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1.
On the basis of solar flare forecasts, balloon flights were made from Hyderabad, India (vertical geomagnetic threshold rigidity of 16.9 GV), to detect the possible emission of high energy neutrons during solar flares. The detector comprised of a central plastic scintillator, completely surrounded by an anticoincidence plastic scintillator shield. The instrument responds to neutrons of about 15–150 MeV and gamma rays of about 5–30 MeV with about the same efficiency. The detector was flown to an atmospheric depth of 25 g cm-2 on February 26, 1969; while the balloon was at ceiling a flare of importance 2B and one of 1N occurred. No perceptible flare associated increase in the counting rate was observed. Using the observed counting rates, an upper limit of 1.2 × 10-2 neutrons cm-2 sec-1 is obtained for the first time for a flare of importance 2B for neutrons of energy 15–150 MeV. The corresponding upper limit for gamma rays of energy 5–30 MeV is found to be 10-2 photons cm-2 sec-1. The neutron flux limits are compared with the recent calculations of Lingenfelter. 相似文献
2.
On December 15, 1978, an omnidirectional gamma-ray detector for the energy range 0.3 to 10 MeV was flown from São José dos Campos, Brazil at a latitude of about -23°. Around noon time, when the Sun was in the field of view of the detector, various solar flares of importance SN and SF occurred. The 2.2 MeV line flux was monitored during this time. A statistically significant line flux of (1.55 ± 0.50) × 10–2 photons cm–2 s–1 and (9.97 ± 4.85) × 10–3 photons cm–2 s–1 was observed within a few minutes of t maxima of the two long-duration SN flares respectively, whereas during SF flares only upper limits were obtained. 相似文献
3.
A series of telescopes having approximately a 30° half opening angle and responding to neutrons in the energy range 50 MeV to 350 MeV has been flown to the top of the atmosphere on balloons released from an equatorial launching site at Kampala, Uganda, between 1967 and 1969. The aim of the experiment was to attempt to detect solar neutrons during periods of enhanced solar activity. No neutrons of solar origin were detected, but an upper limit of the order of 30 neutrons m–2 s–1 at the Earth has been placed on the continuous solar neutron flux in the above energy range, and a limit of four photons m–2 s–1 has also been placed on the corresponding -ray flux above 80 MeV. Limits have likewise been placed on the total emission from various flares. For a 1B flare the values were 23 × 104 neutrons m–2 and 6 × 104 photons m–2. 相似文献
4.
An experiment has been performed to search for the existence of a flux of solar neutrons at the earth using a detector sensitive to neutrons in the energy region 20–120 MeV. The instrument was carried by balloon to an atmospheric depth of 4 g/cm2, from Palestine, Texas on the morning of November 2, 1967 and flown through sunrise and for about 7 hours into the day. Numerous flares of importance 1B or less occurred during the float period. By comparison of night and day counting rates we have deduced that the upper limit to the continuous emission of solar neutrons at the earth is 2 × 10–2 neutrons/cm2 sec in the above energy region. Using a theoretical form for the neutron differential energy spectrum we have expressed this result as an upper limit differential solar neutron flux. If neutrons were emitted in association with any of the small flares then the maximum flux at the earth was less than 4 × 10–2 neutron/cm2 sec in the same energy region. The minimum detectable flux with the present instrument is therefore well below the predicted flux from a 3B flare (e.g., Nov. 12, 1960) of 550 neutrons/cm2 sec. 相似文献
5.
E. Kirsch 《Solar physics》1973,28(1):233-246
Solar neutron emission during large flares is investigated by using neutron monitor data from the mountain stations Chacaltaya (Bolivia), Mina Aguilar (Argentine), Pic-du-Midi (France) and Jungfraujoch (Switzerland). Registrations from such days on which large flares appeared around the local noon time of the monitor station are superimposed with the time of the optical flare as reference point.No positive evidence for a solar neutron emission was found with this method, However, by using an extrapolation of the neutron transport functions given by Alsmiller and Boughner a rough estimation of mean upper limits for the solar neutron flux is possible. The flux limits are compared with Lingenfelter's model calculations.From the Chacaltaya measurements it follows: N
02.8 × 10–3 N cm–2 s–1 per proton flare, E > 50 MeV, if P0 = 125 MV N
01.4 × 10–2 N cm–2 s–1 per proton flare, E > 50 MeV, if P
0 = 60 MV and from Pic-du-Midi measurements: N
06.7 × 10–3 N cm–2 s–1 per proton flare, E > 50 MeV, if P
0 = 125 MV N
04 × 10–2 N cm–2 s–1 per proton flare, E > 50 MeV, if P
0 = 60 MV P
0 = characteristic rigidity of the producing proton spectrum on the Sun.The flux limits estimated for some special proton flares are consistent with Lingenfelter's predictions for the acceleration phase but are too small for the slowing down phase. Therefore it is believed that Lingenfelter's assumption of isotropic proton emission from the flare region is not fulfilled. 相似文献
6.
