkina, V.L.

    1987-01-10

    In the mass spectra of carbomethoxyl derivatives of cyclopropylthiophene, intense ion peaks are observed, corresponding to successive elimination of MeO and COOMe radicals and the neutral fragments MeOH, HCOOMe, and CO from M/sup +./, so that the number of carbomethoxyl substituents in CPR can be determined. Mono- and gem-dicarbomethoxyl derivatives of cyclopropylthiophenes are characterized by rearrangements of M/sup +./ with migration of the MeO groups to the carbon atom adjacent to the thiophene ring. The presence of a methyl substituent at this carbon atom hinders this rearrangement. For the monocarbomethoxyl derivatives of cyclopropylthiophenes under electron impact, a splitting off of the methyl substituent of the ester groups is observed.

  12. Investigation of Zebra-structure in the flare of 4 April 2011 associated with electron beam precipitation from the corona

    NASA Astrophysics Data System (ADS)

    Zharkova, Valentina; Meshalkina, Natalia; Altyntsev, Alexander; Dobranskis, Rytis; Zhdanov, Dmitrii

    We present the study of multi-wavelength observations of the flare of 4th April 2011 obtained by Siberian Solar Radio Telescope (SSRT) , Siberian Solar Broadband Spectropolarimeter 4-8 GHz (SSBS) and other instruments. We report a burst-like increase of radio emission and the occurrence of well defined zebra-structure firstly registered by the new instrument (SBRS). The findings are tested by the model of electron beam precipitation with return current while generating of Langmuir turbulence and causing a formation of negative charge condensations induced by anomalous doppler resonance of electrons on the generated Langmuir waves.

  13. CONSTRAINING SOLAR FLARE DIFFERENTIAL EMISSION MEASURES WITH EVE AND RHESSI

    SciTech Connect

    Caspi, Amir; McTiernan, James M.; Warren, Harry P.

    2014-06-20

    Deriving a well-constrained differential emission measure (DEM) distribution for solar flares has historically been difficult, primarily because no single instrument is sensitive to the full range of coronal temperatures observed in flares, from ≲2 to ≳50 MK. We present a new technique, combining extreme ultraviolet (EUV) spectra from the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory with X-ray spectra from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), to derive, for the first time, a self-consistent, well-constrained DEM for jointly observed solar flares. EVE is sensitive to ∼2-25 MK thermal plasma emission, and RHESSI to ≳10 MK; together, the two instruments cover the full range of flare coronal plasma temperatures. We have validated the new technique on artificial test data, and apply it to two X-class flares from solar cycle 24 to determine the flare DEM and its temporal evolution; the constraints on the thermal emission derived from the EVE data also constrain the low energy cutoff of the non-thermal electrons, a crucial parameter for flare energetics. The DEM analysis can also be used to predict the soft X-ray flux in the poorly observed ∼0.4-5 nm range, with important applications for geospace science.

  14. A thermal/nonthermal approach to solar flares

    NASA Technical Reports Server (NTRS)

    Benka, Stephen G.

    1991-01-01

    An approach for modeling solar flare high-energy emissions is developed in which both thermal and nonthermal particles coexist and contribute to the radiation. The thermal/nonthermal distribution function is interpreted physically by postulating the existence of DC sheets in the flare region. The currents then provide both primary plasma heating through Joule dissipation, and runaway electron acceleration. The physics of runaway acceleration is discussed. Several methods are presented for obtaining approximations to the thermal/nonthermal distribution function, both within the current sheets and outside of them. Theoretical hard x ray spectra are calculated, allowing for thermal bremsstrahlung from the heated plasma electrons impinging on the chromosphere. A simple model for hard x ray images of two-ribbon flares is presented. Theoretical microwave gyrosynchrotron spectra are calculated and analyzed, uncovering important new effects caused by the interplay of thermal and nonthermal particles. The theoretical spectra are compared with observed high resolution spectra of solar flares, and excellent agreement is found, in both hard x rays and microwaves. The future detailed application of this approach to solar flares is discussed, as are possible refinements to this theory.

  15. On the dependence of solar flare X-ray spectral line intensity ratios of highly ionized sulfur, calcium, and iron on electron temperature, differential emission measure, and atomic physics

    NASA Technical Reports Server (NTRS)

    Doschek, G. A.; Fludra, A.; Bentley, R. D.; Lang, J.; Phillips, K. J. H.

    1990-01-01

    This paper focuses on what can be learned about the emission measure distribution and certain atomic physics parameters from spectral lines of highly ionized ions of sulfur, calcium, and iron that appear in solar flare spectra. The particular lines chosen for analysis allow the electron temperature to be determined independently of the assumption of ionization equilibrium. An attempt is made to find emission measure models based on selected functional dependences of emission measure on temperature that reproduce the observed temperatures deduced from spectral line ratios as well as the relative intensities of resonance lines of different elements.

  16. Electron acceleration in a flare plasma via coronal circuits. (German Title: Elektronenbeschleunigung im Flareplasma modelliert mit koronalen Schaltkreisen)

    NASA Astrophysics Data System (ADS)

    Önel, Hakan

    2008-08-01

    The Sun is a star, which due to its proximity has a tremendous influence on Earth. Since its very first days mankind tried to "understand the Sun", and especially in the 20th century science has uncovered many of the Sun's secrets by using high resolution observations and describing the Sun by means of models. As an active star the Sun's activity, as expressed in its magnetic cycle, is closely related to the sunspot numbers. Flares play a special role, because they release large energies on very short time scales. They are correlated with enhanced electromagnetic emissions all over the spectrum. Furthermore, flares are sources of energetic particles. Hard X-ray observations (e.g., by NASA's RHESSI spacecraft) reveal that a large fraction of the energy released during a flare is transferred into the kinetic energy of electrons. However the mechanism that accelerates a large number of electrons to high energies (beyond 20 keV) within fractions of a second is not understood yet. The thesis at hand presents a model for the generation of energetic electrons during flares that explains the electron acceleration based on real parameters obtained by real ground and space based observations. According to this model photospheric plasma flows build up electric potentials in the active regions in the photosphere. Usually these electric potentials are associated with electric currents closed within the photosphere. However as a result of magnetic reconnection, a magnetic connection between the regions of different magnetic polarity on the photosphere can establish through the corona. Due to the significantly higher electric conductivity in the corona, the photospheric electric power supply can be closed via the corona. Subsequently a high electric current is formed, which leads to the generation of hard X-ray radiation in the dense chromosphere. The previously described idea is modelled and investigated by means of electric circuits. For this the microscopic plasma parameters

  17. On the analysis of photo-electron spectra

    SciTech Connect

    Gao, C.-Z.; Dinh, P.M.; Reinhard, P.-G.; Suraud, E.

    2015-09-15

    We analyze Photo-Electron Spectra (PES) for a variety of excitation mechanisms from a simple mono-frequency laser pulse to involved combination of pulses as used, e.g., in attosecond experiments. In the case of simple pulses, the peaks in PES reflect the occupied single-particle levels in combination with the given laser frequency. This usual, simple rule may badly fail in the case of excitation pulses with mixed frequencies and if resonant modes of the system are significantly excited. We thus develop an extension of the usual rule to cover all possible excitation scenarios, including mixed frequencies in the attosecond regime. We find that the spectral distributions of dipole, monopole and quadrupole power for the given excitation taken together and properly shifted by the single-particle energies provide a pertinent picture of the PES in all situations. This leads to the derivation of a generalized relation allowing to understand photo-electron yields even in complex experimental setups.

  18. Electronic spectra of Yb2+-doped SrCl2

    NASA Astrophysics Data System (ADS)

    Sánchez-Sanz, Goar; Seijo, Luis; Barandiarán, Zoila

    2010-09-01

    The absorption and emission spectra of Yb2+-doped SrCl2 have been calculated on the basis of ab initio quantum chemical calculations which consider recently found, unexpected excited states with double-well energy curves and complex electronic structure, resulting from avoided crossings between Yb-trapped excitons and Yb impurity states, which influence prominent spectral features. The root mean square deviation and largest absolute error of the calculated energy levels are 394 and -826 cm-1, respectively. The YbCl8 moiety breathing mode vibrational frequencies and bond lengths of the lowest states are consistent with observed vibrational progressions and energy shifts induced by uniaxial compression. Photoionization is predicted above 49 000 cm-1 as a consequence of the spin-orbit induced spreading of the Yb-trapped exciton character in the upper part of the spectrum and three new emission bands are predicted with origins at about 33 800, 36 400, and 43 600 cm-1. The electron correlation methods used overestimate the relative stabilization of the 4f14 ground state and this leads to a constant error of the whole absorption spectrum of about 3500 cm-1 (23%-7%). Although this energy shift is customarily considered an adjustable parameter, it is a nonparametric, direct product in an ab initio route which shows the limitations on the proper representation of differential correlation between the 4fN and 4fN -15d (or similar) configurations and the need for theoretical improvement.

  19. A new path for the electron bulk energization in solar flares: Fermi acceleration by magnetohydrodynamic turbulence in reconnection outflows

    NASA Technical Reports Server (NTRS)

    Larosa, T. N.; Moore, R. L.; Shore, S. N.

    1994-01-01

    We recently proposed that a magnetohydrodynamic (MHD) turbulent cascade produces the bulk energization of electrons to approximately 25 keV in the impulsive phase of solar flares (LaRosa & Moore 1993). In that scenario, (1) the cascading MHD turbulence is fed by shear-unstable Alfvenic outflows from sites of strongly driven reconnection in the low corona, and (2) the electrons are energized by absorbing the energy that flows down through the cascade. We did not specify the physical mechanism by which the cascading energy is ultimately transferred to the electrons. Here we propose that Fermi acceleration is this mechanism, the process by which the electrons are energized and by which the cascading MHD turbulence is dissipated. We point out that in the expected cascade MHD fluctuations of scale 1 km can Fermi-accelerate electrons from 0.1 keV to approximately 25 keV on the subsecond timescales observed in impulsive flares, provided there is sufficient trapping and scattering of electrons in the MHD turbulence. We show that these same fluctuations provide the required trapping; they confine the electrons within the turbulent region until the turbulence eis dissipated. This results in the energization of all of the lectrons in each large-scale (5 x 10(exp 7)cm) turbulent eddy to 25 keV. The Fermi process also requires efficient scattering so that the pitch-angle distribution of the accelerating electrons remains isotropic. We propose that the electrons undergo resonant scattering by high-frequency plasma R-waves that, as suggested by others (Hamilton & Petrosian 1992), are generated by the reconnection. Ions are not scattered by R-waves. Provided that there is negligible generation of ion-scattering plasma turbulence (e.g., L-waves) by the reconnection or the MHD turbulence, the ions will not Fermi-accelerate and the cascading energy is transferred only to the electrons. We conclude that, given this situation, electron Fermi acceleration can plausibly account for the

  20. Two-dimensional electronic-vibrational spectra: modeling correlated electronic and nuclear motion.

    PubMed

    Terenziani, F; Painelli, A

    2015-05-21

    We calculate 2D electronic-vibrational (2D-EV) spectra of solvated organic dyes modeled in terms of a reduced set of electronic diabatic states (the essential states) non-adiabatically coupled to molecular vibrations. An effective overdamped coordinate, whose dynamics is described by the Smoluchowski diffusion equation, accounts for polar solvation. Results are discussed for two dyes with distinctively different spectroscopic behavior: 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) and 8-(N,N-dibutylamino)-2-azachrysene (AAC). Linear absorption and fluorescence spectra of DCM are well reproduced based on a minimal two-state model. The same model leads to 2D-EV spectra in good agreement with the recent experimental data reported by Oliver and coworkers for DCM in DMSO. In contrast, linear spectra of AAC show a subtle interplay between a locally-excited (LE) and a charge-transfer (CT) excitation, calling for a three-state model. Calculated 2D-EV spectra for AAC show a qualitatively different behavior, demonstrating that the experimental data for DCM do not support a LE/CT interplay. This resolves the long-lasting discussion about the nature of low-lying excitations of DCM in favor of the simplest picture. PMID:25912698

  1. Solar flare particle radiation

    NASA Technical Reports Server (NTRS)

    Lanzerotti, L. J.

    1972-01-01

    The characteristics of the solar particles accelerated by solar flares and subsequently observed near the orbit of the earth are studied. Considered are solar particle intensity-time profiles, the composition and spectra of solar flare events, and the propagation of solar particles in interplanetary space. The effects of solar particles at the earth, riometer observations of polar cap cosmic noise absorption events, and the production of solar cell damage at synchronous altitudes by solar protons are also discussed.

  2. Flare Hybrids

    NASA Astrophysics Data System (ADS)

    Tomczak, M.; Dubieniecki, P.

    2015-12-01

    On the basis of the Solar Maximum Mission observations, Švestka ( Solar Phys. 121, 399, 1989) introduced a new class of flares, the so-called flare hybrids. When they start, they look like typical compact flares (phase 1), but later on, they look like flares with arcades of magnetic loops (phase 2). We summarize the characteristic features of flare hybrids in soft and hard X-rays as well as in the extreme ultraviolet; these features allow us to distinguish flare hybrids from other flares. In this article, additional energy release or long plasma cooling timescales are suggested as possible causes of phase 2. We estimate the frequency of flare hybrids, and study the magnetic configurations favorable for flare hybrid occurrence. Flare hybrids appear to be quite frequent, and the difference between the lengths of magnetic loops in the two interacting loop systems seem to be a crucial parameter for determining their characteristics.

  3. Particle-in-cell simulations of electron energization from low Mach number quasi-perpendicular shocks in solar flares

    NASA Astrophysics Data System (ADS)

    Blackman, Eric; Park, Jaehong; Ren, Chuang; Workman, Jared

    2012-10-01

    Low Mach/high beta fast mode shocks can occur in the magnetic reconnection outflows of solar flares. These shocks, which occur above flare loop tops, may provide electron energization responsible for some of the hard X-rays detected by YOHKO and the RHESSE, and radio emission. There has been a dearth of work on understanding the microphysics of these low Mach number shocks. We present new 2D particle-in-cell simulations of low Mach/high beta shocks for the general quasi-perpendicular geometry of field and shock normal to compare with the results for the purely perpendicular case considered in Park et. al. (2012)[Phys.Plasmas 19,062904]. Our aim is to study shock structure and particle acceleration. We find that the modified-two-stream instability sustains the shock and accounts for the entropy creation downstream. We observe the electron Whistler instability in the transition region due to the temperature anisotropy. To have enough simulation electrons above the threshold energy for shock-drift-acceleration (SDA), we inject a two-temperature Maxwellian distribution represented by two separate species, which is approximated to a kappa distribution with κ=10. From particle tracking and the particle energy distribution, we find copious high-energy electrons experiencing SDA.

  4. Electron acceleration in solar flares and the transition from nonthermal to thermal hard X-ray phases

    NASA Technical Reports Server (NTRS)

    Smith, D. F.

    1985-01-01

    Observations are reviewed which indicate that hard X-rays during the impulsive phase of a flare typically start with a primarily nonthermal phase which undergoes a transition to a primarily thermal phase as the flare progresses. Recent theoretical work on the modified two-stream instability as an efficient electron accelerator and modeling of thermal hard X-ray sources is considered. A scenario which is termed the dissipative thermal model is proposed to explain the observations. Fast tearing modes occurring in a loop give rise to cross-field ion motion. This in turn excites the modified two-stream instability which converts about 50 percent of the ion energy into accelerated electrons along the loop as long as the plasma beta is less than 0.3. These electrons impact the chromosphere and boil off a part of it which rises up the loop. This density increase coupled with the temperature increase due to tearing causes the beta to increase beyond 0.3 and efficient electron acceleration ceases. This leads to the primarily thermal phase.

  5. Implications of RHESSI Observations for Solar Flare Models and Energetics

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.

    2006-01-01

    Observations of solar flares in X-rays and gamma-rays provide the most direct information about the hottest plasma and energetic electrons and ions accelerated in flares. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has observed over 18000 solar flares in X-rays and gamma-rays since its launch in February of 2002. RHESSI observes the full Sun at photon energies from as low as 3 keV to as high as 17 MeV with a spectral resolution on the order of 1 keV. It also provides images in arbitrary bands within this energy range with spatial resolution as good as 3 seconds of arc. Full images are typically produced every 4 seconds, although higher time resolution is possible. This unprecedented combination of spatial, spectral, and temporal resolution, spectral range and flexibility has led to fundamental advances in our understanding of flares. I will show RHESSI and coordinated observations that confirm coronal magnetic reconnection models for eruptive flares and coronal mass ejections, but also present new puzzles for these models. I will demonstrate how the analysis of RHESSI spectra has led to a better determination of the energy flux and total energy in accelerated electrons, and of the energy in the hot, thermal flare plasma. I will discuss how these energies compare with each other and with the energy contained in other flare-related phenomena such as interplanetary particles and coronal mass ejections.

  6. Interpretation of the electronic spectra of four disilanes.

    PubMed

    Piqueras, Mari Carmen; Crespo, Raül; Michl, Josef

    2008-12-18

    Time-dependent density functional theory (TD-DFT/B3LYP(AC)/cc-pVTZ/cc-pVTZ/6-311G//MP2/cc-pVTZ/cc-pVTZ/6-31G**) has been used to compute vertical excitation energies and oscillator strengths of the six low-lying excited states of four peralkylated disilanes, hexamethyldisilane (1), hexa-tert-butyldisilane (2), 1,6-disila[4.4.4]propellane (3), and 1,7-disila[5.5.5]propellane (4). The results provide an accurate interpretation of the reported UV absorption spectra of 1-4 in solution, and for 1 also in the gas phase up to 62,000 cm(-1). The excellent agreement of the calculated with the available experimental energies and oscillator strengths, and with magnetic circular (MCD) and linear (LD) dichroism, gives us confidence that the method will be useful for dependable interpretation of the electronic spectra of longer oligosilanes. Although the disilane chromophore finds itself in quite different environments in 1-4, its fundamental characteristics remain the same, with one important exception. In all four compounds, the first valence excited state is due to an electron promotion from the sigma(1) HOMO to the pi(1)* orbital, and the second valence excited state to a promotion from the sigma(1) HOMO to the sigma(1)* orbital. Surprisingly, however, it is only in 2, which has an extraordinarily long SiSi bond, that the terminating sigma(1)* orbital is the sigma*(SiSi) antibond, as anticipated, and the sigma sigma* transition has the expected very high oscillator strength. In 1, 3, and 4, the sigma*(SiSi) antibonding orbital is high in energy and does not play any role in low-energy excitations. Instead, the terminating orbital of the sigma(1)sigma(1)* excitation is represented by Si-alkyl antibonds, combined symmetrically with respect to rotation around the SiSi axis and antisymmetrically with respect to operations that interchange the two Si atoms. The common assumption that the characteristic intense sigma sigma* transitions of longer peralkylated oligosilanes

  7. Non-thermal electron acceleration in low Mach number collisionless shocks. I. Particle energy spectra and acceleration mechanism

    SciTech Connect

    Guo, Xinyi; Narayan, Ramesh; Sironi, Lorenzo

    2014-10-20

    Electron acceleration to non-thermal energies in low Mach number (M{sub s} ≲ 5) shocks is revealed by radio and X-ray observations of galaxy clusters and solar flares, but the electron acceleration mechanism remains poorly understood. Diffusive shock acceleration, also known as first-order Fermi acceleration, cannot be directly invoked to explain the acceleration of electrons. Rather, an additional mechanism is required to pre-accelerate the electrons from thermal to supra-thermal energies, so they can then participate in the Fermi process. In this work, we use two- and three-dimensional particle-in-cell plasma simulations to study electron acceleration in low Mach number shocks. We focus on the particle energy spectra and the acceleration mechanism in a reference run with M{sub s} = 3 and a quasi-perpendicular pre-shock magnetic field. We find that about 15% of the electrons can be efficiently accelerated, forming a non-thermal power-law tail in the energy spectrum with a slope of p ≅ 2.4. Initially, thermal electrons are energized at the shock front via shock drift acceleration (SDA). The accelerated electrons are then reflected back upstream where their interaction with the incoming flow generates magnetic waves. In turn, the waves scatter the electrons propagating upstream back toward the shock for further energization via SDA. In summary, the self-generated waves allow for repeated cycles of SDA, similarly to a sustained Fermi-like process. This mechanism offers a natural solution to the conflict between the bright radio synchrotron emission observed from the outskirts of galaxy clusters and the low electron acceleration efficiency usually expected in low Mach number shocks.

  8. An investigation of small goes flares with intense hard x-ray bursts

    NASA Astrophysics Data System (ADS)

    McDonald, L.; Harra-Murnion, L. K.; Culhane, J. L.; Schwartz, A.

    1997-01-01

    Most solar flare observations show that intense hard X-ray bursts come from large flares that have a large GOES classification (large peak 1 - 8 A˚ flux). This correlation, known as the ``Big Flare Syndrome'', suggests that more intense flares tend to have harder spectra. We have observed 7 flares that are exceptions to this. These flares have small GOES classifications ranging from B1.4 to C5.5 and peak hard X-ray count rates similar to those often observed from M class flares. This paper examines the cause of this anomoly using the Yohkoh Soft X-Ray Telescope, Hard X-Ray Telescope, and Bragg Crystal Spectrometer. Two hypotheses are proposed for the exceptions: (1) flares with multiple magnetic loops and common footpoints, producing multiple hard X-ray emission regions and low density thermal plasma distributed over a large volume, and (2) high densities in the magnetic loops restricting the propagation of the non-thermal electrons in the loop after magnetic reconnection has occurred and suppressing chromospheric evaporation. Two of the flares support the first hypothesis. The other flares either have data missing or are too small to be properly analysed by the Yohkoh instruments.

  9. Nonthermal X-ray Spectral Flattening toward Low Energies in Early Impulsive Flares

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.

    2007-01-01

    The determination of the low-energy cutoff to nonthermal electron distributions is critical to the calculation of the nonthermal energy in solar flares. The most direct evidence for low-energy cutoffs is flattening of the power-law, nontherma1 X-ray spectra at low energies. However, because of the plasma preheating often seen in flares, the thermal emissions at low energies may hide such spectral flattening of the nonthermal component. We select a category of flares, which we call "early impulsive flares", in which the > 25 keV hard X-ray (HXR) flux increase is delayed by less than 30 s after the flux increase at lower energies. Thus, the plasma preheating in these flares is minimal, so the nonthermal spectrum can be determined to lower energies than in flares with significant preheating. Out of a sample of 33 early impulsive flares observed by the Ramaty High Energy Solar Spectroscopy Imager (RHESSI), 9 showed spectral flattening toward low energies. In these events, the break energy of the double power-law fit to the HXR spectra lies in the range of 10-50 keV, significantly lower than the value we have seen for other flares that do not show such early impulsive emissions. In particular, it correlates with the HXR flux. After correcting the spatially-integrated spectra for albedo from isotropically emitted X-rays and using RHESSI imaging spectroscopy to exclude the extended albedo halo, we find that albedo associated with isotropic or nearly isotropic electrons can only account for the spectral flattening in 3 flares near Sun center. The spectral flattening in the remaining 6 flares is found to be consistent with the existence of a low-energy cutoff in the electron spectrum, falling in the range of 15-50 keV, which also correlates with the HXR flux.

  10. Ab initio electronic and optical spectra of free-base porphyrins: The role of electronic correlation.

    PubMed

    Palummo, Maurizia; Hogan, Conor; Sottile, Francesco; Bagalá, Paolo; Rubio, Angel

    2009-08-28

    We present a theoretical investigation of electronic and optical properties of free-base porphyrins based on density functional theory and many-body perturbation theory. The electronic levels of free-base porphine (H(2)P) and its phenyl derivative, free-base tetraphenylporphyrin (H(2)TPP) are calculated using the ab initio GW approximation for the self-energy. The approach is found to yield results that compare favorably with the available photoemission spectra. The excitonic nature of the optical peaks is revealed by solving the Bethe-Salpeter equation, which provides an accurate description of the experimental absorption spectra. The lowest triplet transition energies are in good agreement with the measured values. PMID:19725603

  11. Radio and Hard X-Ray Images of High-Energy Electrons in an X-Class Solar Flare

    NASA Technical Reports Server (NTRS)

    White, S. M.; Krucker, S.; Shibasaki, K.; Yokoyama, T.; Shimojo, M.; Kundu, Mukul R.

    2003-01-01

    We present the first comparison between radio images of high-energy electrons accelerated by a solar flare and images of hard X-rays produced by the same electrons at photon energies above 100 keV. The images indicate that the high-energy X-rays originate at the footpoints of the loops dominating the radio emission. The radio and hard X-ray light curves match each other well and are quantitatively consistent with an origin in a single population of nonthermal electrons with a power-law index of around 4.5-5. The high-frequency radio spectral index suggests a flatter energy spectrum, but this is ruled out by the X-ray spectrum up to 8 MeV.

  12. Exciton Scattering approach for conjugated macromolecules: from electronic spectra to electron-phonon coupling

    NASA Astrophysics Data System (ADS)

    Tretiak, Sergei

    2014-03-01

    The exciton scattering (ES) technique is a multiscale approach developed for efficient calculations of excited-state electronic structure and optical spectra in low-dimensional conjugated macromolecules. Within the ES method, the electronic excitations in the molecular structure are attributed to standing waves representing quantum quasi-particles (excitons), which reside on the graph. The exciton propagation on the linear segments is characterized by the exciton dispersion, whereas the exciton scattering on the branching centers is determined by the energy-dependent scattering matrices. Using these ES energetic parameters, the excitation energies are then found by solving a set of generalized ``particle in a box'' problems on the graph that represents the molecule. All parameters can be extracted from quantum-chemical computations of small molecular fragments and tabulated in the ES library for further applications. Subsequently, spectroscopic modeling for any macrostructure within considered molecular family could be performed with negligible numerical effort. The exciton scattering properties of molecular vertices can be further described by tight-binding or equivalently lattice models. The on-site energies and hopping constants are obtained from the exciton dispersion and scattering matrices. Such tight-binding model approach is particularly useful to describe the exciton-phonon coupling, energetic disorder and incoherent energy transfer in large branched conjugated molecules. Overall the ES applications accurately reproduce the optical spectra compared to the reference quantum chemistry results, and make possible to predict spectra of complex macromolecules, where conventional electronic structure calculations are unfeasible.

  13. Solar Flares Observed with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI)

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.

    2004-01-01

    Solar flares are impressive examples of explosive energy release in unconfined, magnetized plasma. It is generally believed that the flare energy is derived from the coronal magnetic field. However, we have not been able to establish the specific energy release mechanism(s) or the relative partitioning of the released energy between heating, particle acceleration (electrons and ions), and mass motions. NASA's RHESSI Mission was designed to study the acceleration and evolution of electrons and ions in flares by observing the X-ray and gamma-ray emissions these energetic particles produce. This is accomplished through the combination of high-resolution spectroscopy and spectroscopic imaging, including the first images of flares in gamma rays. RHESSI has observed over 12,000 solar flares since its launch on February 5, 2002. I will demonstrate how we use the RHESSI spectra to deduce physical properties of accelerated electrons and hot plasma in flares. Using images to estimate volumes, w e typically find that the total energy in accelerated electrons is comparable to that in the thermal plasma. I will also present flare observations that provide strong support for the presence of magnetic reconnection in a large-scale, vertical current sheet in the solar corona. RHESSI observations such as these are allowing us to probe more deeply into the physics of solar flares.

  14. On the threshold of proton acceleration in solar flares

    NASA Astrophysics Data System (ADS)

    Miroshnichenko, L. I.

    1995-01-01

    Based on the reconnection theory of a flare and on recent observational and statistical findings, the problem of the initial acceleration of solar cosmic rays (SCR) is discussed. Simple estimates of the electric fields required to start the electron acceleration are obtained and the problem of proton ionization losses for overcoming the Coulomb barrier is considered. We take into account also the possible differences between proton and electron spectra from the very beginning of the acceleration process. Special attention is paid to the distribution functions of solar flare events in various parameters (peak fluxes and/or energy fluences in X-ray and radio wave bursts, in proton and electron emissions, etc.). It is shown that the distribution functions allow the interpretation of some scale and time flare parameters in terms of expected threshold effects. However, these functions are still insuffienet to evaluate the relative share of different emissions in the global energy budget of a flare. In this context, a more promising approach is to derive the direct ratio between the number of accelerated protons, Np, and total flare energy, Wf, within the frame of a certain acceleration model. It is argued that an absolute threshold for proton production (in Hudson's formulation) does not exist. Meanwhile, the flux and threshold energy of accelerated protons overcoming the Coulomb loss maximum, in fact, may depend heavily on the global output of flare energy.

  15. Late variability of flux and spectra of the tTidal disruption flare Sw J1644+57 from XMM-Newton data

    NASA Astrophysics Data System (ADS)

    González-Rodríguez, A.; Castro-Tirado, A. J.; Guerrero, M. A.; Castellón, A.

    2014-12-01

    We describe the late spectral variability and flux evolution of TDF Sw J1644+57, a Tidal Disruption Flare which left the typical potential trend proportional to t(-5/3) in 2012, maintaining a quiescent flux until nowadays. Sixteen X-ray observations of ESA satellite XMM-Newton have been used in this study, including the one performed on 17th July, 2013. A search for optical emission in BOOTES/CASANDRA database has been performed too. Late X-ray fluxes show that the source flux decline does not follow the expected TDF trend at the time of the last XMM-Newton observation. Moreover, the spectra fitting parameters, in particular the neutral hydrogen column density, N_{H}, and the power-law index, Γ, indicate that the source darkening has diminished and that the spectral shape has flattened with time. The disruption of the star could have come to an end. Nevertheless, a quiescent X-ray flux continues. Evidence for a quiescent X-ray flux is presented.

  16. High-Cadence and High-Resolution Halpha Imaging Spectroscopy of a Circular Flare's Remote Ribbon with IBIS

    NASA Astrophysics Data System (ADS)

    Deng, Na; Tritschler, A.; Jing, J.; Chen, X.; Liu, C.; Reardon, K. P.; Denker, C.; Xu, Y.; Wang, H.

    2013-07-01

    We present an unprecedented high-resolution halpha imaging spectroscopic observation of a C4.1 flare taken with IBIS on 2011 October 22. The flare consists of a main circular ribbon that occurred in a parasitic magnetic configuration and a remote ribbon that was observed by the IBIS. Such a circular-ribbon flare with a remote brightening is predicted in 3D fan-spine reconnection but so far has been rarely reported. During the flare impulsive phase, we define "core" and "halo" structures in the observed ribbon. Examining the halpha emission spectra averaged in the flare core and halo areas, we find that only those from the flare cores show typical nonthermal electron beam heating characteristics. These characteristics include: broad and centrally reversed emission spectra, excess emission in the red wing with regard to the blue wing (i.e., red asymmetry), and redshifted bisectors of the emission spectra. We also observe rather quick timescales for the heating (30 s) and cooling (14--33 s) in the flare core locations. Therefore, we suggest that the flare cores revealed by IBIS track the sites of electron beam precipitation with exceptional spatial and temporal resolution. The flare cores show two-stage motion (a parallel motion along the ribbon followed by an expansion motion perpendicular to the ribbon) during the two impulsive phases of the flare. Some cores jump quickly (30 km/s) between discrete magnetic elements implying reconnection involving different flux tubes. We observe a very high temporal correlation (>0.9) between the integrated halpha and HXR emission during the flare impulsive phase. A short time delay (4.6 s) is also found in the halpha emission spikes relative to HXR bursts. The ionization timescale of the cool chromosphere and the extra time taken for the electrons to travel to the remote ribbon site may contribute to this delay.

  17. Solar flares

    NASA Technical Reports Server (NTRS)

    Zirin, H.

    1974-01-01

    A review of the knowledge about solar flares which has been obtained through observations from the earth and from space by various methods. High-resolution cinematography is best carried out at H-alpha wavelengths to reveal the structure, time history, and location of flares. The classification flares in H alpha according to either physical or morphological criteria is discussed. The study of flare morphology, which shows where, when, and how flares occur, is important for evaluating theories of flares. Consideration is given to studies of flares by optical spectroscopy, radio emissions, and at X-ray and XUV wavelengths. Research has shown where and possibly why flares occur, but the physics of the instability involved, of the particle acceleration, and of the heating are still not understood.

  18. Combined Particle Acceleration in Solar Flares and Associated CME Shocks

    NASA Astrophysics Data System (ADS)

    Petrosian, Vahe

    2016-07-01

    I will review some observations of the characteristics of accelerated electrons seen near Earth (as SEPs) and those producing flare radiation in the low corona and chromosphere. The similarities and differences between the numbers, spectral distribution, etc. of the two population can shed light on the mechanism and sites of the acceleration. I will show that in some events the origin of both population appears to be the flare site while in others, with harder SEP spectra, in addition to acceleration at the flare site, there appears to be a need for a second stage re-acceleration in the associated fast Coronal Mass Ejection (CME) environment. This scenario can also describe a similar dichotomy that exists between the so called impulsive, highly enriched (3He and heavy ions) and softer SEP ion events, and stronger more gradual SEP events with near normal ionic abundances and harder spectra. I will also describe under what conditions such hardening can be achieved.

  19. Electronic states and spectra of BiH

    NASA Astrophysics Data System (ADS)

    Setzer, Klaus-Dieter; Fink, Ewald H.; Hill, Christian; Brown, John M.

    2015-06-01

    Emission spectra of bismuth monohydride (BiH) radicals excited by energy transfer from O2(a1Δg) or NF(a1Δ) or by a DC discharge in a mixture of bismuth vapor and hydrogen in a fast-flow system were studied in the wavenumber range from 4000 to 25 000 cm-1 with a Fourier-transform spectrometer. The X21 → X10+ transition between the spin components of the X3Σ- ground state was remeasured at high spectral resolution and signal/noise. Six bands of the Δv = 0 and +1 sequences near 4950 and 6600 cm-1 have been observed. The low-J lines of these bands are split into up to 10 hfs components due to magnetic hyperfine structure splitting of the X21 levels. In addition to the previously observed electric dipole lines, weak magnetic dipole lines show up in the Δv = 0 but not in the Δv = +1 bands. The intensities of the Δv = +1 bands are about a factor of 10 higher than expected from Franck-Condon factors indicating that the electric dipole transition moment μX2-X1 shows a strong dependence on internuclear distance. Near 5450 cm-1, the 0-0 and 1-1 bands of the transition a2 → X21 from the hitherto unknown first excited state a1Δ(a2) to the upper component of the ground state have been observed. The lines in these bands show the magnetic hfs splitting of both the a2 and X21 states. In the visible range near 21 300 and 16 300 cm-1, the 0-0 and 1-1 bands of the b0+ → X10+ system and the 0-0 band of the b0+ → X21 transition likewise have been measured at high resolution. The lines of the latter band also show the hfs splitting of the X21 state. Least-squares fits have yielded rotational and vibrational constants of the X10+, X21, a2, and b0+ states as well as hfs parameters of the X21 and a2 states and the electronic energy of the hitherto unknown a1Δ(a2) level.

  20. Polarization evidence for the isotropy of electrons responsible for the production of 5-20 keV X-rays in solar flares

    NASA Astrophysics Data System (ADS)

    Tramiel, L. J.; Novick, R.; Chanan, G. A.

    1984-05-01

    We have flown a solar flare X-ray polarimeter on the third flight (STS 3) of the Space Shuttle Columbia as part of the OSS-1 pallet of instruments. We observed eight solar flares in the 5-20 keV band on 1982 March 28. The signal-to-background ratio in all cases exceeded 25. A preflight contamination problem invalidated the earlier laboratory calibration, and the instrument had to be calibrated in-flight against two flares near the center of the solar disk, which are expected to be unpolarized on geometric grounds in a variety of models. No statistically significant polarization was then detected in any of the other six flares. Upper limits (99% confidence level) range from 2.5% to 12.7%. For two of the observed flares these results disagree with the predictions of a simple radially beamed, linear bremsstrahlung model at greater than 99% confidence. One of these flares had a hard impulsive burst; the measured upper limit on this burst (10%) also disagrees with the predictions of the beamed hypothesis. If the calibration flares were polarized, then the above upper limits can be interpreted as limits on the changes in polarization from flare to flare. Because the observed flares spanned a large longitude range and because the predictions of the beamed models depend fairly sensitively on viewing angle, the small relative polarizations are still difficult to reconcile with simple beamed models. The results are also compared with recent, more sophisticated models of Leach and Petrosian, which generally predict lower polarizations. We find that the observations are marginally inconsistent with a model in which the electrons are initially strongly beamed, but subsequently become largely isotropic as a result of the effects of a converging magnetic field; they are consistent with a model in which the electrons are injected isotropically, but in which the preference for motion along the magnetic field lines is explicitly taken into account. The results are also consistent

  1. Formation of the 0.511.-MeV line in solar flares. [statistical mechanics of line spectra for gamma rays

    NASA Technical Reports Server (NTRS)

    Crannell, C. J.; Joyce, G.; Ramaty, R.; Werntz, C.

    1976-01-01

    The gamma-ray line produced at 0.51-MeV was studied and is shown to be the result of either of free annihilation of positrons with electrons or of the decay of positronium by 2-photon emission. Positron annihilation from the bound state of positronium may also proceed by 3-photon emission, resulting in a continuum with energies up to 0.51-MeV. Accurate calculations of the rates of free annihilation and positronium formation in a solar-flare plasma are presented. Estimates of the positronium-formulation rates by charge exchange and the rates of dissociation and quenching are also considered. The temperature and density dependence of the ratio of 3-photon to 2-photon emission was obtained. It is shown that when the ratio of free electrons to neutral atoms in the plasma is approximately unity or greater, the Doppler width of the 0.51-MeV line is a function of the temperature of the annihilation region. For the small ion densities characteristics of the photosphere, the width is predominantly a function of the density.

  2. Maps of precipitating electron spectra characterized by Maxwellian and kappa distributions

    NASA Astrophysics Data System (ADS)

    McIntosh, R. C.; Anderson, P. C.

    2014-12-01

    Maps of characterized auroral electron spectra, developed using 8 years of particle spectrometer data from the Defense Meteorological Satellite Program (DMSP) suite of polar-orbiting spacecraft are presented. The electron spectra, which were sampled from both hemispheres, are categorized as either diffuse or accelerated. Diffuse spectra were best-fit with Maxwellian or kappa distributions, and accelerated spectra were identified as displaying characteristics of either monoenergetic or broadband acceleration. A total of 30 million spectra were characterized, with 47.05% being best-fit with Maxwellian distributions, 31.37% being best-fit with kappa distributions, 12.20% as monoenergetic, and 9.38% as broadband. The spectra from both hemispheres were then binned in MLAT-MLT using a bin size of (MLAT, MLT) = (1°, 0.25 h), for the ranges of 50° ≤ MLAT < 90° and 0000 ≤ MLT < 2400, and further separated into seven levels of Kp. Within each MLAT-MLT-Kp bin, the fraction of the bin total number of accelerated and best-fit spectra corresponding to each spectral type was calculated. Consideration of the global distribution of these fractions showed the following results. For Kp< 2, diffuse electron spectra were predominantly best-fit by Maxwellian distributions. With increasing Kp, more of the diffuse spectra were best-fit by kappa distributions, especially within 0000 < MLT < 0600. For Kp< 2, monoenergetic spectra occurred throughout the oval at MLAT > 70° and broadband spectra occurred within 75° < MLAT < 80° and the local time regions of 0600 < MLT < 1000 and 1300 < MLT < 1500. For Kp≥ 2, coverage of accelerated spectra varied with Kp. For low levels of Kp, accelerated spectra, primarily monoenergetic spectra, predominated above 70°. With increasing activity, broadband spectra covered more of the daytime MLT sectors, while diffuse spectra (Maxwellian and Lorentzian) became increasingly frequent on the nightside due to the poleward expansion of the diffuse

  3. The runaway of fast electrons into turbulent plasma of solar flares

    NASA Astrophysics Data System (ADS)

    Charikov, Yu. E.; Kudryavtsev, I. V.

    1992-08-01

    Attention is given to the problem in which a beam of fast particles falls into a layer of plasma with induced ion-sound waves and propagates inside the layer scattering by plasmons. A solution is obtained for a turbulent plasma, and, as an application, two model cases are considered: the nonthermal distribution of fast particles and the quasi-thermal one, which are discussed in interpretations of the emissions from solar flares. The scattering on the front with ion-sound waves considerably changes the distribution both quantitatively and qualitatively.

  4. Electron transport estimated from electron spectra using electron spectrometer in LFEX laser target experiments

    NASA Astrophysics Data System (ADS)

    Ozaki, T.; Hata, M.; Matsuo, K.; Kojima, S.; Arikawa, Y.; Fujioka, S.; Sakagami, H.; Sunahara, A.; Nagatomo, H.; Johzaki, T.; Yogo, A.; Morace, A.; Zhang, Z.; Shiraga, H.; Sakata, S.; Nagai, T.; Abe, Y.; Lee, S.; Nakai, M.; Nishimura, H.; Azechi, H.; FIREX group; GXII-LFEX group

    2016-05-01

    Hot electrons which are generated from targets irradiated by a high-intense laser are measured by two electron spectrometers (ESMs). However, total electron energy observed by the ESM is only less than 1%. Hot electrons are confined by self-fields due to the huge current. When an external magnetic field of several hundred Tesla is applied during the laser irradiation on targets, the ESM signals always increase. In the simulation, the same result can be obtained. The reason is that the Alfvén limit can be mitigated due to the external longitudinal magnetic field.

  5. Observations of the scatter-free solar-flare electrons in the energy range 20-1000 keV

    NASA Technical Reports Server (NTRS)

    Wang, J. R.; Fisk, L. A.; Lin, R. P.

    1971-01-01

    Observations of the scatter-free electron events from solar active region McMath No. 8905 are presented. The measurements were made on Explorer 33 satellite. The data show that more than 80% of the electrons from these events undergo no or little scattering and that these electrons travel only approximately 1.5 a.u. between the sun and the earth. The duration of these events cannot be accounted fully by velocity dispersion alone. It is suggested that these electrons could be continuously injected into interplanetary medium for a time interval of approximately 2 to 3 minutes. Energy spectra of these electrons are discussed.

  6. Measurements of Absolute Abundances in Solar Flares

    NASA Astrophysics Data System (ADS)

    Warren, Harry P.

    2014-05-01

    We present measurements of elemental abundances in solar flares with the EUV Variability Experiment (EVE) on the Solar Dynamics Observatory. EVE observes both high temperature Fe emission lines (Fe XV-Fe XXIV) and continuum emission from thermal bremsstrahlung that is proportional to the abundance of H. By comparing the relative intensities of line and continuum emission it is possible to determine the enrichment of the flare plasma relative to the composition of the photosphere. This is the first ionization potential or FIP bias (f). Since thermal bremsstrahlung at EUV wavelengths is relatively insensitive to the electron temperature, it is important to account for the distribution of electron temperatures in the emitting plasma. We accomplish this by using the observed spectra to infer the differential emission measure distribution and FIP bias simultaneously. In each of the 21 flares that we analyze we find that the observed composition is close to photospheric. The mean FIP bias in our sample is f = 1.17 ± 0.22. This analysis suggests that the bulk of the plasma evaporated during a flare comes from deep in the chromosphere, below the region where elemental fractionation occurs.

  7. MEASUREMENTS OF ABSOLUTE ABUNDANCES IN SOLAR FLARES

    SciTech Connect

    Warren, Harry P.

    2014-05-01

    We present measurements of elemental abundances in solar flares with the EUV Variability Experiment (EVE) on the Solar Dynamics Observatory. EVE observes both high temperature Fe emission lines (Fe XV-Fe XXIV) and continuum emission from thermal bremsstrahlung that is proportional to the abundance of H. By comparing the relative intensities of line and continuum emission it is possible to determine the enrichment of the flare plasma relative to the composition of the photosphere. This is the first ionization potential or FIP bias (f). Since thermal bremsstrahlung at EUV wavelengths is relatively insensitive to the electron temperature, it is important to account for the distribution of electron temperatures in the emitting plasma. We accomplish this by using the observed spectra to infer the differential emission measure distribution and FIP bias simultaneously. In each of the 21 flares that we analyze we find that the observed composition is close to photospheric. The mean FIP bias in our sample is f = 1.17 ± 0.22. This analysis suggests that the bulk of the plasma evaporated during a flare comes from deep in the chromosphere, below the region where elemental fractionation occurs.

  8. Electronic structures and electronic spectra of all-boron fullerene B40.

    PubMed

    He, Rongxing; Zeng, Xiao Cheng

    2015-02-21

    This study is motivated by the recent discovery of the first all-boron fullerene analogue, a B40 cluster with D(2d) point-group symmetry, dubbed borospherene (Nat. Chem., 2014, 6, 727). Insight into the electronic structures and spectral properties of B40 is timely and important to understand the borospherene and the transition from open-ended plate or ribbon-like structures to a hollow-cage structure at B40. Optimized geometries of borospherene B40 for both the ground state and the first excited state allow us to compute spectral properties including UV-vis absorption, infrared (IR) and Raman spectra. Highly resolved absorption and emission spectra are obtained, for the first time, for the fullerene at the time-dependent density-functional theory (TD-DFT) level within the Franck-Condon approximation and including the Herzberg-Teller effect. Assigned vibrational modes in absorption and emission spectra are readily compared with future spectroscopy measurements to distinguish the hollow-cage structure of D(2d)-B40 from other quasi-planar boron structures. PMID:25604937

  9. Cumulant approach for electronic excitations in x-ray and electron spectra

    NASA Astrophysics Data System (ADS)

    Rehr, J. J.

