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1.
Share  G.H.  Murphy  R.J.  Dennis  B.R.  Schwartz  R.A.  Tolbert  A.K.  Lin  R.P.  Smith  D.M. 《Solar physics》2002,210(1-2):357-372
The RHESSI high-resolution spectrometer detected γ-ray lines and continuum emitted by the Earth's atmosphere during impact of solar energetic particles in the south polar region from 16:00–17:00 UT on 21 April 2002. The particle intensity at the time of the observation was a factor of 10–100 weaker than previous events when gamma-rays were detected by other instruments. This is the first high-resolution observation of atmospheric gamma-ray lines produced by solar energetic particles. De-excitation lines were resolved that, in part, come from 14N at 728, 1635, 2313, 3890, and 5106 keV, and the 12C spallation product at ∼ 4439 keV. Other unresolved lines were also detected. We provide best-fit line energies and widths and compare these with moderate resolution measurements by SMM of lines from an SEP event and with high-resolution measurements made by HEAO 3 of lines excited by cosmic rays. We use line ratios to estimate the spectrum of solar energetic particles that impacted the atmosphere. The 21 April spectrum was significantly harder than that measured by SMM during the 20 October 1989 shock event; it is comparable to that measured by Yohkoh on 15 July 2000. This is consistent with measurements of 10–50 MeV protons made in space at the time of the γ-ray observations.  相似文献   

2.
Krucker  Säm  Lin  R.P. 《Solar physics》2002,210(1-2):229-243
Hard X-ray lightcurves, spectrograms, images, and spectra of three medium-sized flares observed by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) are presented. Imaging spectroscopy of the 20 February 2002, 11:06 UT flare at 10′′ spatial resolution, comparable to the best previous hard X-ray imaging from Yohkoh, shows two footpoints with an ∼ 8 s delay of peak emission between footpoints. Subsequent imaging at le4′′ shows three sources consistent with two separate loops and simultaneous brightening in connected footpoints. Imaging for the simple two footpoint flare of 2 June 2002 also shows simultaneous footpoint brightening. The more complex 17 March 2002 flare shows at least four different sources during the main peak of the event, and it is difficult to clearly demonstrate simultaneous brightening of connected footpoints. Non-thermal power laws are observed down to ∼ 12–13 keV without flattening in all these events, indicating the energy content in energetic electrons may be significantly greater than previously estimated from assumed 25 keV low energy cutoff. Simultaneously brightening footpoints show similar spectra, at least in the three flares investigated. Double-power-law spectra with a relatively sharp break are often observed. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022469902940  相似文献   

3.
The gamma-ray imager (GRI) is a novel mission concept that will provide an unprecedented sensitivity leap in the soft gamma-ray domain by using for the first time a focusing lens built of Laue diffracting crystals. The lens will cover an energy band from 200–1,300 keV with an effective area reaching 600 cm2. It will be complemented by a single reflection multilayer coated mirror, extending the GRI energy band into the hard X-ray regime, down to ∼10 keV. The concentrated photons will be collected by a position sensitive pixelised CZT stack detector. We estimate continuum sensitivities of better than 10 − 7 ph cm − 2s − 1keV − 1 for a 100 ks exposure; the narrow line sensitivity will be better than 3 × 10 − 6 ph cm − 2s − 1 for the same integration time. As focusing instrument, GRI will have an angular resolution of better than 30 arcsec within a field of view of roughly 5 arcmin—an unprecedented achievement in the gamma-ray domain. Owing to the large focal length of 100 m of the lens and the mirror, the optics and detector will be placed on two separate spacecrafts flying in formation in a high elliptical orbit. R&D work to enable the lens focusing technology and to develop the required focal plane detector is currently underway, financed by ASI, CNES, ESA, and the Spanish Ministery of Education and Science. The GRI mission has been proposed as class M mission for ESAs Cosmic Vision 2015–2025 program. GRI will allow studies of particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the universe. All authors are on behalf of a large international collaboration The GRI mission has been proposed as an international collaboration between (in alphabetical order) Belgium (CSR), China (IHEP, Tsinghua Univ.), Denmark (DNSC, Southern Univ.), France (CESR, APC, ILL, CSNSM, IAP, LAM), Germany (MPE), Ireland (UCD School of Physics), Italy (INAF/IASF Rome, Bologna, Milano, Palermo; INAF/OA Brera, Roma; UNIFE, CNR/IMEM), Poland (NCAC), Portugal (Combra Univ., Evora Univ.), Russia (SINP, MSU, Ioffe Inst.), Spain (IEEC-CSIC-IFAE, CNM-IMB), the Netherlands (SRON, Utrecht Univ.), Turkey (Sabanci Univ.), United Kingdom (Univ. of Southampton, MSSL, RAL, Edinburgh Univ.), and the United States of America (SSL UC Berkeley, Argonne National Lab., MSFC, GSFC, US NRL).  相似文献   