BF3 counters on OSO-1 were used to look for solar neutrons by trying to observe a diurnal variation in count rate. No effect was observed and an upper limit was placed on the solar neutron flux at the earth of J
n < 2 × 10–3 neut/cm2/sec of 10 keV < E
n < 10 meV for the period March to May 1962. No proton-producing flares occurred during this time, so the most obvious source of solar neutrons could not be studied. The emulsion experiment of Apparao et al., flown during this period, which seemed to indicate solar neutrons has probably been misinterpreted. 相似文献
7.
Data accumulated by the Solar Maximum Mission Gamma Ray Spectrometer (GRS) have been searched for evidence of the 2.223 MeV neutron capture line from the Sun, outside the times of -ray-emitting solar flares. Background-corrected spectra accumulated over 3-day intervals between 1980 and 1989 show no evidence of the line. Upper limits are reported separately for periods of high and low solar activity.A conservative 3 upper limit of 5.7 × 10–5 (cm2 s)–1 is placed on the steady flux in the 2.223 MeV line during inactive periods, which is nearly two orders of magnitude lower than previously published results. After correction for limb darkening of the line emission from off-center positions, this upper limit becomes 7.1 × 10–5 (cm2s)–1. Our 3 upper limit on the steady flux in the line during periods of high solar activity is 6.9 × 10–5 (cm2 s)–1, or 8.6 × 10–5 (cm2 s)–1 after correction for limb darkening. Our results imply that the quiescent solar corona cannot be heated by ions accelerated above 1 MeV in microflares (or a continuous acceleration process), so long as the ion energy spectrum is similar to that measured in large flares. We also use our results to derive the rate of tritium production at the solar surface; our upper limit of 9 nuclei (cm2 s)–1 is about a factor of 9 below the upper limit from searches for 3H in the solar wind. We place upper limits of the order 1033 on the number of energetic (> 30 MeV) protons which can be stored in active regions prior to being released in solar flares, which imply that the strongest observed flares cannot be produced by such a mechanism. 相似文献
8.
The upper limit on the quiet time solar neutron flux from 1–20 MeV has been measured to be less than 2 × 10-3
n cm-2 s–1 at the 95% confidence level. This result is deduced from the OGO-6 neutron detector measurements of the day-night effect near the equator at low altitudes for the period from June 7, 1969, to December 23, 1969. The OGO-6 detector had very low (< 4%) counting rate contributions from locally produced neutrons in the detecting system and the spacecraft and from charged-particle interactions in the neutron sensor.Communications Research Center, Ottawa, Ontario, Canada. 相似文献
9.
We briefly describe our recent Monte Carlo calculations of the energy and angular distributions of neutrons escaping from the solar atmosphere. Comparing the calculation results with measurements of the neutron flux from the flares, we determined the angular distribution and energy spectrum of the accelerated ions. We also describe our calculations of the time dependence of the 2.223 MeV line emission, which provide a sensitive measure of the photospheric 3He abundance. We find that the SMM measurements of the time dependence of the 2.2 MeV line emission from the flare of 1982 June 3 imply a 3He/H ratio of (2.3±1.2)×10–5 at the 90% confidence level. 相似文献
10.
A plastic scintillator counter with anticoincidence screen has been flown in two 4-hour balloon flights, at a floating altitude of 3.2 and 3.5 mb, during day-and night-time respectively. Comparison between the day-and night-time counting-rates gives an upper limit of 10–2n/cm2 sec above 45 MeV for the continuous emission flux.This upper limit is compared with those derived from other experiments in function of the neutron energy spectrum assumed, and also with the expected continuous emission deduced from solar proton fluxes reported in non-flare conditions. It is concluded that with present experimental techniques, non-flare solar neutron emission can be detected only if the proton fluxes observed represent less than 10–3 of the protons accelerated in the sun.This research has been sponsored in part by the Air Force Cambridge Research Laboratories through the European Office of Aerospace Research, OAR, USAF under contract F 61052-68-C-050.0 相似文献
11.