    A quantitative treatment of electronic excitations and other many-body effects in x-ray and electron spectra has long been challenging. Physically, electronic correlations and atomic vibrations lead to inelastic losses and damping effects that are ignored in ground state methods or approximations such as TDDFT. Quasi-particle (QP) approaches such as the GW approximation yield significant improvements, as demonstrated in real-space Green's function and GW/Bethe-Salpeter equation calculations, but still ignore multi-electron excitations. Recently such excitations have been treated with considerable success using cumulant expansion techniques and the quasi-boson approximation. In this beyond QP approach, excitations such as plasmons and electron-hole excitations appear as satellites in the spectral function. The method naturally accounts for multiple-satellites and can be extended to include extrinsic losses and interference effects. Extensions for effects of vibrations and strong correlations including charge-transfer satellites may also be possible. These advances are illustrated with a number of applications. Supported by DOE Grant DE-FG02-97ER45623.

  10. Investigations of turbulent motions and particle acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Jakimiec, J.; Fludra, A.; Lemen, J. R.; Dennis, B. R.; Sylwester, J.

    1986-01-01

    Investigations of X-raya spectra of solar flares show that intense random (turbulent) motions are present in hot flare plasma. Here it is argued that the turbulent motions are of great importance for flare development. They can efficiently enhance flare energy release and accelerate particles to high energies.

  11. Electron-phonon interaction on optical spectra of nanoelectronic devices

    NASA Technical Reports Server (NTRS)

    Kim, Q.

    2002-01-01

    Information obtained on the solid-state lattice dynamics by electron-phonon interaction between lattice phonons and electrons could open up to learn more about lattice dynamics and to apply it in nanoelectronic devices including software reliability, nano-size capacitors, master clock sources, as well as non-contact temperature probes on nano-electronic and photonicdevices.

  12. Analytic and numerical calculations of quantum synchrotron spectra from relativistic electron distributions

    NASA Technical Reports Server (NTRS)

    Brainerd, J. J.; Petrosian, V.

    1987-01-01

    Calculations are performed numerically and analytically of synchrotron spectra for thermal and power-law electron distributions using the single-particle synchrotron power spectrum derived from quantum electrodynamics. It is found that the photon energy at which quantum effects appear is proportional to temperature and independent of field strength for thermal spectra; quantum effects introduce an exponential roll-off away from the classical spectra. For power law spectra, the photon energy at which quantum effects appear is inversely proportional to the magnetic field strength; quantum effects produce a steeper power law than is found classically. The results are compared with spectra derived from the classical power spectrum with an energy cutoff ensuring conservation of energy. It is found that an energy cutoff is generally an inadequate approximation of quantum effects for low photon energies and for thermal spectra, but gives reasonable results for high-energy emission from power-law electron distributions.

  13. HARD X-RAY AND MICROWAVE EMISSIONS FROM SOLAR FLARES WITH HARD SPECTRAL INDICES

    SciTech Connect

    Kawate, T.; Nishizuka, N.; Oi, A.; Ohyama, M.; Nakajima, H.

    2012-03-10

    We analyze 10 flare events that radiate intense hard X-ray (HXR) emission with significant photons over 300 keV to verify that the electrons that have a common origin of acceleration mechanism and energy power-law distribution with solar flares emit HXRs and microwaves. Most of these events have the following characteristics. HXRs emanate from the footpoints of flare loops, while microwaves emanate from the tops of flare loops. The time profiles of the microwave emission show delays of peak with respect to those of the corresponding HXR emission. The spectral indices of microwave emissions show gradual hardening in all events, while the spectral indices of the corresponding HXR emissions are roughly constant in most of the events, though rather rapid hardening is simultaneously observed in some for both indices during the onset time and the peak time. These characteristics suggest that the microwave emission emanates from the trapped electrons. Then, taking into account the role of the trapping of electrons for the microwave emission, we compare the observed microwave spectra with the model spectra calculated by a gyrosynchrotron code. As a result, we successfully reproduce the eight microwave spectra. From this result, we conclude that the electrons that have a common acceleration and a common energy distribution with solar flares emit both HXR and microwave emissions in the eight events, though microwave emission is contributed to by electrons with much higher energy than HXR emission.

  14. Analysis of flares in the chromosphere and corona of main- and pre-main-sequence M-type stars

    NASA Astrophysics Data System (ADS)

    Crespo-Chacón, I.

    2015-11-01

    having an accretion disk) we carry out a detailed analysis of an extremely long rise phase and of a shorter, weaker flare (allowing us to compare the results with those reported for young stars but surrounded by disks). Assuming multitemperature models to describe the coronal flaring plasma, we have calculated the metal abundance, the electron temperatures and the respective emission measures by fitting the spectra with the Astrophysical Plasma Emission Code included in the XSPEC software, which calculates spectral models for hot, optically thin plasmas. Moreover, we are able to estimate the size of the flaring loops by using theoretical models. These sizes give us an idea about the extent of the corona. For those flares in which heating does not entirely drive the flare evolution we use the models reported by Reale (2007) and Reale et al. (1997) for the rise and decay phases, respectively, including the effect of sustained heating during the decay. Instead, the stellar version of the Kopp & Poletto (1984)'s solar two-ribbon flare model (Poletto et al. 1988) is used when the residual heating completely drives the flare over the plasma cooling. Later, we apply the so-called RTV scaling laws (Rosner et al. 1978) and other fundamental laws of physics to determine additional characteristics of the plasma contained in the flaring loops (electron density and pressure), as well as the volume of the flaring region, the heating rate per unit volume, and the strength of the magnetic field required to confine this plasma. Making some assumptions we are also able to estimate the number of loops involved in the observed flares and the kind of magnetic structures present in the atmosphere of these types of stars. Finally, we discuss and interpret the results in the context of solar and stellar flares reported so far.

  15. Coincidence studies of diffraction structures in binary encounter electron spectra

    SciTech Connect

    Liao, C.; Hagmann, S.; Richard, P.

    1994-12-31

    The authors have measured binary encounter electron (BEe) production in collisions of 0.3 MeV/u Cu{sup q+} (q=4,12) projectiles on H{sub 2} targets from 0 to 70 degrees with respect to the beam direction. Prominent features are the appearance of the BEe peak splitting and a very strong forward peaked angular distribution which are attributed to the diffractive scattering of the quasifree target electrons in the short range potential of the projectile. Using electron-projectile final charge state coincidence techniques, different collision reaction channels can be separated. Measurements of this type are being pursued.

  16. Vibronic modulation of lineshapes in two-dimensional electronic spectra

    NASA Astrophysics Data System (ADS)

    Nemeth, Alexandra; Milota, Franz; Mančal, Tomáš; Lukeš, Vladimír; Kauffmann, Harald F.; Sperling, Jaroslaw

    2008-06-01

    We report and analyze oscillatory behavior of lineshapes in two-dimensional photon-echo relaxation spectra of a perylene-based dye molecule, whose four-wave-mixing signals are strongly modulated by coupling to low-frequency vibrational modes. Vibrational wavepacket motion is found to induce a pronounced beating of the anti-diagonal absorptive peak width, accompanied by orientational changes in the dispersive signal part. The effects are reproduced well by simulations based on a Brownian oscillator model, and can be assigned to periodic alternations in the relative amplitudes of rephasing and non-rephasing contributions to the spectrum.

  17. 1980 to 1989 Observations of Nuclear Gamma-Rays from Solar Flares

    NASA Astrophysics Data System (ADS)

    Share, G. H.; Murphy, R. J.; MacKinnon, R. J.

    1992-05-01

    We present a study of background-corrected spectra, 0.3 <= E_γ <=8.5 MeV, observed by the Gamma Ray Spectrometer on the Solar Maximum Mission satellite from 1980 to 1989. A total of 192 spectra covering the impulsive phases of these flares were fit by a model containing a power-law electron bremsstrahlung component and a nuclear component. The nuclear model was derived from the 1981 April 27 flare (Murphy et al. 1990). About 60\\ the flares exhibit evidence for a nuclear component in addition to bremsstrahlung. We have summed spectra from flares into 16 groups according to their observed bremsstrahlung flux, extending over a dynamic range of 100. These summed spectra were fit once again with the two component model to compare average nuclear and bremsstrahlung emissions. The average nuclear and bremstrahlung fluxes are strongly correlated over the full range of study. On average we find evidence for nuclear emission even for the lowest range of bremsstrahlung fluxes observable >=300 keV ( ~ 5 times 10(-2) gamma cm(-2) s(-1) ). We also find that the average nuclear/bremsstrahlung ratio decreases and the average bremsstrahlung spectrum hardens with increasing heliocentric angle. This is consistent with earlier studies suggesting that the electrons producing the bremsstrahlung are not isotropically distributed. On the other hand the nuclear/bremsstrahlung ratio exhibits large scatter from flare to flare. A study of the temporal variations of the prompt nuclear and bremsstrahlung emissions, and of the delayed lines at 0.511 and 2.223 MeV, within individual flares is in progress. The nuclear/bremsstrahlung ratio exhibits significant variation during some of the flares. This work is supported under NASA DPR's W-17,972 and W-17,973. Murphy, R.J., et al. 1990, Ap. J., 358, 298.

  18. Dynamics of quantal heating in electron systems with discrete spectra

    NASA Astrophysics Data System (ADS)

    Dietrich, Scott; Mayer, William; Vitkalov, Sergey; Bykov, A. A.

    2015-05-01

    The temporal evolution of quantal Joule heating of two-dimensional (2D) electrons in a GaAs quantum well placed in quantizing magnetic fields is studied using a difference-frequency method. The method is based on measurements of the electron conductivity oscillating at the beat frequency f =f1-f2 between two microwaves applied to the 2D system at frequencies f1 and f2. The method provides direct access to the dynamical characteristics of the heating and yields the inelastic-scattering time τi n of 2D electrons. The obtained τi n is strongly temperature dependent, varying from 0.13 ns at 5.5 K to 1 ns at 2.4 K in magnetic field B =0.333 T . When the temperature T exceeds the Landau-level separation, the relaxation rate 1 /τi n is proportional to T2, indicating electron-electron interaction as the dominant mechanism limiting the quantal heating. At lower temperatures, the rate tends to be proportional to T3, indicating considerable contribution from electron-phonon scattering.

  19. Pulsed HF radiowave absorption measurements at 2.1 MHZ. over Delhi under quiet and solar flare conditions and related electron density height profiles

    NASA Astrophysics Data System (ADS)

    Balachandra Swamy, A. C.

    EXTENDED ABSTRACT Pulsed HF radiowave absorption measurements at 2.1 MHZ. over Delhi under quiet and solar flare conditions and related electron density height profiles A.C.Balachandra swmay & Late C.S.G.K. Setty Absorption of radio waves in the ionosphere is of great practical importance for radio communication and navigation systems. The first attempt to measure the absolute magnitude of the radiowave absorption were made by appletion and Ratcliffe (1930) using the frequency change method for medium frequency waves reflected from the E-region. They concluded from their experiment that the main part of the attenuation occurred below the reflection level and named the absorption region, D-region of the ionosphere. One of the basic properties of the ionosphere is the absorption of high Frequency Radiowaves. HF radiowave absorption results mainly from collisions between electrons (which are set into forced oscillations by the electric field of the wave) and neutral air particles, the RF energy abstracted from the wave being converted into thermal energy. The radiowave absorption in the ionosphere depends on electron density and collision frequency. The most important absorbing regions are the D-region and the lower E-region (50-100 Km.) The regular diurnal variation of the electron density in this height range is caused mainly by the changes in the depth of penetration of solar XUV radiations with solar zenith angle under quiet solar conditions. In 1937 Dellinger J.H.identified fade outs in high frequency radio circuits as due to abnormal ionospheric absorption associated with solar flares. The onset of the fade out was usually rapid and the duration was typically tens of minutes like that of the visible flare, because of the sudden onset, the immediate effects of solar flares are known collectively as sudden Ionospheric Disturbances (STD). The phenomenon discovered by Dellinger is usually called a short Wave Fadeout(SWF). Since the SWF is due to abnormal absorption

  20. Track Structure Model for Radial Distributions of Electron Spectra and Event Spectra from High-Energy Ions

    NASA Technical Reports Server (NTRS)

    Cucinotta, F. A.; Katz, R.; Wilson, J. W.

    1998-01-01

    An analytic method is described for evaluating the average radial electron spectrum and the radial and total frequency-event spectrum for high-energy ions. For high-energy ions, indirect events make important contributions to frequency-event spectra. The method used for evaluating indirect events is to fold the radial electron spectrum with measured frequency-event spectrum for photons or electrons. The contribution from direct events is treated using a spatially restricted linear energy transfer (LET). We find that high-energy heavy ions have a significantly reduced frequency-averaged final energy (yF) compared to LET, while relativistic protons have a significantly increased yF and dose-averaged lineal energy (yD) for typical site sizes used in tissue equivalent proportional counters. Such differences represent important factors in evaluating event spectra with laboratory beams, in space- flight, or in atmospheric radiation studies and in validation of radiation transport codes. The inadequacy of LET as descriptor because of deviations in values of physical quantities, such as track width, secondary electron spectrum, and yD for ions of identical LET is also discussed.

  1. Simulation of two-dimensional electronic spectra of phycoerythrin 545 at ambient temperature.

    PubMed

    Leng, Xuan; Liang, Xian-Ting

    2014-10-30

    By using a hierarchical equations-of-motion approach, we reproduce the two-dimensional electronic spectra of phycoerythrin 545 from Rhodomonas CS24 at ambient temperature (294 K). The simulated spectra are in agreement with the experimental results reported in Wong et al. (Nat. Chem. 2012, 4, 396). The evolutions of cross peaks for rephasing spectra and diagonal peaks for nonrephasing spectra have also been plotted. The peaks oscillate with the population times, with frequencies, phases, and amplitudes of the oscillating curves also being qualitatively consistent with the experimental results. PMID:25299464

  2. Prevailing Features of X-Ray-Induced Molecular Electron Spectra Revealed with Fullerenes

    NASA Astrophysics Data System (ADS)

    Camacho Garibay, Abraham; Saalmann, Ulf; Rost, Jan M.

    2014-08-01

    X-ray photoabsorption from intense short pulses by a molecule triggers complicated electron and subsequently ion dynamics, leading to photoelectron spectra, which are difficult to interpret. Illuminating fullerenes offers a way to separate out the electron dynamics since the cage structure confines spatially the origin of photo- and Auger electrons. Together with the sequential nature of the photoprocesses at intensities available at x-ray free-electron lasers, this allows for a remarkably detailed interpretation of the photoelectron spectra, as we will demonstrate. The general features derived can serve as a paradigm for less well-defined situations in other large molecules or clusters.

  3. Discovery of the Electronic Spectra of Hps and Dps

    NASA Astrophysics Data System (ADS)

    Grimminger, Robert A.; Wei, Jie; Ellis, Blaine; Clouthier, Dennis J.; Wang, Zhong; Sears, Trevor

    2009-06-01

    The hitherto unknown electronic spectrum of the closed shell transient molecule HPS has been observed in the 685 - 846 nm region by laser-induced fluorescence and single vibronic level emission techniques. HPS (and DPS) were produced in a pulsed electric discharge jet using a precursor mixture of 3% PH_3 and 1% H_2S (or PD_3 and D_2S) in high pressure argon. The weak set of observed bands are assigned to the à ^1A^''-X˜ ^1A^' electronic transition on the basis of chemical evidence, isotope shifts and the correspondence of the vibrational frequencies, excitation energy, and band contours with predictions based on our own high level ab initio calculations. Theory predicts that the HPS bond angle decreases on electronic excitation, contrary to expectations based on Walsh diagrams.

  4. Substorm effects in auroral spectra. [electron spectrum hardening

    NASA Technical Reports Server (NTRS)

    Eather, R. H.; Mende, S. B.

    1973-01-01

    A substorm time parameter is defined and used to order a large body of photometric data obtained on aircraft expeditions at high latitudes. The statistical analysis demonstrates hardening of the electron spectrum at the time of substorm, and it is consistent with the accepted picture of poleward expansion of aurora at the time of substorm and curvature drift of substorm-injected electrons. These features are not evident from a similar analysis in terms of magnetic time. We conclude that the substorm time concept is a useful ordering parameter for auroral data.

  5. Electronic and Vibrational Spectra of InP Quantum Dots Formed by Sequential Ion Implantation

    NASA Technical Reports Server (NTRS)

    Hall, C.; Mu, R.; Tung, Y. S.; Ueda, A.; Henderson, D. O.; White, C. W.

    1997-01-01

    We have performed sequential ion implantation of indium and phosphorus into silica combined with controlled thermal annealing to fabricate InP quantum dots in a dielectric host. Electronic and vibrational spectra were measured for the as-implanted and annealed samples. The annealed samples show a peak in the infrared spectra near 320/cm which is attributed to a surface phonon mode and is in good agreement with the value calculated from Frolich's theory of surface phonon polaritons. The electronic spectra show the development of a band near 390 nm that is attributed to quantum confined InP.

  6. Understanding X-Ray Source Motions in a Solar Flare Loop

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.; Sui, L.; Dennis, B. R.

    2006-01-01

    RHESSI images of a solar flare on 2002 November 28 showed a 3-6 keV hard X-ray source that was initially located at the flare loop top, split and propagated to the foot points of the loop during the flare rise phase, and then propagated back up to the loop top during the declining phase of the flare (Sai, Holman, & Dennis 2006). Higher energy X-ray sources were located lower in the legs of the loop during this period of source evolution, with X-rays above 25 keV seen only at the foot points. Sui, Holman, & Dennis suggested that this spatial evolution reflected the evolution of the spectral index and low-energy cutoff to the distribution of accelerated electrons in the flare. We construct a model flare loop and electron distribution injected at the top of this loop to reproduce the source evolution of the November 28 flare. We determine the constraints on the loop model and the evolution of the accelerated electron distribution. We also study the implications of the model for energy deposition into the loop plasma, and the integrated and imaged X-ray spectra. This work is supported in part by the RHESSI Project and the NASA Guest Investigator Program.

  7. Spectra of energetic electrons in teh space: dependence on solar activity

    NASA Astrophysics Data System (ADS)

    Mineev, Yu. V.

    2001-08-01

    The work examines the dataset of the energetic (0.1-6.0 MeV) electron fluxes and spectra measured on the Prognoz 4-10, IMP 6-8, Ohzora, Soho, and Intercosmos 19 satellites during solar cycles 21-23. The energetic electrons are treated to originate mainly from the Galaxy, the Sun, Jupiter and (in some cases) from the Earth s magnetosphere. The differential electron energy spectra throughout different solar activity cycles and their variations during solar minima and maxima are analyzed. The reasons for the variations in the electron energy spectra are discussed. Simultaneous measurements on near-Earth satellile IMP and Prognoz types showed, that the magnitoshere of Jupiter is a source of near to Earth electrons with energy > 0.3 MeV. The Earth magnetoshere serves a source of energetic electron fluxes. This phenomenon was determined with a help of measurements on anisotropy and asymmetry in fluxes on satellites Prognoz and Intercosmos series. During solar bursts conciderable increasing in electron fluxes with small and middle energies can be observed in the space. Satellites Prognoz and Ohzora for example registrated spectra of space electrons which originated from the Sun. Contribution of different sources into comulative electron spectra in dependence on a level of the solar activity was estimated as a result of series of experiments on a number of satellites.On the basis of measurements on satellites Prognoz, IMP, Ohzora and Soho characteristics of fluxes and spectra of energetic electrons in dependence of solar activity were predicted for 23-rd cycle.

  8. Solar Flares

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina

    2013-01-01

    Because the Earth resides in the atmosphere of our nearest stellar neighbor, events occurring on the Sun's surface directly affect us by interfering with satellite operations and communications, astronaut safety, and, in extreme circumstances, power grid stability. Solar flares, the most energetic events in our solar system, are a substantial source of hazardous space weather affecting our increasingly technology-dependent society. While flares have been observed using ground-based telescopes for over 150 years, modern space-bourne observatories have provided nearly continuous multi-wavelength flare coverage that cannot be obtained from the ground. We can now probe the origins and evolution of flares by tracking particle acceleration, changes in ionized plasma, and the reorganization of magnetic fields. I will walk through our current understanding of why flares occur and how they affect the Earth and also show several examples of these fantastic explosions.

  9. Flare Plasma Iron Abundance

    NASA Technical Reports Server (NTRS)

    Dennis, Brian R.; Dan, Chau; Jain, Rajmal; Schwartz, Richard A.; Tolbert, Anne K.

    2008-01-01

    The equivalent width of the iron-line complex at 6.7 keV seen in flare X-ray spectra suggests that the iron abundance of the hottest plasma at temperatures >approx.10 MK may sometimes be significantly lower than the nominal coronal abundance of four times the photospheric value that is commonly assumed. This conclusion is based on X-ray spectral observations of several flares seen in common with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Solar X-ray Spectrometer (SOXS) on the second Indian geostationary satellite, GSAT-2. The implications of this will be discussed as it relates to the origin of the hot flare plasma - either plasma already in the corona that is directly heated during the flare energy release process or chromospheric plasma that is heated by flare-accelerated particles and driven up into the corona. Other possible explanations of lower-than-expected equivalent widths of the iron-line complex will also be discussed.

  10. Flare-antenna unit for system in which flare is remotely activated by radio

    NASA Astrophysics Data System (ADS)

    Hiltz, Frederick F.; Wilson, Charles E.

    1995-06-01

    A flare-antenna assembly has flare material enclosed in a cylindrical antenna and forms part of a marker beacon. The flare aids in the search for the marker beacon by providing means for both visual and infrared detection. The flare is actuated in response to a specific remote radio signal being received by the antenna. The received signal is decoded by the electronic system within the marker beacon. If the received signal meets the necessary criteria the electronic system generates an electrical signal that detonates a squib embedded in the flare material. The detonation of the squib activates the flare.

  11. Soft X-ray spectroscopy of solar flares - An overview

    NASA Technical Reports Server (NTRS)

    Doschek, G. A.

    1990-01-01

    An overview of the current status of high spectral resolution soft X-ray observations of solar flares is given. The review concentrates primarily on recent results and interpretations of results obtained from orbiting Bragg crystal spectrometers flow during the last solar maximum on the US DoD P78-1 spacecraft, the NASA SMM, and the ISAS Hinotori spacecraft. Results and several key issues regarding interpretation of the spectra are presented. Specifically, the dynamics of coronal flare plasmas as revealed by X-ray line profiles and wavelength shifts are discussed. Recent results concerning the theory of chromospheric evaporation are given. The temperature of coronal flare plasma is discussed within the context of a differential mission measure. Results concerning electron density measurements, nonequilibrium processes, and relative element abundances are also reviewed.

  12. Lunar surface cosmic ray experiment. [including solar flare studies

    NASA Technical Reports Server (NTRS)

    Price, P. B.

    1974-01-01

    The galactic cosmic ray and solar flare experiment on Apollo 16 is reported. The published papers presented describe the experiment, equipment, data processing techniques, and operational history. The principle findings include: (1) The composition of heavy ions in interplanetary space at energies between approximately 30 and 130 MeV/nucleon is the same, within experimental errors. (2) The ability of a Lexan stack to determine simultaneously the energy spectra of major elements from He up to Fe in the energy interval 0.2 to 30 MeV/nucleon revealed systematic changes in the composition of solar flare particles as a function of energy. (3) Heavy ions emitted in a solar flare appear to be completely stripped of electrons, and are not in charge equilibrium at the time of acceleration and releases from the sun.

  13. Reliable Modeling of the Electronic Spectra of Realistic Uranium Complexes

    SciTech Connect

    Tecmer, Pawel; Govind, Niranjan; Kowalski, Karol; De Jong, Wibe A.; Visscher, Lucas

    2013-07-21

    We present an EOMCCSD (equation of motion coupled cluster with singles and doubles) study of excited states of the small [UO2]2+ and [UO2]+ model systems as well as the larger UV IO2(saldien) complex. In addition, the triples contribution within the EOMCCSDT and CR-EOMCCSD(T) (completely renormalized EOMCCSD with non-iterative triples) approaches for the [UO2]2+ and [UO2]+ systems as well as the active-space variant of the CR-EOMCCSD(T) method | CREOMCCSd(t) | for the UV IO2(saldien) molecule are investigated. The coupled cluster data was employed as benchmark to chose the "best" appropriate exchange--correlation functional for subsequent time-dependent density functional (TD-DFT) studies on the transition energies for closed-shell species. Furthermore, the influence of the saldien ligands on the electronic structure and excitation energies of the [UO2]+ molecule is discussed. The electronic excitations as well as their oscillator dipole strengths modeled with TD-DFT approach using the CAM-B3LYP exchange{correlation functional for the [UV O2(saldien)]- with explicit inclusion of two DMSOs are in good agreement with the experimental data of Takao et al. [Inorg. Chem. 49, 2349-2359, (2010)].

  14. Reliable modeling of the electronic spectra of realistic uranium complexes

    NASA Astrophysics Data System (ADS)

    Tecmer, Paweł; Govind, Niranjan; Kowalski, Karol; de Jong, Wibe A.; Visscher, Lucas

    2013-07-01

    We present an EOMCCSD (equation of motion coupled cluster with singles and doubles) study of excited states of the small [UO2]2+ and [UO2]+ model systems as well as the larger UVIO2(saldien) complex. In addition, the triples contribution within the EOMCCSDT and CR-EOMCCSD(T) (completely renormalized EOMCCSD with non-iterative triples) approaches for the [UO2]2+ and [UO2]+ systems as well as the active-space variant of the CR-EOMCCSD(T) method—CR-EOMCCSd(t)—for the UVIO2(saldien) molecule are investigated. The coupled cluster data were employed as benchmark to choose the "best" appropriate exchange-correlation functional for subsequent time-dependent density functional (TD-DFT) studies on the transition energies for closed-shell species. Furthermore, the influence of the saldien ligands on the electronic structure and excitation energies of the [UO2]+ molecule is discussed. The electronic excitations as well as their oscillator dipole strengths modeled with TD-DFT approach using the CAM-B3LYP exchange-correlation functional for the [UVO2(saldien)]- with explicit inclusion of two dimethyl sulfoxide molecules are in good agreement with the experimental data of Takao et al. [Inorg. Chem. 49, 2349 (2010), 10.1021/ic902225f].

  15. X-ray spectra from the Cornell Electron-Beam Ion Source (CEBIS I)

    SciTech Connect

    Johnson, B.M.; Jones, K.W.; Kostroun, V.O.; Ghanbari, E.; Janson, S.W.

    1985-01-01

    Radiation emitted from the Cornell electron beam ion source (CEBIS I) has been surveyed with a Si(Li) x-ray detector. These spectra can be used to estimate backgrounds from electron bremsstrahlung and to evaluate the feasibility of atomic physics experiments using the CEBIS I source in this configuration. 1 ref., 2 figs.

  16. Particle acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Forman, M. A.

    1987-01-01

    The most direct signatures of particle acceleration in flares are energetic particles detected in interplanetary space and in the Earth atmosphere, and gamma rays, neutrons, hard X-rays, and radio emissions produced by the energetic particles in the solar atmosphere. The stochastic and shock acceleration theories in flares are reviewed and the implications of observations on particle energy spectra, particle confinement and escape, multiple acceleration phases, particle anistropies, and solar atmospheric abundances are discussed.

  17. The Energetics of Wight-light Flares Observed in Visible Continuum and Hard X-ray

    NASA Astrophysics Data System (ADS)

    Huang, Nengyi; Xu, Yan; Wang, Haimin

    2016-05-01

    White-light (WL) flares have been observed and studied more than a century since the first discovery. However, some fundamental physics behind the brilliant emission remains highly controversial. One of the important facts in addressing the flare energetics is the spatial-temporal correlation between the white-light emission and the hard X-ray radiation, presumably suggesting that the energetic electrons are the energy sources. In this study, we present a statistical analysis of 26 strong flares (>M5) observed simultaneously by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Among these events, WL emission was detected by SDO/HMI in 13 flares, associated with HXR emission. To quantitatively describe the strength of WL emission, equivalent area is defined as the integrated contrast enhancement over the entire flaring area. Our results show that the equivalent area is inversely proportional to the HXR power index, indicating that stronger WL emission tends to be associated with larger population of high energy electrons. Furthermore, we studied an M6.6 flare on 2015 June 22 observed by BBSO’s New Solar Telescope (NST), showing WL emission in TiO continuum (705.7 nm), but no detectable WL signal from SDO/HMI. The power index- equivalent area relationship of this flare matches the trend found in the statistical analysis. In addition, for the other group of 13 flares without detectable WL emission, the HXR spectra are softer (larger power index) than those flares with WL emission, especially for the X-class flares in this group.

  18. Transport of energetic electrons in a fully ionized hydrogen plasma. [in solar flares

    NASA Technical Reports Server (NTRS)

    Bai, T.

    1982-01-01

    A Monte Carlo method for calculating energetic electron transport in a plasma is presented. The energy loss and angular deflection due to Coulomb collisions as a function of travel distance and energy are derived for energetic electrons in a fully ionized plasma with a uniform magnetic field. Formulas which include the effect of nonuniform B fields on the angular deflection are derived. The Monte Carlo method is applied to the thick-target beam model in which the energetic electrons are injected vertically downward.

  19. Mirroring of fast solar flare electrons on a downstream corotating interaction region

    NASA Technical Reports Server (NTRS)

    Anderson, K. A.; Sommers, J.; Lin, R. P.; Pick, M.; Chaizy, P.; Murphy, N.; Smith, E. J.; Phillips, J. L.

    1995-01-01

    We discuss an example of confinement of fast solar electrons by a discrete solar wind-interplanetary magnetic field structure on February 22, 1991. The structure is about 190,000 km in width and is clearly defined by changes in the direction of the magnetic field at the Ulysses spacecraft. This structure carries electrons moving toward the Sun as well as away from the Sun. A loss cone in the angular distribution of the fast electrons shows that mirroring, presumably magnetic, takes place downstream from the spacecraft. Following passage of this narrow structure, the return flux vanishes for 21 min after which time the mirroring resumes and persists for several hours. We identify the enhanced magnetic field region lying downstream from the Ulysses spacecraft that is responsible for the mirroring to be a corotating stream interaction region. Backstreaming suprathermal electron measurements by the Los Alamos National Laboratory plasma experiment on the Ulysses spacecraft support this interpretation.

  20. Mirroring of fast solar flare electrons on a downstream corotating interaction region

    SciTech Connect

    Anderson, K.A.; Sommers, J.; Lin, R.P.; Pick, M.; Chaizy, P.; Murphy, N.; Smith, E.J.; Phillips, J.L.

    1995-01-01

    The authors discuss an example of confinement of fast solar electrons by a discrete solar wind-interplanetary magnetic field structure on February 22, 1991. The structure is about 190,000 km in width and is clearly defined by changes in the direction of the magnetic field at the Ulysses spacecraft. This structure carries electrons moving toward the Sun as well as away from the Sun. A loss cone in the angular distribution of the fast electrons shows that mirroring, presumably magnetic, takes place downstream from the spacecraft. Following passage of this narrow structure, the return flux vanishes for 21 min after which time the mirroring resumes and persists for several hours. The authors identify the enhanced magnetic field region lying downstream from the Ulysses spacecraft that is responsible for the mirroring to be a corotating stream interaction region. Backstreaming suprathermal electron measurements by the Los Alamos National Laboratory plasma experiment on the Ulysses spacecraft support this interpretation. 12 refs., 9 figs.

  1. Simulation of electron energy loss spectra of nanomaterials with linear-scaling density functional theory.

    PubMed

    Tait, E W; Ratcliff, L E; Payne, M C; Haynes, P D; Hine, N D M

    2016-05-18

    Experimental techniques for electron energy loss spectroscopy (EELS) combine high energy resolution with high spatial resolution. They are therefore powerful tools for investigating the local electronic structure of complex systems such as nanostructures, interfaces and even individual defects. Interpretation of experimental electron energy loss spectra is often challenging and can require theoretical modelling of candidate structures, which themselves may be large and complex, beyond the capabilities of traditional cubic-scaling density functional theory. In this work, we present functionality to compute electron energy loss spectra within the onetep linear-scaling density functional theory code. We first demonstrate that simulated spectra agree with those computed using conventional plane wave pseudopotential methods to a high degree of precision. The ability of onetep to tackle large problems is then exploited to investigate convergence of spectra with respect to supercell size. Finally, we apply the novel functionality to a study of the electron energy loss spectra of defects on the (1 0 1) surface of an anatase slab and determine concentrations of defects which might be experimentally detectable. PMID:27094207

  2. Simulation of electron energy loss spectra of nanomaterials with linear-scaling density functional theory

    NASA Astrophysics Data System (ADS)

    Tait, E. W.; Ratcliff, L. E.; Payne, M. C.; Haynes, P. D.; Hine, N. D. M.

    2016-05-01

    Experimental techniques for electron energy loss spectroscopy (EELS) combine high energy resolution with high spatial resolution. They are therefore powerful tools for investigating the local electronic structure of complex systems such as nanostructures, interfaces and even individual defects. Interpretation of experimental electron energy loss spectra is often challenging and can require theoretical modelling of candidate structures, which themselves may be large and complex, beyond the capabilities of traditional cubic-scaling density functional theory. In this work, we present functionality to compute electron energy loss spectra within the onetep linear-scaling density functional theory code. We first demonstrate that simulated spectra agree with those computed using conventional plane wave pseudopotential methods to a high degree of precision. The ability of onetep to tackle large problems is then exploited to investigate convergence of spectra with respect to supercell size. Finally, we apply the novel functionality to a study of the electron energy loss spectra of defects on the (1 0 1) surface of an anatase slab and determine concentrations of defects which might be experimentally detectable.

  3. Pitch Angle Scattering of Solar Flare Electrons in the Interplanetary Medium: Observations and Modelling

    NASA Astrophysics Data System (ADS)

    Alcock, B.; Kontar, E.; Agueda, N.

    2015-12-01

    In the past decade, analysis of near-relativistic (~27 keV - 300 keV) electron events at 1 AU have highlighted two transport effects which require explanation. Firstly, several events feature delayed electron arrival with respect to solar radio and hard x-ray emission, and secondly, the peak-flux spectrum of electrons at 1 AU does not match the predicted spectrum from hard x-ray observations. We analyse several near-relativistic electron events observed via both RHESSI hard x-ray observations at the Sun and in-situ measurements from the Wind/3DP detector at 1 AU. Numerical simulations of electron transport outwards from the Sun are made, which take the electron injection time and peak-flux spectrum from RHESSI data, and the flux subsequently passing 1 AU is calculated. We consider the effects of adiabatic focusing and pitch angle diffusion on the particle transport, and a momentum and distance dependent form of the parallel mean free path for electrons is employed. The simulated lightcurves, peak-flux spectrum, pitch angle distribution, and delay times are then compared with Wind observations. We find that, for higher energy electrons (>40 keV), the simulated flux matches well with observations, showing that stochastic pitch angle scattering is able to explain apparent delayed particle injection at the Sun. The lower energy observations, however, remain unmatched by models, which predict much more impulsive events at Earth than are observed. We also find that pitch angle scattering is too weak to vary the peak-flux spectrum sufficiently, thus requiring further exploration.

  4. Results of spectrum studies of energetic flare particles by the Venera 11 and 12, and Prognoz 5 and 6 spacecraft

    NASA Astrophysics Data System (ADS)

    Grigorian, O. R.; Daibog, E. I.; Devicheva, E. A.; Kurt, V. G.; Logachev, Iu. I.; Riumin, S. P.; Stolpovskii, V. G.; Shesterikov, V. F.

    1982-09-01

    The generation and propagation of energetic solar particles in the proton energy range of 0.1-500 MeV and the electron energy range of 0.03-3.0 MeV were investigated by Venera 11 and 12 and by Prognoz 5 and 6 during December 1976 to September 1979. In this paper, an analysis of the particle spectra in connection with solar-flare parameters is presented. Integrated electron and proton spectra are displayed for a number of flares.

  5. Optical spectra and electronic structure of actinide ions in compounds and in solution

    SciTech Connect

    Carnall, W.T.; Crosswhite, H.M.

    1985-08-01

    This report provides a summary of theoretical and experimental studies of actinide spectra in condensed phases. Much of the work was accomplished at Argonne National Laboratory, but references to related investigations by others are included. Spectroscopic studies of the trivlent actinides are emphasized, as is the use of energy level parameters, evaluated from experimental data, to investigate systematic trends in electronic structure and other properties. Some reference is made to correlations with atomic spectra, as well as with spectra of the (II), (IV), and higher valence states. 207 refs., 39 figs., 38 tabs.

  6. Reestimation of the production spectra of cosmic ray secondary positrons and electrons in the ISM

    NASA Technical Reports Server (NTRS)

    Wong, C. M.; Ng, L. K.

    1985-01-01

    A detailed calculation of the production spectra of charged hadrons produced by interactions of cosmic rays in the interstellar medium is presented along with a thorough treatment of pion and muon decays. Newly parameterized inclusive cross sections of hadrons were used and exact kinematic limitations were taken into account. Single parametrized expressions for the production spectra of both secondary positrons and electrons in the energy range .1 to 100 GeV are presented. The results are compared with other authors' predictions. Equilibrium spectra using various models are also presented.

  7. Complex time dependent wave packet technique for thermal equilibrium systems - Electronic spectra

    NASA Technical Reports Server (NTRS)

    Reimers, J. R.; Wilson, K. R.; Heller, E. J.

    1983-01-01

    A time dependent wave packet method is presented for the rapid calculation of the properties of systems in thermal equilibrium and is applied, as an illustration, to electronic spectra. The thawed Gaussian approximation to quantum wave packet dynamics combined with evaluation of the density matrix operator by imaginary time propagation is shown to give exact electronic spectra for harmonic potentials and excellent results for both a Morse potential and for the band contours of the three transitions of the visible electronic absorption spectrum of the iodine molecule. The method, in principle, can be extended to many atoms (e.g., condensed phases) and to other properties (e.g., infrared and Raman spectra and thermodynamic variables).

  8. Solar flare model atmospheres

    NASA Technical Reports Server (NTRS)

    Hawley, Suzanne L.; Fisher, George H.

    1993-01-01

    Solar flare model atmospheres computed under the assumption of energetic equilibrium in the chromosphere are presented. The models use a static, one-dimensional plane parallel geometry and are designed within a physically self-consistent coronal loop. Assumed flare heating mechanisms include collisions from a flux of non-thermal electrons and x-ray heating of the chromosphere by the corona. The heating by energetic electrons accounts explicitly for variations of the ionized fraction with depth in the atmosphere. X-ray heating of the chromosphere by the corona incorporates a flare loop geometry by approximating distant portions of the loop with a series of point sources, while treating the loop leg closest to the chromospheric footpoint in the plane-parallel approximation. Coronal flare heating leads to increased heat conduction, chromospheric evaporation and subsequent changes in coronal pressure; these effects are included self-consistently in the models. Cooling in the chromosphere is computed in detail for the important optically thick HI, CaII and MgII transitions using the non-LTE prescription in the program MULTI. Hydrogen ionization rates from x-ray photo-ionization and collisional ionization by non-thermal electrons are included explicitly in the rate equations. The models are computed in the 'impulsive' and 'equilibrium' limits, and in a set of intermediate 'evolving' states. The impulsive atmospheres have the density distribution frozen in pre-flare configuration, while the equilibrium models assume the entire atmosphere is in hydrostatic and energetic equilibrium. The evolving atmospheres represent intermediate stages where hydrostatic equilibrium has been established in the chromosphere and corona, but the corona is not yet in energetic equilibrium with the flare heating source. Thus, for example, chromospheric evaporation is still in the process of occurring.

  9. Dielectronic satellite lines and double layers in solar flares

    NASA Astrophysics Data System (ADS)

    Dzifčáková, E.; Karlický, M.; Dudík, J.

    2013-02-01

    Context. Particle acceleration during solar flares results in departures of the distribution of particle energies from the Maxwellian distribution. Apart from the high-energy tail, the bulk of the distribution was recently also found to be significantly affected, due, e.g., to the presence of double layers. Aims: We investigate the influence of several proposed non-Maxwellian distribution functions on the X-ray flare line spectra. The distribution functions considered are sharply peaked and include the n-distribution, the moving Maxwellian distribution, and the distribution formed in strong double layers in the flaring plasma. Methods: Synthetic Si xiid-Si xiv spectra involving allowed and dielectronic transitions at 5 - 6 Å are calculated numerically. The parameters chosen for the calculations correspond to the impulsive phase of solar flares, as inferred by previous authors. Results: The Si xiid λ5.56/Si xiii λ5.68 and Si xiid λ5.82/Si xiii λ5.68 ratios depend on the relative number of electrons at energies corresponding to the formation of the Si xiid lines. Therefore, these ratios increase with the increasing narrowness of the peak of the electron distribution function. The highest ratios are achieved for the distribution formed in double layers, while the moving Maxwellian distribution is less likely to reproduce the observed enhancement of Si xiid intensities. However, the ratio of the allowed Si xiv λ5.22/Si xiii λ5.68 transitions depends on the ionization equilibrium. This ratio is very small for the double-layer distribution. Combination of the double-layer distribution with a Maxwellian distribution with the same mean energy significantly enhances this ratio, while keeping the Si xiid intensities sufficiently increased to explain the characteristics of the observed spectra. Conclusions: These results support the presence of double layers in the plasma during impulsive phase of solar flares.

  10. Detection Improvement for Electron Energy Spectra for Surface Analysis Using a Field Emission Scanning Tunneling Microscope

    NASA Astrophysics Data System (ADS)

    Hirade, Masato; Arai, Toyoko; Tomitori, Masahiko

    2003-07-01

    For identification of the atomic species on a sample surface with high spatial resolution, we developed a field emission scanning tunneling microscopy (FE-STM) combined with an energy analyzer to perform surface electron spectroscopy: the primary electrons are field-emitted from the STM tip to excite sample surfaces. The energy spectra of backscattered electrons obtained using this combined instrument exhibited the elemental features, though the energy peaks and their signal height in the spectra were affected by the electric field between the tip and the sample. In the present study, we have examined and improved the electric shield of an STM tip holder. The metal parts of the holder at a high voltage, which face the gap left for electrons to pass through, were shielded to reduce the electric field. We have successfully demonstrated the effect of the field reduction for surface electron spectroscopy with the FE-STM.

  11. The quasi-linear relaxation of thick-target electron beams in solar flares

    NASA Technical Reports Server (NTRS)

    Mcclements, K. G.; Brown, J. C.; Emslie, A. G.

    1986-01-01

    The effects of quasi-linear interactions on thick-target electron beams in the solar corona are investigated. Coulomb collisions produce regions of positive gradient in electron distributions which are initially monotonic decreasing functions of energy. In the resulting two-stream instability, energy and momentum are transferred from electrons to Langmuir waves and the region of positive slope in the electron distribution is replaced by a plateau. In the corona, the timescale for this quasi-linear relaxation is very short compared to the collision time. It is therefore possible to model the effects of quasi-linear relaxation by replacing any region of positive slop in the distribution by a plateau at each time step, in such a way as to conserve particle number. The X-ray bremsstrahlung and collisional heating rate produced by a relaxed beam are evaluated. Although the analysis is strictly steady state, it is relevant to the theoretical interpretation of hard X-ray bursts with durations of the order of a few seconds (i.e., the majority of such bursts).

