共查询到20条相似文献，搜索用时 15 毫秒
1.
We have re-examined and extended the measurements of the primary cosmic ray proton and helium nuclei intensities in the range from a few MeV nuc–1 to 100 GeV nuc–1 using a considerable body of recently published data. The differential spectra obtained from this data are determined as a function of both energy and rigidity. The exponents of the energy spectra of both protons and helium nuclei are found to be different at the same energy/nucleon and to increase with increasing energy between 1 and 100 GeV nuc–1 reaching a value=–2.70 at higher energies and in addition, theP/He ratio changes from a value 5 at 1 GeV nuc–1 and below to a value 30 at 100 GeV nuc–1. On a rigidity representation the spectral exponent for each species is nearly identical and remains virtually constant above several GV at a value of –2.70, and in addition, theP/He ratio is also a constant 7 above 3 GeV. The changingP/He ratio and spectral exponent on an energy representation occur at energies well above those at which interplanetary modulation effects or interstellar ionization energy loss effects can significantly affect the spectra. In effect by comparing energy spectra and rigidity spectra in the intermediate energy range above the point where solar modulation effects and interstellar energy loss effects are important, but in the range where there are significant differences between energy and rigidity spectra, we deduce that the cosmic ray source spectra are effectively rigidity spectra. This fact has important implications regarding the mechanism of acceleration of this radiation and also with regard to the form of the assumed galactic spectrum at low energies. The relationship between the proton and helium spectra derived here and the heavier nuclei spectral differences recently reported in the literature is also examined.If rigidity spectra are adopted for protons and helium nuclei, then the source abundance ratio of these two components is determined to be 7:1. Some cosmological implications of this ratio are discussed. 相似文献
2.
S. Hayakawa T. Kato F. Makino H. Ogawa Y. Tanaka K. Yamashita M. Matsuoka S. Miyamoto M. Oda Y. Ogawara 《Astrophysics and Space Science》1971,12(1):104-117
Cosmic soft X-rays in the energy range between 0.14 and 7 keV were observed with thin polypropylene window proportional counters on board a sounding rocket. The field of view crossed the galactic plane in the Cygnus-Cassiopeia region at a large angle and reached the galactic latitudes of –55° and +30°. Referring also to the result with Be window counters, we obtained the energy spectrum of Cyg XR-2, the flux from the Cas A region and the distribution of the intensity of diffuse X-rays over the scanned region. The turn-over of the Cyg XR-2 spectrum at about 1 keV indicates that the distance of the Cyg XR-2 source lies between 600 and 800 pc, if the turn-over is due entirely to interstellar absorption. The flux from the Cas A region is obtained as 0.23±0.05 photons cm–2 sec–1 in the energy range between 1.1 and 4.1 keV. The intensity of diffuse soft X-rays depends on the galactic latitude more weakly than expected from the interstellar absorption of extragalactic X-rays and shows asymmetry with respect to the galactic equator, thus suggesting a contribution of galactic X-rays. The spectrum of extragalactic X-rays is approximately represented by a power lawE
–1.8. 相似文献
3.
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
4.
An object located approximately atl=8°,b=–4° with a mean radial velocity of –212.3 km s–1 has been observed in the 21 cm neutral hydrogen line. The mean weighted velocity dispersion is 11.2 km s–1 and the total mass is estimated to be 190R
2 (kpc) solar masses. We discuss possible interpretations of the origin and nature of this object. The most likely interpretation is that we observe an expanding object which has been ejected from the galactic nucleus. 相似文献
5.
The energy spectra of protons at energies in the range of about 1–100 MeV are investigated during time periods of low solar activity using data sets from near Earth spacecraft. These populations pose a tough experimental and theoretical problem that remains unsolved up to now. We attempt to provide a consistent definition of low-flux quiet-time periods relevant to low solar activity as well as quasi-stationary periods useful at higher levels of solar activity. Using statistical methods, the possible instrumental contribution to the lowest observed proton fluxes for various detectors is estimated. We suggest and prove that there exists a low-flux population of charged particles in the energy range of about 1–10 MeV, which is present in the inner heliosphere even during the quietest conditions at lowest solar activity. The dynamics of the variations of proton spectra over the solar cycle is investigated. A series of low-flux periods is examined in detail and energy spectra of protons are approximated in the form of J(E)=AE
–+CE. By determining the best fitting parameters to the energy spectra correlations are made among them as well as with monthly sunspot numbers characterizing solar activity. It has been demonstrated that the value of the energy minimum of proton spectrum E
min that `divides' the two populations – `solar/heliospheric' and `galactic' – is shifted towards higher values with increasing solar activity. Protons have been argued to be predominantly of solar origin up to several MeV near the solar cycle minimum and up to 20–30 MeV at maximum. The slope of the lower spectrum branch (parameter ) slightly decreases with increasing solar activity. The minimum fluxes observed during the last 3 minima of solar activity are compared; the lowest fluxes were those during the 1985–1987 period. 相似文献
6.