Power-law distribution for solar energetic proton events 总被引：1，自引：0，他引：1
Analyses of the time-integrated fluxes of solar energetic particle events during the period 1965–1990 show that the differential distribution of events with flux F is given by a power law, with indices between 1.2 and 1.4 depending on energy. The power law represents a good fit over three to four orders of magnitude in fluence. Similar power-law distributions have been found for peak proton and electron fluxes, X-ray flares and radio and type III bursts. At fluences greater than 109 cm–2, the slope of the distribution steepens and beyond 1010 cm–2 the power-law index is estimated to be 3.5. At energies greater than 10 MeV, the slope of the distribution was found to be essentially independent of solar cycle, when the active years of solar cycles 20, 21, and 22 were analysed. The results presented are the first for a complete period of 27 years, covering nearly 3 complete solar cycles. Other new aspects of the results include the invariance of the exponent with solar cycle and also with integral energy. 相似文献
12.
A plastic scintillator counter with anticoincidence screen has flown in four balloon flights at a floating altitude variable between 4 and 5 mb, during night to day, day-time and night-time flights. The analysis and comparison of the day-time and night-time parts of the flights has given for the continuous emission flux an upper limit of 5.5 × 10–3 n/cm2s over the energy range from 10 MeV to 200 MeV. This upper limit is converted into upper limit differential solar neutron spectrum to be compared with the results obtained from other experiments.An irregular excess in counting rate observed in one of the flights, resulting in a day-night difference, is discussed.Finally the problems encountered in the operation of this type of detector at a high level of sensitivity are also discussed.This research has been sponsored in part by the Air Force Cambridge Research Laboratories through the European Office of Aerospace Research, OAR, USAF under contract F61052-68-C-0050. 相似文献
13.
During the 1990–1991 solar maximum, the CRRES satellite measured helium from 38 to 110 MeV n–1, with isotopic resolution, during both solar quiet periods and a number of large solar flares, the largest of which were seen during March and June 1991. Helium differential energy spectra and isotopic ratios are analyzed and indicate that (1) the series of large solar energetic particle (SEP) events of 2–22 June display characteristics consistent with CME-driven interplanetary shock acceleration; (2) the SEP events of 23–28 March exhibit signatures of both CME-driven shock acceleration and impulsive SEP acceleration; (3) below about 60 MeV n–1, the helium flux measured by CRRES is dominated by solar helium even during periods of least solar activity; (4) the solar helium below 60 MeV n–1 is enriched in 3He, with a mean 3He/4He ratio of about 0.18 throughout most of the CRRES mission `quiet' periods; and (5) an association of this solar component with small CMEs occurring during the periods selected as solar `quiet' times. 相似文献
14.
Second-step acceleration of nonrelativistic protons and ions in impulsive solar flares is discussed extending our earlier calculations for relativistic electrons. We derive the relevant particle transport equation, discussing in detail the influence of the particle's effective charge and mass number on the various momentum gain (stochastic acceleration, diffusive shock wave acceleration) and loss (Coulomb interactions, particle escape) processes. Analytical solutions for the ion-momentum spectra in the hard-sphere approximation are given. The inclusion of Coulomb losses modify the particle spectra significantly at kinetic energies smaller than E
B
= 0.64(
e
/5.0) MeV nucl.–1 from the well-known Bessel function variation in long-duration flares. For equal injection conditions this modification explains the observed much smaller ion fluxes from impulsive flares at high energies as compared to long-duration flares. We also calculate the 3He/4He-isotope variation as a function of momentum in impulsive flares in the hard-sphere approximation and find significant variations near E
m
= 0.38(T
e
/2 × 106 K) MeV nucl.–1, where T
e
is the electron temperature of the coronal medium. 相似文献
15.
Measurements of electron concentrations in the ionosphere, between 100 and 250 km altitude, were used to compute the increase in solar ionizing radiation during two flares on 21 and 23 May 1967. Since the altitude of maximum absorption of the solar energy (approximately unit optical depth) depends on the wavelength of the radiation, it is possible to estimate separately the energy enhancement in different portions of the spectrum. An ionizing energy flux increase of nearly 5 erg cm–2 sec–1 was observed on 21 May, while on the 23rd, the increase was over 7 erg cm–2 sec–1. In both flares, most of the absolute increase occurred in the 20–205 Å region of the spectrum, although the relative increase was much larger at the shorter wavelengths. 相似文献
16.
K. Kai 《Solar physics》1986,104(1):235-241
In attempting to explain observed hard X-ray and microwave flux from solar flares by a single population of energetic electrons, one has met a serious discrepancy of the order of 103–105 between the calculated and observed microwave flux. In this paper it is shown that this discrepancy can be removed for impulsive flares by the assumption of a precipitation model for both X-ray and microwave sources and that the magnetic field of 500–1000 G is required in the microwave emitting region. The precipitation model is consistent with the rapid time variation exhibited in both hard X-rays and microwaves.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985. 相似文献
17.