  12. High-cadence and high-resolution Hα imaging spectroscopy of a circular flare's remote ribbon with IBIS

    SciTech Connect

    Deng, Na; Jing, Ju; Chen, Xin; Liu, Chang; Xu, Yan; Wang, Haimin; Tritschler, Alexandra; Reardon, Kevin; Denker, Carsten

    2013-06-01

    We present an unprecedented high-resolution Hα imaging spectroscopic observation of a C4.1 flare taken with the Interferometric Bidimensional Spectrometer (IBIS) in conjunction with the adaptive optics system at the 76 cm Dunn Solar Telescope on 2011 October 22 in the active region NOAA 11324. Such a two-dimensional spectroscopic observation covering the entire evolution of a flare ribbon with high spatial (0.''1 pixel{sup –1} image scale), cadence (4.8 s), and spectral (0.1 Å step size) resolution is rarely reported. The flare consists of a main circular ribbon that occurred in a parasitic magnetic configuration and a remote ribbon that was observed by the IBIS. Such a circular-ribbon flare with a remote brightening is predicted in three-dimensional fan-spine reconnection but so far has been rarely studied. During the flare impulsive phase, we define 'core' and 'halo' structures in the observed ribbon based on IBIS narrowband images in the Hα line wing and line center. Examining the Hα emission spectra averaged in the flare core and halo areas, we find that only those from the flare cores show typical nonthermal electron beam heating characteristics that have been revealed by previous theoretical simulations and observations of flaring Hα line profiles. These characteristics include broad and centrally reversed emission spectra, excess emission in the red wing with regard to the blue wing (i.e., red asymmetry), and redshifted bisectors of the emission spectra. We also observe rather quick timescales for the heating (∼30 s) and cooling (∼14-33 s) in the flare core locations. Therefore, we suggest that the flare cores revealed by IBIS track the sites of electron beam precipitation with exceptional spatial and temporal resolution. The flare cores show two-stage motion (a parallel motion along the ribbon followed by an expansion motion perpendicular to the ribbon) during the two impulsive phases of the flare. Some cores jump quickly (30 km s{sup –1

  13. High-cadence and High-resolution Hα Imaging Spectroscopy of a Circular Flare's Remote Ribbon with IBIS

    NASA Astrophysics Data System (ADS)

    Deng, Na; Tritschler, Alexandra; Jing, Ju; Chen, Xin; Liu, Chang; Reardon, Kevin; Denker, Carsten; Xu, Yan; Wang, Haimin

    2013-06-01

    We present an unprecedented high-resolution Hα imaging spectroscopic observation of a C4.1 flare taken with the Interferometric Bidimensional Spectrometer (IBIS) in conjunction with the adaptive optics system at the 76 cm Dunn Solar Telescope on 2011 October 22 in the active region NOAA 11324. Such a two-dimensional spectroscopic observation covering the entire evolution of a flare ribbon with high spatial (0.''1 pixel-1 image scale), cadence (4.8 s), and spectral (0.1 Å step size) resolution is rarely reported. The flare consists of a main circular ribbon that occurred in a parasitic magnetic configuration and a remote ribbon that was observed by the IBIS. Such a circular-ribbon flare with a remote brightening is predicted in three-dimensional fan-spine reconnection but so far has been rarely studied. During the flare impulsive phase, we define "core" and "halo" structures in the observed ribbon based on IBIS narrowband images in the Hα line wing and line center. Examining the Hα emission spectra averaged in the flare core and halo areas, we find that only those from the flare cores show typical nonthermal electron beam heating characteristics that have been revealed by previous theoretical simulations and observations of flaring Hα line profiles. These characteristics include broad and centrally reversed emission spectra, excess emission in the red wing with regard to the blue wing (i.e., red asymmetry), and redshifted bisectors of the emission spectra. We also observe rather quick timescales for the heating (~30 s) and cooling (~14-33 s) in the flare core locations. Therefore, we suggest that the flare cores revealed by IBIS track the sites of electron beam precipitation with exceptional spatial and temporal resolution. The flare cores show two-stage motion (a parallel motion along the ribbon followed by an expansion motion perpendicular to the ribbon) during the two impulsive phases of the flare. Some cores jump quickly (30 km s-1) between discrete

  14. Spectral Analysis on Solar Flares with an Emission > 300 keV

    NASA Astrophysics Data System (ADS)

    Vargas, R.; Connaughton, V.

    2013-12-01

    The continuum gamma-ray emission from solar flares is caused when a population of electrons is accelerated to relativistic speeds and interacts with the solar plasma. However, it has been theorized that the gamma-ray emission from some brighter flares comes from two populations of electrons. Using the Gamma-Ray Burst Monitor (GBM), we studied the gamma-ray emission spectra of solar flares and paid special attention to the solar flares that showed emission above 300 keV. We found that the emission above 300 keV was better fit with a broken power-law than a single power-law, evidence that the gamma-ray emission from certain solar flares involved two populations of electrons. Specifically, our best model involved a broken power law that had a steeper slope before the break in energy than after. We studied the spectral parameters as a function of time during the period of the high-energy emission. We also found that solar flares with emission above 300 keV form a small subset (~4%) of flares that trigger GBM above 20 keV. One of the flares with an emission greater than 300 keV was fitted with a Broken Power Law model. Only data from the BGO detector was used in making the plots. Various parameters of the fit have been plotted vs. time with the top two graphs representing the light curves of the flare from different detectors (BGO-0 and NaI-4). A spectral fit for bn100612038 for the time interval of [45s-50s] using only the BGO (0) detector file. Data from this fit was used in creating the other plots.

  15. Microplume model of spatial-yield spectra. [applying to electron gas degradation in molecular nitrogen gas

    NASA Technical Reports Server (NTRS)

    Green, A. E. S.; Singhal, R. P.

    1979-01-01

    An analytic representation for the spatial (radial and longitudinal) yield spectra is developed in terms of a model containing three simple 'microplumes'. The model is applied to electron energy degradation in molecular nitrogen gas for 0.1 to 5 keV incident electrons. From the nature of the cross section input to this model it is expected that the scaled spatial yield spectra for other gases will be quite similar. The model indicates that each excitation, ionization, etc. plume should have its individual spatial and energy dependence. Extensions and aeronomical and radiological applications of the model are discussed.

  16. Unfolding linac photon spectra and incident electron energies from experimental transmission data, with direct independent validation

    SciTech Connect

    Ali, E. S. M.; McEwen, M. R.; Rogers, D. W. O.

    2012-11-15

    Purpose: In a recent computational study, an improved physics-based approach was proposed for unfolding linac photon spectra and incident electron energies from transmission data. In this approach, energy differentiation is improved by simultaneously using transmission data for multiple attenuators and detectors, and the unfolding robustness is improved by using a four-parameter functional form to describe the photon spectrum. The purpose of the current study is to validate this approach experimentally, and to demonstrate its application on a typical clinical linac. Methods: The validation makes use of the recent transmission measurements performed on the Vickers research linac of National Research Council Canada. For this linac, the photon spectra were previously measured using a NaI detector, and the incident electron parameters are independently known. The transmission data are for eight beams in the range 10-30 MV using thick Be, Al and Pb bremsstrahlung targets. To demonstrate the approach on a typical clinical linac, new measurements are performed on an Elekta Precise linac for 6, 10 and 25 MV beams. The different experimental setups are modeled using EGSnrc, with the newly added photonuclear attenuation included. Results: For the validation on the research linac, the 95% confidence bounds of the unfolded spectra fall within the noise of the NaI data. The unfolded spectra agree with the EGSnrc spectra (calculated using independently known electron parameters) with RMS energy fluence deviations of 4.5%. The accuracy of unfolding the incident electron energy is shown to be {approx}3%. A transmission cutoff of only 10% is suitable for accurate unfolding, provided that the other components of the proposed approach are implemented. For the demonstration on a clinical linac, the unfolded incident electron energies and their 68% confidence bounds for the 6, 10 and 25 MV beams are 6.1 {+-} 0.1, 9.3 {+-} 0.1, and 19.3 {+-} 0.2 MeV, respectively. The unfolded spectra

  17. COMPARISON OF PHOTOMETRIC VARIABILITY BEFORE AND AFTER STELLAR FLARES

    SciTech Connect

    Karoff, C.

    2014-01-20

    The energy in the solar acoustic spectrum is known to be correlated with flares, but it is not known if the same is true for stellar flares. In order to answer this question, we have analyzed 73 flares in 39 solar-like stars. These flares were identified in the 854 solar-like stars observed by the Kepler spacecraft that have stellar parameters measured with asteroseismology. Though we were not able to identify a statistically significant enhancement of the energy in the high-frequency part of the post-flare acoustic spectra compared to the pre-flare spectra of these stars, we did identify a larger variability between the energy in the high-frequency part of the post- and pre-flare acoustic spectra compared to spectra taken at random times.

  18. Ion acceleration in impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Steinacker, Jurgen; Jaekel, Uwe; Schlickeiser, Reinhard

    1993-01-01

    Nonrelativistic spectra of protons and ions accelerated in impulsive solar flares are derived using more realistic turbulence power spectra. The calculation is based on a particle transport equation extracted from a second step acceleration model containing stochastic acceleration. The turbulence model is generalized to waves with a small angle to the magnetic field vector and to turbulence power spectra with spectral indices s smaller than 2. Due to the occurrence of impulsive flares at low coronal heights, Coulomb losses at the dense coronal plasma and diffusive particle escape are taken into account. The ion spectra show deviations from long-duration spectra near the Coulomb barrier, where the losses become maximal. The Z-squared/A-dependence of the Coulomb losses leads to spectral variations for different ions. We present a method to estimate the turbulence parameters and injection conditions of the flare particles using ion ratios like Fe/O of impulsive flares.

  19. Photoelectron spectra and electronic structure of nitrogen analogues of boron β-diketonates

    NASA Astrophysics Data System (ADS)

    Tikhonov, Sergey A.; Vovna, Vitaliy I.; Borisenko, Aleksandr V.

    2016-07-01

    The electronic structure of the valence levels of seven nitrogen-containing boron complexes was investigated using methods of ultraviolet photoelectron spectroscopy and density functional theory. The ionization energies of π- and σ-levels were obtained from photoelectron spectra. The electronic structure of nitrogen-containing compounds was compared with the electronic structure of β-diketonates. It was shown the influence of various substituents on carbon and nitrogen atoms of six-membered ring on the electronic structure of complexes. The changes in the electronic structure after the substitution of atoms in condensed cycles have been identified. In order to compare the experimental vertical ionization energies IEi with Kohn-Sham orbital energies εi we used the analogue of Koopmans theorem and average amendment to the orbital energy of the electrons (δbari). For 26 electronic levels of seven studied complexes, the calculated values are in good accordance with experimental energy intervals between electron levels.

  20. A Unified Computational Model for Solar and Stellar Flares

    NASA Astrophysics Data System (ADS)

    Allred, Joel; Kowalski, Adam; Carlsson, Mats

    2015-04-01

    We describe a unified computational framework which can be used to model impulsive flares on the Sun and on dMe stars. The models are constructed assuming that the flare impulsive phase is caused by a beam of charged particles (primarily electrons and protons) that is accelerated in the corona and propagates downward depositing energy and momentum along the way. This rapidly heats the lower stellar atmosphere causing it to explosively expand and emission to dramatically brighten. Our models consist of flux tubes that extend from the sub-photosphere into the corona. We simulate how these flare-accelerated particles propagate down one dimensional flux tubes and heat the stellar atmosphere using Fokker-Planck kinetic theory. Detailed radiative transfer is included so that model predictions can be directly compared with observations. The flux of flare-accelerated particles drives return currents which additionally heat the stellar atmosphere, and these effects are also included in our models. We examine the impact of the flare-accelerated particle beams on model solar and dMe stellar atmospheres and perform parameter studies varying the injected particle energy spectra. We find the atmospheric response is strongly dependent on the accelerated particle cutoff energy and spectral index.

  1. Solar Flare Effects on the Thermosphere and Ionosphere

    NASA Astrophysics Data System (ADS)

    Solomon, S.; Qian, L.; Rodgers, E.; Bailey, S.

    The Solar Extreme-ultraviolet Experiment SEE on the TIMED satellite and by the X-ray Photometer System XPS on the SORCE satellite provide the first comprehensive irradiance measurements of the complete solar spectrum during large solar flares However the soft X-ray portion of these observations are performed using silicon photodiodes coated with metallic filters to provide photometric measurements with multiple band passes which leads to complexities in obtaining spectral information A new analysis technique developed specifically for flare conditions is used to infer flare spectra in this region These are combined with spectrographic measurements in the extreme ultraviolet and far ultraviolet and applied to the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model TIE-GCM The electron content neutral density and airglow response to large flares during the declining phase of solar cycle 23 are calculated using this model and compared to several measurement sets obtaining good agreement This supports both the validity of the solar X-ray analysis and the modeling methodology showing that although flare-driven effects in the upper atmosphere are significant they are shorter and of much smaller magnitude than geomagnetic disturbances

  2. Electronic structure of some adenosine receptor antagonists. III. Quantitative investigation of the electronic absorption spectra of alkyl xanthines

    NASA Astrophysics Data System (ADS)

    Moustafa, H.; Shalaby, Samia H.; El-sawy, K. M.; Hilal, Rifaat

    2002-07-01

    Quantitative and comparative investigation of the electronic absorption spectra of theophylline, caffeine and their derivatives is reported. The spectra of theophylline, caffeine and theobromine were compared to establish the predominant tautomeric species in solution. This comparison, analysis of solvent effects and assignments of the observed transitions via MO computations indicate the exits of only one tautomeric species in solution that is the N7 form. A low-lying triplet state was identified which corresponds to a HOMO-LUMO transition. This relatively long-lived T 1 state is always less polar than the ground state and may very well underlie the photochemical reactivity of alkyl xanthines. Substituents of different electron donating or withdrawing strengths and solvent effects are investigated and analyzed. The present analysis is facilitated via computer deconvolution of the observed spectra and MO computation.

  3. Plasma scale-length effects on electron energy spectra in high-irradiance laser plasmas

    NASA Astrophysics Data System (ADS)

    Culfa, O.; Tallents, G. J.; Rossall, A. K.; Wagenaars, E.; Ridgers, C. P.; Murphy, C. D.; Dance, R. J.; Gray, R. J.; McKenna, P.; Brown, C. D. R.; James, S. F.; Hoarty, D. J.; Booth, N.; Robinson, A. P. L.; Lancaster, K. L.; Pikuz, S. A.; Faenov, A. Ya.; Kampfer, T.; Schulze, K. S.; Uschmann, I.; Woolsey, N. C.

    2016-04-01

    An analysis of an electron spectrometer used to characterize fast electrons generated by ultraintense (1020W cm-2 ) laser interaction with a preformed plasma of scale length measured by shadowgraphy is presented. The effects of fringing magnetic fields on the electron spectral measurements and the accuracy of density scale-length measurements are evaluated. 2D EPOCH PIC code simulations are found to be in agreement with measurements of the electron energy spectra showing that laser filamentation in plasma preformed by a prepulse is important with longer plasma scale lengths (>8 μ m ).

  4. Simulation of femtosecond two-dimensional electronic spectra of conical intersections.

    PubMed

    Krčmář, Jindřich; Gelin, Maxim F; Domcke, Wolfgang

    2015-08-21

    We have simulated femtosecond two-dimensional (2D) electronic spectra for an excited-state conical intersection using the wave-function version of the equation-of-motion phase-matching approach. We show that 2D spectra at fixed values of the waiting time provide information on the structure of the vibronic eigenstates of the conical intersection, while the evolution of the spectra with the waiting time reveals predominantly ground-state wave-packet dynamics. The results show that 2D spectra of conical intersection systems differ significantly from those obtained for chromophores with well separated excited-state potential-energy surfaces. The spectral signatures which can be attributed to conical intersections are discussed. PMID:26298135

  5. Simulation of femtosecond two-dimensional electronic spectra of conical intersections

    SciTech Connect

    Krčmář, Jindřich; Gelin, Maxim F.; Domcke, Wolfgang

    2015-08-21

    We have simulated femtosecond two-dimensional (2D) electronic spectra for an excited-state conical intersection using the wave-function version of the equation-of-motion phase-matching approach. We show that 2D spectra at fixed values of the waiting time provide information on the structure of the vibronic eigenstates of the conical intersection, while the evolution of the spectra with the waiting time reveals predominantly ground-state wave-packet dynamics. The results show that 2D spectra of conical intersection systems differ significantly from those obtained for chromophores with well separated excited-state potential-energy surfaces. The spectral signatures which can be attributed to conical intersections are discussed.

  6. SUB-THz RADIATION MECHANISMS IN SOLAR FLARES

    SciTech Connect

    Fleishman, Gregory D.; Kontar, Eduard P.

    2010-02-01

    Observations in the sub-THz range of large solar flares have revealed a mysterious spectral component increasing with frequency and hence distinct from the microwave component commonly accepted to be produced by gyrosynchrotron (GS) emission from accelerated electrons. Evidently, having a distinct sub-THz component requires either a distinct emission mechanism (compared to the GS one), or different properties of electrons and location, or both. We find, however, that the list of possible emission mechanisms is incomplete. This Letter proposes a more complete list of emission mechanisms, capable of producing a sub-THz component, both well known and new in this context, and calculates a representative set of their spectra produced by (1) free-free emission, (2) GS emission, (3) synchrotron emission from relativistic positrons/electrons, (4) diffusive radiation, and (5) Cherenkov emission. We discuss the possible role of the mechanisms in forming the sub-THz emission and emphasize their diagnostics potential for flares.

  7. Solar Flares

    NASA Astrophysics Data System (ADS)

    Rust, David

    1998-01-01

    The Sun is constantly changing. Not an hour goes by without a rise or fall in solar x-radiation or radio emission. Not a day goes by without a solar flare. Our active star, this inconsistent Sun, this gaseous cloud that blows in all directions, warms the air we breathe and nourishes the food we eat. From Earth, it seems the very model of stability, but in space it often creates havoc. Over the past century, solar physicists have learned how to detect even the weakest of solar outbursts or flares. We know that flares must surely trace their origins to the magnetic strands stretched and tangled by the rolling plasma of the solar interior. Although a century of astrophysical research has produced widely accepted, fundamental understanding about the Sun, we have yet to predict successfully the emergence of any magnetic fields from inside the Sun or the ignition of any flare. As in any physical experiment, the ability to predict events not only validates the scientific ideas, it also has practical value. In astrophysics, a demonstrated understanding of sunspots, flares, and ejections of plasma would allow us to approach many other mysteries, such as stellar X-ray bursters, with tested theories.

  8. Effects of Electronic-State-Dependent Solute Polarizability: Application to Solute-Pump/Solvent-Probe Spectra.

    PubMed

    Sun, Xiang; Ladanyi, Branka M; Stratt, Richard M

    2015-07-23

    Experimental studies of solvation dynamics in liquids invariably ask how changing a solute from its electronic ground state to an electronically excited state affects a solution's dynamics. With traditional time-dependent-fluorescence experiments, that means looking for the dynamical consequences of the concomitant change in solute-solvent potential energy. But if one follows the shift in the dynamics through its effects on the macroscopic polarizability, as recent solute-pump/solvent-probe spectra do, there is another effect of the electronic excitation that should be considered: the jump in the solute's own polarizability. We examine the spectroscopic consequences of this solute polarizability change in the classic example of the solvation dye coumarin 153 dissolved in acetonitrile. After demonstrating that standard quantum chemical methods can be used to construct accurate multisite models for the polarizabilities of ground- and excited-state solvation dyes, we show via simulation that this polarizability change acts as a contrast agent, significantly enhancing the observable differences in optical-Kerr spectra between ground- and excited-state solutions. A comparison of our results with experimental solute-pump/solvent-probe spectra supports our interpretation and modeling of this spectroscopy. We predict, in particular, that solute-pump/solvent-probe spectra should be sensitive to changes in both the solvent dynamics near the solute and the electronic-state-dependence of the solute's own rotational dynamics. PMID:25299940

  9. Spectral study of suggested Apollo sites. [proposals for financial support and the electronic spectra of pyroxenes

    NASA Technical Reports Server (NTRS)

    Mccord, T. B.

    1973-01-01

    The spectrophotometry (0.3 to 1.1 microns) of visited and proposed Apollo landing sites is presented along with proposals for financial support of the spectral study. The electronic spectra of pyroxenes is investigated along with an interpretation of telescopic spectral reflectivity curves of the moon. Reprints of published articles related to these studies are included.

  10. Two-dimensional spectra of electron collisions with acrylonitrile and methacrylonitrile reveal nuclear dynamics

    SciTech Connect

    Regeta, K. Allan, M.

    2015-05-14

    Detailed experimental information on the motion of a nuclear packet on a complex (resonant) anion potential surface is obtained by measuring 2-dimensional (2D) electron energy loss spectra. The cross section is plotted as a function of incident electron energy, which determines which resonant anion state is populated, i.e., along which normal coordinate the wave packet is launched, and of the electron energy loss, which reveals into which final states each specific resonant state decays. The 2D spectra are presented for acrylonitrile and methacrylonitrile, at the incident energy range 0.095-1.0 eV, where the incoming electron is temporarily captured in the lowest π{sup ∗} orbital. The 2D spectra reveal selectivity patterns with respect to which vibrations are excited in the attachment and de-excited in the detachment. Further insight is gained by recording 1D spectra measured along horizontal, vertical, and diagonal cuts of the 2D spectrum. The methyl group in methacrylonitrile increases the resonance width 7 times. This converts the sharp resonances of acrylonitrile into boomerang structures but preserves the essence of the selectivity patterns. Selectivity of vibrational excitation by higher-lying shape resonances up to 8 eV is also reported.

  11. FUV Continuum in Flare Kernels Observed by IRIS

    NASA Astrophysics Data System (ADS)

    Daw, Adrian N.; Kowalski, Adam; Allred, Joel C.; Cauzzi, Gianna

    2016-05-01

    Fits to Interface Region Imaging Spectrograph (IRIS) spectra observed from bright kernels during the impulsive phase of solar flares are providing long-sought constraints on the UV/white-light continuum emission. Results of fits of continua plus numerous atomic and molecular emission lines to IRIS far ultraviolet (FUV) spectra of bright kernels are presented. Constraints on beam energy and cross sectional area are provided by cotemporaneous RHESSI, FERMI, ROSA/DST, IRIS slit-jaw and SDO/AIA observations, allowing for comparison of the observed IRIS continuum to calculations of non-thermal electron beam heating using the RADYN radiative-hydrodynamic loop model.

  12. Spectral Diagnostics and Radiative Hydrodynamics of Solar Flares

    NASA Astrophysics Data System (ADS)

    Cheng, J. X.

    2011-03-01

    Solar flares are one of the most significant active phenomena in the solar atmosphere. It is involved in very complicated physical processes, including energy release, plasma instability, acceleration and propagation of energetic particles, radiation and dynamics of the flaring atmosphere, mass motions and ejections, and so on. Enhanced radiation during flares spans virtually the entire electromagnetic spectrum originating from different layers of the solar atmosphere. High energetic particles and strong radiations that are produced during the flare eruptions play a major role in space weather. Therefore, it is very important and necessary to study the mechanisms of solar flares. In this thesis, combined with ground and space observations, the theoretical calculations are used to study the spectral features and radiation mechanisms of solar flares. In particular, our research is concentrated on the diagnostics of non-thermal processes and origin of the white-light flares. The main contents are described as follows: (1) Different chromospheric lines are used to diagnose the heating mechanisms in flares. We calculate the Hα and Ca II 8542 Å line profiles based on four different atmospheric models, including the effects of non-thermal electron beams with various energy fluxes. These two lines have different responses to the thermal and non-thermal effects, and can be used to diagnose the thermal and non-thermal heating processes. We apply our method to an X-class flare occurred on 2001 October 19 and find that the non-thermal effects at the outer edge of the flare ribbon are more notable than that at the inner edge, while the temperature at the inner edge seems higher. On the other hand, the results show that non-thermal effects increase rapidly in the rise phase and decrease quickly in the decay phase, but the atmospheric temperature can still keep relatively high for some time after getting to its maximum. For the two kernels that we analyze, the maximum energy

  13. Vibrationally high-resolved electronic spectra of MCl2 (M=C, Si, Ge, Sn, Pb) and photoelectron spectra of MCl2(.).

    PubMed

    Ran, Yibin; Pang, Min; Shen, Wei; Li, Ming; He, Rongxing

    2016-10-01

    We systematically studied the vibrational-resolved electronic spectra of group IV dichlorides using the Franck-Condon approximation combined with the Duschinsky and Herzberg-Teller effects in harmonic and anharmonic frameworks (only the simulation of absorption spectra includes the anharmonicity). Calculated results showed that the band shapes of simulated spectra are in accordance with those of the corresponding experimental or theoretical ones. We found that the symmetric bend mode in progression of absorption is the most active one, whereas the main contributor in photoelectron spectra is the symmetric stretching mode. Moreover, the Duschinsky and anharmonic effects exert weak influence on the absorption spectra, except for PbCl2 molecule. The theoretical insights presented in this work are significant in understanding the photophysical properties of MCl2 (M=C, Si, Ge, Sn, Pb) and studying the Herzberg-Teller and the anharmonic effects on the absorption spectra of new dichlorides of this main group. PMID:27280730

  14. Adiabatic heating in impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Maetzler, C.; Bai, T.; Crannell, C. J.; Frost, K. J.

    1978-01-01

    A study is made of adiabatic heating in two impulsive solar flares on the basis of dynamic X-ray spectra in the 28-254 keV range, H-alpha, microwave, and meter-wave radio observations. It is found that the X-ray spectra of the events are like those of thermal bremsstrahlung from single-temperature plasmas in the 10-60 keV range if photospheric albedo is taken into account. The temperature-emission correlation indicates adiabatic compression followed by adiabatic expansion and that the electron distribution remains isotropic. H-alpha data suggest compressive energy transfer. The projected areas and volumes of the flares are estimated assuming that X-ray and microwave emissions are produced in a single thermal plasma. Electron densities of about 10 to the 9th/cu cm are found for homogeneous, spherically symmetric sources. It is noted that the strong self-absorption of hot-plasma gyrosynchrotron radiation reveals low magnetic field strengths.

  15. THE SOLAR FLARE IRON ABUNDANCE

    SciTech Connect

    Phillips, K. J. H.; Dennis, B. R. E-mail: Brian.R.Dennis@nasa.gov

    2012-03-20

    The abundance of iron is measured from emission line complexes at 6.65 keV (Fe line) and 8 keV (Fe/Ni line) in RHESSI X-ray spectra during solar flares. Spectra during long-duration flares with steady declines were selected, with an isothermal assumption and improved data analysis methods over previous work. Two spectral fitting models give comparable results, viz., an iron abundance that is lower than previous coronal values but higher than photospheric values. In the preferred method, the estimated Fe abundance is A(Fe) = 7.91 {+-} 0.10 (on a logarithmic scale, with A(H) = 12) or 2.6 {+-} 0.6 times the photospheric Fe abundance. Our estimate is based on a detailed analysis of 1898 spectra taken during 20 flares. No variation from flare to flare is indicated. This argues for a fractionation mechanism similar to quiet-Sun plasma. The new value of A(Fe) has important implications for radiation loss curves, which are estimated.

  16. Statistical Analyses of White-Light Flares: Two Main Results about Flare Behaviour

    NASA Astrophysics Data System (ADS)

    Dal, Hasan Ali

    2012-08-01

    We present two main results, based on models and the statistical analyses of 1672 U-band flares. We also discuss the behaviour of white-light flares. In addition, the parameters of the flares detected from two years of observations on CR Dra are presented. By comparing with flare parameters obtained from other UV Ceti-type stars, we examine the behaviour of the optical flare processes along with the spectral types. Moreover, we aimed, using large white-light flare data, to analyse the flare time-scales with respect to some results obtained from X-ray observations. Using SPSS V17.0 and GraphPad Prism V5.02 software, the flares detected from CR Dra were modelled with the OPEA function, and analysed with the t-Test method to compare similar flare events in other stars. In addition, using some regression calculations in order to derive the best histograms, the time-scales of white-light flares were analysed. Firstly, CR Dra flares have revealed that white-light flares behave in a similar way as their counterparts observed in X-rays. As can be seen in X-ray observations, the electron density seems to be a dominant parameter in white-light flare process, too. Secondly, the distributions of the flare time-scales demonstrate that the number of observed flares reaches a maximum value in some particular ratios, which are 0.5, or its multiples, and especially positive integers. The thermal processes might be dominant for these white-light flares, while non-thermal processes might be dominant in the others. To obtain better results for the behaviour of the white-light flare process along with the spectral types, much more stars in a wide spectral range, from spectral type dK5e to dM6e, must be observed in white-light flare patrols.

  17. Stochastic Gyroresonant Acceleration for Hard Electron Spectra of Blazars: Effect of Damping of Cascading Turbulence

    NASA Astrophysics Data System (ADS)

    Kakuwa, Jun

    2016-01-01

    Stochastic acceleration of nonthermal electrons is investigated in the context of hard photon spectra of blazars. It is well known that this acceleration mechanism can produce a hard electron spectrum of m≡ ∂ {ln}{n}{{e}}(γ )/∂ {ln}γ =2 with the high-energy cutoff, called an ultrarelativistic Maxwellian-like distribution, where {n}{{e}}(γ ) is an electron energy spectrum. We revisit the formation of this characteristic spectrum, considering a particular situation where the electrons are accelerated through gyroresonant interaction with magnetohydrodynamic wave turbulence driven by the turbulent cascade. By solving kinetic equations of the turbulent fields, electrons, and photons emitted via the synchrotron self-Compton (SSC) process, we demonstrate that in the non-test-particle treatment, the formation of a Maxwellian-like distribution is prevented by the damping effect on the turbulent fields due to the electron acceleration, at least unless an extreme parameter value is chosen. Instead, a softer electron spectrum with the index of m ≈ -1 is produced if the Kolmogorov-type cascade is assumed. The SSC spectrum that originates from the resultant softer electron spectrum is still hard, but somewhat softer and broader than the case of m = 2. This change of achievable hardness should be noted when this basic particle acceleration scenario is accurately tested with observations of hard photon spectra.

  18. A satellite investigation of energy flux and inferred potential drop in auroral electron energy spectra

    NASA Technical Reports Server (NTRS)

    Menietti, J. D.; Burch, J. L.

    1981-01-01

    The relationship between auroral electron energy flux and the inferred accelerating potential drop for accelerated Maxwellian distributions is investigated on the basis of Atmospheric Explorer D spectral measurements. An analytical approximation for the total downward energy flux carried by an isotropic Maxwellian electron population accelerated by a field-aligned electrostatic potential drop is derived which is valid for values of the electron energy/characteristic accelerated Maxwellian distribution energy which are less than the difference between the ratio of the magnetic field strengths at the altitude of observation and the altitude of potential drop, and unity. Data from the Low Energy Electron Experiment on board AE D obtained on both the dayside and the nightside during periods of significant inverted-V type electron precipitation shows that the 455 energy spectra considered, 160 of them, obtained between 60 and 85 deg invariant latitude, could be fit to accelerated Maxwellian distributions. The 160 Maxwellian spectra are then shown to be in agreement with the predictions of the accelerated Maxwellian model. Finally, analysis of individual spectra suggests that the altitude of the inferred potential drop is at a maximum near the center of the inverted-V structures.

  19. Helium induced fine structure in the electronic spectra of anthracene derivatives doped into superfluid helium nanodroplets

    SciTech Connect

    Pentlehner, D.; Slenczka, A.

    2015-01-07

    Electronic spectra of organic molecules doped into superfluid helium nanodroplets show characteristic features induced by the helium environment. Besides a solvent induced shift of the electronic transition frequency, in many cases, a spectral fine structure can be resolved for electronic and vibronic transitions which goes beyond the expected feature of a zero phonon line accompanied by a phonon wing as known from matrix isolation spectroscopy. The spectral shape of the zero phonon line and the helium induced phonon wing depends strongly on the dopant species. Phonon wings, for example, are reported ranging from single or multiple sharp transitions to broad (Δν > 100 cm{sup −1}) diffuse signals. Despite the large number of example spectra in the literature, a quantitative understanding of the helium induced fine structure of the zero phonon line and the phonon wing is missing. Our approach is a systematic investigation of related molecular compounds, which may help to shed light on this key feature of microsolvation in superfluid helium droplets. This paper is part of a comparative study of the helium induced fine structure observed in electronic spectra of anthracene derivatives with particular emphasis on a spectrally sharp multiplet splitting at the electronic origin. In addition to previously discussed species, 9-cyanoanthracene and 9-chloroanthracene will be presented in this study for the first time.

  20. Detection of nanoscale electron spin resonance spectra demonstrated using nitrogen-vacancy centre probes in diamond

    NASA Astrophysics Data System (ADS)

    Hall, L. T.; Kehayias, P.; Simpson, D. A.; Jarmola, A.; Stacey, A.; Budker, D.; Hollenberg, L. C. L.

    2016-01-01

    Electron spin resonance (ESR) describes a suite of techniques for characterizing electronic systems with applications in physics, chemistry, and biology. However, the requirement for large electron spin ensembles in conventional ESR techniques limits their spatial resolution. Here we present a method for measuring ESR spectra of nanoscale electronic environments by measuring the longitudinal relaxation time of a single-spin probe as it is systematically tuned into resonance with the target electronic system. As a proof of concept, we extracted the spectral distribution for the P1 electronic spin bath in diamond by using an ensemble of nitrogen-vacancy centres, and demonstrated excellent agreement with theoretical expectations. As the response of each nitrogen-vacancy spin in this experiment is dominated by a single P1 spin at a mean distance of 2.7 nm, the application of this technique to the single nitrogen-vacancy case will enable nanoscale ESR spectroscopy of atomic and molecular spin systems.

  1. Valence photoelectron spectra of an electron-beam-irradiated C{sub 60} film

    SciTech Connect

    Onoe, Jun; Nakao, Aiko; Hida, Akira

    2004-10-04

    Valence photoelectron spectra of an electron-beam (EB) irradiated C{sub 60} film, which exhibited metallic electron-transport properties in air at room temperature, are presented. The electronic structure of the C{sub 60} film became closer to that of graphite as the EB-irradiation time increased, and its density of states around the Fermi level was eventually greater than for the graphite. This suggests that the electronic structure of the C{sub 60} film changed from a semiconductor to a semimetal and/or metal by EB irradiation. Interestingly, the electronic structure remained metallic even after five days of air exposure, which is the reason for the metallic electron-transport property in our previous report [Appl. Phys. Lett. 82, 595 (2003)].

  2. Simulation of High Resolution Vibrational and Electronic Spectra with a Multifrequency Virtual Spectrometer

    NASA Astrophysics Data System (ADS)

    Biczysko, Malgorzata; Bloino, Julien; Barone, Vincenzo

    2013-06-01

    Moving from the common practice of extracting numerical data from experiment to be compared with quantum mechanical (QM) results toward a direct vis-à-vis} comparison of experimental and simulated spectra would strongly reduce any arbitrariness in analysis of complex experimental outcomes and allow a proper account of the information connected to both position and shape of spectral bands. The development of such ``virtual ab initio spectrometers'' for a wide range of wavelengths has been one of our major research goals in the last years [1,2]. Recent methodological advances from our group allow simulation of optical (IR, Raman, UV-vis, etc.) spectra line-shapes for medium-to-large closed- and open-shell molecular systems. Vibrational spectra are computed including anharmonicities through perturbative corrections while electronic spectra line-shapes are simulated accounting for the vibrational structure. Well resolved and accurate theoretical spectra provide data as close as possible to the results directly available from experiment allowing to avoid ambiguities in analysis of the latter. Several examples illustrating interpretation, assignment or revision of experimental spectra for prototypes of bio-molecular systems (phenyl radical, glycine, thymine, pyrimidine, anisole dimer) will be presented. 1. V. Barone, A. Baiardi, M. Biczysko, J. Bloino, C. Cappelli, F. Lipparini Phys. Chem. Chem. Phys, 14, 12404, 2012 2. M. Biczysko, J. Bloino, G. Brancato, et al. Theor. Chem. Acc. 113, 1201, 2012

  3. Pressure dependence of Hexanitrostilbene Raman/ electronic absorption spectra to validate DFT EOS

    NASA Astrophysics Data System (ADS)

    Farrow, Darcie; Alam, Kathleen; Martin, Laura; Fan, Hongyou; Kay, Jeffrey; Wixom, Ryan

    2015-06-01

    Due to its thermal stability and low vapor pressure, Hexanitrostilbene (HNS) is often used in high-temperature or vacuum applications as a detonator explosive or in mild detonating fuse. Toward improving the accuracy of the equation of state used in hydrodynamic simulations of the performance of HNS, we have measured the Raman and electronic absorption spectra of this material under static pressure in a diamond anvil cell. Density functional theory calculations were used to simulate the pressure dependence of the Raman/Electronic spectra along the Hugoniot and 300K isotherm for comparison and to aid in interpreting the data. We will discuss changes in the electronic structure of HNS under pressure, validation of a DFT predicted equation of state (EOS), and using this data as a basis for understanding future pulsed Raman measurements on dynamically compressed HNS samples.

  4. Computational Prediction of Electron Ionization Mass Spectra to Assist in GC/MS Compound Identification.

    PubMed

    Allen, Felicity; Pon, Allison; Greiner, Russ; Wishart, David

    2016-08-01

    We describe a tool, competitive fragmentation modeling for electron ionization (CFM-EI) that, given a chemical structure (e.g., in SMILES or InChI format), computationally predicts an electron ionization mass spectrum (EI-MS) (i.e., the type of mass spectrum commonly generated by gas chromatography mass spectrometry). The predicted spectra produced by this tool can be used for putative compound identification, complementing measured spectra in reference databases by expanding the range of compounds able to be considered when availability of measured spectra is limited. The tool extends CFM-ESI, a recently developed method for computational prediction of electrospray tandem mass spectra (ESI-MS/MS), but unlike CFM-ESI, CFM-EI can handle odd-electron ions and isotopes and incorporates an artificial neural network. Tests on EI-MS data from the NIST database demonstrate that CFM-EI is able to model fragmentation likelihoods in low-resolution EI-MS data, producing predicted spectra whose dot product scores are significantly better than full enumeration "bar-code" spectra. CFM-EI also outperformed previously reported results for MetFrag, MOLGEN-MS, and Mass Frontier on one compound identification task. It also outperformed MetFrag in a range of other compound identification tasks involving a much larger data set, containing both derivatized and nonderivatized compounds. While replicate EI-MS measurements of chemical standards are still a more accurate point of comparison, CFM-EI's predictions provide a much-needed alternative when no reference standard is available for measurement. CFM-EI is available at https://sourceforge.net/projects/cfm-id/ for download and http://cfmid.wishartlab.com as a web service. PMID:27381172

  5. Partial intensity approach for quantitative analysis of reflection-electron-energy-loss spectra

    NASA Astrophysics Data System (ADS)

    Calliari, L.; Filippi, M.; A. Varfolomeev

    2011-08-01

    We have considered a formalism, known as partial intensity approach (PIA), previously developed to quantitatively analyze reflection electron energy loss (REEL) spectra [1,2]. The aim of the approach is, in particular, to recover the single scattering distribution of energy losses and to separate it into bulk and surface contributions, respectively referred to as the differential inverse inelastic mean free path (DIIMFP) and the differential surface excitation parameter (DSEP). As compared to [1] and [2], we have implemented a modified approach, and we have applied it to the specific geometry of the cylindrical mirror analyzer (CMA), used to acquire the REEL spectra shown here. Silicon, a material with well-defined surface and bulk plasmons, is taken as a case study to investigate the approach as a function of electron energy over the energy range typical of REELS, i.e. from 250 eV to 2 keV. Our goal is, on the one hand, to examine possible limits for the applicability of the approach and, on the other hand, to test a basic assumption of the PIA, namely that a unique DIIMFP and a unique DSEP account for REEL spectra, whatever the acquisition conditions (i.e. electron energy or angle of surface crossing) are. We find that a minimum energy exists below which the PIA cannot be applied and that the assumption of REEL spectra accounted for by unique DIIMFP and DSEP is indeed an approximation.

  6. Theoretical Study of the Electronic Spectra of a Polycyclic Aromatic Hydrocarbon, Naphthalene, and its Derivatives

    NASA Technical Reports Server (NTRS)

    Du, Ping; Salama, Farid; Loew, Gilda H.

    1993-01-01

    In order to preselect possible candidates for the origin of diffuse interstellar bands observed, semiempirical quantum mechanical method INDO/S was applied to the optical spectra of neutral, cationic, and anionic states of naphthalene and its hydrogen abstraction and addition derivatives. Comparison with experiment shows that the spectra of naphthalene and its ions were reliably predicted. The configuration interaction calculations with single-electron excitations provided reasonable excited state wavefunctions compared to ab initio calculations that included higher excitations. The degree of similarity of the predicted spectra of the hydrogen abstraction and derivatives to those of naphthalene and ions depends largely on the similarity of the it electron configurations. For the hydrogen addition derivatives, very little resemblance of the predicted spectra to naphthalene was found because of the disruption of the aromatic conjugation system. The relevance of these calculations to astrophysical issues is discussed within the context of these polycyclic aromatic hydrocarbon models. Comparing the calculated electronic energies to the Diffuse Interstellar Bands (DIBs), a list of possible candidates of naphthalene derivatives is established which provides selected candidates for a definitive test through laboratory studies.

  7. Environmental Factors Influencing the Hyperfine Structure of Manganous Low-Temperature Electron Paramagnetic Resonance Spectra

    PubMed Central

    Nebert, D. W.; Allen, B. T.

    1966-01-01

    Hyperfine structure is observed in low temperature (T = -180°C) EPR (electron paramagnetic resonance) spectra of a number of solutions containing Mn++ ions 13, 15) which have characteristics in common with low temperature EPR spectra from biological substances such as mitochondria and microsomes (1-4). This investigation is an attempt to understand the features of these signals in terms of the molecular environment of the manganous ion, and a qualitative explanation for the observations reported here is advanced in terms of the amount of axial distortion of a manganese hydrate in different environments. PMID:4289642

  8. Recoil-nucleus spectra in the interaction of cosmic-ray protons with spacecraft electronics

    SciTech Connect

    Chuvilskaya, T. V.; Shirokova, A. A.; Kadmenskii, A. G.; Chechenin, N. G.

    2008-07-15

    The cross sections for nuclear reactions induced by 50-to 1000-MeV protons in silicon and the angular distributions of products of these reactions are calculated, along with the recoil-nucleus spectra. The recoil-nucleus spectra are shown to contain a monotonically decreasing portion and a recoil peak, which is manifested most clearly at incident-proton energies in excess of 100 MeV. The possibility of employing these results to derive more reliable estimates of single-event upsets in onboard spacecraft electronics is discussed.

  9. Comparative analysis of the optical spectra of the holmium atom excited by electron impact and ionic bombardment

    SciTech Connect

    Vasileva, E.K.; Morozov, S.N.; Ryskin, B.V.

    1988-02-01

    A comparative analysis of the optical spectra of holmium excited by electron impact and ionic bombardment is given. It is shown that under ionic bombardment, the probability of excitation of screened transitions is significantly higher than under electron impact.

  10. Characteristics of gamma-ray line flares

    NASA Technical Reports Server (NTRS)

    Bai, T.; Dennis, B.

    1983-01-01

    Observations of solar gamma rays by the Solar Maximum Mission (SMM) demonstrate that energetic protons and ions are rapidly accelerated during the impulsive phase. To understand the acceleration mechanisms for these particles, the characteristics of the gamma ray line flares observed by SMM were studied. Some very intense hard X-ray flares without detectable gamma ray lines were also investigated. Gamma ray line flares are distinguished from other flares by: (1) intense hard X-ray and microwave emissions; (2) delay of high energy hard X-rays; (3) emission of type 2 and/or type 4 radio bursts; and (4) flat hard X-ray spectra (average power law index: 3.1). The majority of the gamma ray line flares shared all these characteristics, and the remainder shared at least three of them. Positive correlations were found between durations of spike bursts and spatial sizes of flare loops as well as between delay times and durations of spike bursts.

  11. Theoretical Study of FH2– Electron Photodetachment Spectra on New Ab Initio Potential Energy Surfaces.

    PubMed

    Yu, Dequan; Chen, Jun; Cong, Shulin; Sun, Zhigang

    2015-12-17

    The FH2– anion has a stable structure that resembles a configuration in the vicinity of the transition state for neutral reaction F + H2 → HF + H. Electron photodetachment spectra of the FH2– anion reveal the neutral reaction dynamics in the critical transition-state region. Accurate quantum dynamics simulations of the photodetachment spectra using highly accurate new ab initio potential energy surfaces for both anionic and neutral FH2 are performed and compared with all available experimental results. The results provide reliable interpretations for the experimental observations of FH2– photoelectron detachment and reveal a detailed picture of the molecular dynamics around the transition state of the F + H2 reaction. The latest high-resolution photoelectron detachment spectra [Kim et al. Science, 2015, 349, 510-513] confirm the high accuracy of our new potential energy surface for describing the resonance-enhanced reactivity of the neutral F + H2 reaction. PMID:26550683

  12. Signatures of current loop coalescence in solar flares

    NASA Technical Reports Server (NTRS)

    Sakai, J.; Nakajima, H.; Zaidman, E.; Tajima, T.; Kosugi, T.; Brunel, F.

    1986-01-01

    The nonlinear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic emission as well as the characteristics of 2-D microwave images obtained during a solar flare. The physical characteristics of the explosive coalescence of currents are presented in detail through computer simulation and theory. Canonical characteristics of the explosive coalescence are: (1) a large amount of impulsive increase of kinetic energies of electrons and ions; (2) simultaneous heating and acceleration of electrons and ions in high and low energy spectra; (3) ensuing quasi-periodic amplitude oscillations in fields and particle quantities; and (4) the double peak (or triple peak) structure in these profiles, participate in the coalescence process, yielding varieties of phenomena.

  13. Effects of the Electron Energy Distribution Function on Modeled X-ray Spectra

    SciTech Connect

    Shlyaptseva, A S; Hansen, S B

    2004-02-19

    This paper presents the results of a broad investigation into the effects of the electron energy distribution function on the predictions of non-LTE collisional-radiative atomic kinetics models. The effects of non-Maxwellian and suprathermal (''hot'') electron distributions on collisional rates (including three-body recombination) are studied. It is shown that most collisional rates are fairly insensitive to the functional form and characteristic energy of the electron distribution function as long as the characteristic energy is larger than the threshold energy for the collisional process. Collisional excitation and ionization rates, however, are highly sensitive to the fraction of hot electrons. This permits the development of robust spectroscopic diagnostics that can be used to characterize the electron density, bulk electron temperature, and hot electron fraction of plasmas with non-equilibrium electron distribution functions (EDFs). Hot electrons are shown to increase and spread out plasma charge state distributions, amplify the intensities of emission lines fed by direct collisional excitation and radiative cascades, and alter the structure of satellite features in both K- and L-shell spectra. The characteristic energy, functional form, and spatial properties of hot electron distributions in plasmas are open to characterization through their effects on high-energy continuum and line emission and on the polarization of spectral lines.