K. P. Singh R. K. Manchanda S. Naranan B. V. Sreekantan 《Astrophysics and Space Science》1981,77(1):215-220
Soft X-rays (0.2–1.0 keV) have been detected from the high galactic latitude source MX 2140-60 in a rocket experiment. The measured flux of 10–10 erg cm–2 s–1 combined with OSO-7 measurements in 2–40 keV X-rays, are best fit by a power law photon spectrum with spectral index 2.3 and a neutral hydrogen column densityN
H=(3–7) 1020 atoms cm–2. The observations support the source identification with the cluster of galaxies SC 2146-594, as suggested by Lugger. 相似文献
7.
Power spectra based on Pioneer 6 interplanetary magnetic field data in early 1966 exhibit a frequency dependence of f
–2 in the range 2.8 × 10–4 to 1.6 × 10–2 cps for periods of both quiet and disturbed field conditions. Both the shape and power levels of these spectra are found to be due to the presence of directional discontinuities in the microstructure (< 0.01 AU) of the interplanetary magnetic field. Power spectra at lower frequencies, in the range of 2.3 × 10–6 to 1.4 × 10–4 cps, reflect the field macrostructure (> 0.1 AU) and exhibit a frequency dependence roughly between f
–1 and f
–3/2. The results are related to theories of galactic cosmic-ray modulation and are found to be consistent with recent observations of the modulation. 相似文献
8.
A maximal spectrum of gravitational radiation from sources outside our galaxy is calculated. The sources are galaxies, quasars and events that occur in the early history of the universe. The major contribution is from galaxies whose effect extends over the frequency region 10–810+4Hz, peaking at 10–110 Hz, with a spectral flux of 10 erg cm–2, s–1. The main processes of gravitational radiation in the galaxies are stellar collapse into a black hole and dying binary systems. In the region 10–4104 Hz the background spectrum is well above the detection levels of currently proposed detectors. FromMinimal considerations of this spectrum it is determined that the density of gravitational radiation is 10–39g cm–3. This background spectrum is sensitive to galactic evolution and especially sensitive to the upper mass limits and mass distribution of stars in galactic models. Therefore, the spectrum could provide information about galactic evolution complementary to that obtained by electromagnetic investigations. 相似文献
9.
Numerical solutions of the cosmic-ray equation of transport within the solar cavity and including the effects of diffusion,
convection, and energy losses due to adiabatic deceleration, have been used to reproduce the modulation of galactic electrons,
protons and helium nuclei observed during the period 1965–1970. Kinetic energies between 10 and 104 MeV/nucleon are considered. Computed and observed spectra (where data is available) are given for the years 1965, 1968, 1969
and 1970 together with the diffusion coefficients. These diffusion coefficients are assumed to be of separable form in rigidity
and radial dependence, and are consistent with the available magneticfield power spectra. The force-field solutions are given
for these diffusion coefficients and galactic spectra and compared with the numerical solutions. For each of the above years
we have (i) determined the radial density gradients near Earth; (ii) found the mean energy losses suffered by galactic particles
as they diffuse to the vicinity of the Earth's orbit; (iii) shown quantitatively the exclusion of low-energy galactic protons
and helium nuclei from near Earth by convective effects; and (iv), for nuclei of a given energy near Earth, obtained their
distribution in energy before entering the solar cavity. It is shown that the energy losses and convection lead to near-Earth
nuclei spectra at kinetic energies ≤100 MeV/nucleon in which the differential intensity is proportional to the kinetic energy
with little dependence on the form of the galactic spectrum. This dependence is in agreement with the observed spectra of
all species of atomic nuclei and we argue that this provides strong observational evidence for the presence of energy losses
in the propagation process; and for the exclusion of low energy galactic nuclei from near Earth. 相似文献
10.