4.
Schmahl  E.J.  Hurford  G.J. 《Solar physics》2002,210(1-2):273-286
The Reuven Ramaty High-Energy Solar Spectroscopic Imager RHESSI telescope produces hard X-ray images by Fourier imaging techniques that are capable of determining the sizes and shapes of sources with spatial scales in the range ∼ 2′′–180′′. Applying the method of Unpixelized Forward Fitting to RHESSI modulation profiles from simple flares, we have identified the presence of `halo' sources whose size scale (∼ 40′′) greatly exceeds the `core' sizes (≤ 6′′–14′′). Although such `core-halo' structures have been observed at radio wavelengths using a similar technique, the radio and hard X-ray phenomena may be different. These observations raise questions about the nature of these `halos'. Among the possibilities are that they are albedo sources, thin-target loops, or unidentified diffuse structures. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022484822851  相似文献   

5.
We have used Ramaty High Energy Solar Spectroscopic Imager (RHESSI) modulation profiles in the 25 – 300 keV range to construct high-fidelity visibilities of 25 flares having at least two components. These hard X-ray visibilities, which are mathematically identical to the visibilities of radio imaging, were input to software developed for mapping solar flares in the microwave domain using the Maximum Entropy Method (MEM). We compared and contrasted the MEM maps with Clean and Pixon maps made with RHESSI software. In particular, we assessed the reliability of the maps and their morphologies for future investigations of the symmetry of bipolar electron beaming in the sample set.  相似文献   

6.
The Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) X-ray data base (February 2002 – May 2006) has been searched to find solar flares with weak thermal components and flat photon spectra. Using a regularized inversion technique, we determine the mean electron flux distribution from count spectra for a selection of events with flat photon spectra in the 15 – 20 keV energy range. Such spectral behavior is expected for photon spectra either affected by photospheric albedo or produced by electron spectra with an absence of electrons in a given energy range (e.g., a low-energy cutoff in the mean electron spectra of nonthemal particles). We have found 18 cases that exhibit a statistically significant local minimum (a dip) in the range of 13 – 19 keV. The positions and spectral indices of events with low-energy cutoff indicate that such features are likely to be the result of photospheric albedo. It is shown that if the isotropic albedo correction is applied, all low-energy cutoffs in the mean electron spectrum are removed, and hence the low-energy cutoffs in the mean electron spectrum of solar flares above ∼ 12 keV cannot be viewed as real features. If low-energy cutoffs exist in the mean electron spectra, their energies should be less than ∼ 12 keV.  相似文献   

7.
In 2004 CNES decided to perform 4 phase 0 studies dedicated to Astrophysics and achieved thanks to Formation Flying space systems: ASPICS (A Solar Physics Mission to observe in UV and Visible the Solar Corona between 1.01 and 3.2 Solar Radius), PEGASE (an IR interferometry mission to observe Hot Jupiter, Brown Dwarfs and Proto planetary disks), SIMBOL-X (hard X-rays telescope to observe: Accretion onto compact objects, Black Holes, obscured Galactic Nuclei, ˙˙˙˙) and MAX (a Nuclear Astrophysics Mission to observe: Supernovae, Neutron Stars,˙). For this last mission, presented here, two spectral bands around important gamma-ray lines have been selected (450–530 and 800–900 keV). The formation flight allows to realise a long focal length of 80–90 m which is necessary to build a reasonably sized gamma-ray telescope based on a Laue crystal lens. The Space System design allows to have a good spacecrafts mass margin in High Elliptical Orbit with a Soyuz launch (Initial Orbit: Perigee altitude ∼44,000 km and Apogee altitude ∼253,000 km).  相似文献   