  14. Optical Spectral Observations of a Flickering White-light Kernel in a C1 Solar Flare

    NASA Astrophysics Data System (ADS)

    Kowalski, Adam F.; Cauzzi, Gianna; Fletcher, Lyndsay

    2015-01-01

    We analyze optical spectra of a two-ribbon, long-duration C1.1 flare that occurred on 2011 August 18 within AR 11271 (SOL2011-08-18T15:15). The impulsive phase of the flare was observed with a comprehensive set of space-borne and ground-based instruments, which provide a range of unique diagnostics of the lower flaring atmosphere. Here we report the detection of enhanced continuum emission, observed in low-resolution spectra from 3600 Å to 4550 Å acquired with the Horizontal Spectrograph at the Dunn Solar Telescope. A small, <=0.''5 (1015 cm2) penumbral/umbral kernel brightens repeatedly in the optical continuum and chromospheric emission lines, similar to the temporal characteristics of the hard X-ray variation as detected by the Gamma-ray Burst Monitor on the Fermi spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal electron beam energy flux high enough to produce the optical contrast in our flare spectra would predict a large Balmer jump in emission, indicative of hydrogen recombination radiation from the upper flare chromosphere. However, we find no evidence of such a Balmer jump in the bluemost spectral region of the continuum excess. Just redward of the expected Balmer jump, we find evidence of a "blue continuum bump" in the excess emission which may be indicative of the merging of the higher order Balmer lines. The large number of observational constraints provides a springboard for modeling the blue/optical emission for this particular flare with radiative-hydrodynamic codes, which are necessary to understand the opacity effects for the continuum and emission line radiation at these wavelengths.

  15. OPTICAL SPECTRAL OBSERVATIONS OF A FLICKERING WHITE-LIGHT KERNEL IN A C1 SOLAR FLARE

    SciTech Connect

    Kowalski, Adam F.; Cauzzi, Gianna; Fletcher, Lyndsay

    2015-01-10

    We analyze optical spectra of a two-ribbon, long-duration C1.1 flare that occurred on 2011 August 18 within AR 11271 (SOL2011-08-18T15:15). The impulsive phase of the flare was observed with a comprehensive set of space-borne and ground-based instruments, which provide a range of unique diagnostics of the lower flaring atmosphere. Here we report the detection of enhanced continuum emission, observed in low-resolution spectra from 3600 Å to 4550 Å acquired with the Horizontal Spectrograph at the Dunn Solar Telescope. A small, ≤0.''5 (10{sup 15} cm{sup 2}) penumbral/umbral kernel brightens repeatedly in the optical continuum and chromospheric emission lines, similar to the temporal characteristics of the hard X-ray variation as detected by the Gamma-ray Burst Monitor on the Fermi spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal electron beam energy flux high enough to produce the optical contrast in our flare spectra would predict a large Balmer jump in emission, indicative of hydrogen recombination radiation from the upper flare chromosphere. However, we find no evidence of such a Balmer jump in the bluemost spectral region of the continuum excess. Just redward of the expected Balmer jump, we find evidence of a ''blue continuum bump'' in the excess emission which may be indicative of the merging of the higher order Balmer lines. The large number of observational constraints provides a springboard for modeling the blue/optical emission for this particular flare with radiative-hydrodynamic codes, which are necessary to understand the opacity effects for the continuum and emission line radiation at these wavelengths.

  16. Flare models: Chapter 9 of solar flares

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A. (Editor)

    1979-01-01

    By reviewing the properties of solar flares analyzed by each of the seven teams of the Skylab workshop, a set of primary and secondary requirements of flare models are derived. A number of flare models are described briefly and their properties compared with the primary requirements. It appears that, at this time, each flare model has some strong points and some weak points. It has not yet been demonstrated that any one flare model meets all the proposed requirements.

  17. Theoretical analysis of electronic absorption spectra of vitamin B12 models

    NASA Astrophysics Data System (ADS)

    Andruniow, Tadeusz; Kozlowski, Pawel M.; Zgierski, Marek Z.

    2001-10-01

    Time-dependent density-functional theory (TD-DFT) is applied to analyze the electronic absorption spectra of vitamin B12. To accomplish this two model systems were considered: CN-[CoIII-corrin]-CN (dicyanocobinamide, DCC) and imidazole-[CoIII-corrin]-CN (cyanocobalamin, ImCC). For both models 30 lowest excited states were calculated together with transition dipole moments. When the results of TD-DFT calculations were directly compared with experiment it was found that the theoretical values systematically overestimate experimental data by approximately 0.5 eV. The uniform adjustment of the calculated transition energies allowed detailed analysis of electronic absorption spectra of vitamin B12 models. All absorption bands in spectral range 2.0-5.0 eV were readily assigned. In particular, TD-DFT calculations were able to explain the origin of the shift of the lowest absorption band caused by replacement of the-CN axial ligand by imidazole.

  18. F region electron density irregularity spectra near auroral acceleration and shear regions

    NASA Technical Reports Server (NTRS)

    Basu, S.; Basu, S.; Mackenzie, E.; Coley, W. R.; Hanson, W. B.; Lin, C. S.

    1984-01-01

    Two orbits of the Atmosphere Explorer D yielded data on F region electron irregularities in the high latitude ionosphere. Data were taken with a retarding potential analyzer, an ion drift meter, a low energy electron experiment and a photoelectron spectrometer. Auroral forms were simultaneously visually sighted by DMSP spacecraft. The irregularities were associated with auroral excitation and large structured flow regions. Steep spectra with one-dimensional spectral index values for wavelengths over 1 km were observed in the acceleration region. Large amplitude irregularities appeared in large structured flow regions and displayed shallow spectra, indicating the presence of large power spectral densities at scale lengths of about 100 m. It is suspected that large velocities or shears in the velocities in adjacent precipitation regions cause the F region density perturbations.

  19. Electronic and vibrational spectra of matrix isolated anthracene radical cations - Experimental and theoretical aspects

    NASA Technical Reports Server (NTRS)

    Szczepanski, Jan; Vala, Martin; Talbi, Dahbia; Parisel, Olivier; Ellinger, Yves

    1993-01-01

    The IR vibrational and visible/UV electronic absorption spectra of the anthracene cation, An(+), were studied experimentally, in argon matrices at 12 K, as well as theoretically, using ab initio calculations for the vibrational modes and enhanced semiempirical methods with configuration interaction for the electronic spectra. It was found that both approaches predicted well the observed photoelectron spectrum. The theoretical IR intensities showed some remarkable differences between neutral and ionized species (for example, the CH in-plane bending modes and CC in-plane stretching vibrations were predicted to increase by several orders of magnitude upon ionization). Likewise, estimated experimental IR intensities showed a significant increase in the cation band intensities over the neutrals. The implication of these findings for the hypothesis that polycyclic aromatic hydrocarbon cations are responsible for the unidentified IR emission bands from interstellar space is discussed.

  20. Vibronic and Vibrational Coherences in Two-Dimensional Electronic Spectra of Supramolecular J-Aggregates

    PubMed Central

    2013-01-01

    In J-aggregates of cyanine dyes, closely packed molecules form mesoscopic tubes with nanometer-diameter and micrometer-length. Their efficient energy transfer pathways make them suitable candidates for artificial light harvesting systems. This great potential calls for an in-depth spectroscopic analysis of the underlying energy deactivation network and coherence dynamics. We use two-dimensional electronic spectroscopy with sub-10 fs laser pulses in combination with two-dimensional decay-associated spectra analysis to describe the population flow within the aggregate. Based on the analysis of Fourier-transform amplitude maps, we distinguish between vibrational or vibronic coherence dynamics as the origin of pronounced oscillations in our two-dimensional electronic spectra. PMID:23461650

  1. DFT computation and experimental analysis of vibrational and electronic spectra of phenoxy acetic acid herbicides

    NASA Astrophysics Data System (ADS)

    Arul Dhas, D.; Hubert Joe, I.; Roy, S. D. D.; Balachandran, S.

    2013-05-01

    An absolute vibrational analysis has been attempted on the basis of experimental FTIR and NIR-FT Raman spectra with calculated vibrational wavenumbers and intensities of phenoxy acetic acids. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers have been calculated with the help of B3LYP method with Dunning correlation consistent basis set aug-cc-pVTZ. The electronic structures of molecular fragments were described in terms of natural bond orbital analysis, which shows intermolecular Osbnd H⋯O and intramolecular Csbnd H⋯O hydrogen bonds. The electronic absorption spectra with different solvents have been investigated in combination with time-dependent density functional theory calculation. The pKa values of phenoxy acetic acids were compared.

  2. Density functional theory studies on the electronic and vibrational spectra of octaethylporphyrin diacid.

    PubMed

    Li, Zun-Yun; Wang, Hai-Long; Lu, Tong-Tong; He, Tian-Jing; Liu, Fan-Chen; Chen, Dong-Ming

    2007-08-01

    The ground-state structure and electronic and vibrational spectra of octaethylporphyrin diacid (H4OEP2+) have been studied with the density functional theory. The geometrical parameters computed with B3LYP, PBE1PBE and mPW1PW91 functionals and 6-31G* basis sets are well consistent with the experimental values. Electronic absorption spectrum of H4OEP2+ has been studied with the time-dependent DFT method, and the calculated excitation energies and oscillator strengths are compared with the experimental results. The Raman and IR spectra of H4OEP2+ and the Raman spectrum of its N-deuterated analogue (D4OEP2+) were measured. The observed Raman and IR bands have been assigned based on the frequency calculations at the B3LYP/6-31G* level of theory. PMID:17142087

  3. Sensitivity Analysis of X-ray Spectra from Scanning Electron Microscopes

    SciTech Connect

    Miller, Thomas Martin; Patton, Bruce W.; Weber, Charles F.; Bekar, Kursat B.

    2014-10-01

    The primary goal of this project is to evaluate x-ray spectra generated within a scanning electron microscope (SEM) to determine elemental composition of small samples. This will be accomplished by performing Monte Carlo simulations of the electron and photon interactions in the sample and in the x-ray detector. The elemental inventories will be determined by an inverse process that progressively reduces the difference between the measured and simulated x-ray spectra by iteratively adjusting composition and geometric variables in the computational model. The intended benefit of this work will be to develop a method to perform quantitative analysis on substandard samples (heterogeneous phases, rough surfaces, small sizes, etc.) without involving standard elemental samples or empirical matrix corrections (i.e., true standardless quantitative analysis).

  4. SCATTERING POLARIZATION IN SOLAR FLARES

    SciTech Connect

    Štěpán, Jiří; Heinzel, Petr

    2013-11-20

    There is ongoing debate about the origin and even the very existence of a high degree of linear polarization of some chromospheric spectral lines observed in solar flares. The standard explanation of these measurements is in terms of the impact polarization caused by non-thermal proton and/or electron beams. In this work, we study the possible role of resonance line polarization due to radiation anisotropy in the inhomogeneous medium of the flare ribbons. We consider a simple two-dimensional model of the flaring chromosphere and we self-consistently solve the non-LTE problem taking into account the role of resonant scattering polarization and of the Hanle effect. Our calculations show that the horizontal plasma inhomogeneities at the boundary of the flare ribbons can lead to a significant radiation anisotropy in the line formation region and, consequently, to a fractional linear polarization of the emergent radiation of the order of several percent. Neglecting the effects of impact polarization, our model can provide a clue for resolving some of the common observational findings, namely: (1) why a high degree of polarization appears mainly at the edges of the flare ribbons; (2) why polarization can also be observed during the gradual phase of a flare; and (3) why polarization is mostly radial or tangential. We conclude that radiation transfer in realistic multi-dimensional models of solar flares needs to be considered as an essential ingredient for understanding the observed spectral line polarization.

  5. Relativistic model of secondary-electron energy spectra in electron-impact ionization

    SciTech Connect

    Miller, J.H. ); Manson, S.T. )

    1991-10-01

    A relativistic model for differential electron-impact-ionization cross sections that allows the energy spectrum of secondary electrons to be calculated over a wide range of primary-electron energies is presented. The semiempirical method requires only experimental total ionization cross sections and optical oscillator strengths for the target species of interest, but other information, if available, can be incorporated to make the formulation still more accurate. Results for ionization of helium indicate that the lower limit on primary-electron energy for application of the model is about 100 eV. The simple analytic form of the model facilitates investigation of the regions of the secondary-electron energy spectrum where relativistic effects are important.

  6. Raman spectra and electron-phonon coupling in disordered graphene with gate-tunable doping

    NASA Astrophysics Data System (ADS)

    Childres, Isaac; Jauregui, Luis A.; Chen, Yong P.

    2014-12-01

    We report a Raman spectroscopy study of graphene field-effect transistors with a controlled amount of defects introduced in graphene by exposure to electron-beam irradiation. Raman spectra are taken at T = 8 K over a range of back gate voltages (Vg) for various irradiation dosages (Re). We study effects in the Raman spectra due to Vg-induced doping and artificially created disorder at various Re. With moderate disorder (irradiation), the Raman G peak with respect to the graphene carrier density (nFE) exhibits a minimum in peak frequency and a maximum in peak width near the charge-neutral point (CNP). These trends are similar to those seen in previous works on pristine graphene and have been attributed to a reduction of electron-phonon coupling strength (D) and removal of the Kohn anomaly as the Fermi level moves away from the CNP. We also observe a maximum in I2D/IG and weak maximum in ID/IG near the CNP. All the observed dependences of Raman parameters on nFE weaken at stronger disorder (higher Re), implying that disorder causes a reduction of D as well. Our findings are valuable for understanding Raman spectra and electron-phonon physics in doped and disordered graphene.

  7. Kinetic energies to analyze the experimental auger electron spectra by density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Endo, Kazunaka

    2016-02-01

    In the Auger electron spectra (AES) simulations, we define theoretical modified kinetic energies of AES in the density functional theory (DFT) calculations. The modified kinetic energies correspond to two final-state holes at the ground state and at the transition-state in DFT calculations, respectively. This method is applied to simulate Auger electron spectra (AES) of 2nd periodic atom (Li, Be, B, C, N, O, F)-involving substances (LiF, beryllium, boron, graphite, GaN, SiO2, PTFE) by deMon DFT calculations using the model molecules of the unit cell. Experimental KVV (valence band electrons can fill K-shell core holes or be emitted during KVV-type transitions) AES of the (Li, O) atoms in the substances agree considerably well with simulation of AES obtained with the maximum kinetic energies of the atoms, while, for AES of LiF, and PTFE substance, the experimental F KVV AES is almost in accordance with the spectra from the transitionstate kinetic energy calculations.

  8. Raman spectra and electron-phonon coupling in disordered graphene with gate-tunable doping

    SciTech Connect

    Childres, Isaac; Jauregui, Luis A.; Chen, Yong P.

    2014-12-21

    We report a Raman spectroscopy study of graphene field-effect transistors with a controlled amount of defects introduced in graphene by exposure to electron-beam irradiation. Raman spectra are taken at T = 8 K over a range of back gate voltages (V{sub g}) for various irradiation dosages (R{sub e}). We study effects in the Raman spectra due to V{sub g}-induced doping and artificially created disorder at various R{sub e}. With moderate disorder (irradiation), the Raman G peak with respect to the graphene carrier density (n{sub FE}) exhibits a minimum in peak frequency and a maximum in peak width near the charge-neutral point (CNP). These trends are similar to those seen in previous works on pristine graphene and have been attributed to a reduction of electron-phonon coupling strength (D) and removal of the Kohn anomaly as the Fermi level moves away from the CNP. We also observe a maximum in I{sub 2D}/I{sub G} and weak maximum in I{sub D}/I{sub G} near the CNP. All the observed dependences of Raman parameters on n{sub FE} weaken at stronger disorder (higher R{sub e}), implying that disorder causes a reduction of D as well. Our findings are valuable for understanding Raman spectra and electron-phonon physics in doped and disordered graphene.

  9. [INDO/CI studies on the electronic spectra of tetraphenylporphyrin and its derivatives].

    PubMed

    Li, L; Zheng, S; Meng, L; Chen, R

    1999-06-01

    MNDO calculations and group theory were carried out on tetraphenylporphyrine (TPP) to obtain its optimum molecular geometry. We employed an INDO/CI method to study the electronic structures of tetraphenylporphyrine and its derivatives and identify their main electonic absorption bands. Five-orbital model was advanced to explain the typical characteristics of electronic spectra of H2TPP and its derivatives. The calculated wavelengths were in good agreement with the experimental values. The effects of the substitution of variant group were discussed and some helpful conclusions were drawn. PMID:15819039

  10. Reconstruction of the energy spectrum of electrons accelerated in the April 15, 2002 solar flare based on IRIS X-ray spectrometer measurements

    NASA Astrophysics Data System (ADS)

    Motorina, G. G.; Kudryavtsev, I. V.; Lazutkov, V. P.; Savchenko, M. I.; Skorodumov, D. V.; Charikov, Yu. E.

    2016-04-01

    We reconstruct the energy distribution of electrons accelerated in the April 15, 2002 solar flare on the basis of the data from the IRIS X-ray spectrometer onboard the CORONAS-F satellite. We obtain the solution to the integral equations describing the transformation of the spectrum of X-ray photons during the recording and reconstruction of the spectrum of accelerated electrons in the bremsstrahlung source using the random search method and the Tikhonov regularization method. In this event, we detected a singularity in the electron spectrum associated with the existence of a local minimum in the energy range 40-60 keV, which cannot be detected by a direct method.

  11. The 5p autoionization spectra of Ba atoms excited by electron impact: identification of lines

    NASA Astrophysics Data System (ADS)

    Hrytsko, V.; Kerevičius, G.; Kupliauskienė, A.; Borovik, A.

    2016-07-01

    The ejected-electron spectra corresponding to the radiationless decay of 5p5 {n}1{l}1{n}2{l}2{n}3{l}3 states in Ba atoms have been measured precisely for different incident electron energies ranging from the appearance of the first autoionizing line at 15.68 eV up to 140 eV. The spectra have been obtained at an observation angle of 54.7° and with incident-electron and ejected-electron energy resolutions of 0.2 eV and 0.07 eV, respectively. In total, 63 lines with excitation thresholds below 22 eV have been observed between 9.8 and 16.6 eV ejected-electron kinetic energy. Based on measured excitation energies, intensity behavior of lines, calculated excitation energies, cross sections and decay rates of states in 5p56s{}2{nl}, 5p55d{}2{nl} and 5p55d6snl configurations, assignments for all 63 lines are proposed. The excitation and decay processes for classified autoionizing states have been examined and compared with existing data. The excitation threshold of the 5{{{p}}}6 subshell has been established at 15.61 ± 0.05 eV.

  12. Limiting Superluminal Electron and Neutrino Velocities Using the 2010 Crab Nebula Flare and the IceCube PeV Neutrino Events

    NASA Technical Reports Server (NTRS)

    Stecker, Floyd W.

    2014-01-01

    The observation of two PetaelectronVolt (PeV)-scale neutrino events reported by Ice Cube allows one to place constraints on Lorentz invariance violation (LIV) in the neutrino sector. After first arguing that at least one of the PetaelectronVolt IceCube events was of extragalactic origin, I derive an upper limit for the difference between putative superluminal neutrino and electron velocities of less than or equal to approximately 5.6 x 10(exp -19) in units where c = 1, confirming that the observed PetaelectronVolt neutrinos could have reached Earth from extragalactic sources. I further derive a new constraint on the superluminal electron velocity, obtained from the observation of synchrotron radiation from the Crab Nebula flare of September, 2010. The inference that the greater than 1 GigaelectronVolt gamma-rays from synchrotron emission in the flare were produced by electrons of energy up to approx. 5.1 PetaelectronVolt indicates the nonoccurrence of vacuum Cerenkov radiation by these electrons. This implies a new, strong constraint on superluminal electron velocities delta(sub e) less than or equal to approximately 5 x 10(exp -21). It immediately follows that one then obtains an upper limit on the superluminal neutrino velocity alone of delta(sub v) less than or equal to approximately 5.6 x 10(exp -19), many orders of magnitude better than the time-of-flight constraint from the SN1987A neutrino burst. However, if the electrons are subluminal the constraint on the absolute value of delta(sub e) less than or equal to approximately 8 x 10(exp -17), obtained from the Crab Nebula gamma-ray spectrum, places a weaker constraint on superluminal neutrino velocity of delta(sub v) less than or equal to approximately 8 x 10(exp -17).

  13. Electronic structure and UV spectra of N-arylthio-1,4-benzoquinone imines

    SciTech Connect

    Pirozhenko, V.V.; Boldeskul, I.E.; Kolesnikov, V.T.; Vid, L.V.; Kuz'menko, L.O.

    1986-01-01

    The electronic structure of N-arylthio-1,4-benzoquinone imines (II) was studied by quantum-chemical methods (CNDO/2). It was shown that the special characteristics of the reactivity of the compounds in reaction with chlorine compared with sulfenylketimines R/sub 2/C=N-S-Ar not containing a quinonoid ring may be due to the different nature of the lowest unoccupied molecular orbitals (LUMO). The UV spectra of compounds (II) were investigated. In the visible region the spectra of all the compounds contain strong absorption (R/sub 1/ = R/sub 2/ = R/sub 3/ = R/sub 4/ = R/sub 5/ = H, lambda/sub m/ = 433 nm, epsilon/sub m/ = 2.12 x 10/sup 4/ liters/mole x cm), due to intramolecular charge transfer from the sulfur atom to the quinonoid fragment of the molecule. It was established that there is a linear relation between the energy of the transition and the sigma/sup +/ constants of the substituents in the aryl fragment. The assignment of the transitions was confirmed by calculations of the UV spectra of N-arylthio-1,4-benzoquinone imines by the PPP method. Comparison of the UV spectra of these compounds with the UV spectra of N-arylsulfonyl-1,4-benzoquinone imines makes it possible to conclude that the sulfur atom of the SO/sub 2/ group, unlike the divalent sulfur atom, is not capable of transmitting the electronic effects of the substituents from one part of the molecule to the other.

  14. A STATISTICAL STUDY OF THE SPECTRAL HARDENING OF CONTINUUM EMISSION IN SOLAR FLARES

    SciTech Connect

    Kong, X.; Chen, Y.; Li, G. E-mail: gang.li@uah.edu

    2013-09-10

    The observed hard X-ray and {gamma}-ray continuum in solar flares is interpreted as Bremsstrahlung emission of accelerated non-thermal electrons. It has been noted for a long time that in many flares the energy spectra show hardening at energies around or above 300 keV. In this paper, we first conduct a survey of spectral hardening events that were previously studied in the literature. We then perform a systematic examination of 185 flares from the Solar Maximum Mission. We identify 23 electron-dominated events whose energy spectra show clear double power laws. A statistical study of these events shows that the spectral index below the break ({gamma}{sub 1}) anti-correlates with the break energy ({epsilon}{sub b}). Furthermore, {gamma}{sub 1} also anti-correlates with Fr, the fraction of photons above the break compared to the total photons. A hardening spectrum, as well as the correlations between ({gamma}{sub 1}, {epsilon}{sub b}) and ({gamma}{sub 1}, Fr), provide stringent constraints on the underlying electron acceleration mechanism. Our results support a recent proposal that electrons are being accelerated diffusively at a flare termination shock with a width of the order of an ion inertial length scale.

  15. Theoretical investigation on the vibrational and electronic spectra of three isomeric forms of dicobalt octacarbonyl

    NASA Astrophysics Data System (ADS)

    Karakaş, Duran; Kariper, Sultan Erkan

    2014-03-01

    Three isomeric forms of dicobalt octacarbonyl, [Co2(CO)8], with C2v, D3d and D2d point group were optimized by using density functional theory (DFT/B3LYP) method with LANL2DZ basis set for the cobalt atoms and 6-31G(d) basis set for the other atoms in the gas phase. Electronic structures, carbonyl stretching frequencies and Mulliken population analysis were determined from the optimized structures. Electronic structures indicate that each of the dicobalt octacarbonyl isomers have been constituted from two trigonal bipyramidal geometry. While the isomer C2v has two bridged carbonyl groups, in the isomers D3d and D2d all carbonyl groups are coordinating as terminal. The calculated C-O stretching frequencies are in a good agreement with experimental frequencies. Experimental C-O stretching frequencies were assigned to isomers according to the calculated frequencies. Mulliken population analysis show that free carbonyl ligands transfer their electron to the cobalt atoms during formation of the complexes. The electronic spectra of isomers were obtained by using time dependent density functional theory (TD-DFT/B3LYP) method with LANL2DZ basis set for the cobalt atoms and 6-31G(d) basis set for the other atoms in the gas phase. The theoretical electronic spectra of isomers are in a good agreement with experimental spectra. The calculated bands at 277.9, 278.1 and 284.1 nm for isomers C2v, D2d and D3d were assigned to metal-ligand charge transfer transitions and the shoulder at 344.6 nm was assigned to pure metal center transitions for isomer D3d.

  16. Evolution of electron spectra and pitch angle distributions during the September 2012 electron storage-ring event

    NASA Astrophysics Data System (ADS)

    Hoxie, V. C.; Kanekal, S. G.; Baker, D. N.; Blake, J. B.; Claudepierre, S. G.; Fennell, J. F.; Jaynes, A. N.; Li, X.; Reeves, G. D.; Spence, H.; Thorne, R. M.

    2013-12-01

    Recent observations by the twin Van Allen probes flying identical suites of instruments have revealed the existence of long lasting, isolated torus of energetic electrons in the region between L~3-3.5, the traditional "outer zone". It has been suggested that the plasmapause which was located at higher L values (L >~ 4) prevented the rapid decay of the torus since lifetimes due to pitch angle scattering by plasmaspheric hiss are long for relativistic electrons. In this presentation we examine the temporal and spatial evolution of electron spectra and pitch angle distributions (PAD) spanning both relativistic energy (>~ 1 MeV) and lower energy (~100-1000 keV) during September 2013. The spectral and PAD evolution are investigated as a function of plasmapause location and L regions corresponding to the distinct morphological features.

  17. Electronic spectra and DFT calculations of some pyrimido[1,2-a]benzimidazole derivatives

    NASA Astrophysics Data System (ADS)

    Elshakre, Mohamed E.; Moustafa, H.; Hassaneen, Huwaida. M. E.; Moussa, Abdelrahim. Z.

    2015-06-01

    Ground state properties of 2,4-diphenyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine, compound 1, and its derivatives are investigated experimentally and theoretically in Dioxane and DMF. The calculations show that all the studied compounds (1-7) are non-planar, resulting in a significant impact on the electronic and structural properties. The ground state properties of compounds 1-7 at B3LYP/6-311G (d, p) show that compound 5 has the lowest EHOMO, ELUMO, and ΔE indicating highest reactivity. Compound 7 is found to have the highest polarity. The observed UV spectra in Dioxane and DMF of compounds 1-4 show 2 bands, while compounds 5-7 show 4 bands in both solvents. Band maxima (λmax) and intensities of the spectra are found to have solvent dependence reflected as blue and red shifts. The theoretical spectra computed at TD-B3LYP/6-311G (d, p) in gas phase, Dioxane and DMF indicate a good agreement with the observed spectra.

  18. Perturbation method to calculate the interaction potentials and electronic excitation spectra of atoms in He nanodroplets.

    PubMed

    Callegari, Carlo; Ancilotto, Francesco

    2011-06-30

    A method is proposed for the calculation of potential energy curves and related electronic excitation spectra of dopant atoms captured in/on He nanodroplets and is applied to alkali metal atoms. The method requires knowledge of the droplet density distribution at equilibrium (here calculated within a bosonic-He density functional approach) and of a set of valence electron orbitals of the bare dopant atom (here calculated by numeric solution of the Schrödinger equation in a suitably parametrized model potential). The electron-helium interaction is added as a perturbation, and potential energy curves are obtained by numeric diagonalization of the resulting Hamiltonian as a function of an effective coordinate z(A) (here the distance between the dopant atom and center of mass of the droplet, resulting in a pseudodiatomic potential). Excitation spectra are calculated for Na in the companion paper as the Franck-Condon factors between the v = 0 vibrational state in the ground electronic state and excited states of the pseudodiatomic molecule. They agree well with available experimental data, even for highly excited states where a more traditional approach fails. PMID:21434657

  19. Electron-momentum distributions and photoelectron spectra of atoms driven by an intense spatially inhomogeneous field

    NASA Astrophysics Data System (ADS)

    Ciappina, M. F.; Pérez-Hernández, J. A.; Shaaran, T.; Roso, L.; Lewenstein, M.

    2013-06-01

    We use the three-dimensional time-dependent Schrödinger equation (3 D-TDSE) to calculate angular electron momentum distributions and photoelectron spectra of atoms driven by spatially inhomogeneous fields. An example for such inhomogeneous fields is the locally enhanced field induced by resonant plasmons, appearing at surfaces of metallic nanoparticles, nanotips, and gold bow-tie shaped nanostructures. Our studies show that the inhomogeneity of the laser electric field plays an important role on the above-threshold ionization process in the tunneling regime, causing significant modifications on the electron momentum distributions and photoelectron spectra, while its effects in the multiphoton regime appear to be negligible. Indeed, through the tunneling above-threshold ionization (ATI) process, one can obtain higher energy electrons as well as a high degree of asymmetry in the momentum space map. In this study we consider near infrared laser fields with intensities in the mid- 1014 W/cm2 range and we use a linear approximation to describe their spatial dependence. We show that in this case it is possible to drive electrons with energies in the near-keV regime. Furthermore, we study how the carrier envelope phase influences the emission of ATI photoelectrons for few-cycle pulses. Our quantum mechanical calculations are fully supported by their classical counterparts.

  20. Experimental and theoretical study on the structure and electronic spectra of imiquimod and its synthetic intermediates.

    PubMed

    Zhao, Bo; Rong, Yu-Zhi; Huang, Xiao-Hua; Shen, Jing-Shan

    2007-09-01

    Crystal structure of the imiquimod has been determined by single crystal X-ray analysis, imiquimod crystallizes in orthorhombic space group P2(1)2(1)2(1) and the molecules are linked along the c axis by the strong N-H ... N hydrogen bonds. A density functional theory (DFT) study on the electronic properties of imiquimod and its synthetic intermediates has been performed at B3LYP/6-31G* level, while taking solvent effects into account. Both the single configuration interaction (CIS) method and the time-dependent DFT (TDDFT) approaches have been used to calculate the electronic absorption spectra, and there is a good agreement between the calculated and experimental UV-visible absorption spectra. The fluorescence emission spectra of these three compounds in solution have also been measured, the relatively low fluorescence intensity is attributed to a chlorine-modulated heavy atom effect that enhances intersystem crossing between excited singlet and triplet states, and the relatively high fluorescence intensity of imiquimod results from an extended pi-conjugated system which enhances S(1)-->S(0) radiant transition. PMID:17601733

  1. Where Is the Electronic Oscillator Strength? Mapping Oscillator Strength across Molecular Absorption Spectra.

    PubMed

    Zheng, Lianjun; Polizzi, Nicholas F; Dave, Adarsh R; Migliore, Agostino; Beratan, David N

    2016-03-24

    The effectiveness of solar energy capture and conversion materials derives from their ability to absorb light and to transform the excitation energy into energy stored in free carriers or chemical bonds. The Thomas-Reiche-Kuhn (TRK) sum rule mandates that the integrated (electronic) oscillator strength of an absorber equals the total number of electrons in the structure. Typical molecular chromophores place only about 1% of their oscillator strength in the UV-vis window, so individual chromophores operate at about 1% of their theoretical limit. We explore the distribution of oscillator strength as a function of excitation energy to understand this circumstance. To this aim, we use familiar independent-electron model Hamiltonians as well as first-principles electronic structure methods. While model Hamiltonians capture the qualitative electronic spectra associated with π electron chromophores, these Hamiltonians mistakenly focus the oscillator strength in the fewest low-energy transitions. Advanced electronic structure methods, in contrast, spread the oscillator strength over a very wide excitation energy range, including transitions to Rydberg and continuum states, consistent with experiment. Our analysis rationalizes the low oscillator strength in the UV-vis spectral region in molecules, a step toward the goal of oscillator strength manipulation and focusing. PMID:26950828

  2. Data-driven Radiative Hydrodynamic Modeling of the 2014 March 29 X1.0 Solar Flare

    NASA Astrophysics Data System (ADS)

    Rubio da Costa, Fatima; Kleint, Lucia; Petrosian, Vahé; Liu, Wei; Allred, Joel C.

    2016-08-01

    Spectroscopic observations of solar flares provide critical diagnostics of the physical conditions in the flaring atmosphere. Some key features in observed spectra have not yet been accounted for in existing flare models. Here we report a data-driven simulation of the well-observed X1.0 flare on 2014 March 29 that can reconcile some well-known spectral discrepancies. We analyzed spectra of the flaring region from the Interface Region Imaging Spectrograph (IRIS) in Mg ii h&k, the Interferometric BIdimensional Spectropolarimeter at the Dunn Solar Telescope (DST/IBIS) in Hα 6563 Å and Ca ii 8542 Å, and the Reuven Ramaty High Energy Solar Spectroscope Imager (RHESSI) in hard X-rays. We constructed a multithreaded flare loop model and used the electron flux inferred from RHESSI data as the input to the radiative hydrodynamic code RADYN to simulate the atmospheric response. We then synthesized various chromospheric emission lines and compared them with the IRIS and IBIS observations. In general, the synthetic intensities agree with the observed ones, especially near the northern footpoint of the flare. The simulated Mg ii line profile has narrower wings than the observed one. This discrepancy can be reduced by using a higher microturbulent velocity (27 km s‑1) in a narrow chromospheric layer. In addition, we found that an increase of electron density in the upper chromosphere within a narrow height range of ≈800 km below the transition region can turn the simulated Mg ii line core into emission and thus reproduce the single peaked profile, which is a common feature in all IRIS flares.

  3. An optimal target-filter system for electron beam generated x-ray spectra

    SciTech Connect

    Hsu, Hsiao-Hua; Vasilik, D.G.; Chen, J.

    1994-04-01

    An electron beam generated x-ray spectrum consists of characteristic x rays of the target and continuous bremsstrahlung. The percentage of characteristic x rays over the entire energy spectrum depends on the beam energy and the filter thickness. To determine the optimal electron beam energy and filter thickness, one can either conduct many experimental measurements, or perform a series of Monte Carlo simulations. Monte Carlo simulations are shown to be an efficient tool for determining the optimal target-filter system for electron beam generated x-ray spectra. Three of the most commonly used low-energy x-ray metal targets (Cu, Zn and Mo) are chosen for this study to illustrate the power of Monte Carlo simulations.

  4. Ab Initio Infrared Spectra and Electronic Response Calculations for the Insulating Phases of VO2

    NASA Astrophysics Data System (ADS)

    Hendriks, Christopher; Huffman, Tyler; Walter, Eric; Qazilbash, Mumtaz; Krakauer, Henry

    Previous studies have shown that, under doping or tensile strain and upon heating, the well-known vanadium dioxide (VO2) transition from an insulating monoclinic (M1) to a metallic rutile (R) phase progresses through a triclinic symmetry (T) phase and a magnetic monoclinic phase (M2), both of which are insulating. Structurally, this progression from M1 to R through T and M2 can be characterized by the progressive breaking of the V dimers. Investigation of the effect of these structural changes on the insulating phases of VO2 may help resolve questions surrounding the long-debated issue of the respective roles of electronic correlation and Peierls mechanisms in driving the MIT. We investigated electronic and vibrational properties of the insulating phases of VO2 in the framework of DFT+U. We will present ab initio calculations of infrared spectra and optical electronic responses for the insulating phases and compare these to available experimental measurements. Supported by ONR.

  5. Numerical simulation of strong-field electron spectra of Xe in the rescattering region

    NASA Astrophysics Data System (ADS)

    Liang, Yaqiu

    2010-11-01

    We investigate the high-energy above-threshold ionization (HATI) plateau for Xe in a strong laser field at peak intensity of about 0.85×1014W/cm2 with wavelengths of 800, 1250, 1500, and 2000 nm. Numerical simulations are performed using a recently developed quantitative rescattering (QRS) model. According to the QRS model, the two-dimensional (2D) photoelectron momentum distribution can be treated as a product of the returning electron wave packet and the elastic differential cross section (DCS) for free electrons scattered with the parent ion. From the 2D momentum distributions, the HATI plateau can be obtained. By using different single-active electron potentials in the DCS calculations, we test the potential dependence of the high-energy plateau spectra. Good agreement between the simulated results and the experimental data confirms again the validity of the QRS model.

  6. Experimental and DFT studies on the vibrational and electronic spectra of 9-anthracenemethanol

    NASA Astrophysics Data System (ADS)

    Kou, Shanshan; Zhou, Hu; Tang, Guodong; Li, Rongqing; Zhang, Yu; Zhao, Jianying; Wei, Changmei

    2012-10-01

    Vibrational spectral measurements were made for 9-anthracenemethanol. Optimized geometrical structure and harmonic vibration frequencies were computed based on ab initio and density functional theory B3LYP methods using 6-311G∗∗ and LANL2DZ basis sets. The equilibrium geometries got from all of the methods and basis were compared with X-ray diffraction results. The IR and UV-vis spectra of the title compound were computed using all of the methods and choose the most appropriate way to discuss. And the absorption spectra were calculated both in gas phase and in CH3CH2OH and CH3CN solution. The calculated results matched well with the experimental values. On the basis, the first excited state electronic transition energy has been calculated using time-dependent density functional theory.

  7. Magnetic phases in lunar material and their electron magnetic resonance spectra - Apollo 14.

    NASA Technical Reports Server (NTRS)

    Weeks, R. A.

    1972-01-01

    Electron magnetic resonance spectra of soil samples 14163,68, 14148,31, 14149,47, 14156,31, and 14003,60, and of fragmental rocks 14301,66, 14303,42, 14310,68, 14311,36, 14318,36, and 14321,166 have been recorded at 9 and 35 GHz at 300 K and at 9 GHz at 130 K. One spectral component, the characteristic ferromagnetic resonance, of all the soil samples is 50 to 1000 times more intense than any other component in the soils or in the spectra of the rocks. The intensity of this component in Apollo 11, Apollo 12, and Apollo 14 soils varies only within one order of magnitude. It varies with depth below lunar surface but is not correlated with depth. The intensity does not have any correlation with the fraction of glassy particles nor with the fraction of anorthositic particles.

  8. Using Markov models to simulate electron spin resonance spectra from molecular dynamics trajectories.

    PubMed

    Sezer, Deniz; Freed, Jack H; Roux, Benoit

    2008-09-01

    Simulating electron spin resonance (ESR) spectra directly from molecular dynamics simulations of a spin-labeled protein necessitates a large number (hundreds or thousands) of relatively long (hundreds of nanoseconds) trajectories. To meet this challenge, we explore the possibility of constructing accurate stochastic models of the spin label dynamics from atomistic trajectories. A systematic, two-step procedure, based on the probabilistic framework of hidden Markov models, is developed to build a discrete-time Markov chain process that faithfully captures the internal spin label dynamics on time scales longer than about 150 ps. The constructed Markov model is used both to gain insight into the long-lived conformations of the spin label and to generate the stochastic trajectories required for the simulation of ESR spectra. The methodology is illustrated with an application to the case of a spin-labeled poly alanine alpha helix in explicit solvent. PMID:18698714

  9. Determining the spectra of radiation belt electron losses: Fitting DEMETER electron flux observations for typical and storm times

    NASA Astrophysics Data System (ADS)

    Whittaker, Ian C.; Gamble, Rory J.; Rodger, Craig J.; Clilverd, Mark A.; Sauvaud, Jean-André

    2013-12-01

    The energy spectra of energetic electron precipitation from the radiation belts are studied in order to improve our understanding of the influence of radiation belt processes. The Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) microsatellite electron flux instrument is comparatively unusual in that it has very high energy resolution (128 channels with 17.9 keV widths in normal survey mode), which lends itself to this type of spectral analysis. Here electron spectra from DEMETER have been analyzed from all six years of its operation, and three fit types (power law, exponential, and kappa-type) have been applied to the precipitating flux observations. We show that the power law fit consistently provides the best representation of the flux and that the kappa-type is rarely valid. We also provide estimated uncertainties in the flux for this instrument as a function of energy. Average power law gradients for nontrapped particles have been determined for geomagnetically nondisturbed periods to get a typical global behavior of the spectra in the inner radiation belt, slot region, and outer radiation belt. Power law spectral gradients in the outer belt are typically -2.5 during quiet periods, changing to a softer spectrum of ˜-3.5 during geomagnetic storms. The inner belt does the opposite, hardening from -4 during quiet times to ˜-3 during storms. Typical outer belt e-folding values are ˜200 keV, dropping to ˜150 keV during geomagnetic storms, while the inner belt e-folding values change from ˜120 keV to >200 keV. Analysis of geomagnetic storm periods show that the precipitating flux enhancements evident from such storms take approximately 13 days to return to normal values for the outer belt and slot region and approximately 10 days for the inner belt.

  10. Decimetric gyrosynchrotron emission during a solar flare

    NASA Technical Reports Server (NTRS)

    Batchelor, D. A.; Benz, A. O.; Wiehl, H. J.

    1983-01-01

    A decimetric, microwave, and hard X-ray burst was observed during a solar flare in which the radio spectrum below peak flux fits an f+2 power law over more than a decade in frequency. The spectrum is interpreted to mean that the radio emission originated in a homogeneous, thermal, gyrosynchrotron source. This is the first time that gyrosynchrotron radiation has been identified at such low decimetric frequencies (900-998) MHz). The radio emission was cotemporal with the largest single hard X-ray spike burst ever reported. The spectrum of the hard X-ray burst can be well represented by a thermal bremsstrahlung function over the energy range from 30 to 463 keV at the time of maximum flux. The temporal coincidence and thermal form of both the X-ray and radio spectra suggest a common source electron distribution. The unusual low-frequency extent of the single-temperature thermal radio spectrum and its association with the hard X-ray burst imply that the source had an area approx. 10(18) sq cm a temperature approx 5x10(8) K, an electron density approx. 7.10(9) cu cm and a magnetic field of approx. 120 G. H(alpha) and 400-800 MHz evidence suggest that a loop structure of length 10,000 km existed in the flare active region which could have been the common, thermal source of the observed impulsive emissions.

  11. PROBING DYNAMICS OF ELECTRON ACCELERATION WITH RADIO AND X-RAY SPECTROSCOPY, IMAGING, AND TIMING IN THE 2002 APRIL 11 SOLAR FLARE

    SciTech Connect

    Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E.; Kontar, Eduard P.

    2013-05-10

    Based on detailed analysis of radio and X-ray observations of a flare on 2002 April 11 augmented by realistic three-dimensional modeling, we have identified a radio emission component produced directly at the flare acceleration region. This acceleration region radio component has distinctly different (1) spectrum, (2) light curves, (3) spatial location, and, thus, (4) physical parameters from those of the separately identified trapped or precipitating electron components. To derive evolution of physical parameters of the radio sources we apply forward fitting of the radio spectrum time sequence with the gyrosynchrotron source function with five to six free parameters. At the stage when the contribution from the acceleration region dominates the radio spectrum, the X-ray- and radio-derived electron energy spectral indices agree well with each other. During this time the maximum energy of the accelerated electron spectrum displays a monotonic increase with time from {approx}300 keV to {approx}2 MeV over roughly one minute duration indicative of an acceleration process in the form of growth of the power-law tail; the fast electron residence time in the acceleration region is about 2-4 s, which is much longer than the time of flight and so requires a strong diffusion mode there to inhibit free-streaming propagation. The acceleration region has a relatively strong magnetic field, B {approx} 120 G, and a low thermal density, n{sub e} {approx}< 2 Multiplication-Sign 10{sup 9} cm{sup -3}. These acceleration region properties are consistent with a stochastic acceleration mechanism.

  12. Detection of nanoscale electron spin resonance spectra demonstrated using nitrogen-vacancy centre probes in diamond

    PubMed Central

    Hall, L. T.; Kehayias, P.; Simpson, D. A.; Jarmola, A.; Stacey, A.; Budker, D.; Hollenberg, L. C. L.