A model is presented which shows that large numbers of energetic electrons (0.3-> 10 MeV) and protons (1–30 MeV) can be stored in the solar corona at altitudes around 3 × 105 km for periods in excess of 5 days. Specific reference is made to the time period July 6–16 1968 as an excellent example of energetic solar particle storage. Time histories of interplanetary charged particle intensities observed by the IMP-4 and Pioneer 8 satellites are used to substantiate this contention. Detailed reference is also made to solar X-ray, optical and radio data obtained during the period in question, in addition to interplanetary magnetometer data. This model provides a unique solution to many hitherto unexplained solar particle events, and can also account for the lack of prompt particle emission from certain large solar flares recorded in the past. 相似文献
18.
The cosmic-ray 1.68-year variation: A clue to understand the nature of the solar cycle? 总被引：1，自引：0，他引：1
Using the maximum entropy method (MEM), the cosmic-ray power spectral density in the frequency range 3 × 10–9–2 × 10–7 Hz has been estimated for the period 1947–1990. Cosmic-ray intensity data were integrated from the ion chamber at Huancayo and the neutron monitor at Deep River, following the method of Nagashima and Morishita (1980). The estimated spectrum shows power-law dependence (f
–1.62), with several peaks superimposed. Periodicities of the different peaks are identified and related to solar activity phenomena; most of them were reported in the past. Once the 11-yr variation is eliminated, the most prominent feature in the spectrum is a variation, not reported before, with a period of 1.68 yr (604.8 d). This peak is correlated with fluctuations of similar periodicities found in the southern coronal hole area and in large active regions. The importance that this variation may have to elucidate the solar magnetic flux emergence and the activity cycle is discussed.Deceased 10 April, 1995. 相似文献
19.
Feffer P. T. Lin R. P. Slassi-Sennou S. McBride S. Primbsch J. H. Zimmer G. Pelling R. M. Pehl R. Madden N. Malone D. Cork C. Luke P. Vedrenne G. Cotin F. 《Solar physics》1997,171(2):419-445
The HIgh-REsolution Gamma-ray and hard X-ray Spectrometer (HIREGS) consists of an actively shielded array of twelve liquid-nitrogen-cooled germanium detectors designed to provide unprecedented spectral resolution and narrow-line sensitivity for solar gamma-ray line observations. Two long-duration, circumpolar balloon flights of HIREGS in Antarctica (10–24 January, 1992 and 31 December, 1992–10 January, 1993) provided 90.9 and 20.4 hours of solar observations, respectively. During the observations, eleven soft X-ray bursts at C levels and above (largest M1.7) occurred, and three small solar hard X-ray bursts were detected by the Compton Gamma-Ray Observatory. HIREGS detected a significant increase above 30 keV in one. No solar gamma-ray line emission was detected. Limits on the 2.223-MeV line and the hard X-ray emission are used to estimate the relative contribution of protons and electrons to the energy in flares, and to coronal heating. For the 2.223-MeV line, the upper limit fluence is 0.8 ph cm-2 in the flares, and the upper limit flux is 1.8 × 10-4 ph s-1 cm-2 in the absence of flares. These limits imply that 6 × 1030 (2) protons above 30 MeV were accelerated in the flares, assuming standard photospheric abundances and a thick target model. The total energy contained in the accelerated protons >30 MeV is 4 × 1026 ergs, but this limit can be more than 1030 ergs if the spectrum extends down to 1 MeV. The upper limit on the total energy in accelerated electrons during the observed flares can also exceed 1030 ergs if the spectrum goes down to 7 keV. Quiet-Sun observations indicate that 1026erg s-1 are deposited by energetic protons >1 MeV, well below the1027 –1028 erg s-1 required for coronal heating, while <3 × 1027 erg s-1 are deposited by energetic electrons, which does not exclude the possibility of coronal heating by quiet-time accelerated electrons. The quiet-Sun observations also suggest that if protons stored in the corona are to supply the energy for flares, as suggested by Elliot (1964), the proton spectrum must extend down to at least 2 MeV. However, collisional losses at typical coronal-loop densities prevent those low-energy protons from being stored for 104 s. It therefore seems unlikely that the energy for flares could come from energetic protons stored over long periods. 相似文献
20.
R. K. Sood 《Solar physics》1972,23(1):183-190
The Elliot model for solar flares predicts weak -ray emission from the flare region prior to large flares. A search has been made for such -radiation of energy > 50 MeV. The experiment was performed using balloon-borne detectors flown from an equatorial station during the 1967/1968 solar maximum. A number of small flares were observed, but no associated -rays were detected. A limit of 2.3 × 104 photons/cm2 s was placed on the emission from an importance 1N flare. The general lack of major solar activity during the period of the balloon flights precluded a test for the Elliot model. 相似文献