8.
Share  G.H.  Murphy  R.J.  Tylka  A.J.  Schwartz  R.A.  Yoshimori  M.  Suga  K.  Nakayama  S.  Takeda  H. 《Solar physics》2001,204(1-2):41-53
The HXS and GRS detectors on Yohkoh observed the 14 July 2000, X5.7 flare, beginning at ∼ 10:20 UT, ∼ 4 min before the peak in soft X-rays. The hard X-rays and γ-rays peaked ∼ 3 min later at ∼ 10:27 UT. Solar γ-ray emission lasted until ∼ 10:40 UT. Impact of high-energy ions at the Sun is revealed by the γ-ray lines from neutron capture, annihilation radiation and de-excitation that are visible above the bremsstrahlung continuum. From measurement of these lines we find that the flare-averaged spectrum of accelerated protons is consistent with a power law ge10 MeV with index 3.14±0.15 and flux 1.1×1032 protons MeV−1 at 10 MeV. We estimate that there were ∼1.5×1030 erg in accelerated ions if the power law extended without a break down to 1 MeV; this is about 1% of the energy in electrons > 20 keV from measurements of the hard X-rays. We find no evidence for spectral hardening in the hard X-rays that has been suggested as a predictor for the occurrence of solar energetic particle (SEP) events. This was the third largest proton event above 10 MeV since 1976. The GRS and HXS also observed γ-ray lines and continuum produced by the impact of SEP on the Earth's atmosphere beginning about 13 UT on 14 July. These measurements show that the SEP spectrum softened considerably over the next 24 hours. We compare these measurements with proton measurements in space.  相似文献   

9.
We explore the hard X-ray source distributions of an C1.1 flare occurred on 14 December 2007. Both Hinode/EIS and RHESSI observations are used. One of EIS rasters perfectly covers the double hard X-ray footpoints, where the EUV emission appears strong from the cool line of He ii (log T=4.7) to the hot line of Fe xvi (log T=6.4). We analyze RHESSI X-ray images at different energies and different times before the hard X-ray maximum. The results show a similar topology for the time-dependent source distribution (i.e. at 14:14:35 UT) as that for energy-dependent source distribution (i.e. at a given energy band of 6 – 9 keV) overlapped on EUV bright kernels, which seems to be consistent with the evaporation model.  相似文献   

10.
The next generation of instrumentation for nuclear astrophysics will have to achieve a factor of 10–100 improvement in sensitivity over present technologies. With the focusing gamma-ray telescope MAX we take up this challenge: combining unprecedented sensitivity with high spectral and angular resolution, and the capability of measuring the polarization of the incident photons. The feasibility of such a crystal diffraction gamma-ray lens has recently been demonstrated with the prototype lens CLAIRE. MAX is a proposed mission which will make use of satellite formation flight to achieve 86 m focal length, with the Laue lens being carried by one satellite and the detector by the other. In the current design, the Laue diffraction lens of MAX will consist of 13740 copper and germanium (Ge1−x Si x , x ∼ 0.02) crystal tiles arranged on 36 concentric rings. It simultaneously focuses in two energy bands, each centred on one of the main scientific objectives of the mission: the 800–900 keV band is dedicated to the study of nuclear gamma-ray lines from type Ia supernovae (e.g. 56 Co decay line at 847 keV) while the 450–530 keV band focuses on electron-positron annihilation (511 keV emission) from the Galactic centre region with the aim of resolving potential point sources. MAX promises a breakthrough in the study of point sources at gamma-ray energies by combining high narrow-line sensitivity (better than 10−6 cm−2 s−1) and high energy resolution (E/dE ∼ 500). The mission has successfully undergone a pre-phase A study with the French Space Agency CNES, and continues to evolve: new diffracting materials such as bent or composite crystals seem very promising. PACS: 95.55.Ka, 29.30.Kv, 61.10.-i  相似文献   