    2016-01-01

    Electron spin resonance (ESR) describes a suite of techniques for characterizing electronic systems with applications in physics, chemistry, and biology. However, the requirement for large electron spin ensembles in conventional ESR techniques limits their spatial resolution. Here we present a method for measuring ESR spectra of nanoscale electronic environments by measuring the longitudinal relaxation time of a single-spin probe as it is systematically tuned into resonance with the target electronic system. As a proof of concept, we extracted the spectral distribution for the P1 electronic spin bath in diamond by using an ensemble of nitrogen-vacancy centres, and demonstrated excellent agreement with theoretical expectations. As the response of each nitrogen-vacancy spin in this experiment is dominated by a single P1 spin at a mean distance of 2.7 nm, the application of this technique to the single nitrogen-vacancy case will enable nanoscale ESR spectroscopy of atomic and molecular spin systems. PMID:26728001

  13. Twin-peaks absorption spectra of excess electron in ionic liquids

    NASA Astrophysics Data System (ADS)

    Musat, Raluca M.; Kondoh, Takafumi; Yoshida, Yoichi; Takahashi, Kenji

    2014-07-01

    The solvated electron in room temperature ionic liquids (RTILs) has been the subject of several investigations and several reports exist on its nature and absorption spectrum. These studies concluded that the solvated electron exhibits an absorption spectrum peaking in the 1000-1400 nm region; a second absorption band peaking in the UV region has been assigned to the hole or dication radicals simultaneously formed in the system. Here we report on the fate of the excess electron in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, P14+/NTf2- using nanosecond pulse radiolysis. Scavenging experiments allowed us to record and disentangle the complex spectrum measured in P14+/NTf2-. We identified a bi-component absorption spectrum, due to the solvated electron, the absorption maxima located at 1080 nm and around 300 nm, as predicted by previous ab-initio molecular dynamics simulations for the dry excess electron. We also measured the spectra using different ionic liquids and confirmed the same feature of two absorption peaks. The present results have important implications for the characterization of solvated electrons in ionic liquids and better understanding of their structure and reactivity.

  14. Understanding the inelastic electron-tunneling spectra of alkanedithiols on gold.

    PubMed

    Solomon, Gemma C; Gagliardi, Alessio; Pecchia, Alessandro; Frauenheim, Thomas; Di Carlo, Aldo; Reimers, Jeffrey R; Hush, Noel S

    2006-03-01

    We present results for a simulated inelastic electron-tunneling spectra (IETS) from calculations using the "gDFTB" code. The geometric and electronic structure is obtained from calculations using a local-basis density-functional scheme, and a nonequilibrium Green's function formalism is employed to deal with the transport aspects of the problem. The calculated spectrum of octanedithiol on gold(111) shows good agreement with experimental results and suggests further details in the assignment of such spectra. We show that some low-energy peaks, unassigned in the experimental spectrum, occur in a region where a number of molecular modes are predicted to be active, suggesting that these modes are the cause of the peaks rather than a matrix signal, as previously postulated. The simulations also reveal the qualitative nature of the processes dominating IETS. It is highly sensitive only to the vibrational motions that occur in the regions of the molecule where there is electron density in the low-voltage conduction channel. This result is illustrated with an examination of the predicted variation of IETS with binding site and alkane chain length. PMID:16526869

  15. General properties of the radiation spectra from relativistic electrons moving in Langmuir turbulence

    SciTech Connect

    Teraki, Yuto; Takahara, Fumio

    2014-05-20

    Using a numerical method, we examine the radiation spectra from relativistic electrons moving in Langmuir turbulence, which are expected to exist in high energy astrophysical objects. The spectral shape is characterized by the spatial scale λ, field strength σ, and frequency of the Langmuir waves, and in terms of frequency they are represented by ω{sub 0} = 2πc/λ, ω{sub st} = eσ/mc, and ω{sub p}, respectively. We normalize ω{sub st} and ω {sub p} by ω{sub 0} as a ≡ ω{sub st}/ω{sub 0} and b ≡ ω{sub p}/ω{sub 0}, and examine the spectral shape in the a–b plane. An earlier study based on the diffusive radiation in Langmuir turbulence (DRL) theory by Fleishman and Toptygin showed that the typical frequency is γ{sup 2}ω{sub p} and that the low frequency spectrum behaves as F {sub ω}∝ω{sup 1} for b > 1 irrespective of a. Here, we adopt the first principle numerical approach to obtain the radiation spectra in more detail. We generate Langmuir turbulence by superposing Fourier modes, injecting monoenergetic electrons, solving the equation of motion, and calculating the radiation spectra using a Lienard-Wiechert potential. We find different features from the DRL theory for a > b > 1. The peak frequency turns out to be γ{sup 2}ω{sub st}, which is higher than the γ{sup 2}ω{sub p} predicted by the DRL theory, and the spectral index of the low frequency region is not 1 but 1/3. This is because the typical deflection angle of electrons is larger than the angle of the beaming cone ∼1/γ. We call the radiation for this case 'wiggler radiation in Langmuir turbulence'.

  16. Solar flare nomenclature

    NASA Astrophysics Data System (ADS)

    Cliver, E. W.

    1995-03-01

    The evolution of solar flare nomenclature is reviewed in the context of the paradigm shift, in progress, from flares to coronal mass ejections (CMEs) in solar-terrestrial physics. Emphasis is placed on: the distinction between eruptive (Class II) flares and confined (Class I) flares; and the underlying similarity of eruptive flares inside (two-ribbon flares) and outside (flare-like brightenings accompanying disappearing filaments) of active regions. A list of reserach questions/ problems raised, or brought into focus, by the new paradigm is suggested; in general, these questions bear on the inter- relationships and associations of the two classes (or phases) or flares. Terms such as 'eruptive flare' and 'eruption' (defined to encompass both the CME and its associated eruptive flare) may be useful as nominal links between opposing viewpoints in the 'flares vs CMEs' controversy.

  17. Improved methods of measurement and analysis of conversion electron and beta-particle spectra

    PubMed

    Dragoun; Spalek; Rysavy; Kovalik; Yakushev; Brabec; Frana; Venos

    2000-03-01

    A general statistical test of the stability of measurement conditions was demonstrated on the beta-spectra of 241Pu cumulated during four years. The alpha- and gamma-ray spectroscopy indicated stability of the 241Pu source. Monte Carlo modelling of individual collision events clarified the role of electron scattering and energy losses within a radioactive source down to energies of several hundreds of eV. The impact ionization by beta-particles of carbon and oxygen atoms in a surface contamination layer on the 241Pu and 63Ni sources was observed. PMID:10724379

  18. The beta-SiC(100) surface studied by low energy electron diffraction, Auger electron spectroscopy, and electron energy loss spectra

    NASA Technical Reports Server (NTRS)

    Dayan, M.

    1986-01-01

    The beta-SiC(100) surface has been studied by low energy electron diffraction, Auger electron spectroscopy, high resolution electron energy loss spectra (HREELS), and core level excitation EELS. Two new Si-terminated phases have been discovered, one with (3 x 2) symmetry, and the other with (2 x 1) symmetry. Models are presented to describe these phases. New results, for the C-rich surface, are presented and discussed. In addition, core level excitation EELS results are given and compared with theory.

  19. Two-electron ionization in strong laser fields below intensity threshold: Signatures of attosecond timing in correlated spectra

    NASA Astrophysics Data System (ADS)

    Bondar, Denys I.; Liu, Wing-Ki; Ivanov, Misha Yu.

    2009-02-01

    We develop an analytical model of correlated two-electron ionization in strong infrared laser fields. The model includes all relevant interactions between the electrons, the laser field, and the ionic core nonperturbatively. We focus on the deeply quantum regime, where the energy of the active electron driven by the laser field is insufficient to collisionally ionize the parent ion, and the assistance of the laser field is required to create a doubly charged ion. In this regime, the electron-electron and the electron-ion interactions leave distinct footprints in the correlated two-electron spectra, recording the mutual dynamics of the escaping electrons.

  20. Solvation dependence observed in the electronic dissymmetry factor spectra: how much information are we missing by analyzing the circular dichroism spectra alone?

    PubMed

    Covington, Cody L; Polavarapu, Prasad L

    2016-05-18

    A study utilizing the newly developed electronic dissymmetry factor (EDF) spectral analysis reveals that for [1,1'-binaphthalene]-2,2'-diol (BN) the experimental EDF spectra show differences due to solvent complexation following the trend in solvent polarity, that are not apparent in the electronic circular dichroism (ECD) or corresponding electronic absorption (EA) spectra. Large experimental EDF spectral magnitudes for BN are seen to peak in regions with no corresponding peaks in the EA spectrum and only a shoulder in the ECD spectrum. This observation indicates that EDF analysis is a new complementary method to conventional ECD analysis of chiral molecules. TD-DFT calculations predict similar EDF peaks as in the experimental EDF spectra, however, the experimentally observed solvation dependent behaviour of the EDF peaks was not reproduced in the calculations. Studies on 6,6'-dibromo-[1,1'-binaphthalene]-2,2'-diol also show similar characteristics in the EDF spectra, though not as pronounced and with different solvent effects. This report thus identifies a new means of chiral molecular structural analysis, hitherto unnoticed, and establishes the use of the dissymmetry factor spectrum as yielding new insight, but at no added cost. PMID:27149694

  1. Electronic and vibrational spectra of novel Lanreotide peptide capped gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Molina-Trinidad, E. M.; Estévez-Hernández, O.; Rendón, L.; Garibay-Febles, V.; Reguera, E.

    2011-11-01

    Lanreotide, a somatostatin analogue peptide used for peptide receptor mediated therapy in metastatic neuroendocrine tumors, was used as capping agent of gold nanoparticles (GNPs) obtained by citrate reduction method. The displacement of the citrate groups from the GNPs surface by Lanreotide (LAN) molecules was evidenced by infrared and Raman spectra. The nanoparticles system, Au@LAN, was also characterized from HRTEM (High-Resolution Transmission Electron Microscopy) and Z-contrast images, UV-vis and EDS spectra. The stability on aging in water solution of the composite is discussed from the UV-vis spectra. The affinity constant of Au@LAN conjugate, calculated from Capillary Zone Electrophoresis data, was found to be 0.52. All the experimental evidence supports that the gold nanoparticles are effectively capped by the Lanreotide molecules through relatively strong covalent interactions. This result opens the possibility of combining the optical properties of gold nanoparticles and of Lanreotide molecule to form a bifunctional system for potential biomedical applications.

  2. Photospheric abundances of oxygen, neon, and argon derived from the XUV spectrum of an impulsive flare

    SciTech Connect

    Feldman, U.; Widing, K.G. )

    1990-11-01

    Relative elemental abundances of O, Ne, Na, Mg, Ar, and Ca are determined from detailed analysis of XUV spectra emitted by an impulsive flare. The electron density measured from three diagnostic line ratios is 2-3 x 10 to the 12th/cu cm. It was found that the relative abundances in the flare are similar to values obtained from or proposed for photospheric material. The ratios of O/Mg, Ne/Mg, and Ar/Mg are about four times higher in the impulsive flare than the values typically observed in the average corona. It is suggested that electric fields above the photosphere may be responsible for the order of magnitude variations between the abundances of the group of elements with high first ionization potentials (FIP) and the group with low FIP. 18 refs.

  3. Measurement of Separate Cosmic-Ray Electron and Positron Spectra with the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Allafort, A.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Brogland, A. W.; Bouvier, A.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Ferrara, E. C.; Harding, A. K.; McEnery, J. E.

    2011-01-01

    We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting the Earth's shadow, which is offset in opposite directions for opposite charges due to the Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 GeV and 200 GeV, We confirm that the fraction rises with energy in the 20-100 GeV range and determine for the first time that it continues to rise between 100 and 200 GeV,

  4. Measurement of Separate Cosmic-Ray Electron and Positron Spectra with the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Ferrara, E. C.; Harding, A. K.; McEnery, J. E.; Moiseev, A. A.; Ackemann, M.

    2012-01-01

    We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because the instrument does not have an onboard magnet, we distinguish the two species by exploiting Earth's shadow, which, is offset in opposite directions for opposite charges due to Earth's magnetic field. We estimate and subtract the cosmic-ray proton background using two different methods that produce consistent results. We report the electron-only spectrum, the positron-only spectrum, and the positron fraction between 20 and 200 Ge V. We confirm that the fraction rises with energy in the 20-100 Ge V range. The three new spectral points between 100 and 200 GeV are consistent with a fraction that is continuing to rise with energy.

  5. Composition and spectra of primary cosmic-ray electrons and nuclei above 10 GeV

    NASA Technical Reports Server (NTRS)

    Meyer, P.

    1975-01-01

    Recent experiments have extended the knowledge of the flux and energy spectra of individual cosmic-ray components to much higher energies than had previously been accessible. Both electron and nuclear components show a behavior at high energy which is unexpected, and which carries information regarding the sources and the propagation of particles between sources and observer. Electromagnetic interactions which are suffered by the electrons in interstellar space should steepen their spectrum, a steepening that would reveal the average lifetime a cosmic-ray particle spends in the galaxy. Measurements up to 1000 GeV show no such steepening. It was discovered that the composition of the nuclear species which is now measured up to 100 GeV/nucleon changes with energy. This change indicates traversal of less interstellar matter by the high energy particles than by those of lower energy.-

  6. Understanding the formation of the Mg II h&k lines during solar flares

    NASA Astrophysics Data System (ADS)

    Rubio Da Costa, Fatima; Kleint, Lucia; Petrosian, Vahe'; Liu, Wei; Allred, Joel C.

    2016-05-01

    The Mg II h&k lines are useful diagnostics for physical processes in the solar chromosphere. Understanding the line formation is crucial for the correct interpretation of spectral observations and characteristics such as line asymmetries or how their central reversals in the line cores disappear and turn into emission during flares are manifestations of various physical processes.Focusing on the well-observed X1.0 flare on 2014 March 29, we carried out a joint observational and modeling study to analyze the Mg II h&k spectra observed by IRIS. We constructed a multi-threaded flare loop model and used the time-dependent electron flux inferred from the RHESSI hard X-ray data as the input to the radiative hydrodynamic code RADYN to simulate the atmospheric response. Using the RH code we conducted a detailed modeling on line shape and evolution to derive how different atmospheric parameters may affect the MgII line emission.We successfully simulated the single-peaked Mg II h&k line profiles by increasing electron density in the upper chromosphere within a narrow height range of ≈ 800 km below the transition region. To our knowledge, this is the first successful attempt in reproducing such line-profile shapes under flaring conditions. We will discuss the implications of this result for diagnosing atmospheric dynamics and energy transport in solar flares.

  7. M Dwarf Flare Continuum Variations on One-second Timescales: Calibrating and Modeling of ULTRACAM Flare Color Indices

    NASA Astrophysics Data System (ADS)

    Kowalski, Adam F.; Mathioudakis, Mihalis; Hawley, Suzanne L.; Wisniewski, John P.; Dhillon, Vik S.; Marsh, Tom R.; Hilton, Eric J.; Brown, Benjamin P.

    2016-04-01

    We present a large data set of high-cadence dMe flare light curves obtained with custom continuum filters on the triple-beam, high-speed camera system ULTRACAM. The measurements provide constraints for models of the near-ultraviolet (NUV) and optical continuum spectral evolution on timescales of ≈1 s. We provide a robust interpretation of the flare emission in the ULTRACAM filters using simultaneously obtained low-resolution spectra during two moderate-sized flares in the dM4.5e star YZ CMi. By avoiding the spectral complexity within the broadband Johnson filters, the ULTRACAM filters are shown to characterize bona fide continuum emission in the NUV, blue, and red wavelength regimes. The NUV/blue flux ratio in flares is equivalent to a Balmer jump ratio, and the blue/red flux ratio provides an estimate for the color temperature of the optical continuum emission. We present a new “color-color” relationship for these continuum flux ratios at the peaks of the flares. Using the RADYN and RH codes, we interpret the ULTRACAM filter emission using the dominant emission processes from a radiative-hydrodynamic flare model with a high nonthermal electron beam flux, which explains a hot, T ≈ 104 K, color temperature at blue-to-red optical wavelengths and a small Balmer jump ratio as observed in moderate-sized and large flares alike. We also discuss the high time resolution, high signal-to-noise continuum color variations observed in YZ CMi during a giant flare, which increased the NUV flux from this star by over a factor of 100. Based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium, based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofsica de Canarias, and observations, and based on observations made with the ESO Telescopes

  8. Theoretical calculations on the electron absorption spectra of selected Polycyclic Aromatic Hydrocarbons (PAH) and derivatives

    NASA Technical Reports Server (NTRS)

    Du, Ping

    1993-01-01

    As a theoretical component of the joint effort with the laboratory of Dr. Lou Allamandola to search for potential candidates for interstellar organic carbon compound that are responsible for the visible diffuse interstellar absorption bands (DIB's), quantum mechanical calculations were performed on the electron absorption spectra of selected polycyclic aromatic hydrocarbons (PAH) and derivatives. In the completed project, 15 different species of naphthalene, its hydrogen abstraction and addition derivatives, and corresponding cations and anions were studied. Using semiempirical quantum mechanical method INDO/S, the ground electronic state of each species was evaluated with restricted Hartree-Fock scheme and limited configuration interaction. The lowest energy spin state for each species was used for electron absorption calculations. Results indicate that these calculations are accurate enough to reproduce the spectra of naphthalene cation and anion observed in neon matrix. The spectral pattern of the hydrogen abstraction and addition derivatives predicted based on these results indicate that the electron configuration of the pi orbitals of these species is the dominant determinant. A combined list of 19 absorptions calculated from 4500 A to 10,400 A were compiled and suggested as potential candidates that are relevant for the DIB's absorptions. Continued studies on pyrene and derivatives revealed the ground state symmetries and multiplicities of its neutral, anionic, and cationic species. Spectral calculations show that the cation (B(sub 3g)-2) and the anion (A(sub u)-2) are more likely to have low energy absorptions in the regions between 10 kK and 20 kK, similar to naphthalene. These absorptions, together with those to be determined from the hydrogen abstraction and addition derivatives of pyrene, can be used to provide additional candidates and suggest experimental work in the search for interstellar compounds that are responsible for DIB's.

  9. Vibrationally resolved optical spectra and ultrafast electronic relaxation dynamics of diamantane.

    PubMed

    Röhr, Merle I S; Mitrić, Roland; Petersen, Jens

    2016-03-28

    We present theoretical simulations of the vibrationally resolved photoabsorption and photoemission spectra of diamantane combined with nonadiabatic dynamics simulations in order to identify the state responsible for the measured photoluminescence of diamantane and to determine the mechanism and the time-scales of the electronic state relaxation. Diamantane is a prototype representative of the diamondoid class of hydrocarbons which have recently gained significant interest due to their unique electronic properties. This molecule is characterised by an almost dark first excited state, which therefore cannot be directly excited. Moreover, the calculated vertical transition from the geometrically relaxed first excited state to the ground state also bears no intensity. However, recent experiments suggest that the observed photoluminescence originates from the lowest excited state. We have performed spectral simulations in the frame of the Herzberg-Teller approximation for vibronic transitions, which goes beyond the Franck-Condon approximation of constant transition dipole moments and takes into account their linear dependence on the geometrical deformations. In this way, the available experimental spectrum could be fully reproduced, resolving the issue about the origin of the photoluminescence. Moreover, the photoemission from the first excited state also implies that ultrafast nonradiative processes have to take place after the initial excitation of the bright electronic states. We have determined the mechanism and time-scales of these relaxation processes by performing nonadiabatic dynamics simulations in the manifold of s- and p-type Rydberg excited states. The simulations demonstrate that the lowest excited electronic state of diamantane gains significant population from higher-lying states already after several hundreds of femtoseconds. Thus, our dynamics simulations combined with spectra calculated using the Herzberg-Teller approximation allow us to fully explain

  10. COMBUSTION EFFICIENCY OF FLARES

    EPA Science Inventory

    The paper gives results of a study to provide data on industrial flare emissions. (Emissions of incompletely burned hydrocarbons from industrial flares may contribute to air pollution. Available data on flare emissions are sparse, and methods to sample operating flares are unavai...

  11. Interplay between structural and electronic properties of various fullerene derivatives, and their absorption spectra

    NASA Astrophysics Data System (ADS)

    Park, Sora; Ahn, Jeung Sun; Kwon, Young-Kyun

    2011-03-01

    Using density functional theory (DFT), we investigate the geometrical structures and electronic properties of various fullerene derivatives formed by attaching several kinds of addends on C60 through [2+2] cycloaddition. Various forms of such derivatives are modeled by considering different kinds, different positions and different numbers of addends to study how structural configurations will affect their electronic structures. Our results reveal that some derivatives with certain symmetries determined by the configuration of addends may have wider energy gap than that of pristine C60 . This suggests that absorption properties could be adjusted by controlling the addends configurations. To describe the excited state properties, such as absorption spectra, of various C60 derivatives more accurately, we performed time-dependent (TD) DFT calculations. We find the position and the intensity of the peak of absorption spectra of derivatives are affected by the specific symmetry of the derivatives defined by the configurations of the addends. To explore such peculiar effects, we analyze the charge distribution and orbital mixing characters.

  12. A comparison of theoretical and solar-flare intensity ratios for the Fe XIX X-ray lines

    NASA Technical Reports Server (NTRS)

    Bhatia, A. K.; Fawcett, B. C.; Phillips, K. J. H.; Lemen, J. R.; Mason, H. E.

    1989-01-01

    Atomic data including energy levels, gf-values, and wavelengths are given for the Fe XIX transitions that give rise to lines in solar-flare and active-region X-ray spectra. Collision strengths and theoretical intensity ratios are presented for lines which occur in the 13.2-14.3-A range. Observed spectra are found to be consistent with those derived from the present Fe XIX atomic data. For the case of spectra in which the Fe XIX lines are very strong, such as those at the maxima of hot flares, two observed line features due to Fe XIX are shown to have larger intensities than calculated. The calculated Fe XIX and Ne IX line spectra are used to determine electron densities from Ne IX line ratios.

  13. Spatially and momentum resolved energy electron loss spectra from an ultra-thin PrNiO{sub 3} layer

    SciTech Connect

    Kinyanjui, M. K. Kaiser, U.; Benner, G.; Pavia, G.; Boucher, F.; Habermeier, H.-U.; Keimer, B.

    2015-05-18

    We present an experimental approach which allows for the acquisition of spectra from ultra-thin films at high spatial, momentum, and energy resolutions. Spatially and momentum (q) resolved electron energy loss spectra have been obtained from a 12 nm ultra-thin PrNiO{sub 3} layer using a nano-beam electron diffraction based approach which enabled the acquisition of momentum resolved spectra from individual, differently oriented nano-domains and at different positions of the PrNiO{sub 3} thin layer. The spatial and wavelength dependence of the spectral excitations are obtained and characterized after the analysis of the experimental spectra using calculated dielectric and energy loss functions. The presented approach makes a contribution towards obtaining momentum-resolved spectra from nanostructures, thin film, heterostructures, surfaces, and interfaces.

  14. E-Layer Variations During X-Class Flares Inferred from Far Ultraviolet Dayglow Observations

    NASA Astrophysics Data System (ADS)

    Strickland, D. J.; Daniell, R. E.; Meier, R. R.; Lean, J. L.; Straus, P. R.; Morrison, M. D.; Paxton, L. J.

    2005-12-01

    A study is reported that addresses dayglow and ionospheric response to X-class flares that occurred on Oct 28 and Nov 4 2003. Data of interest are 1) the dayglow observations by GUVI and solar EUV/X-ray observations by SEE (both on NASA's TIMED satellite), 2) E-region measurements made by the EISCAT radar (on Oct 28) located at Tromsø, Norway, and 3) E-region/F-region IOX GPS occultation measurements (on Nov 4). The timing of the flares was fortunate in that TIMED was on the dayside portion of its orbit when activity peaked for both flares. During the Oct 28 flare, the EISCAT measurements were made near local noon under low geomagnetic activity conditions. Key results are the modeled and measured preflare and flare E-region electron densities. The basis of the modeled densities is QEUV, an integrated measure of solar EUV/XUV energy flux from 0 to 45 nm (that portion of the irradiance spectrum responsible for far ultraviolet dayglow). Use is made of spectra from SEE and the NRLEUV model along with GUVI nadir dayglow observations within its 135.6 and LBHS spectral channels to derive preflare and flare QEUV. The GUVI data are used to derive QEUV with the use of lookup tables, each distinguished by solar EUV/X-ray spectral shape, not by magnitude. Lookup tables have been produced using SEE and NRLEUV flare and preflare spectral shapes. The AURIC model is used to calculate the E-layer with the key input being a solar spectrum with a given shape (those discussed above) and magnitude (set by QEUV). The two sets of ionospheric measurements on their respective flare days show increases in NmE (E-layer peak density) by approximately a factor of three. The QEUV-based NmE agrees well with the measurements before and during these flares. NmE based on SEE spectra, on the other hand, exceeds the observed values, especially during the flares. The favorable agreement supports the derived GUVI QEUV values and argues for a significant reduction in SEE energy fluxes during periods of

  15. Solar flares with similar soft but different hard X-ray emissions: case and statistical studies

    NASA Astrophysics Data System (ADS)

    Sharykin, Ivan N.; Struminsky, Alexei B.; Zimovets, Ivan V.; Gan, Wei-Qun

    2016-01-01

    From the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) catalog we select events which have approximately the same GOES class (high C - low M or 500-1200 counts s-1 within the RHESSI 6-12 keV energy band), but with different maximal energies of detected hard X-rays. The selected events are subdivided into two groups: (1) flares with X-ray emissions observed by RHESSI up to only 50 keV and (2) flares with hard X-ray emission observed also above 50 keV. The main task is to understand observational peculiarities of these two flare groups. We use RHESSI X-ray data to obtain spectral and spatial information in order to find differences between selected groups. Spectra and images are analyzed in detail for six events (case study). For a larger number of samples (85 and 28 flares in the low-energy and high-energy groups respectively) we only make some generalizations. In spectral analysis we use the thick-target model for hard X-ray emission and one temperature assumption for thermal soft X-ray emission. RHESSI X-ray images are used for determination of flare region sizes. Although thermal and spatial properties of these two groups of flares are not easily distinguishable, power law indices of hard X-rays show significant differences. Events from the high-energy group generally have a harder spectrum. Therefore, the efficiency of chromospheric evaporation is not sensitive to the hardness of nonthermal electron spectra but rather depends on the total energy flux of nonthermal electrons.

  16. Helios 1 energetic particle observations of the solar gamma ray flare events of 7, 21 June 1980 and 3 June 1982

    NASA Technical Reports Server (NTRS)

    Mcdonald, F. B.; Vanhollebeke, M. A. I.; Trainor, J. H.

    1985-01-01

    The observed characteristics of the energetic particles associated with the solar gamma-ray events of 3, 21 June 1980 and 3 June 1982 differ in several important aspects from the typical solar particle increases. They have flat energy spectra, are electron rich and have small precursors increases that begin some hours before the impulsive flare increase.

  17. Solvent effects on the resonance Raman and electronic absorption spectra of bacteriochlorophyll a cation radical

    SciTech Connect

    Misono, Yasuhito; Itoh, Koichi; Limanatara, Leenawaty; Koyama, Yasushi

    1996-02-08

    Resonance Raman and electronic absorption spectra of bacteriocholrophyll a cation radical (BChl a{sup .+}) were recorded in 14 different kinds of solvents. The frequency of the ring-breathing Raman band of BChl a{sup .+} was in the region of 1596-1599 cm{sup -1} in solvents forming the pentacoordinated state in neutral bacteriochlorophyll a (BChl a), while it was in the region of 1584-1588 cm{sup -1} in solvents forming the hexacoordinated state. BChl a{sup .+} exhibited a key absorption band in the regions 546-554 and 557-563 nm in the above penta- and hexa-coordinating solvents. Therefore, it has been concluded that the penta- and hexa-coordinated states are retained even after conversion of BChl a into BChl a{sup .+} (one-electron oxidization). Application of this rule to the case of 2-propanol solution showed transformation from the penta- to the hexa-coordinated state upon one-electron oxidation in this particular solution. The coordination states of BChl a{sup .+} could be correlated with the donor number(DN) and the Taft parameters, {Beta} and {pi}{sup *}, of the solvent: The hexacoordinated state was formed in solvents with DN >= 18 or {Beta} > 0.5 showing higher electron donating power, while the pentacoordinated state was formed in solvents with {pi}{sup *} > 0.65 showing higher dielectric stabilization. 27 refs., 8 figs., 3 tabs.

  18. Study of non-thermal photon production under different scenarios in solar flares. 2: The Compton inverse and Bremsstrahlung models and fittings

    NASA Technical Reports Server (NTRS)

    Perez-Peraza, J.; Alvarez, M.; Laville, A.; Gallegos, A.

    1985-01-01

    Energy spectra of photons emitted from Bremsstrahlung (BR) of energetic electrons with matter, is obtained from the deconvolution of the electron energy spectra. It can be inferred that the scenario for the production of X-rays and gamma rays in solar flares may vary from event to event. However, it is possible in many cases to associated low energy events to impulsive acceleration, and the high energy phase of some events to stochastic acceleration. In both cases, flare particles seem to be strongly modulated by local energy losses. Electric field acceleration, associated to neutral current sheets is a suitable candidate for impulsive acceleration. Finally, that the predominant radiation process of this radiation is the inverse Compton effect due to the local flare photon field.

  19. Relation between fine structure of energy spectra for pulsating aurora electrons and frequency spectra of whistler mode chorus waves

    NASA Astrophysics Data System (ADS)

    Miyoshi, Y.; Saito, S.; Seki, K.; Nishiyama, T.; Kataoka, R.; Asamura, K.; Katoh, Y.; Ebihara, Y.; Sakanoi, T.; Hirahara, M.; Oyama, S.; Kurita, S.; Santolik, O.

    2015-09-01

    We investigate the origin of the fine structure of the energy spectrum of precipitating electrons for the pulsating aurora (PsA) observed by the low-altitude Reimei satellite. The Reimei satellite achieved simultaneous observations of the optical images and precipitating electrons of the PsA from satellite altitude (~620 km) with resolution of 40 ms. The main modulation of precipitation, with a few seconds, and the internal modulations, with a few hertz, that are embedded inside the main modulations are identified above ~3 keV. Moreover, stable precipitations at ~1 keV are found for the PsA. A "precipitation gap" is discovered between two energy bands. We identify the origin of the fine structure of the energy spectrum for the precipitating electrons using the computer simulation on the wave-particle interaction between electrons and chorus waves. The lower band chorus (LBC) bursts cause the main modulation of energetic electrons, and the generation and collapse of the LBC bursts determines on-off switching of the PsA. A train of rising tone elements embedded in the LBC bursts drives the internal modulations. A close set of upper band chorus (UBC) waves causes the stable precipitations at ~1 keV. We show that a wave power gap around the half gyrofrequency at the equatorial plane in the magnetosphere between LBC and UBC reduces the loss rate of electrons at the intermediate energy range, forming a gap of precipitating electrons in the ionosphere.

  20. Quiescent and Flaring Structure in RS Canum Venaticorum Stars

    NASA Astrophysics Data System (ADS)

    Sanz-Forcada, J.; Brickhouse, N. S.; Dupree, A. K.

    2002-05-01

    Four of the most active RS CVn stars (V711 Tau, II Peg, σ Gem, and UX Ari) have been observed for a total of 3 Ms with the Extreme Ultraviolet Explorer satellite (EUVE) between 1992 and 2000 January. Flaring and quiescent states of extreme ultraviolet spectra (λλ70-740) and light curves (λλ75-175) have been analyzed to provide emission measure distributions (EMD) for these systems in the range logTe(K)~5.6-7.4, based principally on iron lines. Flux measurements obtained with IUE and the Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer (ORFEUS) complete the EMD in the lower temperature range [logTe(K)~4.0-5.6]. Frequent flaring activity has been found in the systems, including an increase during the rise phase by a factor of ~9 in the flux of σ Gem, the largest flare enhancement observed with EUVE. Analyses of the EUVE emission in the active single star AB Dor and the low-rotation giant star β Cet are also included. The EMDs are remarkably similar among all the stars, showing a narrow enhancement or ``bump'' around logTe(K)~6.9. These narrow bumps are apparently unrelated to rotation rate, spectral type, binarity, or evolutionary stage. Significant material is found at logTe(K)>~7.0 for the most active stars. Modulation of the EUV flux outside of flaring occurs in four of the stars (σ Gem, V711 Tau, UX Ari, AB Dor). The electron density ranges between Ne~1012 and ~1013 cm-3, measured at logTe(K)~7.0, and may reach higher values during flares. These densities and EMD values imply small scale sizes for emitting regions.

  1. Spectral investigations of 2,5-difluoroaniline by using mass, electronic absorption, NMR, and vibrational spectra

    NASA Astrophysics Data System (ADS)

    Kose, Etem; Karabacak, Mehmet; Bardak, Fehmi; Atac, Ahmet

    2016-11-01

    One of the most significant aromatic amines is aniline, a primary aromatic amine replacing one hydrogen atom of a benzene molecule with an amino group (NH2). This study reports experimental and theoretical investigation of 2,5-difluoroaniline molecule (2,5-DFA) by using mass, ultraviolet-visible (UV-vis), 1H and 13C nuclear magnetic resonance (NMR), Fourier transform infrared and Raman (FT-IR and FT-Raman) spectra, and supported with theoretical calculations. Mass spectrum (MS) of 2,5-DFA is presented with their stabilities. The UV-vis spectra of the molecule are recorded in the range of 190-400 nm in water and ethanol solvents. The 1H and 13C NMR chemical shifts are recorded in CDCl3 solution. The vibrational spectra are recorded in the region 4000-400 cm-1 (FT-IR) and 4000-10 cm-1 (FT-Raman), respectively. Theoretical studies are underpinned the experimental results as described below; 2,5-DFA molecule is optimized by using B3LYP/6-311++G(d,p) basis set. The mass spectrum is evaluated and possible fragmentations are proposed based on the stable structure. The electronic properties, such as excitation energies, oscillator strengths, wavelengths, frontier molecular orbitals (FMO), HOMO and LUMO energies, are determined by time-dependent density functional theory (TD-DFT). The electrostatic potential surface (ESPs), density of state (DOS) diagrams are also prepared and evaluated. In addition to these, reduced density gradient (RDG) analysis is performed, and thermodynamic features are carried out theoretically. The NMR spectra (1H and 13C) are calculated by using the gauge-invariant atomic orbital (GIAO) method. The vibrational spectra of 2,5-DFA molecule are obtained by using DFT/B3LYP method with 6-311++G(d,p) basis set. Fundamental vibrations are assigned based on the potential energy distribution (PED) of the vibrational modes. The nonlinear optical properties (NLO) are also investigated. The theoretical and experimental results give a detailed description of

  2. Flare instability and driving mechanism

    NASA Astrophysics Data System (ADS)

    Raychaudhuri, Probhas

    A mechanism is described for the generation of solar flares in which a Buneman instability is produced by electrons moving faster than thermal speed. A trapped population of particles accelerates in the magnetic field of active solar regions causing a streaming of ions relative to electrons which moves and heats the electrons. The theoretical argument also concludes that instability at the inner solar core directly bears on solar activities at the outer heliosphere.

  3. KEPLER FLARES. I. ACTIVE AND INACTIVE M DWARFS

    SciTech Connect

    Hawley, Suzanne L.; Davenport, James R. A.; Kowalski, Adam F.; Wisniewski, John P.; Deitrick, Russell; Hilton, Eric J.; Hebb, Leslie

    2014-12-20

    We analyzed Kepler short-cadence M dwarf observations. Spectra from the Astrophysical Research Consortium 3.5 m telescope identify magnetically active (Hα in emission) stars. The active stars are of mid-M spectral type, have numerous flares, and have well-defined rotational modulation due to starspots. The inactive stars are of early M type, exhibit less starspot signature, and have fewer flares. A Kepler to U-band energy scaling allows comparison of the Kepler flare frequency distributions with previous ground-based data. M dwarfs span a large range of flare frequency and energy, blurring the distinction between active and inactive stars designated solely by the presence of Hα. We analyzed classical and complex (multiple peak) flares on GJ 1243, finding strong correlations between flare energy, amplitude, duration, and decay time, with only a weak dependence on rise time. Complex flares last longer and have higher energy at the same amplitude, and higher energy flares are more likely to be complex. A power law fits the energy distribution for flares with log E{sub K{sub p}}> 31 erg, but the predicted number of low-energy flares far exceeds the number observed, at energies where flares are still easily detectable, indicating that the power-law distribution may flatten at low energy. There is no correlation of flare occurrence or energy with starspot phase, the flare waiting time distribution is consistent with flares occurring randomly in time, and the energies of consecutive flares are uncorrelated. These observations support a scenario where many independent active regions on the stellar surface are contributing to the observed flare rate.

  4. Analysis of Gamma-Ray Data from Solar Flares in Cycles 21 and 22

    NASA Technical Reports Server (NTRS)

    Vestrand, W. Thomas

    1998-01-01

    One of our primary accomplishments under grant NAGW-35381 was the systematic derivation and compilation, for the first time, of physical parameters for all gamma-ray flares detected by the SMM GRS during its ten year lifetime. The flare parameters derived from the gamma-ray spectra include: bremsstrahlung fluence and best-fit power-law parameters, narrow nuclear line fluence, positron annihilation line fluence, neutron capture line fluence, and an indication of whether or not greater than 10 MeV emissions were present. We combined this compilation of flare parameters with our plots of counting rate time histories and flare spectra to construct an atlas of gamma-ray flare characteristics. The atlas time histories display four energy bands: 56-199 kev, 298526 keV, 4-8 MeV, and 10-25 MeV. These energy bands respectively measure nonrelativistic bremsstrahlung, trans-relativistic bremsstrahlung, nuclear de-excitation, and ultra-relativistic bremsstrahlung. The atlas spectra show the integrated high-energy spectra measured for all GRS flares and dissects them into electron bremsstrahlung, positron annihilation and nuclear emission components. The atlas has been accepted for publication in the Astrophysical Journal Supplements and is currently in press. The atlas materials were also supplied to the Solar Data Analysis Center at Goddard Space Flight Center and were made available through a web site at the University of New Hampshire. Since a uniform methodology was adopted for deriving the flare parameters, this atlas will be very useful for future statistical and correlative studies of solar flares-three independent groups are presently using it to correlate interplanetary energetic particle measurements with our gamma-ray measurements. A better model for the response of the GRS instrument to high energy radiation was also developed. A refined response model was needed because the old model was not adequate for predicting the first and second escape peaks associated with

  5. Spectral analysis and modeling of solar flares chromospheric condensation

    NASA Astrophysics Data System (ADS)

    Cauzzi, Gianna; Graham, David; Kowalski, Adam; Zangrilli, Luca; Simoes, Paulo; Allred, Joel C.

    2016-05-01

    We follow up on our recent analysis of the X1.1 flare SOL2014-09-10T17:45, where we studied the impulsive phase dynamics of tens of individual flaring "kernels", in both coronal (Fe XXI) and chromospheric (MgII) lines observed at high cadence with IRIS.We concentrate here on the chromospheric aspect of the phenomenon, extending the analysis to multiple spectral lines of Mg II, Fe II, Si I, C II. We show that many flaring kernels display high velocity downflows in the spectra of all these chromospheric lines, exhibiting distinct, transient and strongly redshifted spectral components.From modeling using RADYN with the thick-target interpretation, the presence of two spectral components appears to be consistent with a high flux beam of accelerated electrons, characterized by a hard spectrum. In particular the highest energy electrons heat the denser, lower layers of the atmosphere, while the bulk of the beam energy, deposited higher in the atmosphere, is sufficient to produce chromospheric evaporation with a corresponding condensation.

  6. Study of polymorphism in imatinib mesylate: A quantum chemical approach using electronic and vibrational spectra

    NASA Astrophysics Data System (ADS)

    Srivastava, Anubha; Joshi, B. D.; Tandon, Poonam; Ayala, A. P.; Bansal, A. K.; Grillo, Damián

    2013-02-01

    Imatinib mesylate, 4-(4-methyl-piperazin-1-ylmethyl)-N-u[4-methyl-3-(4-pyridin-3-yl)pyrimidine-2-ylamino)phenyl]benzamide methanesulfonate is a therapeutic drug that is approved for the treatment of chronic myelogeneous leukemia (CML) and gastrointestinal stromal tumors (GIST). It is known that imatinib mesylate exists in two polymorphic forms α and β. However, β-form is more stable than the α-form. In this work, we present a detailed vibrational spectroscopic investigation of β-form by using FT-IR and FT-Raman spectra. These data are supported by quantum mechanical calculations using DFT employing 6-311G(d,p) basis set, which allow us to characterize completely the vibrational spectra of this compound. The FT-IR spectrum of α-form has also been discussed. The importance of hydrogen-bond formation in the molecular packing arrangements of both forms has been examined with the vibrational shifts observed due to polymorphic changes. The red shift of the NH stretching bands in the infrared spectrum from the computed wavenumber indicates the weakening of the NH bond. The UV-vis spectroscopic studies along with the HOMO-LUMO analysis of both polymorphs (α and β) were performed and their chemical activity has been discussed. The TD-DFT method was used to calculate the electronic absorption spectra in the gas phase as well as in the solvent environment using IEF-PCM model and 6-31G basis set. Finally, the results obtained complements to the experimental findings.

  7. Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra

    NASA Astrophysics Data System (ADS)

    Fujihashi, Yuta; Fleming, Graham R.; Ishizaki, Akihito

    2015-06-01

    Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications.

  8. Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra

    SciTech Connect

    Fujihashi, Yuta; Ishizaki, Akihito; Fleming, Graham R.

    2015-06-07

    Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications.

  9. Properties of electron flux spectra around the plasmapause in the chorus and hiss regions using POES.

    NASA Astrophysics Data System (ADS)

    Whittaker, Ian; Rodger, Craig; Clilverd, Mark

    2014-05-01

    The European FP7 PLASMON project aims to provide observations of plasmaspheric densities, and link the plasmaspheric variations to relativistic electron precipitation from the radiation belts. This is intended to assist in the estimation and prevent damage of space assets from space weather events as well as to improve forecasting (http://plasmon.elte.hu). As part of the PLASMON project, electron fluxes from the POES series of satellites are being used to determine the link between energetic electron precipitation energy spectra and magnitude to the position of the plasmapause. The MEPED instrument onboard POES measures electron flux from 90° (trapped particles) and 0° (losscone) telescopes, in 3 integral energy channels (>30, >100 and >300 keV). These fluxes have been compared to the DEMETER/IDP instrument to confirm that published geometric factor corrections (Yando et al. 2011) can be accurately applied to the POES data to produce as accurate as possible fluxes. These global fluxes have then been separated into regions in which Chorus (23:00-11:00 MLT) and Hiss (11:00-16:00 MLT) whistler mode waves are expected to occur, in 0.2 L-shell bins with a 20 minute temporal resolution. The plasmapause locations have been determined from the O'Brien and Moldwin (2003) models based on Kp, Ae and Dst peaks. We are currently comparing the POES spectral gradient and flux magnitude with plasmapause location and geomagnetic activity for the locations in which chorus and hiss are known to occur. This presentation will focus on the electron flux spectral gradient behaviour either side of the plasmapause, a value that is difficult to measure from ground based techniques.

  10. Effect of surface topography on reflection electron energy loss plasmon spectra of group III metals

    SciTech Connect

    Strawbridge, B.; Singh, R. K.; Beach, C.; Mahajan, S.; Newman, N.

    2006-09-15

    In situ reflection electron energy loss spectroscopy (REELS) and reflection high energy electron diffraction employing a 20 keV electron beam at a 2 deg. grazing angle were used to characterize the surface properties of molecular beam epitaxy (MBE) grown Al, Ga, and In metals on silicon and sapphire substrates. In our study we found that the surface topography strongly influences the REELS plasmon spectra. Smooth Al films with <1 nm rms roughness exhibited surface plasmon peaks. Both surface and bulk plasmons are seen from an Al film with a rms roughness of 3.5 nm. Aluminum surfaces with >5 nm rms roughness yielded only bulk plasmon peaks. To understand the EELS spectrum for the Ga and In films, the rms roughness alone is not the relevant figure of merit as the electron beam interaction with the surface is influenced most by the shape of the tops of the surface grains and the grain size. Indium films on Si with a rms roughness of 52 nm were found to excite predominantly surface plasmons as the grazing angle electron beam scattered mostly off the flat top surface of each grain and was not strongly influenced by the crevices between the grains. The rounded tops of the Ga topography with 31 nm rms roughness facilitated transmission through the grains and therefore excited a combination of bulk and surface plasmons. This experimental method is very surface sensitive, as a probe depth of 0.8 nm was inferred from the diminishing intensity of the substrate peak with increasing coverage of a flat metal surface. The techniques and methods discussed here can be readily applied to other thin film systems such as MBE-grown III-V semiconductors, sputtered oxides, and other vacuum deposited materials.

  11. Electron densities inferred from plasma wave spectra obtained by the Waves instrument on Van Allen Probes

    NASA Astrophysics Data System (ADS)

    Kurth, W. S.; De Pascuale, S.; Faden, J. B.; Kletzing, C. A.; Hospodarsky, G. B.; Thaller, S.; Wygant, J. R.

    2015-02-01

    The twin Van Allen Probe spacecraft, launched in August 2012, carry identical scientific payloads. The Electric and Magnetic Field Instrument Suite and Integrated Science suite includes a plasma wave instrument (Waves) that measures three magnetic and three electric components of plasma waves in the frequency range of 10 Hz to 12 kHz using triaxial search coils and the Electric Fields and Waves triaxial electric field sensors. The Waves instrument also measures a single electric field component of waves in the frequency range of 10 to 500 kHz. A primary objective of the higher-frequency measurements is the determination of the electron density ne at the spacecraft, primarily inferred from the upper hybrid resonance frequency fuh. Considerable work has gone into developing a process and tools for identifying and digitizing the upper hybrid resonance frequency in order to infer the electron density as an essential parameter for interpreting not only the plasma wave data from the mission but also as input to various magnetospheric models. Good progress has been made in developing algorithms to identify fuh and create a data set of electron densities. However, it is often difficult to interpret the plasma wave spectra during active times to identify fuh and accurately determine ne. In some cases, there is no clear signature of the upper hybrid band, and the low-frequency cutoff of the continuum radiation is used. We describe the expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum.