Numerical calculations have been made of the radial gradients and the anisotropyvector atr=1 AU due to galactic cosmic-ray protons and helium nuclei. The model used assumes transport by convection and anisotropic diffusion, and includes the energy losses due to adiabatic deceleration. The present calculations are for the 1964–65 solar minimum. An important constraint applied ineach case was that the model reproduces the electron modulation known from deductions of the galactic spectrum and observations of the near-Earth spectrum; and also reproduces the near-Earth proton and helium nuclei spectra. The diffusion coefficients have been based upon those deduced from magnetic-field power spectra.The principal aim has been to provide estimates of radial gradients and anisotropies, particularly at kinetic energiesT100 MeV/nucleon, by the complete solution of realistic models. Typical values for protons, obtained with a galactic differential number density (total energy)–2.5, atT50 MeV are: radial gradient, 25%/AU; radial anisotropy, –0.2%; azimuthal anisotropy, 0.2%. These values change markedly when the galactic spectrum is cut-off or greatly enhanced atT<150 MeV, but the intensity spectrum near Earth remains substantially unchanged.It has been shown that it is possible to obtain negative radial gradients and positive radial anisotropies atT50 MeV for galactic particles and thus to mimic solar sources. The radial gradient for 1964–65 reported by Anderson (1968) and by Krimigis and Venkatesan (1969) are shown to be consistent with the diffusion coefficient deduced from the magnetic-field power spectrum; those reported by O'Gallagher are higher than expected and that for 20T30 MeV protons appears to be inconsistent. More precise data on conditions throughout the solar cavity are required if more definitive gradients and anisotropies are to be determined. 相似文献
11.
N. Durgaprasad 《Astrophysics and Space Science》1977,47(2):435-445
The origin of the new component of cosmic ray nuclei in 1–30 MeV amu–1 recently detected through space vehicles in interplanetary space is investigated in detail. It is assumed that these particles may originate from nearby sources, e.g., from novae type explosions, which have peculiar C, N and O compositions. These particles are further assumed to be accelerated and modulated within the heliosphere. The charged states of these ions in the interstellar space have been calculated in detail and it is shown that the same charged states are preserved in the heliosphere when they are accelerated to energies of the order of 107eV amu–1 from energies of 105 ev amu–1. Modulation of these ions are calculated and it is found that because of low charged states of the ions these have high rigidities and are modulated in such a way as to enhance the O-ion abundances as compared to C-ions. A comparison is made of the demodulated composition of C to Si-ions with available abundance data of some novae. 相似文献
12.
We propose a model of chemical evolution of the galactic halo which consists of a succession of two different evolutionary stages; each stage is characterized by different outflow rate of gas from the star-forming region so that different metal-enrichment rate is resulted. The low-metal stars with [Fe/H]<–0.8 are formed mainly during the first 3×108 yr, and most of the high-metal stars with [Fe/H]–0.8 are formed during the succeeding 2×109 yr. This model naturally explains the metallicity distribution of globular clusters in the galactic halo including both the metal-rich and the metal-poor clusters. We also discuss the implications of the present model on the formation and evolution of the galactic halo. 相似文献
13.
R.K. Manchanda 《Astrophysics and Space Science》2002,282(1):149-160
The spectral and temporal measurements in the hard X-ray region between 20-200 keV not only determines the extended behaviour
of thermal X-ray spectrum below 10 keV but also provide a unique insight into the non-thermal processes in relativistic astrophysical
plasma. From our present understanding of the X-ray sources, a significant fluxin the 20-200 keV band is expected from a variety
of astrophysical phenomena, however, the available spectral data on the galactic and extragalactic X-ray source is very limited.
This is mainly due to the fact that sensitivity of the detector systems used for earlier measurements was relatively poor.