11.
Previous observations show that in many solar flares there is a causal correlation between the hard X-ray flux and the derivative of the soft X-ray flux. This so-called Neupert effect is indicative of a strong link between the primary energy release to accelerate particles and plasma heating. It suggests a flare model in which the hard X-rays are electron – ion bremsstrahlung produced by energetic electrons as they lose their energy in the lower corona and chromosphere and the soft X-rays are thermal bremsstrahlung from the “chromospheric evaporation” plasma heated by those same electrons. Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observes in a broad energy band and its high spectral resolution and coverage of the low-energy range allow us to separate the thermal continuum from the nonthermal component, which gives us an opportunity to investigate the Neupert effect. In this paper, we use the parameters derived from RHESSI observations to trace the primary energy release and the plasma response: The hard X-ray flux or spectral hardness is compared with the derivative of plasma thermal energy in three impulsive flares on 10 November 2002 and on 3 and 25 August 2005. High correlations show that the Neupert effect does hold for the two hard X-ray peaks of the 10 November 2002 flare, for the first peaks of the 3 August 2005 flare, and for the beginning period of the 25 August 2005 flare.  相似文献   

12.
Spectroscopic observation of solar flares in the hard X-ray energy range, particularly the 20 ∼ 100 keV region, is an invaluable tool for investigating the flare mechanism. This paper describes the design and performance of a balloon-borne hard X-ray spectrometer using CdTe detectors developed for solar flare observation. The instrument is a small balloon payload (gondola weight 70 kg) with sixteen 10×10×0.5 mm CdTe detectors, designed for a 1-day flight at 41 km altitude. It observes in an energy range of 20−120 keV and has an energy resolution of 3 keV at 60 keV. The second flight on 24 May 2002 succeeded in observing a class M1.1 flare.  相似文献   

13.
《Experimental Astronomy》2009,23(1):91-120
The primary scientific goal of the GRIPS mission is to revolutionize our understanding of the early universe using γ-ray bursts. We propose a new generation gamma-ray observatory capable of unprecedented spectroscopy over a wide range of γ-ray energies (200 keV–50 MeV) and of polarimetry (200–1000 keV). The γ-ray sensitivity to nuclear absorption features enables the measurement of column densities as high as 1028cm − 2. Secondary goals achievable by this mission include direct measurements of all types of supernova interiors through γ-rays from radioactive decays, nuclear astrophysics with massive stars and novae, and studies of particle acceleration near compact stars, interstellar shocks, and clusters of galaxies. See for the authors’ affiliations.  相似文献   

14.
We revisit the flare that occurred on 13 January 1992, which is now universally termed the “Masuda flare”. The new analysis is motivated not just by its uniqueness despite the increasing number of coronal observations in hard X-rays, but also by the improvement of Yohkoh hard X-ray image processing, which was achieved after the intensive investigations on this celebrated event. Using an uncertainty analysis, we show that the hard X-ray coronal source is located closer to the soft X-ray loop by about 5000 km (or 7 arcsec) in the re-calibrated Hard X-ray Telescope (HXT) images than in the original ones. Specifically, the centroid of the M1-band (23 – 33 keV) coronal source is above the maximum brightness of the Soft X-ray Telescope (SXT) loop by 5000±1000 km (9600 km in the original data) and above the apex of the SXT loop represented by the 30% brightness contour by 2000±1000 km (∼ 7000 km in the original data). The change is obviously significant, because most coronal sources are above the thermal loop by less than 6 arcsec. We suggest that this change may account for the discrepancy in the literature, i.e., the spectrum of the coronal emission was reported to be extremely hard below ∼ 20 keV in the pre-calibration investigations, whereas it was reported to be considerably softer in the literature after the re-calibration done by Sato, Kosugi, and Makishima (Pub. Astron. Soc. Japan 51, 127, 1999). Still, the coronal spectrum is flatter at lower energies than at higher energies, due to the lack of a similar, co-spatial source in the L-band (14 – 23 keV), for which a convincing explanation is absent.  相似文献   