  12. A comparison between spectra of runaway electron beams in SF{sub 6} and air

    SciTech Connect

    Zhang, Cheng; Wang, Ruexue; Yan, Ping; Shao, Tao; Tarasenko, Victor; Gu, Jianwei; Baksht, Evgenii

    2015-12-15

    Runaway electron (RAE) with extremely high-energy plays important role on the avalanche propagation, streamer formation, and ionization waves in nanosecond-pulse discharges. In this paper, the generation of a supershort avalanche electron beam (SAEB) in SF{sub 6} and air in an inhomogeneous electric field is investigated. A VPG-30-200 generator with a pulse rise time of ∼1.6 ns and a full width at half maximum of 3–5 ns is used to produce RAE beams. The SAEBs in SF{sub 6} and air are measured by using aluminum foils with different thicknesses. Furthermore, the SAEB spectra in SF{sub 6} and air at pressures of 7.5 Torr, 75 Torr, and 750 Torr are compared. The results showed that amplitude of RAE beam current generated at the breakdown in SF{sub 6} was approximately an order of magnitude less than that in air. The energy of SAEB in air was not smaller than that in SF{sub 6} in nanosecond-pulse discharges under otherwise equal conditions. Moreover, the difference between the maximum energy of the electron distributions in air and SF{sub 6} decreased when the rise time of the voltage pulse increased. It was because the difference between the breakdown voltages in air and SF{sub 6} decreased when the rise time of the voltage pulse increased.

  13. A comparison between spectra of runaway electron beams in SF6 and air

    NASA Astrophysics Data System (ADS)

    Zhang, Cheng; Tarasenko, Victor; Gu, Jianwei; Baksht, Evgenii; Wang, Ruexue; Yan, Ping; Shao, Tao

    2015-12-01

    Runaway electron (RAE) with extremely high-energy plays important role on the avalanche propagation, streamer formation, and ionization waves in nanosecond-pulse discharges. In this paper, the generation of a supershort avalanche electron beam (SAEB) in SF6 and air in an inhomogeneous electric field is investigated. A VPG-30-200 generator with a pulse rise time of ˜1.6 ns and a full width at half maximum of 3-5 ns is used to produce RAE beams. The SAEBs in SF6 and air are measured by using aluminum foils with different thicknesses. Furthermore, the SAEB spectra in SF6 and air at pressures of 7.5 Torr, 75 Torr, and 750 Torr are compared. The results showed that amplitude of RAE beam current generated at the breakdown in SF6 was approximately an order of magnitude less than that in air. The energy of SAEB in air was not smaller than that in SF6 in nanosecond-pulse discharges under otherwise equal conditions. Moreover, the difference between the maximum energy of the electron distributions in air and SF6 decreased when the rise time of the voltage pulse increased. It was because the difference between the breakdown voltages in air and SF6 decreased when the rise time of the voltage pulse increased.

  14. ULTRAVIOLET AND INFRARED SPECTRA OF ELECTRON-BOMBARDED SOLID NITROGEN AND METHANE DILUTED IN SOLID NITROGEN

    SciTech Connect

    Wu, Yu-Jong; Chuang, Shiang-Jiun; Huang, Tzu-Ping; Chen, Hui-Fen

    2013-05-01

    The infrared (IR) and ultraviolet (UV) absorption spectra of pure solid N{sub 2} and CH{sub 4} diluted in solid N{sub 2} (1/100) irradiated with energetic electrons at 10 K were obtained. The IR absorption measurements of the electron-bombarded pure N{sub 2} solid reveal the formation of N{sub 3} and N{sub 3} {sup +}, which was confirmed by the observed electronic transitions A {sup 2}{Sigma}{sub u} {sup +}<- X {sup 2}{Pi}{sub g} of N{sub 3} and A {sup 3}{Pi}{sub u} <- X {sup 3}{Sigma}{sub g} {sup -} of N{sub 3} {sup +}. In the case of N{sub 2} ice containing a small proportion of CH{sub 4}, we have identified the products of irradiated CH{sub 4}/N{sub 2} ice, including N{sub 3}, C{sub n} N (n = 1-3), CN{sub 2}, (CN){sub 2}, CH{sub 3}N, HCN{sub 2}, HC{sub 2}N, C(NH){sub 2}, HNC, HCN, CH{sub 3}, C{sub 2}H, C{sub 2}H{sub 2}, CN{sup -}, NH{sub 3} {sup +}, and HC{sub 3}N{sup +}. UV absorption measurement of the ice sample was carried out and the possible carriers associated with the observed absorption bands were assigned and discussed.

  15. Features in the electronic structure and photoemission spectra of organic molecular semiconductors: The molecules of metal-phthalocyanines and PTCDA

    NASA Astrophysics Data System (ADS)

    Tikhonov, E. V.; Uspenskii, Yu. A.; Khokhlov, D. R.

    2013-09-01

    The role of many-electron effects in the formation of electronic quasiparticle spectra in organic molecular semiconductors (OMS) is analyzed. Many-body perturbation theory, ab initio calculations of metal phthalocyanines and PTCDA molecules, and experimental photoemission spectra are applied to this analysis. It is shown that density functional theory (DFT) poorly reproduces the electronic spectra of OMS. The use of a hybrid functional method (HFM) provides precise reproduction of both valence and conducting bands, while the HOMO-LUMO gap remains underestimated. The correct gap width is obtained in both DFT and HFM, when it is calculated through ionization and affinity energies. It is shown that such an approach gives a formula for gap correction due to electron correlations, which is close to an expression derived from the GW approximation.

  16. Electronic spectra of 7-azaindole/ammonia clusters and their photochemical reactivity

    SciTech Connect

    Koizumi, Yuna; Norihiro, Tsuji; Ishiuchi, Shun-ichi; Fujii, Masaaki; Jouvet, Christophe; Dedonder-Lardeux, Claude

    2008-09-14

    The S{sub 1}-S{sub 0} electronic spectra of 7-azaindole-(NH{sub 3}){sub n} clusters (n=1-3) were measured by mass-selected two-color resonance-enhanced multiphoton ionization spectroscopy. The laser-induced fluorescence spectrum obtained by monitoring the UV fluorescence shows well-structured vibrational bands for the monomer and 7-azaindole-(NH{sub 3}){sub 1,2} clusters, while no signals appear for the 7-azaindole-(NH{sub 3}){sub 3} cluster. The action spectrum obtained by monitoring visible emission shows no signal for all species, which suggests little reactivity for excited-state proton/hydrogen transfer. From the observed and calculated IR spectra, the geometry of 7-azaindole-(NH{sub 3}){sub 1,2} was concluded to be a hydrogen-bonded bridge form, which is similar to the photochemically reactive 7-hydroxyquinoline-(NH{sub 3}){sub 3} cluster. The difference in the photochemical reactivity is discussed on the basis of excited-state quantum chemical calculations.

  17. Density functional theory studies on molecular structure, vibrational spectra and electronic properties of cyanuric acid

    NASA Astrophysics Data System (ADS)

    Prabhaharan, M.; Prabakaran, A. R.; Srinivasan, S.; Gunasekaran, S.

    2015-03-01

    The present work has been carried out a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of cyanuric acid. The FT-IR (100-4000 cm-1) and FT-Raman spectra (400-4000 cm-1) of cyanuric acid were recorded. In DFT methods, Becke's three parameter exchange-functional (B3) combined with gradient-corrected correlation functional of Lee, Yang and Parr (LYP) by implementing the split-valence polarized 6-31G(d,p) and 6-31++G(d,p) basis sets have been considered for the computation of the molecular structure optimization, vibrational frequencies, thermodynamic properties and energies of the optimized structures. The density functional theory (DFT) result complements the experimental findings. The electronic properties, such as HOMO-LUMO energies and molecular electrostatic potential (MESP) are also performed. Mulliken population analysis on atomic charges is also calculated. The first order hyperpolarizability (βtotal) of this molecular system and related properties (β, μ and Δα) are calculated using DFT/B3LYP/6-31G (d,p) and B3LYP/6-311++G(d,p) methods. The thermodynamic functions (heat capacity, entropy and enthalpy) from spectroscopic data by statistical methods were also obtained for the range of temperature 50-1000 K.

  18. Synthesis of Electron Energy Loss Spectra for the Quantification of Detection Limits

    NASA Astrophysics Data System (ADS)

    Menon, Nanda K.; Krivanek, Ondrej L.

    2002-06-01

    We describe a method for predicting detection limits of minority elements in electron energy loss spectroscopy (EELS), and its implementation as a software package that gives quantitative predictions for user-specified materials and experimental conditions. The method is based on modeling entire energy loss spectra, including shot noise as well as instrumental noise, and taking into account all the relevant experimental parameters. We describe the steps involved in modeling the entire spectrum, from the zero loss up to inner shell edges, and pay particular attention to the contributions to the pre-edge background. The predicted spectra are used to evaluate the signal-to-noise ratios (SNRs) for inner shell edges from user-specified minority elements. The software also predicts the minimum detectable mass (MDM) and minimum mass fraction (MMF). It can be used to ascertain whether an element present at a particular concentration should be detectable for given experimental conditions, and also to quickly and quantitatively explore ways of optimizing the experimental conditions for a particular EELS analytical task. We demonstrate the usefulness of the software by confirming the recent empirical observation of single atom detection using EELS of phosphorus in thin carbon films, and show the effect on the SNR of varying the acquisition parameters. The case of delta-doped semiconductors is also considered as an important example from materials science where low detection limits and high spatial resolution are essential, and the feasibility of such characterization using EELS is assessed.

  19. Theoretical study of the structure and electronic spectra of fully protonated emeraldine oligomers

    NASA Astrophysics Data System (ADS)

    Zhekova, H.; Tadjer, A.; Ivanova, A.; Petrova, J.; Gospodinova, N.

    Polyaniline (PANI) is one of the most studied conducting polymers. Obtained in its conducting form (known as ?emeraldine salt?) by chemical or electrochemical oxidation of aniline in aqueous acidic medium, this polymer manifests an array of attractive properties. Nevertheless, these properties still need to be described at the molecular level. Intense theoretical investigations during the past few years aim at explaining the chain organization, conductivity mechanism, and other structural and spectral characteristics. Most studies adopt simplified models in which hydration effect is underestimated, since all simulations are performed either in vacuum or in the presence of a limited number of water molecules. The present computational study sheds light on the molecular organization of a number of model PANI hydrated clusters with different alignment and multiplicity, which can explain the experimentally recorded UV/VIS spectra. The influence of hydration and interaction with adjacent oligomers is estimated. Short-chain doubly protonated emeraldine oligomers are used as model systems. The calculations are performed at the semi-empirical (AM1) and/or molecular mechanics (AMBER96) level. Proper configurations of the clusters are selected using Monte Carlo simulations. Electron correlation (CIS) is accounted for upon evaluation of the absorption spectra of the clusters. The relative strength of the interchain coupling is estimated by simulation of PANI clusters consisting of two PANI tetramers in water. Comparison to experimental results is made.

  20. GAS-PHASE ELECTRONIC SPECTRA OF POLYACETYLENE CATIONS: RELEVANCE OF HIGHER EXCITED STATES

    SciTech Connect

    Rice, C. A.; Rudnev, V.; Dietsche, R.; Maier, J. P.

    2010-07-15

    Transitions to higher electronic states of polyacetylene cations (HC{sub 2n}H{sup +}, n = 4, 5, 6) have been measured in the gas phase at {approx}20 K. The absorption spectra were obtained using a resonant two-color, two-photon fragmentation technique in an ion trap, allowing a direct comparison between laboratory and astrophysical data. The purpose was to investigate the relevance of such transitions to astronomical observations because the general expectation is that the bands could be too broad due to fast intramolecular processes. It is shown that the origin bands are still narrow enough (1-10 cm{sup -1}) to be considered, especially as the higher-lying transitions often possess large oscillator strengths.

  1. Electronic Structures of Purple Bronze KMo6O17 Studied by X-Ray Photoemission Spectra

    NASA Astrophysics Data System (ADS)

    Qin, Xiaokui; Wei, Junyin; Shi, Jing; Tian, Mingliang; Chen, Hong; Tian, Decheng

    X-ray photoemission spectroscopy study has been performed for the purple bronze KMo6O17. The structures of conduction band and valence band are analogous to the results of ultraviolet photoemission spectra and are also consistent with the model of Travaglini et al., but the gap between conduction and valence band is insignificant. The shape of asymmetric and broadening line of O-1s is due to unresolved contributions from the many inequivalent oxygen sites in this crystal structure. Mo 3d core-level spectrum reveals that there are two kinds of valence states of Molybdenum (Mo+5 and Mo+6). The calculated average valence state is about +5.6, which is consistent with the expectation value from the composition of this material. The tail of Mo-3d spectrum toward higher binding energy is the consequence of the excitation of electron-hole pairs with singularity index of 0.21.

  2. Combined treatment of relaxation and fluctuation dynamics in the calculation of two-dimensional electronic spectra

    SciTech Connect

    Seibt, Joachim; Pullerits, Tõnu

    2014-09-21

    While the theoretical description of population transfer subsequent to electronic excitation in combination with a line shape function description of vibrational dynamics in the context of 2D-spectroscopy is well-developed under the assumption of different timescales of population transfer and fluctuation dynamics, the treatment of the interplay between both kinds of processes lacks a comprehensive description. To bridge this gap, we use the cumulant expansion approach to derive response functions, which account for fluctuation dynamics and population transfer simultaneously. We compare 2D-spectra of a model system under different assumptions about correlations between fluctuations and point out under which conditions a simplified treatment is justified. Our study shows that population transfer and dissipative fluctuation dynamics cannot be described independent of each other in general. Advantages and limitations of the proposed calculation method and its compatibility with the modified Redfield description are discussed.

  3. Calculation of electron spectra and some problems in the thermodynamics of graphene layers

    NASA Astrophysics Data System (ADS)

    Alisultanov, Z. Z.

    2016-02-01

    The expressions for the energy spectra of monolayer, bilayer, and multilayer graphene, as well as epitaxial graphene, are derived using the quantum Green's functions method. Analytic expressions are obtained for the densities of states of these systems. It is shown that a bandgap can appear the spectrum of an epitaxial graphene bilayer. A number of problems in the thermodynamics of electrons in free and epitaxial graphene layers are considered as applications. Analytic expressions are obtained for the chemical potential and heat capacity in the limiting cases of low and high temperatures. Quantum oscillations of heat capacity in graphene are analyzed taking into account the Coulomb interaction. The Berry phase of epitaxial graphene is investigated.

  4. Ferromagnetic phases of lunar fines and breccias - Electron magnetic resonance spectra of Apollo 16 samples

    NASA Technical Reports Server (NTRS)

    Weeks, R. A.

    1973-01-01

    Electron magnetic resonance measurements have been made at 9 GHz and at temperatures from 1.2 to 400 K and 35 GHz (300 K) on samples of fines and breccias from Apollo 11-16. Unsorted Apollo 16 fines (less than 1 mm) have Delta H (average) = 580 G and specific intensities that have the same range as fines from the other Apollo collections. The magnetic properties of the 'characteristic' resonance are not in accord with those of iron particles. On the bases of the properties of the 'characteristic' resonance as a function of temperature and Apollo site, laboratory heat treatments on synthetic materials and lunar crystalline rocks and a comparison with the 'characteristic' resonance of the resonance spectra of breccia specimens for which iron particle sizes have been determined from other measurements, it is suggested that some fraction (about 20%) of the 'characteristic' resonance is due to sub-micron particles of ferric oxide phases.

  5. Nightmare from which you will never awake: Electronic to vibrational spectra!

    SciTech Connect

    De Silva, Nuwon

    2013-01-01

    The theoretical background of ab initio methods and density functional theory is provided. The anharmonicity associated with weakly bound metal cation dihydrogen complexes is examined using the vibrational self-consistent field (VSCF) method and the interaction between a hydrogen molecule and a metal cation is characterized. A study of molecular hydrogen clustering around the lithium cation and their accompanied vibrational anharmonicity employing VSCF is illustrated. A qualitative interpretation is provided of solvent-induced shifts of amides and simulated electronic absorption spectra using the combined time-dependent density functional theory/effective fragment potential method (TDDFT/EFP). An excited-state solvent assisted quadruple hydrogen atom transfer reaction of a coumarin derivative is elucidated using micro solvated quantum mechanical (QM) water and macro solvated EFP water. A dispersion correction to the QM-EFP1 interaction energy is presented.

  6. Theoretical analysis of structures and electronic spectra in molecular cadmium chalcogenide clusters

    NASA Astrophysics Data System (ADS)

    Nguyen, Kiet A.; Pachter, Ruth; Day, Paul N.; Su, Haibin

    2015-06-01

    We present calculated structural and optical properties of molecular cadmium chalcogenide nonstoichiometric clusters with a size range of less than 1 nm to more than 2 nm with well-defined chemical compositions and structures in comparison to experimental characterization and previous theoretical work. A unified treatment of these clusters to obtain a fundamental understanding of the size, ligand, and solvation effects on their optical properties has not been heretofore presented. The clusters belong to three topological classes, specifically supertetrahedral (Tn), penta-supertetrahedral (Pn), and capped supertetrahedral (Cn), where n is the number of metal layers in each cluster. The tetrahedrally shaped Tn clusters examined in this work are Cd(ER)42- (T1), Cd4(ER)102- (T2), and Cd 10 E4 ' ( ER ) 16 4 - (T3), where R is an organic group, E and E' are chalcogen atoms (sulfur or selenium). The first member of the Pn series considered is M8E'(ER)162-. For the Cn series, we consider the first three members, M 17 E4 ' ( ER ) 28 2 - , M 32 E14 ' ( ER ) 36 L 4 , and M 54 E32 ' ( ER ) 48 L 4 4 - (L = neutral ligand). Mixed ligand clusters with capping ER groups replaced by halogen or neutral ligands were also considered. Ligands and solvent were found to have a large influence on the color and intensity of the electronic absorption spectra of small clusters. Their effects are generally reduced with increasing cluster sizes. Blueshifts were observed for the first electronic transition with reduced size for both cadmium sulfide and cadmium selenide series. Due to weakly absorbing and forbidden transitions underlying the one-photon spectra, more care is needed in interpreting the quantum confinement from the clusters' lowest-energy absorption bands.

  7. Electronic spectra of oxocomplexes of Re(V) with thiolato ligands

    NASA Astrophysics Data System (ADS)

    Gancheff, Jorge S.; Denis, Pablo A.; Hahn, F. Ekkehardt

    2010-08-01

    The electronic spectra of monooxo complexes of rhenium(V) with 1,2-benzenedithiolato (bdt 2-), 3,4-toluenenedithiolato (tdt 2-), maleonitriledithiolato (mnt 2-), and 1,2-dithiooxalato (dto 2-) ligands were investigated at the TD-DFT level employing several functionals and basis sets. The most important transitions are due to ligand-to-metal charge transfer (LMCT) with some minor contribution of ligand-to-metal-ligand charge transfer (LMLCT). However, for [ReO(dto) 2] - this statement does not hold because the transitions are due to metal-ligand-to-metal-ligand charge transfer (MLMLCT). This observation arises from the presence of the oxalate groups. These substituents increase the flexibility of this complex with respect to the complexes containing bdt 2-, mnt 2- and tdt 2-. In these complexes, the C-C backbone imposes a rigid geometry, which leads to the occupied rhenium-orbitals lying energetically below the sulfur-based orbitals. For the complexes [ReO(bdt) 2] -, [ReO(mnt) 2] - and [ReO(tdt) 2] -, the HOMO is a sulfur-based out-of-plane molecular orbital. However, the HOMO of [ReO(dto) 2] - shows a high contribution of the rhenium dx2- y2 and in-plane sulfur-centered orbitals. The comparison of the results obtained with several functionals clearly point to the PBE1PBE/LANL2DZ method as the best TD-DFT method to investigate the electronic spectra of monooxo complexes of Re(V) with thiolato ligands. The results obtained with larger basis sets suggest that the agreement between experiment and theory was due to an error cancellation between basis set incompleteness and deficiencies in the DFT methods.

  8. Determining the band gap and mean kinetic energy of atoms from reflection electron energy loss spectra

    SciTech Connect

    Vos, M.; Marmitt, G. G.; Finkelstein, Y.; Moreh, R.

    2015-09-14

    Reflection electron energy loss spectra from some insulating materials (CaCO{sub 3}, Li{sub 2}CO{sub 3}, and SiO{sub 2}) taken at relatively high incoming electron energies (5–40 keV) are analyzed. Here, one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected to the mean kinetic energy of the atom in the material (Doppler broadening). The experimentally obtained mean kinetic energies of the O, C, Li, Ca, and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding, we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO{sub 2}, good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E − E{sub gap}){sup 1.5}. For CaCO{sub 3}, the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li{sub 2}CO{sub 3} (7.5 eV) is the first experimental estimate.

  9. Electronic structures, vibrational spectra, and revised assignment of aniline and its radical cation: Theoretical study

    NASA Astrophysics Data System (ADS)

    Wojciechowski, Piotr M.; Zierkiewicz, Wiktor; Michalska, Danuta; Hobza, Pavel

    2003-06-01

    Comprehensive studies of the molecular and electronic structures, vibrational frequencies, and infrared and Raman intensities of the aniline radical cation, C6H5NH2+ have been performed by using the unrestricted density functional (UB3LYP) and second-order Møller-Plesset (UMP2) methods with the extended 6-311++G(df,pd) basis set. For comparison, analogous calculations were carried out for the closed-shell neutral aniline. The studies provided detailed insight into the bonding changes that take place in aniline upon ionization. The natural bond orbital (NBO) analysis has revealed that the pπ-radical conjugative interactions are of prime importance in stabilizing the planar, quinoid-type structure of the aniline radical cation. It is shown that the natural charges calculated for aniline are consistent with the chemical properties of this molecule (an ortho- and para-directing power of the NH2 group in electrophilic substitutions), whereas Mulliken charges are not reliable. The theoretical vibrational frequencies of aniline, calculated by the B3LYP method, show excellent agreement with the available experimental data. In contrast, the MP2 method is deficient in predicting the frequencies of several modes in aniline, despite the use of the extended basis set in calculations. The frequencies of aniline radical cation, calculated at the UB3LYP/6-311++G(df,pd) level, are in very good agreement with the recently reported experimental data from zero kinetic energy photoelectron and infrared depletion spectroscopic studies. The clear- cut assignment of the IR and Raman spectra of the investigated molecules has been made on the basis of the calculated potential energy distributions. Several bands in the spectra have been reassigned. It is shown that ionization of aniline can be easily identified by the appearance of the very strong band at about 1490 cm-1, in the Raman spectrum. The redshift of the N-H stretching frequencies and the blueshift of the C-H stretching

  10. Polarized electronic absorption spectra of Cr2SiO4 single crystals

    NASA Astrophysics Data System (ADS)

    Furche, A.; Langer, K.

    Polarized electronic absorption spectra, E∥a(∥X), E∥b(∥Y) and E∥c(∥Z), in the energy range 3000-5000 cm-1 were obtained for the orthorhombic thenardite-type phase Cr2SiO4, unique in its Cr2+-allocation suggesting some metal-metal bonding in Cr2+Cr2+ pairs with Cr-Cr distance 2.75 Å along [001]. The spectra were scanned at 273 and 120 K on single crystal platelets ∥(100), containing optical Y and Z, and ∥(010), containing optical X and Z, with thicknesses 12.3 and 15.6 μm, respectively. Microscope-spectrometric techniques with a spatial resolution of 20 μm and 1 nm spectral resolution were used. The orientations were obtained by means of X-ray precession photographs. The xenomorphic, strongly pleochroic crystal fragments (X deeply greenish-blue, Y faint blue almost colourless, Z deeply purple almost opaque) were extracted from polycrystalline Cr2SiO4, synthesized at 35 kbar, above 1440 °C from high purity Cr2O3, Cr (10% excess) and SiO2 in chromium capsules. The Cr2SiO4-phase was identified by X-ray diffraction (XRD). Four strongly polarized bands, at about 13500 (I), 15700 (II), 18700 (III) and 19700 (IV) cm-1, in the absorption spectra of Cr2SiO4 single crystals show properties (temperature behaviour of linear and integral absorption coefficients, polarization behaviour, molar absorptivities) which are compatible with an assignment to localized spin-allowed transitions of Cr2+ in a distorted square planar coordination of point symmetry C2. The crystal field parameter of Cr2+ is estimated to be 10 Dq =10700 cm-1. A relatively intense, sharp band at 18400 cm-1 and three other minor features can, from their small half widths, be assigned to spin-forbidden dd-transitions of Cr2+. The intensity of such bands strongly decreases on decreasing temperature. The large half widths, near 5000 cm-1 of band III are indicative of some Cr-Cr interactions, i.e. δ-δ* transitions of Cr24+, whereas the latter alone would be in conflict with the strong

  11. Manifestation of Structure of Electron Bands in Double-Resonant Raman Spectra of Single-Walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Stubrov, Yurii; Nikolenko, Andrii; Gubanov, Viktor; Strelchuk, Viktor

    2016-01-01

    Micro-Raman spectra of single-walled carbon nanotubes in the range of two-phonon 2D bands are investigated in detail. The fine structure of two-phonon 2D bands in the low-temperature Raman spectra of the mixture and individual single-walled carbon nanotubes is considered as the reflection of structure of their π-electron zones. The dispersion behavior of 2D band fine structure components in the resonant Raman spectra of single-walled carbon nanotube mixture is studied depending on the energy of excitating photons. The role of incoming and outgoing electron-phonon resonances in the formation of 2D band fine structure in Raman spectra of single-walled carbon nanotubes is analyzed. The similarity of dispersion behavior of 2D phonon bands in single-walled carbon nanotubes, one-layer graphene, and bulk graphite is discussed.

  12. Manifestation of Structure of Electron Bands in Double-Resonant Raman Spectra of Single-Walled Carbon Nanotubes.

    PubMed

    Stubrov, Yurii; Nikolenko, Andrii; Gubanov, Viktor; Strelchuk, Viktor

    2016-12-01

    Micro-Raman spectra of single-walled carbon nanotubes in the range of two-phonon 2D bands are investigated in detail. The fine structure of two-phonon 2D bands in the low-temperature Raman spectra of the mixture and individual single-walled carbon nanotubes is considered as the reflection of structure of their π-electron zones. The dispersion behavior of 2D band fine structure components in the resonant Raman spectra of single-walled carbon nanotube mixture is studied depending on the energy of excitating photons. The role of incoming and outgoing electron-phonon resonances in the formation of 2D band fine structure in Raman spectra of single-walled carbon nanotubes is analyzed. The similarity of dispersion behavior of 2D phonon bands in single-walled carbon nanotubes, one-layer graphene, and bulk graphite is discussed. PMID:26729220

  13. Electronic structure, bonding, spectra, and linear and nonlinear electric properties of Ti@C28.

    PubMed

    Skwara, Bartłomiej; Góra, Robert W; Zaleśny, Robert; Lipkowski, Paweł; Bartkowiak, Wojciech; Reis, Heribert; Papadopoulos, Manthos G; Luis, Josep M; Kirtman, Bernard

    2011-09-22

    The potential energy surface (PES) of Ti@C(28) has been revisited, and the stationary points have been carefully characterized. In particular, the C(2v) symmetry structure considered previously turns out to be a transition state lying 2.3 kcal/mol above the ground state of C(3v) symmetry at the MP2/6-31G(d) level. A large binding energy of 181.3 kcal/mol is found at the ROMP2/6-31G(d) level. Topological analysis of the generalized Ti@C(28) density reveals four bond paths between Ti and carbon atoms of the host. The character of all four contacts corresponds to a partially covalent closed shell interaction. UV-vis, IR, and Raman spectra are calculated and compared with C(28)H(4). The dipole moment and the static electronic and double harmonic vibrational (hyper)polarizabilities have been obtained. Distortion of the fullerene cage due to encapsulation leads to nonzero diagonal components of the electronic first hyperpolarizability β, and to an increase in the diagonal components of the electronic polarizability α and second hyperpolarizability γ. However, introduction of the Ti atom causes a comparable or larger reduction in most cases due to localized bonding interactions. At the double harmonic level, the average vibrational β is much larger than its electronic counterpart, but the opposite is true for α and for the contribution to γ that has been calculated. There is also a very large anharmonic (nuclear relaxation) contribution to β which results from a shallow PES with four minima separated by very low barriers. Thus, the vibrational γ (and α) may, likewise, become much larger when anharmonicity is taken into account. PMID:21790194

  14. Solar flare ionization in the mesosphere observed by coherent-scatter radar

    NASA Technical Reports Server (NTRS)

    Parker, J. W.; Bowhill, S. A.

    1986-01-01

    The coherent-scatter technique, as used with the Urbana radar, is able to measure relative changes in electron density at one altitude during the progress of a solar flare when that altitude contains a statistically steady turbulent layer. This work describes the analysis of Urbana coherent-scatter data from the times of 13 solar flares in the period from 1978 to 1983. Previous methods of measuring electron density changes in the D-region are summarized. Models of X-ray spectra, photoionization rates, and ion-recombination reaction schemes are reviewed. The coherent-scatter technique is briefly described, and a model is developed which relates changes in scattered power to changes in electron density. An analysis technique is developed using X-ray flux data from geostationary satellites and coherent scatter data from the Urbana radar which empirically distinguishes between proposed D-region ion-chemical schemes, and estimates the nonflare ion-pair production rate.

  15. Understanding flaring solar-type stars seen by Kepler

    NASA Astrophysics Data System (ADS)

    Soderblom, David

    2012-02-01

    The early Kepler data show unambiguous and dramatic evidence of large-scale, massive white-light stellar flares on G and early-K dwarfs. The energies released in these flares are at least 103?104 times that of the largest solar flares ever seen, meaning that they put substantial energy into their circumstellar environments, and much of that energy may be in hard x-rays. At the same time, it is not clear from the Kepler data alone why these particular stars flare because there are many other stars with no evident flares that have similar rotation periods and amplitudes of variation. Are bouts of massive flaring episodic? Do the flaring stars have other properties (activity, v sin i, lithium, inter alia) that distinguish them? Are the flaring stars in close binaries? Keck HIRES spectra can address all these questions and more, and help us to more fully understand this important phenomenon that has critical implications for the formation and evolution of planets and, e! specially, for chemistry and astrobiology in those regions. These stars are also of potential great importance for understanding the flaring behavior of the Sun because white-light flares have not been seen on G stars before, and it is crucial to understand if these flaring stars are unusually young, in close pairs, or if they represent a broader phenomenon that has not yet been appreciated.

  16. Electronic spectra of oxygen containing polycyclic hydrocarbon cations and the protonated analogues.

    PubMed

    Chakraborty, Arghya; Fulara, Jan; Maier, John P

    2015-08-28

    The electronic transitions of 9-fluorenone FL(+) and 2,3,6,7-dibenzotropone DBT(+) cations were detected in 6 K neon matrices following a mass-selective deposition. The absorptions at 649.2 and 472.2 nm are assigned to the 2 (2)B1←X̃(2)A2 FL(+) and 2(2)A(')←X̃(2)A(') DBT(+) transitions. Absorption spectra of protonated 9-fluorenone H(+)-FL and 2,3,6,7-dibenzotropone H(+)-DBT have also been measured. Protonation of the oxygenated polycyclic aromatic hydrocarbons is carried out in a hot cathode source via in situ produced protonated ethanol. Vibrationally resolved absorptions commencing at 423.3 nm of H-FL(+) and two band systems of H-DBT(+) with origins at 502.4 and 371.5 nm are assigned to the 2(1)A(')←X̃(1)A(') electronic transition of 9-hydroxy-fluorenyl cation and 1 (1)A←X̃(1)A, 2 (1)A←X̃(1)A of 2,3,6,7-dibenzocycloheptenol cation. The assignments are based on vertical excitation energy calculations with time dependent density functional theory, symmetry adapted cluster configuration interaction, and MS-CASPT2 methods. PMID:26328848

  17. Electronic spectra and reversible photoisomerization of protonated naphthalenes in solid neon.

    PubMed

    Garkusha, Iryna; Nagy, Adam; Fulara, Jan; Rode, Michal F; Sobolewski, Andrzej L; Maier, John P

    2013-01-17

    Alpha- and beta-protonated naphthalenes (α- and β-HN(+)) were investigated by electronic absorption and fluorescence spectroscopies in 6 K neon matrixes using a mass-selected C(10)H(9)(+) ion beam. The absorption spectra reveal S(1)/S(2) ← S(0) transitions with onsets at 502.1 and 396.1 nm for α-HN(+), and 534.5 and 322.3 nm in the case of β-HN(+). Wavelength-dispersed fluorescence was detected for α-HN(+), starting at 504.4 nm. Light-induced α-HN(+) → β-HN(+) isomerization was observed upon S(2) ← S(0) excitation of α-HN(+), whereas β-HN(+) relaxed back into the more stable alpha form either upon excitation to S(1) or via thermal population of the ground state vibrational levels near the top of the energy barrier between the two isomers. The intramolecular proton transfer leading to the α-HN(+) ↔ β-HN(+) photoisomerization is fully reversible. The observations are explained with the support of theoretical calculations on the ground- and excited states of the isomers, vertical excitation and adiabatic energies, minimum-energy pathways along the relevant reaction coordinates, and conical intersections between the electronic states. PMID:23244534

  18. Structure and electronic spectra of purine-methyl viologen charge transfer complexes.

    PubMed

    Jalilov, Almaz S; Patwardhan, Sameer; Singh, Arunoday; Simeon, Tomekia; Sarjeant, Amy A; Schatz, George C; Lewis, Frederick D

    2014-01-01

    The structure and properties of the electron donor-acceptor complexes formed between methyl viologen and purine nucleosides and nucleotides in water and the solid state have been investigated using a combination of experimental and theoretical methods. Solution studies were performed using UV-vis and (1)H NMR spectroscopy. Theoretical calculations were performed within the framework of density functional theory (DFT). Energy decomposition analysis indicates that dispersion and induction (charge-transfer) interactions dominate the total binding energy, whereas electrostatic interactions are largely repulsive. The appearance of charge transfer bands in the absorption spectra of the complexes are well-described by time-dependent DFT and are further explained in terms of the redox properties of purine monomers and solvation effects. Crystal structures are reported for complexes of methyl viologen with the purines 2'-deoxyguanosine 3'-monophosphate (DAD'DAD' type) and 7-deazaguanosine (DAD'ADAD' type). Comparison of the structures determined in the solid state and by theoretical methods in solution provides valuable insights into the nature of charge-transfer interactions involving purine bases as electron donors. PMID:24294996

  19. Observations and Models of the Dynamical Evolution of Solar Flares

    NASA Astrophysics Data System (ADS)

    Grigis, Paolo C.

    2006-11-01

    Solar flares and associated Coronal Mass Ejections (CMEs) are the biggest explosions in the solar system, converting huge amounts of magnetic energy into kinetic energy of accelerated particles and heat. The key questions at the core of flare physics research are: how is the energy stored in the solar corona before the flare? What triggers the sudden release of that energy? How are the particles accelerated and heated during the flare? Notwithstanding the strong theoretical and observational progress of the last few decades, this questions still remain open. Hard X-ray observations of the Sun, such as provided by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI), are the best tools to probe the population of flare-accelerated particles, because X-rays are the direct signature of energetic electrons. In this thesis, novel RHESSI hard X-ray observations of solar flares are compared with quantitative predictions from modern theoretical models of stochastic acceleration of electrons. The focus lies on the spectral evolution, which has been discovered in the early days of hard X-ray observations, but, with a few exceptions, neglected by theorists. The work presented here starts with RHESSI observations of the spectral evolution of the non-thermal component in the hard X-ray spectrum of solar flares. A representative sample of 24 M class impulsive flares is analyzed. They show rapid changes in the spectral hardness during distinct emission spikes. The maximum hardness is reached at peak time, thus the spectral behavior can be classified as soft-hard-soft. A quantitative relation between the normalization of the power-law component and its spectral index is found, holding for single emission spikes, as well as for the whole dataset comprising all events. The analysis is then expanded, transforming the data from photon space to electron space and comparing the results with predictions from simple available electron acceleration models featuring soft

  20. Electron spectra of xenon clusters irradiated with a laser-driven plasma soft-x-ray laser pulse

    SciTech Connect

    Namba, S.; Takiyama, K.; Hasegawa, N.; Kishimoto, M.; Nishikino, M.; Kawachi, T.

    2011-11-15

    Xenon clusters were irradiated with plasma soft-x-ray laser pulses (having a wavelength of 13.9 nm, time duration of 7 ps, and intensities of up to 10 GW/cm{sup 2}). The laser photon energy was high enough to photoionize 4d core electrons. The cross section is large due to a giant resonance. The interaction was investigated by measuring the electron energy spectra. The photoelectron spectra for small clusters indicate that the spectral width due to the 4d hole significantly broadens with increasing cluster size. For larger clusters, the electron energy spectra evolve into a Maxwell-Boltzmann distribution, as a strongly coupled cluster nanoplasma is generated.

  1. Calculation of electron paramagnetic resonance spectra from Brownian dynamics trajectories: application to nitroxide side chains in proteins.

    PubMed Central

    Steinhoff, H J; Hubbell, W L

    1996-01-01

    We present a method to simulate electron paramagnetic resonance spectra of spin-labeled proteins that explicitly includes the protein structure in the vicinity of the attached spin label. The method is applied to a spin-labeled polyleucine alpha-helix trimer. From short (6 ns) stochastic dynamics simulations of this trimer, an effective potential energy function is calculated. Interaction with secondary and tertiary structures determine the reorientational motion of the spin label side chains. After reduction to a single particle problem, long stochastic dynamic trajectories (700 ns) of the spin label side-chain reorientation are calculated from which the Lamor frequency trajectory and subsequently the electron paramagnetic resonance spectrum is determined. The simulated spectra agree well with experimental electron paramagnetic resonance spectra of bacteriorhodopsin mutants with spin labels in similar secondary and tertiary environments as in the polyleucine. Images FIGURE 1 PMID:8889196

  2. Understanding Solar Flare Statistics

    NASA Astrophysics Data System (ADS)

    Wheatland, M. S.

    2005-12-01

    A review is presented of work aimed at understanding solar flare statistics, with emphasis on the well known flare power-law size distribution. Although avalanche models are perhaps the favoured model to describe flare statistics, their physical basis is unclear, and they are divorced from developing ideas in large-scale reconnection theory. An alternative model, aimed at reconciling large-scale reconnection models with solar flare statistics, is revisited. The solar flare waiting-time distribution has also attracted recent attention. Observed waiting-time distributions are described, together with what they might tell us about the flare phenomenon. Finally, a practical application of flare statistics to flare prediction is described in detail, including the results of a year of automated (web-based) predictions from the method.

  3. Electron densities inferred from plasma wave spectra obtained by the Waves instrument on Van Allen Probes

    PubMed Central

    Kurth, W S; De Pascuale, S; Faden, J B; Kletzing, C A; Hospodarsky, G B; Thaller, S; Wygant, J R

    2015-01-01

    The twin Van Allen Probe spacecraft, launched in August 2012, carry identical scientific payloads. The Electric and Magnetic Field Instrument Suite and Integrated Science suite includes a plasma wave instrument (Waves) that measures three magnetic and three electric components of plasma waves in the frequency range of 10 Hz to 12 kHz using triaxial search coils and the Electric Fields and Waves triaxial electric field sensors. The Waves instrument also measures a single electric field component of waves in the frequency range of 10 to 500 kHz. A primary objective of the higher-frequency measurements is the determination of the electron density ne at the spacecraft, primarily inferred from the upper hybrid resonance frequency fuh. Considerable work has gone into developing a process and tools for identifying and digitizing the upper hybrid resonance frequency in order to infer the electron density as an essential parameter for interpreting not only the plasma wave data from the mission but also as input to various magnetospheric models. Good progress has been made in developing algorithms to identify fuh and create a data set of electron densities. However, it is often difficult to interpret the plasma wave spectra during active times to identify fuh and accurately determine ne. In some cases, there is no clear signature of the upper hybrid band, and the low-frequency cutoff of the continuum radiation is used. We describe the expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum. PMID:26167442

  4. Temperature dependence on the electron paramagnetic resonance spectra of natural jasper from Taroko Gorge (Taiwan)

    NASA Astrophysics Data System (ADS)

    Hemantha Kumar, G. N.; Parthasarathy, G.; Chakradhar, R. P. S.; Rao, J. Lakshmana; Ratnakaram, Y. C.

    2010-04-01

    Structural properties of natural jasper from Taroko Gorge (Taiwan) have been investigated by means of powder X-ray diffraction, electron paramagnetic resonance (EPR) and Fourier transform infrared spectroscopic techniques. The EPR spectrum at room temperature exhibits a sharp resonance signal at g = 2.007 and two more resonance signals centered at g ≈ 4.3 and 14.0. The resonance signal at g = 2.007 has been attributed to the E' center and is related to a natural radiation-induced paramagnetic defect. Two more resonance signals centered at g ≈ 4.3 and 14.0 are characteristic of Fe3+ ions. The EPR spectra recorded at room temperature of jasper samples, heat-treated at temperatures ranging from 473 to 1,473 K exhibit marked temperature dependence. The resonance signal corresponding to E' center disappears at elevated temperatures. A broad, intense resonance signal centered at g ≈ 2.0 appears at elevated temperatures. This resonance signal is a characteristic of Fe3+ ions, which are present as hematite in the jasper sample. The intensity of the resonance signal becomes dominant at elevated temperatures at ≥873 K, masking g ≈ 4.3 and g ≈ 14.0 resonance signals. The EPR spectra of jasper heat-treated at 673 K have been recorded at temperatures between 123 and 296 K. The population of spin levels ( N) has been calculated for the broad g ≈ 2.0 resonance signal. It is found that N decreases with decreasing temperature. The linewidth (ΔH) of g ≈ 2.0 resonance signal of the heat-treated jasper is found to increase with decreasing temperature. This has been attributed to spin-spin interaction of the Fe3+ ions present in the form of hematite in the studied jasper sample.

  5. Diagrammatic expansion for positive density-response spectra: Application to the electron gas

    NASA Astrophysics Data System (ADS)

    Uimonen, A.-M.; Stefanucci, G.; Pavlyukh, Y.; van Leeuwen, R.

    2015-03-01

    In a recent paper [Phys. Rev. B 90, 115134 (2014), 10.1103/PhysRevB.90.115134] we put forward a diagrammatic expansion for the self-energy which guarantees the positivity of the spectral function. In this work we extend the theory to the density-response function. We write the generic diagram for the density-response spectrum as the sum of "partitions." In a partition the original diagram is evaluated using time-ordered Green's functions on the left half of the diagram, antitime-ordered Green's functions on the right half of the diagram, and lesser or greater Green's function gluing the two halves. As there exists more than one way to cut a diagram in two halves, to every diagram corresponds more than one partition. We recognize that the most convenient diagrammatic objects for constructing a theory of positive spectra are the half-diagrams. Diagrammatic approximations obtained by summing the squares of half-diagrams do indeed correspond to a combination of partitions which, by construction, yield a positive spectrum. We develop the theory using bare Green's functions and subsequently extend it to dressed Green's functions. We further prove a connection between the positivity of the spectral function and the analytic properties of the polarizability. The general theory is illustrated with several examples and then applied to solve the long-standing problem of including vertex corrections without altering the positivity of the spectrum. In fact already the first-order vertex diagram, relevant to the study of gradient expansion, Friedel oscillations, etc., leads to spectra which are negative in certain frequency domain. We find that the simplest approximation to cure this deficiency is given by the sum of the zeroth-order bubble diagram, the first-order vertex diagram, and a partition of the second-order ladder diagram. We evaluate this approximation in the three-dimensional homogeneous electron gas and show the positivity of the spectrum for all frequencies and

  6. The Multi-Instrument (EVE-RHESSI) DEM for Solar Flares, and Implications for Non-thermal Emission

    NASA Astrophysics Data System (ADS)

    McTiernan, J. M.; Caspi, A.; Warren, H. P.

    2013-12-01

    Observations of hard X-ray bremmstrahlung from solar flares directly probe the non-thermal electron population. For low energies, however, the spectra are typically dominated by thermal emission and the low energy extent of the non-thermal spectrum can be only loosely quantified. To address this issue, we combine observations from the EUV Variability Experiment (EVE) on-board the Solar Dynamics Observatory (SDO) and X-ray data from the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI). For a sample of solar flares, we model the emission using a Differential Emission Measure (DEM) for the thermal emission seen with both instruments and a power law fit for the non-thermal emission observed by RHESSI. Spectra for both instruments are fit simultaneously in a self-consistent manner. This improvement over the traditional isothermal approximation for thermal flare emission is intended to resolve the ambiguity in the range where the thermal and non-thermal components may have similar photon fluxes. This "crossover" range can extend up to 30 keV for medium to large solar flares. It is expected that a low energy cutoff of the non-thermal electron spectrum is in this energy range, but is obscured by thermal emission. For each flare in the sample we establish limits for the low energy cutoff of the non-thermal spectrum. These limits, in turn, can be used to establish limits on the energy of non-thermal electrons accelerated during the flare. This research is supported by NASA contract NAS5-98033 and NASA Heliophysics Guest Investigator Grant NNX12AH48G.