Since 1997, we have been carrying out a programme of hard X-ray observations galactic and extragalactic sources, in the 20-200
keV energy band using a highly sensitive balloon borne experiment. The X-ray telescope consists of three modules of large
area scintillation counters specially configured in the back-to-back geometry and have a combined sensitivity of ∼ 10-6 ph cm-2 s-1 keV-1 for an on-source observations of 3 hrs. A total of 30 hours of ceiling data above an altitude of 3 mbar has been collected
in 4 successful balloon flights from Hyderabad, India. Almost a dozen galactic and extragalactic X-ray sources were targeted
and tracked during these observations. A positive detection was made in each case and in some cases the observed spectra extended
right up to 150 keV. A brief account of the observed spectral and temporal features on some of the sources along with accurate
measurement of diffuse background spectrum and a weak gamma ray burst will be presented in the paper.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
We present a detailed study of the bremsstrahlung gamma-ray emissivity of the galactic disk. We show that there are large uncertainties in the production spectrum of photons in the medium energy range (10–100 MeV) due to our lack of knowledge of the interstellar electron spectrum below a few hundred MeV. In fact, gamma-ray observations can be of great help in determining this spectrum. At present, the spectral shape of the local gamma-ray emissivity above 30 MeV is available, thanks to the SAS-II and the COS-B satellites. Comparing it to our calculations, we determine the local interstellar electron flux in the 50–500 MeV range; the corresponding integrated gamma-ray emissivity above 100 MeV is equal to 2.4×10–25 photons s–1 (H-atom)–1, 60% higher than previously accepted values. 相似文献
15.
Numerical solutions of the cosmic-ray transport equation for the interplanetary region and including the effects of diffusion, convection, and energy loss, have been obtained for a galactic differential number-density spectrum of gaussian form, central kinetic energyT
0, and a width at half height maximum of 0.1T
0. These solutions have been used to show the redistribution in energy, and the reduction in number density, within the solar cavity. The mean energy loss is shown to be usefully approximated by the force-field potential when /T
01/2. The principal finding is that galactic cosmic-ray protons and helium nuclei, with kinetic energies less than about 80 MeV/nucleon, virtually, are completely excluded from near Earth by convective effects. As a result of this exclusion, it is found that it is not possible to demodulate the proton and helium-nuclei spectra, observed in 1964–65, to obtain information about low-energy galactic cosmic rays. 相似文献
16.
The propagation and modulation of electrons in the heliosphere play an important part in improving our understanding and assessment of the modulation processes. A full three-dimensional numerical model is used to study the modulation of galactic electrons, from Earth into the inner heliosheath, over an energy range from 10 MeV to 30 GeV. The modeling is compared with observations of 6–14 MeV electrons from Voyager 1 and observations at Earth from the PAMELA mission. Computed spectra are shown at different spatial positions. Based on comparison with Voyager 1 observations, a new local interstellar electron spectrum is calculated. We find that it consists of two power-laws: In terms of kinetic energy E, the results give E ?1.5 below ～500 MeV and E ?3.15 at higher energies. Radial intensity profiles are computed also for 12 MeV electrons, including a Jovian source, and compared to the 6–14 MeV observations from Voyager 1. Since the Jovian and galactic electrons can be separated in the model, we calculate the intensity of galactic electrons below 100 MeV at Earth. The highest possible differential flux of galactic electrons at Earth with E=12 MeV is found to have a value of 2.5×10?1 electrons m?2?s?1?sr?1?MeV?1 which is significantly lower (a factor of 3) than the Jovian electron flux at Earth. The model can also reproduce the extraordinary increase of electrons by a factor of 60 at 12 MeV in the inner heliosheath. A lower limit for the local interstellar spectrum at 12 MeV is estimated to have a value of (90±10) electrons m?2?s?1?sr?1?MeV?1. 相似文献
17.
D. C. V. Mallik 《Astrophysics and Space Science》1980,69(1):133-145
A new evaluation of chemical evolution coefficients has been made using recent stellar evolution and nucleosynthesis data. The role of the low and intermediate mass stars in galactic nucleosynthesis has been emphasized. A significant amount of4He,12C and neutron-rich species is found to be contributed by these stars. Comparison with observed abundances suggests a primary origin of14N. The simple model of galactic evolution with the new coefficients has been used to derive the ratio of helium to heavy element enrichment in the Galaxy. The new stellar evolution data do not explain the large value of this ratio that has been determined observationally. 相似文献
18.