15.
Vilmer  N.  Krucker  S.  Lin  R.P.  The Rhessi Team 《Solar physics》2002,210(1-2):261-272
The GOES C7.5 flare on 20 February 2002 at 11:07 UT is one of the first solar flares observed by RHESSI at X-ray wavelengths. It was simultaneously observed at metric/decimetric wavelengths by the Nançay radioheliograph (NRH) which provided images of the flare between 450 and 150 MHz. We present a first comparison of the hard X-ray images observed with RHESSI and of the radio emission sites observed by the NRH. This first analysis shows that: (1) there is a close occurrence between the production of the HXR-radiating most energetic electrons and the injection of radio-emitting non-thermal electrons at all heights in the corona, (2) modifications with time in the pattern of the HXR sources above 25 keV and of the decimetric radio sources at 410 MHz are observed occurring on similar time periods, (3) in the late phase of the most energetic HXR peak, a weak radio source is observed at high frequencies, overlying the EUV magnetic loops seen in the vicinity of the X-ray flaring sites above 12 keV. These preliminary results illustrate the potential of combining RHESSI and NRH images for the study of electron acceleration and transport in flares.  相似文献   

16.
Krucker  Säm  Christe  Steven  Lin  R.P.  Hurford  Gordon J.  Schwartz  Richard A. 《Solar physics》2002,210(1-2):445-456
The excellent sensitivity, spectral and spatial resolution, and energy coverage down to 3 keV provided by the Reuven Ramaty High-Energy Solar Spectroscopic Imager mission (RHESSI) allows for the first time the detailed study of the locations and the spectra of solar microflares down to 3 keV. During a one-hour quiet interval (GOES soft X-ray level around B6) on 2 May, 1:40–2:40 UT, at least 7 microflares occurred with the largest peaking at A6 GOES level. The microflares are found to come from 4 different active regions including one behind the west limb. At 7′′ resolution, some events show elongated sources, while others are unresolved point sources. In the impulsive phase of the microflares, the spectra can generally be fitted better with a thermal model plus power law above ∼ 6–7 keV than with a thermal only. The decay phase sometimes can be fitted with a thermal only, but in some events, power-law emission is detected late in the event indicating particle acceleration after the thermal peak of the event. The behind-the-limb microflare shows thermal emissions only, suggesting that the non-thermal power law emission originates lower, in footpoints that are occulted. The power-law fits extend to below 7 keV with exponents between −5 and −8, and imply a total non-thermal electron energy content between 1026–1027 erg. Except for the fact that the power-law indices are steeper than what is generally found in regular flares, the investigated microflares show characteristics similar to large flares. Since the total energy in non-thermal electrons is very sensitive to the value of the power law and the energy cutoff, these observations will give us better estimates of the total energy input into the corona. (Note that color versions of figures are on the accompanying CD-ROM.) Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022404512780  相似文献   

17.
Masuda  S.  Kosugi  T.  Hudson  H.S. 《Solar physics》2001,204(1-2):55-67
The Yohkoh hard X-ray telescope (HXT) observed hard X-rays from the impulsive phase of a long-duration event (LDE) occurring on 14 July 2000. The Yohkoh soft X-ray telescope (SXT) and other instruments observed a large arcade, with width and length ∼30 000 km and ∼120 000 km, respectively. In hard X-rays, for the first time, a two-ribbon structure was clearly observed in the energy range above 30 keV. This result suggests that electrons are in fact accelerated in the whole system of this arcade, not merely in a particular dominant loop. We analyzed the motions of bright kernels in the two hard X-ray ribbons in detail. Assuming these bright kernels to be footpoints of newly reconnected loops, we infer from their motions that the loops reconnecting early are highly sheared, while the loops reconnecting later are less sheared. We have also analyzed the hard X-ray spectra of the two ribbons independently. At the outer edge of a ribbon, the spectrum tends to be harder than that in the inner edge. This suggests that higher-energy electrons precipitate at the footpoints of outer loops and lower ones do at those of inner loops. We discuss what kind of model can support this tendency.  相似文献   