  7. Solar Flare Impulsive Phase Observations from SDO and Other Observatories

    NASA Technical Reports Server (NTRS)

    Chamberlin, Phillip C.; Woods, Thomas N.; Schrijver, Karel; Warren, Harry; Milligan, Ryan; Christe, Steven; Brosius, Jeffrey W.

    2010-01-01

    With the start of normal operations of the Solar Dynamics Observatory in May 2010, the Extreme ultraviolet Variability Experiment (EVE) and the Atmospheric Imaging Assembly (AIA) have been returning the most accurate solar XUV and EUV measurements every 10 and 12 seconds, respectively, at almost 100% duty cycle. The focus of the presentation will be the solar flare impulsive phase observations provided by EVE and AIA and what these observations can tell us about the evolution of the initial phase of solar flares. Also emphasized throughout is how simultaneous observations with other instruments, such as RHESSI, SOHO-CDS, and HINODE-EIS, will help provide a more complete characterization of the solar flares and the evolution and energetics during the impulsive phase. These co-temporal observations from the other solar instruments can provide information such as extending the high temperature range spectra and images beyond that provided by the EUV and XUV wavelengths, provide electron density input into the lower atmosphere at the footpoints, and provide plasma flows of chromospheric evaporation, among other characteristics.

  8. Ion Acceleration in Solar Flares

    NASA Technical Reports Server (NTRS)

    Miller, James A.; Weir, Sue B.

    1996-01-01

    Solar flares are among the most energetic and interesting phenomena in the Solar system, releasing up to 1032 ergs of energy on timescales of several tens of seconds to several tens of minutes. Much of this energy is in the form of suprathermal electrons and ions, which remain trapped at the Sun and produce a wide variety of radiations, as well as escape into interplanetary space, where they can be directly observed. The radiation from trapped particles consists in general of (1) continuum emission; (2) narrow gamma-ray nuclear deexcitation lines; and (3) high-energy neutrons observed in space or by ground-based neutron monitors. The particles that escape into space consist of both electrons and ions, which often have compositions quite different than that of the ambient solar atmosphere. Flares thus present many diagnostics of the particle acceleration mechanism(s), the identification of which is the ultimate goal of flare research. Moreover, flares in fact offer the only opportunity in astrophysics to study the simultaneous energization of both electrons and ions. Hopefully, an understanding of flares with their wealth of diagnostic data will lead to a better understanding of particle acceleration at other sites in the Universe. It is now generally accepted that flares are roughly divided into two classes: impulsive and gradual. Gradual events are large, occur high in the corona, have long-duration soft and hard X-rays and gamma rays, are electron poor, are associated with Type II radio emission and coronal mass ejections (CMEs), and produce energetic ions with coronal abundance ratios. Impulsive events are more compact, occur lower in the corona, produce short-duration radiation, and exhibit dramatic abundance enhancements in the energetic ions. Their He-3/He-4 ratio is - 1, which is a huge increase over the coronal value of about 5 x 10(exp -4), and they also posses smaller but still significant enhancements of Ne, Mg, Si, and Fe relative to He-4, C, N, and O

  9. Vibronic Coupling Explains the Different Shape of Electronic Circular Dichroism and of Circularly Polarized Luminescence Spectra of Hexahelicenes.

    PubMed

    Liu, Yanli; Cerezo, Javier; Mazzeo, Giuseppe; Lin, Na; Zhao, Xian; Longhi, Giovanna; Abbate, Sergio; Santoro, Fabrizio

    2016-06-14

    We present the simulation of the absorption (ABS), electronic circular dichroism (ECD), emission (EMI), and circularly polarized luminescence (CPL) spectra for the weak electronic transition between the ground (S0) and the lowest excited state (S1) of hexahelicene, 2-methylhexahelicene, 2-bromohexahelicene, and 5-azahexahelicene. Vibronic contributions have been computed at zero Kelvin and at room temperature in harmonic approximation including Duschinsky effects and accounting for both Franck-Condon and Herzberg-Teller contributions. Our results nicely capture the effects of the different substituents on the experimental spectra. They also show that HT effects dominate the shape of ECD and CPL spectra where they even induce changes of signs; HT effects are also relevant in ABS and EMI, tuning the relative intensities of the different vibronic bands. HT effects are the main reason for the differences in the line shapes of ABS and ECD and of EMI and CPL spectra and for the mirror-symmetry breaking between ABS and EMI and between ECD and CPL spectra. In order to check the robustness of our results, given also that few examples of calculations of vibronic CPL spectra exist, we adopted both adiabatic and vertical approaches to define the model potential energy surfaces of the (S0) and the (S1) states; moreover we expanded the electric and magnetic dipole transition moments around both the S0 and S1 equilibrium geometries. PMID:27120334

  10. Predicting the Response of the Mars Ionosphere to Solar Flares

    NASA Astrophysics Data System (ADS)

    Fallows, K.; Withers, P.; Gonzalez, G.

    2015-12-01

    The increased soft X-ray irradiance during solar flares generates increased electron densities in the lower ionosphere of Mars. The relative changes in electron density during a flare are greater for larger flares and also at lower altitudes and larger flares, due to the wavelength dependence of both the flux increase during the flare and the absorption of flux by the neutral atmosphere. These relationships have been explored [Bougher et al. 2001, Fox et al. 2004, Mendillo et al. 2006, Mahajan et al. 2011, Lollo et al. 2012] but not quantified, which has impeded the validation of simulations of the ionospheric effects of solar flares. Such simulations are necessary for developing accurate descriptions of the physical processes governing ionospheric behavior under extreme conditions. We present a response function, a mathematical expression for the change in electron density during a solar flare as a function of the change in solar flux and an optical depth proxy. This response function is based on analysis of 20 Mars Global Surveyor (MGS) radio occultation electron density profiles measured during solar flares. Characterizing the response as a function of optical depth, rather than altitude, provides the best description of ionospheric variability during a flare; otherwise non-negligible solar zenith angle effects are present. We demonstrate that the response function can be used to predict ionospheric electron densities during a specified solar flare by reproducing profiles known to be disturbed by a solar flare. We also demonstrate that the response function can be used to infer the strength of solar flares not visible at Earth by finding the flux enhancement required to reproduce an apparently flare affected profile given an undisturbed profile on the same date.

  11. Simulation studies for operating electron beam ion trap at very low energy for disentangling edge plasma spectra

    SciTech Connect

    Jin Xuelong; Fei Zejie; Xiao Jun; Lu Di; Hutton, Roger; Zou Yaming

    2012-07-15

    Electron beam ion traps (EBITs) are very useful tools for disentanglement studies of atomic processes in plasmas. In order to assist studies on edge plasma spectroscopic diagnostics, a very low energy EBIT, SH-PermEBIT, has been set up at the Shanghai EBIT lab. In this work, simulation studies for factors which hinder an EBIT to operate at very low electron energies were made based on the Tricomp (Field Precision) codes. Longitudinal, transversal, and total kinetic energy distributions were analyzed for all the electron trajectories. Influences from the electron current and electron energy on the energy depression caused by the space charge are discussed. The simulation results show that although the energy depression is most serious along the center of the electron beam, the electrons in the outer part of the beam are more likely to be lost when an EBIT is running at very low energy. Using the simulation results to guide us, we successfully managed to reach the minimum electron beam energy of 60 eV with a beam transmission above 57% for the SH-PermEBIT. Ar and W spectra were measured from the SH-PermEBIT at the apparent electron beam energies (read from the voltage difference between the electron gun cathode and the central drift tube) of 60 eV and 1200 eV, respectively. The spectra are shown in this paper.

  12. Simulation studies for operating electron beam ion trap at very low energy for disentangling edge plasma spectra

    NASA Astrophysics Data System (ADS)

    Jin, Xuelong; Fei, Zejie; Xiao, Jun; Lu, Di; Hutton, Roger; Zou, Yaming

    2012-07-01

    Electron beam ion traps (EBITs) are very useful tools for disentanglement studies of atomic processes in plasmas. In order to assist studies on edge plasma spectroscopic diagnostics, a very low energy EBIT, SH-PermEBIT, has been set up at the Shanghai EBIT lab. In this work, simulation studies for factors which hinder an EBIT to operate at very low electron energies were made based on the Tricomp (Field Precision) codes. Longitudinal, transversal, and total kinetic energy distributions were analyzed for all the electron trajectories. Influences from the electron current and electron energy on the energy depression caused by the space charge are discussed. The simulation results show that although the energy depression is most serious along the center of the electron beam, the electrons in the outer part of the beam are more likely to be lost when an EBIT is running at very low energy. Using the simulation results to guide us, we successfully managed to reach the minimum electron beam energy of 60 eV with a beam transmission above 57% for the SH-PermEBIT. Ar and W spectra were measured from the SH-PermEBIT at the apparent electron beam energies (read from the voltage difference between the electron gun cathode and the central drift tube) of 60 eV and 1200 eV, respectively. The spectra are shown in this paper.

  13. Analysis of Electron and Antineutrino Energy Spectra from Fissile Samples under Irradiation based on Gross Theory of Beta-decay

    NASA Astrophysics Data System (ADS)

    Yoshida, T.; Tachibana, T.; Chiba, S.

    2016-06-01

    We applied the gross theory of β-decay to calculate the reactor electron and antineutrino ({{{bar ν }}{e}}) spectra emitted from 235,238U and 239,241Pu by summing up all the contributions from a large number of decaying fission-products (FPs). We make it clear what kinds of transition types and FP nuclides are important to shape the lepton spectra. After taking the ambiguity in the current data for fission yields and Qβ-values into account, we suggested a possibility that the high-energy part of the widely referred electron-spectra by Schreckenbach et al., almost only one experimental data set available now, might possibly be too low. Arguments on a special role of the odd(Z)-odd(N) nuclides and on the consistency between U-238 and other fissiles in the experimental data lead to the importance of a new and independent measurement of electron energy spectra which could be converted into the reactor {{{bar ν }}{e}} spectra.

  14. KINETIC ALFVEN TURBULENCE AND PARALLEL ELECTRIC FIELDS IN FLARE LOOPS

    SciTech Connect

    Zhao, J. S.; Wu, D. J.; Lu, J. Y.

    2013-04-20

    This study investigates the spectral structure of the kinetic Alfven turbulence in the low-beta plasmas. We consider a strong turbulence resulting from collisions between counterpropagating wavepackets with equal energy. Our results show that (1) the spectra of the magnetic and electric field fluctuations display a transition at the electron inertial length scale, (2) the turbulence cascades mainly toward the magnetic field direction as the cascade scale is smaller than the electron inertial length, and (3) the parallel electric field increases as the turbulent scale decreases. We also show that the parallel electric field in the solar flare loops can be 10{sup 2}-10{sup 4} times the Dreicer field as the turbulence reaches the electron inertial length scale.

  15. Accelerating the calculation of time-resolved electronic spectra with the cellular dephasing representation

    NASA Astrophysics Data System (ADS)

    Šulc, Miroslav; Vaníček, Jiří

    2012-05-01

    Dephasing representation of fidelity, also known as the phase averaging method, can be considered as a special case of Miller's linearized semiclassical initial value representation and belongs among the most efficient approximate semiclassical approaches for the calculation of ultrafast time-resolved electronic spectra. Recently it has been shown that the number of trajectories required for convergence of this method is independent of the system's dimensionality. Here we propose a further accelerated version of the dephasing representation in the spirit of Heller's cellular dynamics. The basic idea of the 'cellular dephasing representation' is to decompose the Wigner transform of the initial state into a phase space Gaussian basis and then evaluate the contribution of each Gaussian to the relevant correlation function approximately analytically, using numerically acquired information only along the trajectory of the Gaussian's centre. The approximate nature of the DR classifies it among semiclassical perturbation approximations proposed by Miller and Smith, and suggests its limited accuracy. Yet, the proposed method turns out to be sufficiently accurate whenever the interaction with the environment diminishes the importance of recurrences in the correlation functions of interest. Numerical tests on a collinear NCO molecule indicate that even results based on a single classical trajectory are in a remarkable agreement with the fully converged DR requiring approximately 104 trajectories.

  16. Vibrational and electronic spectra of 2-nitrobenzanthrone: An experimental and computational study

    NASA Astrophysics Data System (ADS)

    Onchoke, Kefa K.; Chaudhry, Saad N.; Ojeda, Jorge J.

    2016-01-01

    The environmental pollutant 2-nitrobenzanthrone (2-NBA) poses human health hazards, and is formed by atmospheric reactions of NOX gases with atmospheric particulates. Though its mutagenic effects have been studied in biological systems, its comprehensive spectroscopic experimental data are scarce. Thus, vibrational and optical spectroscopic analysis (UV-Vis, and fluorescence) of 2-NBA was studied using both experimental and density functional theory employing B3LYP method with 6-311 + G(d,p) basis set. The scaled theoretical vibrational frequencies show good agreement to experiment to within ~ 5 cm- 1 and < 20 cm- 1 for frequencies < 1800 cm- 1 and 2700-3200 cm- 1, respectively. In addition, predictions of the DFT frequencies below 1800 cm- 1 yield an overall root mean square (RMS) of ± 20.1 and ± 20.6 cm- 1 for benzanthrone and 2-NBA, respectively. On the basis of normal coordinate analysis complete assignments of harmonic experimental infrared and Raman bands are made. The influence of the nitro group substitution upon the benzanthrone structure and symmetric CH vibrations, and electronic spectra is noted. This study is useful for the development of spectroscopy-mutagenicity relationships in nitrated polycyclic aromatic hydrocarbons.

  17. Electron-Vibrational Coupling and Fluorescence Spectra of Tetra-, Penta-, and Hexacoordinated Chlorophylls c1 and c2.

    PubMed

    Etinski, Mihajlo; Petković, Milena; Ristić, Miroslav M; Marian, Christel M

    2015-08-13

    Chlorophylls (Chls) are a group of pigments related to light absorption, excitation energy, and electron transfer in photosynthetic complexes. Given the importance of intramolecular nuclear motion for these electronic processes, many experimental studies were performed in order to relate its coupling to electronic coordinates of these pigments, but a detailed analysis is still lacking for isolated Chls c1 and c2. To gain insight into the intramolecular motion and fluoroscence spectra of these two pigments in tetra-, penta-, and hexacoodinated states, we performed a quantum chemical study based on density functional theory and multimode harmonic approximation with displaced, distorted, and rotated normal modes. In order to benchmark the employed methods, we simulated the high-resolution fluorescence spectra of tetracoodinated Chls a, b, and d and compared them with available experimental spectra obtained with fluorescence line-narrowing techniques. Although the experimental spectra were obtained for ligand coordinated Chls, qualitatively good agreement was found between the simulated and experimental spectra. Almost all resonances were reproduced in the spectroscopically interesting region from 200 to 1700 cm(-1). The significance of mode distortion and rotation for the simulated spectra is discussed. The fluorescence spectra of Chls c1 and c2 consist of a group of peaks in the 200-450 cm(-1) spectral range, a group of weak peaks from 700 to 1000 cm(-1), and a large group of strong peaks from 1100 to 1600 cm(-1). Ligand effects are also addressed, and a mode is identified as a sensitive probe for the coordination state of Chls c1 and c2. PMID:26189597

  18. The Moving Lines on Electron Spectra as Charge Reflexes on Non-equilibrium States of Nanostructured Surfaces.

    PubMed

    Mishchuk, Oleg A

    2016-12-01

    The experimental results present the phenomenon of moving lines on electron spectra which are linked spatially and in time with the localization and durability of the processes of new surface producing in folds and grain boundaries. This effect was also realized for a thin-layer composite "organic on metal films on dielectric substrate" in modeling non-equilibrium conditions which are created by the intensive electron beam pulse impact. It was found that the nature of the inceptive adsorption layer, in addition to the metal film, determines the initial positions of moving lines on the spectra. The main accents in these investigations were in observations of appearance of the moving lines, dynamics of their displacements on the spectra, final stages when these lines vanished, and finding the general regularities between the spontaneous and induced events. PMID:27083583

  19. The Moving Lines on Electron Spectra as Charge Reflexes on Non-equilibrium States of Nanostructured Surfaces

    NASA Astrophysics Data System (ADS)

    Mishchuk, Oleg A.

    2016-04-01

    The experimental results present the phenomenon of moving lines on electron spectra which are linked spatially and in time with the localization and durability of the processes of new surface producing in folds and grain boundaries. This effect was also realized for a thin-layer composite "organic on metal films on dielectric substrate" in modeling non-equilibrium conditions which are created by the intensive electron beam pulse impact. It was found that the nature of the inceptive adsorption layer, in addition to the metal film, determines the initial positions of moving lines on the spectra. The main accents in these investigations were in observations of appearance of the moving lines, dynamics of their displacements on the spectra, final stages when these lines vanished, and finding the general regularities between the spontaneous and induced events.

  20. Biggest Solar Flare on Record

    NASA Technical Reports Server (NTRS)

    2002-01-01

    View an animation from the Extreme ultraviolet Imaging Telescope (EIT). At 4:51 p.m. EDT, on Monday, April 2, 2001, the sun unleashed the biggest solar flare ever recorded, as observed by the Solar and Heliospheric Observatory (SOHO) satellite. The flare was definitely more powerful than the famous solar flare on March 6, 1989, which was related to the disruption of power grids in Canada. This recent explosion from the active region near the sun's northwest limb hurled a coronal mass ejection into space at a whopping speed of roughly 7.2 million kilometers per hour. Luckily, the flare was not aimed directly towards Earth. Solar flares, among the solar system's mightiest eruptions, are tremendous explosions in the atmosphere of the Sun capable of releasing as much energy as a billion megatons of TNT. Caused by the sudden release of magnetic energy, in just a few seconds flares can accelerate solar particles to very high velocities, almost to the speed of light, and heat solar material to tens of millions of degrees. Solar ejections are often associated with flares and sometimes occur shortly after the flare explosion. Coronal mass ejections are clouds of electrified, magnetic gas weighing billions of tons ejected from the Sun and hurled into space with speeds ranging from 12 to 1,250 miles per second. Depending on the orientation of the magnetic fields carried by the ejection cloud, Earth-directed coronal mass ejections cause magnetic storms by interacting with the Earth's magnetic field, distorting its shape, and accelerating electrically charged particles (electrons and atomic nuclei) trapped within. Severe solar weather is often heralded by dramatic auroral displays, northern and southern lights, and magnetic storms that occasionally affect satellites, radio communications and power systems. The flare and solar ejection has also generated a storm of high-velocity particles, and the number of particles with ten million electron-volts of energy in the space near

  1. Electronic and oscillation absorption spectra of blood plamsa at surgical diseases of thyroid gland

    NASA Astrophysics Data System (ADS)

    Guminetskiy, S. G.; Motrich, A. V.; Poliansky, I. Y.; Hyrla, Ya. V.

    2012-01-01

    The results of investigating the absorption spectra of blood plasma in the visible and infrared parts of spectra obtained using the techniques of spherical photometer and spectrophotometric complex "Specord IR75" are presented. The possibility of using these spectra for diagnoses the cases of diffuse toxic goiter and nodular goiter and control of treatment process in postsurgical period in the cases of thyroid gland surgery is estimated.

  2. Electronic and oscillation absorption spectra of blood plamsa at surgical diseases of thyroid gland

    NASA Astrophysics Data System (ADS)

    Guminetskiy, S. G.; Motrich, A. V.; Poliansky, I. Y.; Hyrla, Ya. V.

    2011-09-01

    The results of investigating the absorption spectra of blood plasma in the visible and infrared parts of spectra obtained using the techniques of spherical photometer and spectrophotometric complex "Specord IR75" are presented. The possibility of using these spectra for diagnoses the cases of diffuse toxic goiter and nodular goiter and control of treatment process in postsurgical period in the cases of thyroid gland surgery is estimated.

  3. The flare kernel in the impulsive phase

    NASA Technical Reports Server (NTRS)

    Dejager, C.

    1986-01-01

    The impulsive phase of a flare is characterized by impulsive bursts of X-ray and microwave radiation, related to impulsive footpoint heating up to 50 or 60 MK, by upward gas velocities (150 to 400 km/sec) and by a gradual increase of the flare's thermal energy content. These phenomena, as well as non-thermal effects, are all related to the impulsive energy injection into the flare. The available observations are also quantitatively consistent with a model in which energy is injected into the flare by beams of energetic electrons, causing ablation of chromospheric gas, followed by convective rise of gas. Thus, a hole is burned into the chromosphere; at the end of impulsive phase of an average flare the lower part of that hole is situated about 1800 km above the photosphere. H alpha and other optical and UV line emission is radiated by a thin layer (approx. 20 km) at the bottom of the flare kernel. The upward rising and outward streaming gas cools down by conduction in about 45 s. The non-thermal effects in the initial phase are due to curtailing of the energy distribution function by escape of energetic electrons. The single flux tube model of a flare does not fit with these observations; instead we propose the spaghetti-bundle model. Microwave and gamma-ray observations suggest the occurrence of dense flare knots of approx. 800 km diameter, and of high temperature. Future observations should concentrate on locating the microwave/gamma-ray sources, and on determining the kernel's fine structure and the related multi-loop structure of the flaring area.

  4. Rotational modulation and flares on RS CVn and BY Dra-type stars. V - EXOSAT and IUE observations of a flare on EQ Pegasi

    NASA Astrophysics Data System (ADS)

    Haisch, B. M.; Butler, C. J.; Doyle, J. G.; Rodono, M.

    1987-07-01

    Time-trailed UV spectra and a soft X-ray lightcurve were obtained during a flare on the binary dMe star EQ Peg AB. On the basis of solar flare Mg II surface fluxes and an about 70-percent enhancement in the disk-integrated flux during the flare on EQ Peg, it is estimated that the chromospheric flare covered about 1.5 percent of the stellar surface. The size scale is estimated to be comparable to that of a solar two-ribbon flare. This unusual flare is noted to exhibit a low-energy soft X-ray rise phase which is longer than that of most flares; it is longer than the decay phase and peaks much later than the medium energy light curve. Evidence of variable Fe II emission and variable continuum emission in select UV bands during the flare is noted.

  5. Rotational modulation and flares on RS CVn and BY Dra-type stars. V - Exosat and IUE observations of a flare on EQ Pegasi

    NASA Technical Reports Server (NTRS)

    Haisch, B. M.; Butler, C. J.; Doyle, J. G.; Rodono, M.

    1987-01-01

    Time-trailed UV spectra and a soft X-ray lightcurve were obtained during a flare on the binary dMe star EQ Peg AB. On the basis of solar flare Mg II surface fluxes and an about 70-percent enhancement in the disk-integrated flux during the flare on EQ Peg, it is estimated that the chromospheric flare covered about 1.5 percent of the stellar surface. The size scale is estimated to be comparable to that of a solar two-ribbon flare. This unusual flare is noted to exhibit a low-energy soft X-ray rise phase which is longer than that of most flares; it is longer than the decay phase and peaks much later than the medium energy light curve. Evidence of variable Fe II emission and variable continuum emission in select UV bands during the flare is noted.

  6. Pulsed acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Aschwanden, Markus J.; Benz, Arnold O.; Dennis, Brian R.; Kundu, Mukul R.

    1994-01-01

    We study the nonlinear dynamics of particle acceleration in solar flares by analyzing the time series of various quasi-periodic radio signatures during flares. In particular we present the radio and hard X-ray data of three flares which suppport the following tentative conclusions: (1) Particle acceleration and injection into magnetic structures occurs intrinsically in a pulsed mode (with a typical period of 1-2 s), produced by a single, spatially coherent, nonlinear system, rather than by a stochastic system with many spatially independent components ('statistical flare' produced by a fragmented primary energy release). (2) The nonlinear (quasi-periodic) mode of pulsed particle acceleration and injection into a coronal loop can be stabilized by phase locking with an MHD wave (oscillation) mode, if both periods are close to each other. (3) Pulsed injection of electron beams into a coronal loop may trigger nonlinear relaxational oscillations of wave-particle interactions. This is particularly likely when the limit cycles of both systems are similar.

  7. Nonsequential Double Ionization of Atoms in Strong Laser Field: Identifying the Mechanisms behind the Correlated-Electron Momentum Spectra

    NASA Astrophysics Data System (ADS)

    Ye, Difa; Fu, Libin; Liu, Jie

    Within the strong-field physics community, there has been increasing interest on nonsequential double ionization (NSDI) induced by electron-electron (e-e) correlation. A large variety of novel phenomena has been revealed in experiments during the past decades. However, the theoretical understanding and interpretation of this process is still far from being complete. The most accurate simulation, i.e. the exact solution of the time-dependent Schrödinger equation (TDSE) for two electrons in a laser field is computationally expensive. In order to overcome the difficulty, we proposed a feasible semiclassical model, in which we treat the tunneling ionization of the outmost electron quantum mechanically according to the ADK theory, sample the inner electron from microcanonical distribution and then evolve the two electrons with Newton's equations. With this model, we have successfully explained various NSDI phenomena, including the excessive DI yield, the energy spectra and angular distribution of photoelectrons. Very recently, it is adopted to reveal the physical mechanisms behind the fingerlike structure in the correlated electron momentum spectra, the unexpected correlation-anticorrelation transition close to the recollision threshold, and the anomalous NSDI of alkaline-earth-metal atoms in circularly polarized field. The obvious advantage of our model is that it gives time-resolved insights into the complex dynamics of NSDI, from the turn-on of the laser field to the final escape of the electrons, thus allowing us to disentangle and thoroughly analyze the underlying physical mechanisms.

  8. Theoretical polarization-dependent X-ray spectra of Be-like Fe calculated for different electron beam densities

    NASA Astrophysics Data System (ADS)

    Shlyaptseva, Alla; Mancini, Roberto

    1998-05-01

    We study theoretically the polarization properties of X-ray spectra of Be-like Fe ions excited through resonant capture by an electron beam with different electron densities. Our previous work in this area was related to the study of polarization of dielectronic satellite lines of Fe ions excited by a low-density electron beam. (A.S. Shlyaptseva, R.C. Mancini, P. Neill, P. Beiersdorfer, J.R. Crespo López-Urrutia, and K. Widmann, Phys. Rev. A, 57), 888 (1998) Here we extend our work to the case of higher-density electron beams. As the density of the electron beam increases, new channels of electron capture appear. Thus the atomic and polarization characteristics of the satellite lines change. Moreover, additional X-ray satellite lines will appear. Using the density matrix formalism, we calculate the polarization characteristics and polarization-dependent spectra of dielectronic satellite lines of Be-like Fe produced at different energies and densities of the electron beam. We compare the results of the present work with our previous ones for low-density electron beams. These results are relevant to the identification of X-ray polarization-dependent spectral features and for X-ray line polarization spectroscopy.

  9. Modeling of electron energy spectra and mobilities in semi-metallic Hg1-xCdxTe quantum wells

    NASA Astrophysics Data System (ADS)

    Melezhik, E. O.; Gumenjuk-Sichevska, J. V.; Sizov, F. F.

    2015-11-01

    Electron mobility, energy spectra, and intrinsic carrier concentrations in the n-type Hg0.32Cd0.68Te/Hg1-xCdxTe/Hg0.32Cd0.68Te quantum well (QW) in semi-metallic state are numerically modeled. Energy spectra and wave functions were calculated in the framework of the 8-band k-p Hamiltonian. In our model, electron scattering on longitudinal optical phonons, charged impurities, and holes has been taken into account, and the mobility has been calculated by an iterative solution of the Boltzmann transport equation. Our results show that the increase of the electron concentration in the well enhances the screening of the 2D electron gas, decreases the hole concentration, and can ultimately lead to a high electron mobility at liquid nitrogen temperatures. The increase of the electron concentration in the QW could be achieved in situ by delta-doping of barriers or by applying the top-gate potential. Our modeling has shown that for low molar composition x the concentration of holes in the well is high in a wide range of electron concentrations; in this case, the purity of samples does not significantly influence the electron mobility. These results are important in the context of establishing optimal parameters for the fabrication of high-mobility Hg1-xCdxTe quantum wells able to operate at liquid nitrogen temperature and thus suitable for applications in terahertz detectors.

  10. Chromospheric Acoustic Oscillations in Active Flaring Regions

    NASA Astrophysics Data System (ADS)

    Monsue, T.; Hill, F.; Stassun, K.

    2014-12-01

    Chromospheric p-mode oscillations are studied in Hα to obtain helioseismic information regarding the local structural conditions around highly magnetic regions such as sunspots. Solar flares commonly occur in active regions where these sunspots exist therefore boosting the p-mode power. In our current study of analyzing p-modes in the chromosphere we study the time evolution of acoustic p-mode oscillation data taken from the Global Oscillation Network Group (GONG) Hα, and investigate the p-modes across the frequency band (1 < ν < 8.33 mHz). This study entails three active regions directly over sunspots, with accompanying flaring activity from two solar flares, occurring on June 13th and July 12th, 2012. Our analysis utilizes time series data to create Fourier power spectra of individual pixels spatially resolved around the flare region, to study the frequency bands. We then study how the frequency distribution evolves temporally by constructing a Power Map Movie (PMM) of the regions. From these PMMs we can take a survey of the chromospheric oscillations for each frequency band. We found that the intensity of the flare has an effect on the behavior of the p-modes within different frequency bands. The suppression of power was observed in dark anomalous structures within the PMMs and in other regions there was an observed boost in power due to flaring activity.

  11. Electronic spectra of Fe3+ oxides and oxide hydroxides in the near IR to near UV.

    USGS Publications Warehouse

    Sherman, David M.; Waite, T.D.

    1985-01-01

    Optical absorption and diffuse reflectance spectra of several Fe2O3 and FeOOH polymorphs (hematite, maghemite, goethite, lepidocrocite) in the near-IR to near-UV spectral regions (2000-200 nm) are presented. The spectra consist primarily of Fe3+ ligand field and ligand-to-metal charge-transfer transitions.-J.A.Z.

  12. THE EFFECTS OF ELECTRON-BEAM-INDUCED ELECTRIC FIELD ON THE GENERATION OF LANGMUIR TURBULENCE IN FLARING ATMOSPHERES

    SciTech Connect

    Zharkova, Valentina V.; Siversky, Taras V. E-mail: taras.siversky@gmail.com

    2011-05-20

    The precipitation of an electron beam injected into the solar atmosphere is studied for the generation of Langmuir wave turbulence in the presence of collisional and Ohmic losses. The system of quasi-linear time-dependent kinetic equations describing the evolution of beams and Langmuir waves is solved by using the summary approximation method. It is found that at upper atmospheric levels the self-induced electric field suppresses the generation of Langmuir turbulence to very small regions below injection. With further precipitation into deeper atmosphere the initial single power-law distributions of beam electrons are transformed into energy distributions with maxima at lower energies formed by collisional and Ohmic energy depletion. The electrons with lower energies (<20 keV) generate on large spatial scales intense low-hybrid and high-hybrid Langmuir waves with well-defined patterns in the corona while higher energy electrons generate moderate low-hybrid waves in the chromosphere. The maximum wave density appears at the maximum of the ambient density. The self-induced electric field reduces the level and makes the regions with low-hybrid Langmuir turbulence narrower in the corona and upper chromosphere. The higher the beam energy flux or its self-induced electric field, the narrower the regions with Langmuir turbulence. High-hybrid Langmuir waves in the form of multiple patterns in space (in the corona) and energy (below 20 keV) are found to be generated only by a very intense electron beam. The number of patterns in both dimensions is also shown to be significantly reduced by the self-induced electric field.

  13. Non-equilibrium ionization by a periodic electron beam. I. Synthetic coronal spectra and implications for interpretation of observations

    NASA Astrophysics Data System (ADS)

    Dzifčáková, E.; Dudík, J.; Mackovjak, Š.

    2016-05-01

    Context. Coronal heating is currently thought to proceed via the mechanism of nanoflares, small-scale and possibly recurring heating events that release magnetic energy. Aims: We investigate the effects of a periodic high-energy electron beam on the synthetic spectra of coronal Fe ions. Methods: Initially, the coronal plasma is assumed to be Maxwellian with a temperature of 1 MK. The high-energy beam, described by a κ-distribution, is then switched on every period P for the duration of P/ 2. The periods are on the order of several tens of seconds, similar to exposure times or cadences of space-borne spectrometers. Ionization, recombination, and excitation rates for the respective distributions are used to calculate the resulting non-equilibrium ionization state of Fe and the instantaneous and period-averaged synthetic spectra. Results: Under the presence of the periodic electron beam, the plasma is out of ionization equilibrium at all times. The resulting spectra averaged over one period are almost always multithermal if interpreted in terms of ionization equilibrium for either a Maxwellian or a κ-distribution. Exceptions occur, however; the EM-loci curves appear to have a nearly isothermal crossing-point for some values of κs. The instantaneous spectra show fast changes in intensities of some lines, especially those formed outside of the peak of the respective EM(T) distributions if the ionization equilibrium is assumed. Movies 1-5 are available in electronic form at http://www.aanda.org

  14. Non-equilibrium ionization by a periodic electron beam. I. Synthetic coronal spectra and implications for interpretation of observations

    NASA Astrophysics Data System (ADS)

    Dzifčáková, E.; Dudík, J.; Mackovjak, Š.

    2016-04-01

    Context. Coronal heating is currently thought to proceed via the mechanism of nanoflares, small-scale and possibly recurring heating events that release magnetic energy. Aims: We investigate the effects of a periodic high-energy electron beam on the synthetic spectra of coronal Fe ions. Methods: Initially, the coronal plasma is assumed to be Maxwellian with a temperature of 1 MK. The high-energy beam, described by a κ-distribution, is then switched on every period P for the duration of P/ 2. The periods are on the order of several tens of seconds, similar to exposure times or cadences of space-borne spectrometers. Ionization, recombination, and excitation rates for the respective distributions are used to calculate the resulting non-equilibrium ionization state of Fe and the instantaneous and period-averaged synthetic spectra. Results: Under the presence of the periodic electron beam, the plasma is out of ionization equilibrium at all times. The resulting spectra averaged over one period are almost always multithermal if interpreted in terms of ionization equilibrium for either a Maxwellian or a κ-distribution. Exceptions occur, however; the EM-loci curves appear to have a nearly isothermal crossing-point for some values of κs. The instantaneous spectra show fast changes in intensities of some lines, especially those formed outside of the peak of the respective EM(T) distributions if the ionization equilibrium is assumed. Movies 1-5 are available in electronic form at http://www.aanda.org

  15. Independent-electron analysis of the x-ray spectra from single-electron capture in Ne10 + collisions with He, Ne, and Ar atoms

    NASA Astrophysics Data System (ADS)

    Leung, Anthony C. K.; Kirchner, Tom

    2015-09-01

    We present a theoretical study on the x-ray spectra from single-electron capture in 4.54 keV/amu Ne10 +-He, -Ne, and -Ar collisions. Single-particle capture probabilities were calculated using the two-center basis generator method within the independent electron model. In this framework we investigated the effects of a time-dependent screening potential that models target response on capture cross sections and x-ray spectra. Excellent agreement is shown with the previously measured relative cross sections and x-ray spectra and calculations based on the classical trajectory Monte Carlo method using the no-response single-particle electron capture probabilities in a multinomial single-electron capture analysis. Our results demonstrate the importance of using this consistent statistical analysis of single-electron capture within the independent electron model; a requirement that a previous calculation for the same collision problem using the two-center atomic-orbital close-coupling method may not have considered.

  16. DFT analysis on the molecular structure, vibrational and electronic spectra of 2-(cyclohexylamino)ethanesulfonic acid.

    PubMed

    Renuga Devi, T S; Sharmi kumar, J; Ramkumaar, G R

    2015-02-25

    The FTIR and FT-Raman spectra of 2-(cyclohexylamino)ethanesulfonic acid were recorded in the regions 4000-400 cm(-1) and 4000-50 cm(-1) respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using Hartee-Fock and Density functional method (B3LYP) with the correlation consistent-polarized valence double zeta (cc-pVDZ) basis set and 6-311++G(d,p) basis set. The most stable conformer was optimized and the structural and vibrational parameters were determined based on this. The complete assignments were performed based on the Potential Energy Distribution (PED) of the vibrational modes, calculated using Vibrational Energy Distribution Analysis (VEDA) 4 program. With the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. Thermodynamic properties and Atomic charges were calculated using both Hartee-Fock and density functional method using the cc-pVDZ basis set and compared. The calculated HOMO-LUMO energy gap revealed that charge transfer occurs within the molecule. (1)H and (13)C NMR chemical shifts of the molecule were calculated using Gauge Including Atomic Orbital (GIAO) method and were compared with experimental results. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using Natural Bond Orbital (NBO) analysis. The first order hyperpolarizability (β) and Molecular Electrostatic Potential (MEP) of the molecule was computed using DFT calculations. The electron density based local reactivity descriptor such as Fukui functions were calculated to explain the chemical reactivity site in the molecule. PMID:25262144

  17. DFT analysis on the molecular structure, vibrational and electronic spectra of 2-(cyclohexylamino)ethanesulfonic acid

    NASA Astrophysics Data System (ADS)

    Renuga Devi, T. S.; Sharmi kumar, J.; Ramkumaar, G. R.

    2015-02-01

    The FTIR and FT-Raman spectra of 2-(cyclohexylamino)ethanesulfonic acid were recorded in the regions 4000-400 cm-1 and 4000-50 cm-1 respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using Hartee-Fock and Density functional method (B3LYP) with the correlation consistent-polarized valence double zeta (cc-pVDZ) basis set and 6-311++G(d,p) basis set. The most stable conformer was optimized and the structural and vibrational parameters were determined based on this. The complete assignments were performed based on the Potential Energy Distribution (PED) of the vibrational modes, calculated using Vibrational Energy Distribution Analysis (VEDA) 4 program. With the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. Thermodynamic properties and Atomic charges were calculated using both Hartee-Fock and density functional method using the cc-pVDZ basis set and compared. The calculated HOMO-LUMO energy gap revealed that charge transfer occurs within the molecule. 1H and 13C NMR chemical shifts of the molecule were calculated using Gauge Including Atomic Orbital (GIAO) method and were compared with experimental results. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using Natural Bond Orbital (NBO) analysis. The first order hyperpolarizability (β) and Molecular Electrostatic Potential (MEP) of the molecule was computed using DFT calculations. The electron density based local reactivity descriptor such as Fukui functions were calculated to explain the chemical reactivity site in the molecule.

  18. First-principles calculation of electronic spectra of light-harvesting complex II.

    PubMed

    König, Carolin; Neugebauer, Johannes

    2011-06-14

    We report on a fully quantum chemical investigation of important structural and environmental effects on the site energies of chlorophyll pigments in green-plant light-harvesting complex II (LHC II). Among the tested factors are technical and structural aspects as well as effects of neighboring residues and exciton couplings in the chlorophyll network. By employing a subsystem time-dependent density functional theory (TDDFT) approach based on the frozen density embedding (FDE) method we are able to determine site energies and electronic couplings separately in a systematic way. This approach allows us to treat much larger systems in a quantum chemical way than would be feasible with a conventional density functional theory. Based on this method, we have simulated a series of mutagenesis experiments to investigate the effect of a lack of one pigment in the chlorophyll network on the excitation properties of the other pigments. From these calculations, we can conclude that conformational changes within the chlorophyll molecules, direct interactions with neighboring residues, and interactions with other chlorophyll pigments can lead to non-negligible changes in excitation energies. All of these factors are important when site energies shall be calculated with high accuracy. Moreover, the redistribution of the oscillator strengths due to exciton coupling has a large impact on the calculated absorption spectra. This indicates that modeling mutagenesis experiments requires us to consider the entire set of chlorophyll molecules in the wild type and in the mutant, rather than just considering the missing chlorophyll pigment. An analysis of the mixing of particular excitations and the coupling elements in the FDEc calculation indicates that some pigments in the chlorophyll network act as bridges which mediate the interaction between other pigments. These bridges are also supported by the calculations on the "mutants" lacking the bridging pigment. PMID:21369568

  19. Towards Predicting Solar Flares

    NASA Astrophysics Data System (ADS)

    Winter, Lisa; Balasubramaniam, Karatholuvu S.

    2015-04-01

    We present a statistical study of solar X-ray flares observed using GOES X-ray observations of the ~50,000 fares that occurred from 1986 - mid-2014. Observed X-ray parameters are computed for each of the flares, including the 24-hour non-flare X-ray background in the 1-8 A band and the maximum ratio of the short (0.5 - 4 A) to long band (1-8 A) during flares. These parameters, which are linked to the amount of active coronal heating and maximum flare temperature, reveal a separation between the X-, M-, C-, and B- class fares. The separation was quantified and verified through machine-learning algorithms (k nearest neighbor; nearest centroid). Using the solar flare parameters learned from solar cycles 22-23, we apply the models to predict flare categories of solar cycle 24. Skill scores are then used to assess the success of our models, yielding correct predictions for ~80% of M-, C-, and B-class flares and 100% correct predictions for X-flares. We present details of the analysis along with the potential uses of our model in flare forecasting.

  20. On the outer limit for the expansion of magnetic bottles ejected by solar proton flares

    NASA Technical Reports Server (NTRS)

    Sakurai, K.

    1973-01-01

    Pioneer 6 observations of proton flare ejected magnetic bottles are reported. The SSC geomagnetic storms, electron density distribution near the sun, and Faraday rotation induced by the flares are included. Magnetic bottle speed is discussed.

  1. High-energy particle production in solar flares (SEP, gamma-ray and neutron emissions). [solar energetic particles

    NASA Technical Reports Server (NTRS)

    Chupp, E. L.

    1987-01-01

    Electrons and ions, over a wide range of energies, are produced in association with solar flares. Solar energetic particles (SEPs), observed in space and near earth, consist of electrons and ions that range in energy from 10 keV to about 100 MeV and from 1 MeV to 20 GeV, respectively. SEPs are directly recorded by charged particle detectors, while X-ray, gamma-ray, and neutron detectors indicate the properties of the accelerated particles (electrons and ions) which have interacted in the solar atmosphere. A major problem of solar physics is to understand the relationship between these two groups of charged particles; in particular whether they are accelerated by the same mechanism. The paper reviews the physics of gamma-rays and neutron production in the solar atmosphere and the method by which properties of the primary charged particles produced in the solar flare can be deduced. Recent observations of energetic photons and neutrons in space and at the earth are used to present a current picture of the properties of impulsively flare accelerated electrons and ions. Some important properties discussed are time scale of production, composition, energy spectra, accelerator geometry. Particular attention is given to energetic particle production in the large flare on June 3, 1982.

  2. M DWARFS IN SLOAN DIGITAL SKY SURVEY STRIPE 82: PHOTOMETRIC LIGHT CURVES AND FLARE RATE ANALYSIS

    SciTech Connect

    Kowalski, Adam F.; Hawley, Suzanne L.; Hilton, Eric J.; Becker, Andrew C.; Sesar, Branimir; West, Andrew A.; Bochanski, John J.

    2009-08-15

    We present a flare rate analysis of 50,130 M dwarf light curves in Sloan Digital Sky Survey Stripe 82. We identified 271 flares using a customized variability index to search {approx}2.5 million photometric observations for flux increases in the u and g bands. Every image of a flaring observation was examined by eye and with a point-spread function-matching and image subtraction tool to guard against false positives. Flaring is found to be strongly correlated with the appearance of H{alpha} in emission in the quiet spectrum. Of the 99 flare stars that have spectra, we classify eight as relatively inactive. The flaring fraction is found to increase strongly in stars with redder colors during quiescence, which can be attributed to the increasing flare visibility and increasing active fraction for redder stars. The flaring fraction is strongly correlated with |Z| distance such that most stars that flare are within 300 pc of the Galactic plane. We derive flare u-band luminosities and find that the most luminous flares occur on the earlier-type m dwarfs. Our best estimate of the lower limit on the flaring rate (averaged over Stripe 82) for flares with {delta}u {>=} 0.7 mag on stars with u < 22 is 1.3 flares hr{sup -1} deg{sup -2} but can vary significantly with the line of sight.

  3. M Dwarfs in Sloan Digital Sky Survey Stripe 82: Photometric Light Curves and Flare Rate Analysis

    NASA Astrophysics Data System (ADS)

    Kowalski, Adam F.; Hawley, Suzanne L.; Hilton, Eric J.; Becker, Andrew C.; West, Andrew A.; Bochanski, John J.; Sesar, Branimir

    2009-08-01

    We present a flare rate analysis of 50,130 M dwarf light curves in Sloan Digital Sky Survey Stripe 82. We identified 271 flares using a customized variability index to search ~2.5 million photometric observations for flux increases in the u and g bands. Every image of a flaring observation was examined by eye and with a point-spread function-matching and image subtraction tool to guard against false positives. Flaring is found to be strongly correlated with the appearance of Hα in emission in the quiet spectrum. Of the 99 flare stars that have spectra, we classify eight as relatively inactive. The flaring fraction is found to increase strongly in stars with redder colors during quiescence, which can be attributed to the increasing flare visibility and increasing active fraction for redder stars. The flaring fraction is strongly correlated with |Z| distance such that most stars that flare are within 300 pc of the Galactic plane. We derive flare u-band luminosities and find that the most luminous flares occur on the earlier-type m dwarfs. Our best estimate of the lower limit on the flaring rate (averaged over Stripe 82) for flares with Δu >= 0.7 mag on stars with u < 22 is 1.3 flares hr-1 deg-2 but can vary significantly with the line of sight. Based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium.