Cosmic-ray propagation in the vicinity of 1 kpc from the Sun is considered. The data on the 1012–1015 eV particle anisotropy, on 1012 eV electron spectrum, and on temporal cosmic-ray variations are analyzed. The diffusion coefficientD(1012–1013 eV)=1029–1030 cm2s–1 inferred from the analysis coincides with its standard value in the large-halo model withh=15 kpc. The total power of cosmic-ray generation, about 3×1049 erg per SN in the proton component and about 1048 erg per SN in the electron component, typical of the galactic diffusion model is in agreement with the obtained parameters of local sources. 相似文献
19.
Kevin M. Theissen Robert B. Dunbar Alan K. Cooper David A. Mucciarone Dirk Hoffmann 《Global and Planetary Change》2003,39(3-4):227-256
Ocean Drilling Program Leg 188, Prydz Bay, East Antarctica is part of a larger initiative to explore the Cenozoic history of the Antarctic Ice Sheet through direct drilling and sampling of the continental margins. In this paper, we present stable isotopic results from Ocean Drilling Program (ODP) Site 1167 located on the Prydz Channel Trough Mouth Fan (TMF), the first Antarctic TMF to be drilled. The foraminifer-based δ18O record is interpreted along with sedimentary and downhole logging evidence to reconstruct the Quaternary glacial history of Prydz Bay and the adjacent Lambert Glacier Amery Ice Shelf System (LGAISS). We report an electron spin resonance age date of 36.9±3.3 ka at 0.45 m below sea floor and correlate suspected glacial–interglacial cycles with the global isotopic stratigraphy to improve the chronology for Site 1167. The δ18O record based on planktonic (Neogloboquadrina pachyderma (s.)) and limited benthic results (Globocassidulina crassa), indicates a trend of ice sheet expansion that was interrupted by a period of reduced ice volume and possibly warmer conditions during the early–mid-Pleistocene (0.9–1.38 Ma). An increase in δ18O values after 900 ka appears to coincide with the mid-Pleistocene climate transition and the expansion of the northern hemisphere ice sheet. The δ18O record in the upper 50 m of the stratigraphic section indicates as few as three glacial–interglacial cycles, tentatively assigned as marine isotopic stages (MIS) 16–21, are preserved since the Brunhes/Matuyama paleomagnetic reversal (780 ka). This suggests that there is a large unconformity near the top of the section and/or that there may have been few extreme advances of the ice sheet since the mid-Pleistocene climate transition resulting in lowered sedimentation rates on the Prydz Channel TMF. The stable isotopic record from Site 1167 is one of the few available from the area south of the Antarctic Polar Front that has been linked with the global isotopic stratigraphy. Our results suggest the potential for the recovery of useful stable isotopic records in other TMFs. 相似文献
20.
3He is an intermediate product in the proton-proton chain, and standard models of the Sun predict a large bulge of enhanced 3He abundance near M
r
/M
0 = 0.6 in the contemporary Sun. The relatively low abundance of 3He at the solar surface, which is derived from solar wind observations, poses severe constraints to non-standard solar models.Direct measurements of the 3He abundance in the solar atmosphere are extremely difficult, whereas indirect measurements, e.g., in the solar wind, have been performed with considerable precision. The interpretation of solar wind observations with respect to solar surface abundances has been greatly improved in recent years. Abundance measurements have been performed under a large variety of solar wind conditions and refined models have been developed for the transport processes in the chromosphere and the transition region and for the processes occurring in the solar corona. From these measurements we estimate the present isotopic number ratio 3He/4He to be (4.1 ± 1.0) × 10–4 at the solar surface, corresponding to the weight abundance X
3 = (9.0 ± 2.4) × 10–5. The zero-age Main-Sequence abundance of 3He (after burning of D) might have been slightly lower (by about 10 to 20%) than the present-day value.Non-standard solar models involving mild turbulent diffusion (Lebreton and Maeder, 1987) could account for a slow secular increase of the 3He/4He ratio in the solar atmosphere. On the other hand it is difficult to reconcile models with severe mass loss as proposed by Guzik, Willson, and Brunish (1987) with this constraint. The slowing down of the solar rotation during the early Main-Sequence evolution was accompanied by stronger differential rotation probably implying a more effective mixing of the inner parts. Again, the surface abundance of 3He imposes severe limits on the evolution of the distribution of momentum within the early Sun. 相似文献