18.
Aschwanden  Markus J.  Brown  John C.  Kontar  Eduard P. 《Solar physics》2002,210(1-2):383-405
We present an analysis of hard X-ray imaging observations from one of the first solar flares observed with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) spacecraft, launched on 5 February 2002. The data were obtained from the 22 February 2002, 11:06 UT flare, which occurred close to the northwest limb. Thanks to the high energy resolution of the germanium-cooled hard X-ray detectors on RHESSI we can measure the flare source positions with a high accuracy as a function of energy. Using a forward-fitting algorithm for image reconstruction, we find a systematic decrease in the altitudes of the source centroids z(ε) as a function of increasing hard X-ray energy ε, as expected in the thick-target bremsstrahlung model of Brown. The altitude of hard X-ray emission as a function of photon energy ε can be characterized by a power-law function in the ε=15–50 keV energy range, viz., z(ε)≈2.3(ε/20 keV)−1.3 Mm. Based on a purely collisional 1-D thick-target model, this height dependence can be inverted into a chromospheric density model n(z), as derived in Paper I, which follows the power-law function n e(z)=1.25×1013(z/1 Mm)−2.5 cm−3. This density is comparable with models based on optical/UV spectrometry in the chromospheric height range of h≲1000 km, suggesting that the collisional thick-target model is a reasonable first approximation to hard X-ray footpoint sources. At h≈1000–2500 km, the hard X-ray based density model, however, is more consistent with the `spicular extended-chromosphere model' inferred from radio sub-mm observations, than with standard models based on hydrostatic equilibrium. At coronal heights, h≈2.5–12.4 Mm, the average flare loop density inferred from RHESSI is comparable with values from hydrodynamic simulations of flare chromospheric evaporation, soft X-ray, and radio-based measurements, but below the upper limits set by filling-factor insensitive iron line pairs.  相似文献   

19.
We explore the speed distributions of X-ray source motions after the start of chromospheric evaporation in two Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) flares. First, we make CLEAN images at 15 energy bands with a 12 second integration window; then, we outline a flaring loop geometry to cover the looptop and footpoint sources as much as possible. Consistent with the previous steps, we find converging motion of the double footpoint sources along the flaring loop in these two events. This motion is dependent on the energy band and time and is typically seen at 3 – 25 keV, indicating a chromospheric evaporation origin. The speed distributions at various energy bands are measured for the 10 September 2002 flare, which exhibits a separation-to-mergence motion pattern well correlated with the rising-to-decay phases at 50 – 100 keV.  相似文献   

20.
We present the first in-depth statistical survey of flare source heights observed by RHESSI. Flares were found using a flare-finding algorithm designed to search the 6 – 10 keV count-rate when RHESSI’s full sensitivity was available in order to find the smallest events (Christe et al. in Astrophys. J. 677, 1385, 2008). Between March 2002 and March 2007, a total of 25 006 events were found. Source locations were determined in the 4 – 10 keV, 10 – 15 keV, and 15 – 30 keV energy ranges for each event. In order to extract the height distribution from the observed projected source positions, a forward-fit model was developed with an assumed source height distribution where height is measured from the photosphere. We find that the best flare height distribution is given by g(h)∝exp (−h/λ) where λ=6.1±0.3 Mm is the scale height. A power-law height distribution with a negative power-law index, γ=3.1±0.1 is also consistent with the data. Interpreted as thermal loop-top sources, these heights are compared to loops generated by a potential-field model (PFSS). The measured flare heights distribution are found to be much steeper than the potential-field loop height distribution, which may be a signature of the flare energization process.  相似文献   

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