  4. VERITAS Observations of Day-scale Flaring of M 87 in 2010 April

    NASA Technical Reports Server (NTRS)

    Perkins, J. S>

    2012-01-01

    VERITAS has been monitoring the very-high-energy (VHE; > 100 GeV) gamma-ray activity of the radio galaxy M 87 since 2007. During 2008, flaring activity on a timescale of a few days was observed with a peak flux of (0.70 +/- 0.16) x 10(exp -11)/sq cm/s at energies above 350 GeV. In 2010 April, VERITAS detected a flare from M 87 with peak flux of (2.71 +/- 0.68) x 10(exp -11)/sq cm/s for E > 350 GeV. The source was observed for six consecutive nights during the flare, resulting in a total of21 hr of good-quality data. The most rapid flux variation occurred on the trailing edge of the flare with an exponential flux decay time of 0,90 +0.22/-0.15 days, The shortest detected exponential rise time is three times as long, at 2.87 +1.65/-0.99 days. The quality of the data sample is such that spectral analysis can he performed for three periods: rising flux, peak flux, and falling flux. The spectra obtained are consistent with power-law forms. The spectral index at the peak of the flare is equal to 2.19 +/- 0.07, There is some indication that the spectrum is softer in the falling phase of the flare than the peak phase, with a confidence level corresponding to 3.6 standard deviations. We discuss the implications of these results for the acceleration and cooling rates of VHE electrons in M 87 and the constraints they provide on the physical size of the emitting region.

  5. Solar flares and energetic particles.

    PubMed

    Vilmer, Nicole

    2012-07-13

    Solar flares are now observed at all wavelengths from γ-rays to decametre radio waves. They are commonly associated with efficient production of energetic particles at all energies. These particles play a major role in the active Sun because they contain a large amount of the energy released during flares. Energetic electrons and ions interact with the solar atmosphere and produce high-energy X-rays and γ-rays. Energetic particles can also escape to the corona and interplanetary medium, produce radio emissions (electrons) and may eventually reach the Earth's orbit. I shall review here the available information on energetic particles provided by X-ray/γ-ray observations, with particular emphasis on the results obtained recently by the mission Reuven Ramaty High-Energy Solar Spectroscopic Imager. I shall also illustrate how radio observations contribute to our understanding of the electron acceleration sites and to our knowledge on the origin and propagation of energetic particles in the interplanetary medium. I shall finally briefly review some recent progress in the theories of particle acceleration in solar flares and comment on the still challenging issue of connecting particle acceleration processes to the topology of the complex magnetic structures present in the corona. PMID:22665901

  6. Improving the simulation of vibrationally resolved electronic spectra of phenanthrene: A computational Investigation

    NASA Astrophysics Data System (ADS)

    Pang, Min; Yang, Pan; Shen, Wei; Li, Ming; He, Rongxing

    2015-05-01

    Based on the density functional theory and its time-dependent extension, the properties of the ground and the first excited states of phenanthrene were calculated. In harmonic and anharmonic approximations, the well-resolved absorption and emission spectra of phenanthrene were simulated using the Franck-Condon approximation combined with the Herzberg-Teller and Duschinsky effects, and the results reproduced the experimental spectra very well. The mirror symmetry breakdown between absorption and emission spectra is induced mainly from the Herzberg-Teller effect and Duschinsky mode mixing. Moreover, most of the vibrational modes were tentatively assigned and compared with the experiment.

  7. Influence of optical thickness and hot electrons on Rydberg spectra of Ne-like and F-like copper ions.

    PubMed

    Fournier, K B; Faenov, A Ya; Pikuz, T A; Skobelev, I Yu; Belyaev, V S; Vinogradov, V I; Kyrilov, A S; Matafonov, A P; Bellucci, I; Martellucci, S; Petrocelli, G; Auguste, T; Hulin, S; Monot, P; D'Oliveira, P

    2003-01-01

    Spectra in the 7.10 to 8.60 A range from highly charged copper ions are observed from three different laser-produced plasmas (LPPs). The LPPs are formed by a 15-ns Nd:glass laser pulse (type I: E(pulse)=1-8 J, lambda=1.064 microm), a 1-ps Nd:glass laser pulse (type II: E(pulse)=1 J, lambda=1.055 microm), and a 60-fs Ti:sapphire laser pulse (type III: E(pulse)=800 mJ, lambda=790 nm). The spectra of high-n (nspectra to opacity effects and to populations of superthermal electrons is studied. For the type I LPPs, opacity effects, treated with escape factors, are necessary to get the correct relative intensities of high-n (n=5, 6) Ne-like Cu19+ emission features. In the case of the type II LPPs, the contrast between the laser prepulse and the main pulse has been varied from low, I(main)/I(pp)=7 x 10(4), to high, I(main)/I(pp)=3.8 x 10(7). For plasmas from low contrast shots, we find good agreement between the observed spectra and optically thin simulations with bulk electron temperatures T(bulk)=0.4 keV and a small population of superthermal electrons (T(hot)=5.0 keV) that is f(hot)electron population. For high-contrast type II LPPs, we find higher densities and a combination of f(hot) approximately 10(-5) and escape factors best describes the data. For the type III 60-fs LPPs, a population of superthermal electrons (T(hot) approximately 5 keV) that is approximately 5 x 10(-5) of the bulk electron population (T(bulk) approximately 0.2 keV) is required to reproduce the observed spectra. The effect of both escape factors and hot electrons in the CR models is to increase the ionization balance and dramatically increase the number of strong lines

  8. Compton backscattered and primary X-rays from solar flares: angle dependent Green's function correction for photospheric albedo

    NASA Astrophysics Data System (ADS)

    Kontar, E. P.; MacKinnon, A. L.; Schwartz, R. A.; Brown, J. C.

    2006-02-01

    The observed hard X-ray (HXR) flux spectrum I(ɛ) from solar flares is a combination of primary bremsstrahlung photons I_P(ɛ) with a spectrally modified component from photospheric Compton backscatter of downward primary emission. The latter can be significant, distorting or hiding the true features of the primary spectrum which are key diagnostics for acceleration and propagation of high energy electrons and of their energy budget. For the first time in solar physics, we use a Green's function approach to the backscatter spectral deconvolution problem, constructing a Green's matrix including photoelectric absorption. This approach allows spectrum-independent extraction of the primary spectrum for several HXR flares observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). We show that the observed and primary spectra differ very substantially for flares with hard spectra close to the disk centre. We show in particular that the energy dependent photon spectral index γ (ɛ)=-d log I/d log ɛ is very different for I_P(ɛ) and for I(ɛ) and that inferred mean source electron spectra F(E) differ greatly. Even for a forward fitting of a parametric F(E) to the data, a clear low-energy cutoff required to fit I(ɛ) essentially disappears when the fit is to I_P(ɛ) - i.e. when albedo correction is included. The self-consistent correction for backscattered photons is thus shown to be crucial in determining the energy spectra of flare accelerated electrons, and hence their total number and energy.

  9. Two-photon photoemission spectra related to an ultrafast heterogeneous electron transfer from perylene to TiO2

    NASA Astrophysics Data System (ADS)

    Tsivlin, Dmitry V.; Willig, Frank; May, Volkhard

    2008-01-01

    Two-photon photoemission (2PPE) spectra related to sub- 100-fs heterogeneous electron transfer from perylene to TiO2 are calculated. The approach accounts for the dominant intramolecular vibration of perylene as well as for the band structure of TiO2 described in a tight-binding model. The focus is on the influence of the pump and probe laser pulse duration, with the pump laser originating charge injection and the probe laser causing the photoemission process. The latter may proceed directly from the photoexcited molecule or, after charge injection, from the TiO2 conduction band. The time-dependent Schrödinger equation which describes charge injection and accounts for the pump pulse is solved exactly within a time interval of about 250fs . The action of the probe pulse is considered in linear response theory. While the vibrational structure in the 2PPE spectra broadens with decreasing pump pulse length, it is found that this structure is largely preserved when varying the probe pulse duration. In order to estimate dephasing caused by intramolecular vibrational energy redistribution in perylene and electron phonon coupling in TiO2 , a density matrix scheme is also introduced describing heterogeneous electron transfer and the photoelectron emission processes. A finite escape depth for electrons at the TiO2 surface is finally taken into account to evaluate its influence on the spectra.

  10. Recent research directions in Fribourg: nuclear dynamics in resonances revealed by 2-dimensional EEL spectra, electron collisions with ionic liquids and electronic excitation of pyrimidine

    NASA Astrophysics Data System (ADS)

    Allan, Michael; Regeta, Khrystyna; Gorfinkiel, Jimena D.; Mašín, Zdeněk; Grimme, Stefan; Bannwarth, Christoph

    2016-05-01

    The article briefly reviews three subjects recently investigated in Fribourg: (i) electron collisions with surfaces of ionic liquids, (ii) two-dimensional (2D) electron energy loss spectra and (iii) resonances in absolute cross sections for electronic excitation of unsaturated compounds. Electron energy loss spectra of four ionic liquids revealed a number of excited states, including triplet states. A solution of a dye in an ionic liquid showed an energy-loss band of the solute, but not in all ionic liquids. 2D spectra reveal state-to-state information (given resonance to given final state) and are shown to be an interesting means to gain insight into dynamics of nuclear motion in resonances. Absolute cross sections for pyrimidine are reported as a function of scattering angle and as a function of electron energy. They reveal resonant structure which was reproduced very nicely by R-matrix calculations. The calculation provided an assignment of the resonances which reveals common patterns in compounds containing double bonds.

  11. Solar Flares: Magnetohydrodynamic Processes

    NASA Astrophysics Data System (ADS)

    Shibata, Kazunari; Magara, Tetsuya

    2011-12-01

    This paper outlines the current understanding of solar flares, mainly focused on magnetohydrodynamic (MHD) processes responsible for producing a flare. Observations show that flares are one of the most explosive phenomena in the atmosphere of the Sun, releasing a huge amount of energy up to about 10^32 erg on the timescale of hours. Flares involve the heating of plasma, mass ejection, and particle acceleration that generates high-energy particles. The key physical processes for producing a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), local enhancement of electric current in the corona (formation of a current sheet), and rapid dissipation of electric current (magnetic reconnection) that causes shock heating, mass ejection, and particle acceleration. The evolution toward the onset of a flare is rather quasi-static when free energy is accumulated in the form of coronal electric current (field-aligned current, more precisely), while the dissipation of coronal current proceeds rapidly, producing various dynamic events that affect lower atmospheres such as the chromosphere and photosphere. Flares manifest such rapid dissipation of coronal current, and their theoretical modeling has been developed in accordance with observations, in which numerical simulations proved to be a strong tool reproducing the time-dependent, nonlinear evolution of a flare. We review the models proposed to explain the physical mechanism of flares, giving an comprehensive explanation of the key processes mentioned above. We start with basic properties of flares, then go into the details of energy build-up, release and transport in flares where magnetic reconnection works as the central engine to produce a flare.

  12. Emergency flare tip repair

    SciTech Connect

    Harrison, G.A.

    1982-07-01

    Two damaged propane storage tank flares serving a large LPG storage facility near the Arabian Gulf were given emergency service. A diagram of over-all layout and spatial relationships between tanks and piping, and tables with general information relevant to selecting an acceptable radiant heat load factor and flare line flow characteristics were presented. The general equation for predicting radiant heat flux from a point source was used. The ignition of the temporary flare was discussed.

  13. The Impact of Hot Electrons on X-ray Spectra: e-e Bremsstrahlung and κ Distributions

    NASA Astrophysics Data System (ADS)

    Smith, Randall K.; Cui, Xiaohong; Foster, Adam; Yuasa, Takayuki

    2016-06-01

    Shocks, turbulence, and winds all influence the electron velocity distribution in hot plasmas, exciting lower-energy electrons and generating a high-energy (typically power-law) tail. Sufficiently energetic electrons will emit via an electron-electron (e-e) bremsstrahlung, a process not previously included in the AtomDB. We have added this process and calculate the impact e-e bremsstrahlung has on the spectra from the post-shock regions of an accreting magnetic cataclysmic variable (CV). We find the contribution of e-e bremsstrahlung to the total spectra exceeds 10% at ~100 keV, with the total emissivity in the post-shock accretion stream differing by more than 10% at energies above 60 keV. More generally a Maxwellian with a power law tail, typically termed a κ distribution, can have significant effects on the line and continuum X-rays emitted. In addition to the e-e bremsstrahlung term, there will be effects due to the impact of the electrons on the charge state distribution and the collisional excitation rates. We use the ``Maxwellian decomposition'' approach as described in Hahn & Savin (2015) to generate the rate coefficients for a κ distributions based on the recently-released AtomDB v3.0 atomic database. These values are compared to exact calculations done for selected recombination and bremsstrahlung rates, and are also compared to results from the CHIANTI KAPPA package.

  14. Multiple spectra of electron spin resonance in chiral molecule-based magnets networked by a single chiral ligand

    NASA Astrophysics Data System (ADS)

    Mito, M.; Nagano, T.; Tsuruta, K.; Deguchi, H.; Takagi, S.; Kishine, J.; Yoshida, Y.; Inoue, K.

    2013-10-01

    A molecule-based magnet [Cr(CN)6][Mn(R/S)-pnH(H2O)](H2O) (termed R/S-GN) is a chiral crystal without an inversion center and mirror reflection, and its structural network is constructed using a chiral ligand diaminopropane (R/S)-pn. In S-GN, multiple spectra of ESR were observed below the magnetic ordering temperature by Morgunov et al. [Phys. Rev. B 77, 184419 (2008)]. They concluded that the phenomenon at the high field side occurred because the incommensurate magnetic structure resulted in a length-controllable superlattice of domain walls (the so-called chiral soliton lattice, CSL) under a dc magnetic field H applied perpendicular to the magnetic chiral axis. However, there multiple spectra were observed even for H nearly parallel to the chiral axis, a-axis, and their interpretation is unreasonable. Thus, we conducted an X-band electron spin resonance (ESR) measurement of R-GN under conditions similar to those of their experiment and performed Fourier spectrum analyses for the data of R-GN as an approach of physical characterization. By using two Lorentz spectra, the main ESR spectra for H // a were reproduced, and furthermore two prominent periodic modes were found by spectrum analyses based on Fourier transform. Two characteristic periods, p1 and p2 (spectra observed below the magnetic ordering temperature are due not to hyperfine structure but magnetic fine structure, and it certainly originates from the existence of plural nonequivalent magnetic sites. Thus, it is unreasonable to consider CSL to explain the multiple ESR spectra observed independently of the field direction, whereas the observed complex spectra appeal wealthy scientific potentiality in chiral crystals.

  15. Solar flares. [plasma physics

    NASA Technical Reports Server (NTRS)

    Rust, D. M.

    1979-01-01

    The present paper deals with explosions in a magnetized solar plasma, known as flares, whose effects are seen throughout the electromagnetic spectrum, from gamma-rays through the visible and to the radio band. The diverse phenomena associated with flares are discussed, along with the physical mechanisms that have been advanced to explain them. The impact of solar flare research on the development of plasma physics and magnetohydrodynamics is noted. The rapid development of solar flare research during the past 20 years, owing to the availability of high-resolution images, detailed magnetic field measurements, and improved spectral data, is illustrated.

  16. Particle acceleration in flares

    NASA Technical Reports Server (NTRS)

    Benz, Arnold O.; Kosugi, Takeo; Aschwanden, Markus J.; Benka, Steve G.; Chupp, Edward L.; Enome, Shinzo; Garcia, Howard; Holman, Gordon D.; Kurt, Victoria G.; Sakao, Taro

    1994-01-01

    Particle acceleration is intrinsic to the primary energy release in the impulsive phase of solar flares, and we cannot understand flares without understanding acceleration. New observations in soft and hard X-rays, gamma-rays and coherent radio emissions are presented, suggesting flare fragmentation in time and space. X-ray and radio measurements exhibit at least five different time scales in flares. In addition, some new observations of delayed acceleration signatures are also presented. The theory of acceleration by parallel electric fields is used to model the spectral shape and evolution of hard X-rays. The possibility of the appearance of double layers is further investigated.

  17. Flared tube attachment fitting

    NASA Technical Reports Server (NTRS)

    Alkire, I. D.; King, J. P., Jr.

    1980-01-01

    Tubes can be flared first, then attached to valves and other flow line components, with new fitting that can be disassembled and reused. Installed fitting can be disassembled so parts can be inspected. It can be salvaged and reused without damaging flared tube; tube can be coated, tempered, or otherwise treated after it has been flared, rather than before, as was previously required. Fitting consists of threaded male portion with conical seating surface, hexagonal nut with hole larger than other diameter of flared end of tube, and split ferrule.

  18. iSpectra: An Open Source Toolbox For The Analysis of Spectral Images Recorded on Scanning Electron Microscopes.

    PubMed

    Liebske, Christian

    2015-08-01

    iSpectra is an open source and system-independent toolbox for the analysis of spectral images (SIs) recorded on energy-dispersive spectroscopy (EDS) systems attached to scanning electron microscopes (SEMs). The aim of iSpectra is to assign pixels with similar spectral content to phases, accompanied by cumulative phase spectra with superior counting statistics for quantification. Pixel-to-phase assignment starts with a threshold-based pre-sorting of spectra to create groups of pixels with identical elemental budgets, similar to a method described by van Hoek (2014). Subsequent merging of groups and re-assignments of pixels using elemental or principle component histogram plots enables the user to generate chemically and texturally plausible phase maps. A variety of standard image processing algorithms can be applied to groups of pixels to optimize pixel-to-phase assignments, such as morphology operations to account for overlapping excitation volumes over pixels located at phase boundaries. iSpectra supports batch processing and allows pixel-to-phase assignments to be applied to an unlimited amount of SIs, thus enabling phase mapping of large area samples like petrographic thin sections. PMID:26165853

  19. pH-Induced changes in electronic absorption and fluorescence spectra of phenazine derivatives

    NASA Astrophysics Data System (ADS)

    Ryazanova, O. A.; Voloshin, I. M.; Makitruk, V. L.; Zozulya, V. N.; Karachevtsev, V. A.

    2007-04-01

    The visible electronic absorption and fluorescence spectra as well as fluorescence polarization degrees of imidazo-[4,5-d]-phenazine (F1), 2-methylimidazo-[4,5-d]-phenazine (F2), 2-trifluoridemethylimidazo-[4,5-d]-phenazine (F3), 1,2,3-triazole-[4,5-d]-phenazine (F4) and their glycosides, imidazo-[4,5-d]-phenazine-N1-β- D-ribofuranoside (F1rib), 1,2,3-triazole-[4,5-d]-phenazine-N1-β- D-glucopyranoside (F4gl), were investigated in aqueous buffered solutions over the pH range of 0-12, where the spectral transformations were found to be reversible. The effects of protonation and deprotonation on spectral properties of these dyes were studied. We have determined the ranges of pH, where individual ionic species are predominant. In aqueous buffered solutions the fluorescence was found only for neutral species of F1, F1rib, F2, and F4gl dyes, whereas for the ionic forms of these dyes, as well as for F3 and F4 ones, the fluorescence has not been detected. The concentrational deprotonation p Ka values were evaluated from experimental data. It was shown that donor-acceptor properties of the substituent group in the second position of the pentagonal ring substantially affect the values of the deprotonation constants and the character of protonation for chromophore. The substitution of a hydrogen atom in the NH-group by the sugar residue blocks the formation of the anionic species, and results in enhancement of the dye emission intensity. The steep emission dependence for F1 and F1rib over pH range of 0-7 with intensities ratio of IpH 7/ IpH 1 = 60 allows us to propose them as possible indicator dyes in luminescence based pH sensors for investigation of processes accompanied by acidification, e.g. as gastric pH-sensors. A comparative analysis of the studied dyes has shown that F4gl is the most promising compound to be used as a fluorescent probe for investigation of molecular hybridization of nucleic acids.

  20. Quantum Chemical Study of the Reaction of C+ with Interstellar Ice: Predictions of Vibrational and Electronic Spectra of Reaction Products

    NASA Astrophysics Data System (ADS)

    Woon, David E.

    2015-06-01

    The C+ cation (CII) is the dominant form of carbon in diffuse clouds and an important tracer for star formation in molecular clouds. We studied the low energy deposition of C+ on ice using density functional theory calculations on water clusters as large as 18 H2O. Barrierless reactions occur with water to form two dominant sets of products: HOC + H3O+ and CO- + 2H3O+. In order to provide testable predictions, we have computed both vibrational and electronic spectra for pure ice and processed ice clusters. While vibrational spectroscopy is expected to be able to discern that C+ has reacted with ice by the addition of H3O+ features not present in pure ice, it does not provided characteristic bands that would discern between HOC and CO-. On the other hand, predictions of electronic spectra suggest that low energy absorptions may occur for CO- and not HOC, making it possible to distinguish one product from the other.

  1. Theoretical study of the electronic spectra of neutral and cationic NpO and NpO2

    NASA Astrophysics Data System (ADS)

    Kovács, Attila; Infante, Ivan

    2015-08-01

    The electronic spectra of neutral NpO and NpO2 as well as of their mono- (NpO+, NpO2+) and dications (NpO2+, NpO22+) were studied using multiconfigurational relativistic quantum chemical calculations at the complete active space self-consistent field/CASPT2 level of theory taking into account spin-orbit coupling. The active space included 16 orbitals: all the 7s, 6d, and 5f orbitals of neptunium together with selected orbitals of oxygen. The vertical excitation energies on the ground state geometries have been computed up to ca. 35 000 cm-1. The gas-phase electronic spectra were evaluated on the basis of the computed Einstein coefficients at 298 K and 3000 K. The computed vertical transition energies show good agreement with previous condensed-phase results on NpO2+ and NpO22+.

  2. Theoretical study of the electronic spectra of neutral and cationic NpO and NpO2.

    PubMed

    Kovács, Attila; Infante, Ivan

    2015-08-21

    The electronic spectra of neutral NpO and NpO2 as well as of their mono- (NpO(+), NpO2(+)) and dications (NpO(2+), NpO2(2+)) were studied using multiconfigurational relativistic quantum chemical calculations at the complete active space self-consistent field/CASPT2 level of theory taking into account spin-orbit coupling. The active space included 16 orbitals: all the 7s, 6d, and 5f orbitals of neptunium together with selected orbitals of oxygen. The vertical excitation energies on the ground state geometries have been computed up to ca. 35,000 cm(-1). The gas-phase electronic spectra were evaluated on the basis of the computed Einstein coefficients at 298 K and 3000 K. The computed vertical transition energies show good agreement with previous condensed-phase results on NpO2(+) and NpO2(2+). PMID:26298132

  3. Research Investigation Directed Toward Extending the Useful Range of the Electromagnetic Spectrum. [atomic spectra and electronic structure of alkali metals

    NASA Technical Reports Server (NTRS)

    Hartmann, S. R.; Happer, W.

    1974-01-01

    The report discusses completed and proposed research in atomic and molecular physics conducted at the Columbia Radiation Laboratory from July 1972 to June 1973. Central topics described include the atomic spectra and electronic structure of alkali metals and helium, molecular microwave spectroscopy, the resonance physics of photon echoes in some solid state systems (including Raman echoes, superradiance, and two photon absorption), and liquid helium superfluidity.

  4. Translational energy spectra for single-electron capture by O[sup 2+] in He, Ne, and Ar

    SciTech Connect

    Lee, A.R.; Wilkins, A.C.R.; Leather, C.; Brenton, A.G. Mass Spectrometry Research Unit, University College of Swansea, Singleton Park, Swansea SA2 8PP )

    1994-08-01

    High-resolution single-electron capture spectra have been obtained for O[sup 2+] ions colliding with He, Ne, and Ar at 4-keV energy. For the He and Ne targets the dominant capture channels involve transitions from the ground [sup 3][ital P] state of O[sup 2+] to the first and second excited states ([sup 2][ital D][sup [ital o

  5. A simplified Tamm-Dancoff density functional approach for the electronic excitation spectra of very large molecules

    NASA Astrophysics Data System (ADS)

    Grimme, Stefan

    2013-06-01

    Two approximations in the Tamm-Dancoff density functional theory approach (TDA-DFT) to electronically excited states are proposed which allow routine computations for electronic ultraviolet (UV)- or circular dichroism (CD) spectra of molecules with 500-1000 atoms. Speed-ups compared to conventional time-dependent DFT (TD-DFT) treatments of about two to three orders of magnitude in the excited state part at only minor loss of accuracy are obtained. The method termed sTDA ("s" for simplified) employs atom-centered Löwdin-monopole based two-electron repulsion integrals with the asymptotically correct 1/R behavior and perturbative single excitation configuration selection. It is formulated generally for any standard global hybrid density functional with given Fock-exchange mixing parameter ax. The method performs well for two standard benchmark sets of vertical singlet-singlet excitations for values of ax in the range 0.2-0.6. The mean absolute deviations from reference data are only 0.2-0.3 eV and similar to those from standard TD-DFT. In three cases (two dyes and one polypeptide), good mutual agreement between the electronic spectra (up to 10-11 eV excitation energy) from the sTDA method and those from TD(A)-DFT is obtained. The computed UV- and CD-spectra of a few typical systems (e.g., C60, two transition metal complexes, [7]helicene, polyalanine, a supramolecular aggregate with 483 atoms and about 7000 basis functions) compare well with corresponding experimental data. The method is proposed together with medium-sized double- or triple-zeta type atomic-orbital basis sets as a quantum chemical tool to investigate the spectra of huge molecular systems at a reliable DFT level.

  6. Theoretical Study of the Luminescent States and Electronic Spectra of UO2Cl2 in an Argon Matrix

    SciTech Connect

    Su, Jing; Wang, Yi-Lei; Wei, Fan; Schwarz, W H E.; Li, Jun

    2011-08-25

    The electronic absorption and emission spectra of freeUO2Cl2 and its Ar-coordinated complexes below 27 000 cm-1 are investigated at the levels of ab initio complete active space second-order perturbation theory (CASPT2) and coupled-cluster singles and doubles and perturbative triples [CCSD(T)] using valence 3ζ-polarized basis sets. The influence of the argon matrix in the 12K experiment on the electronic spectra is explored by investigating the excited states of argon complexes ArnUO2Cl2. The calculated two most stable complexes with n = 2, 3 can explain the observed two matrix sites corresponding to the experimental twocomponent luminescence decay. In these uranyl complexes, Ar-coordination is found to have little influence on the 3Φ (Ω = 2g) character of the luminescent state and on the electronic spectral shape. The calculations yield a coherent assignment of the experimental excitation spectra that improves on previous assignments. The simulated luminescence spectral curves based on the calculated spectral parameters of UO2Cl2 from both CASPT2 and CCSD(T) agree well with experiment.

  7. Study of electron transition energies between anions and cations in spinel ferrites using differential UV-vis absorption spectra

    NASA Astrophysics Data System (ADS)

    Xue, L. C.; Wu, L. Q.; Li, S. Q.; Li, Z. Z.; Tang, G. D.; Qi, W. H.; Ge, X. S.; Ding, L. L.

    2016-07-01

    It is very important to determine electron transition energies (Etr) between anions and different cations in order to understand the electrical transport and magnetic properties of a material. Many authors have analyzed UV-vis absorption spectra using the curve (αhν)2 vs E, where α is the absorption coefficient and E(=hν) is the photon energy. Such an approach can give only two band gap energies for spinel ferrites. In this paper, using differential UV-vis absorption spectra, dα/dE vs E, we have obtained electron transition energies (Etr) between the anions and cations, Fe2+ and Fe3+ at the (A) and [B] sites and Ni2+ at the [B] sites for the (A)[B]2O4 spinel ferrite samples CoxNi0.7-xFe2.3O4 (0.0≤x≤0.3), CrxNi0.7Fe2.3-xO4 (0.0≤x≤0.3) and Fe3O4. We suggest that the differential UV-vis absorption spectra should be accepted as a general analysis method for determining electron transition energies between anions and cations.

  8. Measurement of the high energy component of the x-ray spectra in the VENUS electron cyclotron resonance ion source

    SciTech Connect

    Leitner, D.; Benitez, J. Y.; Lyneis, C. M.; Todd, D. S.; Ropponen, T.; Ropponen, J.; Koivisto, H.; Gammino, S.

    2008-03-15

    High performance electron cyclotron resonance (ECR) ion sources, such as VENUS (Versatile ECR for NUclear Science), produce large amounts of x-rays. By studying their energy spectra, conclusions can be drawn about the electron heating process and the electron confinement. In addition, the bremsstrahlung from the plasma chamber is partly absorbed by the cold mass of the superconducting magnet, adding an extra heat load to the cryostat. Germanium or NaI detectors are generally used for x-ray measurements. Due to the high x-ray flux from the source, the experimental setup to measure bremsstrahlung spectra from ECR ion sources is somewhat different from that for the traditional nuclear physics measurements these detectors are generally used for. In particular, the collimation and background shielding can be problematic. In this paper, we will discuss the experimental setup for such a measurement, the energy calibration and background reduction, the shielding of the detector, and collimation of the x-ray flux. We will present x-ray energy spectra and cryostat heating rates depending on various ion source parameters, such as confinement fields, minimum B-field, rf power, and heating frequency.

  9. Energy spectra of three electrons in SiGe/Si/SiGe laterally coupled triple quantum dots

    NASA Astrophysics Data System (ADS)

    Ren, Y. F.; Wang, L.; Liu, Z.; Wu, M. W.

    2014-09-01

    We investigate the energy spectra of three electrons in SiGe/Si/SiGe equilateral triangular and symmetric linear triple quantum dots in the presence of magnetic (in either Faraday or Voigt configuration) and electric fields with only the lowest valley eigenstate being relevant by using the real-space configuration interaction method. The strong electron-electron Coulomb interaction, which is crucial to the energy spectra, is explicitly calculated whereas the weak spin-orbit coupling is treated perturbatively. In both equilateral triangular and symmetric linear triple quantum dots, we find doublet-quartet transition of ground-state spin configuration by varying dot size or interdot distance in the absence of external fields. This transition has not been reported in the literature on triple quantum dots. In the magnetic-field (Faraday configuration) dependence of energy spectra, we find anticrossings with large energy splittings between the energy levels with the same spin state in the absence of the spin-orbit coupling. This anticrossing behavior originates from the triple quantum dot confinement potential. In addition, with the inclusion of the spin-orbit coupling, we find that all the intersections shown in the equilateral triangular case become anticrossing whereas only part of the intersections in symmetric linear case show anticrossing behavior in the presence of magnetic field in either the Faraday or Voigt configuration. All the anticrossing behaviors are analyzed based on symmetry consideration. Moreover, we show that the electric field can effectively influence the energy levels and the charge configurations.

  10. A study of tungsten spectra using large helical device and compact electron beam ion trap in NIFS

    SciTech Connect

    Morita, S.; Goto, M.; Murakami, I.; Dong, C. F.; Kato, D.; Sakaue, H. A.; Oishi, T.; Hasuo, M.; Koike, F.; Nakamura, N.; Sasaki, A.; Wang, E. H.

    2013-07-11

    Tungsten spectra have been observed from Large Helical Device (LHD) and Compact electron Beam Ion Trap (CoBIT) in wavelength ranges of visible to EUV. The EUV spectra with unresolved transition array (UTA), e.g., 6g-4f, 5g-4f, 5f-4d and 5p-4d transitions for W{sup +24-+33}, measured from LHD plasmas are compared with those measured from CoBIT with monoenergetic electron beam ({<=}2keV). The tungsten spectra from LHD are well analyzed based on the knowledge from CoBIT tungsten spectra. The C-R model code has been developed to explain the UTA spectra in details. Radial profiles of EUV spectra from highly ionized tungsten ions have been measured and analyzed by impurity transport simulation code with ADPAK atomic database code to examine the ionization balance determined by ionization and recombination rate coefficients. As the first trial, analysis of the tungsten density in LHD plasmas is attempted from radial profile of Zn-like WXLV (W{sup 44+}) 4p-4s transition at 60.9A based on the emission rate coefficient calculated with HULLAC code. As a result, a total tungsten ion density of 3.5 Multiplication-Sign 10{sup 10}cm{sup -3} at the plasma center is reasonably obtained. In order to observe the spectra from tungsten ions in lower-ionized charge stages, which can give useful information on the tungsten influx in fusion plasmas, the ablation cloud of the impurity pellet is directly measured with visible spectroscopy. A lot of spectra from neutral and singly ionized tungsten are observed and some of them are identified. A magnetic forbidden line from highly ionized tungsten ions has been examined and Cd-like WXXVII (W{sup 26+}) at 3893.7A is identified as the ground-term fine-structure transition of 4f{sup 23}H{sub 5}-{sup 3}H{sub 4}. The possibility of {alpha} particle diagnostic in D-T burning plasmas using the magnetic forbidden line is discussed.

  11. Electronic spectra of cationic forms of meso-tetrapropylporphin in a nanoporous silicate gel matrix

    NASA Astrophysics Data System (ADS)

    Arabei, S. M.; Novik, D. V.; Pavich, T. A.; Solov'ev, K. N.

    2006-07-01

    We have studied the fluorescence and fluorescence excitation spectra at 300 K, 77 K, and 4.2 K for silicate gel matrices colored with meso-tetrapropylporphin by impregnation of the matrix with a solution of the pigment. Comparison of the data obtained with the absorption spectra in acidified solutions and analysis of the low-temperature fine-structure vibronic spectra, and also taking into account data obtained earlier for octaethylporphin in a xerogel showed formation of two cationic forms of meso-tetrapropylporphin in the gel matrix: the short-wavelength form has a dicationic structure, while the long-wavelength form has a monocationic structure. We have traced out the correlations of the vibrational structure in the spectra of the dicationic form with data for the porphin dication, and we have drawn a number of conclusions concerning the normal vibrational modes that are active in the vibronic fluorescence and absorption spectra of the studied cationic forms. Using the AM1 semiempirical quantum chemical method, we optimized the geometry of the mesotetrapropylporphin dication: the most stable of the possible conformers is the dication structure with saddleshaped macrocycle nonplanarity.

  12. Prediction soft-X-ray spectrum of solar flares from Very Low Frequency observations: an inverse problem in ionospheric science

    NASA Astrophysics Data System (ADS)

    Palit, Sourav; Chakrabarti, Sandip Kumar; Ray, Suman

    2016-07-01

    Earth's lower ionosphere and upper atmosphere absorb X-rays and gamma-rays from astronomical sources such as solar flares, Short Gamma ray Repeaters (SGRs) or Gamma Ray Bursts (GRBs). The electron-ion production rates due to the ionization of such energetic photons at different heights depend on the intensity and wavelength of the injected spectrum and hence vary from one source to another. Obviously the ion density vs. altitude profile has the imprint of the incident photon spectrum. In this paper, we examine the possibility of inverting the electron density-height profiles uniquely by deconvolution of the VLF amplitude signal to obtain information on the injected spectrum. We have been able to reproduce the soft-X-ray part of the injected spectra from two different classes of solar flares with satisfactory accuracy. With the possibilities of probing even lower parts of the atmosphere, the method presented here is useful to carry out a similar exercise to infer the higher energy part of solar flare spectra and spectra of more energetic events such as the GRBs, SGRs etc. We show that to a certain accuracy, the Earth's atmosphere may be used as a gigantic detector of relatively strong ionizing extra-terrestrial events.

  13. Pre-Impulsive Hard X-Ray Emission from Coronal Sources in X-Class Flares

    NASA Astrophysics Data System (ADS)

    Caspi, A.; Krucker, S.; Lin, R. P.

    2006-12-01

    The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has observed significant non- thermal emission up to ~70~keV from coronal sources prior to the impulsive phase in some flares, which has interesting implications for particle trapping and flare energy release. Images and spectra during the pre- impulsive phase of the GOES-class X4.8 event on 23~July~2002 suggests that the coronal hard X-ray (HXR) emission is non-thermal, as analysis of the Fe (~6.7~keV) and Fe/Ni (~8~keV) line complexes constrains the thermal component to have little or no thermal continuum emission above ~15~keV. The over-the-limb X3.1 event on 24~Aug~2002 displays similar spectral characteristics, and occultation of the footpoints places the non-thermal HXR emission unambiguously in the corona. RHESSI images of this event show an extended source below ~35~keV and a compact looptop source above ~35~keV, possibly indicating trapping of energetic electrons. Spatially-integrated spectra are well-fit by a broken power-law and the spectral indices above and below the break differ by ~2, suggesting an observation of the transition between thin- and thick-target bremsstrahlung. The collisional lifetime of non-thermal electrons is <10~sec at the inferred densities of ~1011~cm-3 and the rising HXR flux thus suggests continuous particle injection. We apply the technique of Johns &Lin (1992) to invert the pre-impulsive phase photon spectra and recover the original electron energy spectra as a function of time, both for spatially-integrated spectra and source-isolated spectra using imaging spectroscopy. We then compare the inverted spectra with a forward-modeling analysis of the photon spectra using the iron line analysis technique of Caspi &Lin (2006) to constrain the thermal model. We compare the results for both 24~Aug~2002 and 23~Jul~2002, and discuss the implications for electron acceleration and flare plasma heating in the corona during this period.

  14. Spatial Size and Plasma Variables of RHESSI Flares

    NASA Astrophysics Data System (ADS)

    Väänänen, Mikko; Pohjolainen, Silja

    2007-04-01

    We have analysed 64 flares observed with GOES and RHESSI in the 3.1 24.8 keV band (0.5 4 Å). Flares were randomly chosen to represent different GOES classes, between B1 and M6. RHESSI was used to image the flaring region on the surface of the Sun. We derived the spatial area of the flare on the surface of the Sun from the imaging observations, scaled it dimensionally to volume, and used the spectroscopically derived emission measure to obtain several flare parameters. We experimented with several imaging methods and selected the use of 50% maximum image photon flux contours to define the flare area ( F 50%). Most of the flares showed a single spherical loop-top source. The volume measurement for V, temperature T, and electron density N produced power indices that showed no correlation within the boundaries of error. Larger flares by loop-top source volume are thus neither hotter nor denser. The background-subtracted GOES flux RHESSI Total Emission Measure ( TEM RHESSI) and TEM GOES TEM RHESSI dependencies were in agreement with the instrument characteristics and earlier studies. Nonthermal flux was noticed to increase with thermal energy and TEM, which can be said to agree with the “Big Flare Syndrome,” with nonthermal photon flux being considered as one flare manifestation.

  15. Effects of Incident Electron Fluence and Energy on the Election Yield Curves and Emission Spectra of Dielectrics

    NASA Technical Reports Server (NTRS)

    Sim, Alec; Dennison, J. R.; Thomson, Clint

    2005-01-01

    We present an experimental study of evolution of electron emission yields and spectra as a result of internal charge build up due to electron dose. Reliable total, backscattered and secondary yield curves and electron emission spectra for un-charged insulators using a low fluence, pulsed electron beam (= or < 5 microsec at = or < 3 nA/sq mm or = or < 10(exp 5) e/sq mm per pulse) with low energy electron and UV flooding to neutralize the charging between pulses. Quantifiable changes in yield curves are observed due to < 100 fC/sq mm fluences for several excellent dielectric thin film materials. We find good agreement with a phenomenological argument based on insulator charging predicted by the yield curve; this includes an approximately linear decrease in the magnitude of the yield as incident energies approach the crossover energies and an exponential decrease in yield as accumulated internal charge reduces the landing energy to asymptotically approach a steady state surface charge and unity yield. We also find that the exponential decay of yield curves with fluence exhibit an energy dependent decay constant, alpha(E), over a broad range of incident energies below, between and above the crossover energies. Finally, we present some preliminary physics-based models for this energy dependence and attempt to relate our charging measurements to knowledge of how charge is deposited within the insulator, the mechanisms for charge trapping and transport, and how the profile of trapped charge affects the transport and emission of charges from insulators.

  16. Observations of particle acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Hudson, H. S.

    1979-01-01

    Solar flares provide several examples of nonthermal particle acceleration. The paper reviews the information gained about these processes via X-ray and gamma-ray astronomy, which can presently distinguish among three separate particle-acceleration processes at the sun: an impulsive accelerator of more than 20 keV electrons, a gradual accelerator of more than 20 keV electrons, and a gradual accelerator of more than 10 MeV ions. The acceleration energy efficiency (total particle energy divided by total flare energy) of any of these mechanisms cannot be less than about 0.1%, although the gradual acceleration does not occur in every flare. The observational material suggests that both the impulsive and gradual accelerations take place preferentially in closed magnetic-field structures, but that the electrons decay in these traps before they can escape. The ions escape very efficiently.

  17. Influence of weak vibrational-electronic couplings on 2D electronic spectra and inter-site coherence in weakly coupled photosynthetic complexes

    SciTech Connect

    Monahan, Daniele M.; Whaley-Mayda, Lukas; Fleming, Graham R.; Ishizaki, Akihito

    2015-08-14

    Coherence oscillations measured in two-dimensional (2D) electronic spectra of pigment-protein complexes may have electronic, vibrational, or mixed-character vibronic origins, which depend on the degree of electronic-vibrational mixing. Oscillations from intrapigment vibrations can obscure the inter-site coherence lifetime of interest in elucidating the mechanisms of energy transfer in photosynthetic light-harvesting. Huang-Rhys factors (S) for low-frequency vibrations in Chlorophyll and Bacteriochlorophyll are quite small (S ≤ 0.05), so it is often assumed that these vibrations influence neither 2D spectra nor inter-site coherence dynamics. In this work, we explore the influence of S within this range on the oscillatory signatures in simulated 2D spectra of a pigment heterodimer. To visualize the inter-site coherence dynamics underlying the 2D spectra, we introduce a formalism which we call the “site-probe response.” By comparing the calculated 2D spectra with the site-probe response, we show that an on-resonance vibration with Huang-Rhys factor as small as S = 0.005 and the most strongly coupled off-resonance vibrations (S = 0.05) give rise to long-lived, purely vibrational coherences at 77 K. We moreover calculate the correlation between optical pump interactions and subsequent entanglement between sites, as measured by the concurrence. At 77 K, greater long-lived inter-site coherence and entanglement appear with increasing S. This dependence all but vanishes at physiological temperature, as environmentally induced fluctuations destroy the vibronic mixing.

  18. Plasma flares in high power impulse magnetron sputtering

    SciTech Connect

    Ni, Pavel A.; Hornschuch, Christian; Panjan, Matjaz; Anders, Andre

    2012-11-26

    Self-organized ionization zones and associated plasma flares were recorded with fast cameras in side-on view. Flare velocities were estimated to be about 20 000 m/s suggesting that the local tangential field E{sub {xi}} is about 2000 V/m based on a concept where flare-causing electrons are initially ejected by E{sub {xi}} Multiplication-Sign B drift. At distances of 10 mm and greater from the target, where the electric field is very small, plasma flares are guided by the magnetic field B.

  19. GeV flares observations with GLAST LAT

    SciTech Connect

    Galli, A.; Omodei, N.; Piro, L.

    2007-07-12

    Early X-ray afterglow observations show that X-ray flares are very common features in GRB light curves. X-ray flares may reflect long duration central engine activity. The delayed flare photons are expected to interact with relativistic electrons by Inverse Compton giving delayed high energy counterparts that potentially will be detected by GLAST LAT, which could observe GRB from 20 MeV to more than 300 GeV. The nature oh high energy spectral components from GRB detected by EGRET is still debated. Observations with GLAST LAT will give useful information to constrain the origin of X-ray flares. In this work we simulate a set of possible GeV emitting flares in the context of External Shock model to study the capability of GLAST LAT to detect GeV flares at different intensities and durations.

  20. CORONAS-F observation of HXR and gamma-ray emissions from the solar flare X10 on 29 October 2003 as a probe of accelerated proton spectrum

    NASA Astrophysics Data System (ADS)

    Kurt, V. G.; Yushkov, B. Yu.; Kudela, K.; Galkin, V. I.; Kashapova, L. K.

    2015-04-01

    HXR and gamma-ray emissions in the 0.04—150 MeV energy range associated with the solar flare on 29 October 2003 (X10/3B) were observed at 20:38—20:58 UT by the SONG instrument aboard the CORONAS-F mission. We restored consecutive flare gamma-emission spectra from SONG and RHESSI data and found a good agreement of these spectra in the 0.1—10 MeV energy range. Two phases were identified which showed major changes in the spectral shape of flare emission: 20:38:00-20:44:20 UT and 20:44:20-20:58:00 UT. During the second phase an efficiency of proton acceleration increased considerably relatively to the efficiency of acceleration of high energy electrons. The pion-decay component of the flare gamma-emission was elicited statistically significant only during the second phase since 20:47:40 UT. A power law spectrum index of accelerated protons was estimated from the ratio between intensities of the pion-decay and gamma-line components. The hardest spectrum (power law index S=3.7) was at 20:48—20:51 UT when the intensity of the pion-decay emission was maximal. Our subdivision of the flare into two phases is consistent with sharp changes in the structure of the flare found by Ji et al. (2008) and Liu et al. (2009). This flare was accompanied by GLE 66. The time profile of the pion-decay gamma-emission was compared with the GLE onset time. It was shown that both protons interacting at the Sun and the particles responsible for the GLE onset could belong to the same population of accelerated particles.