共查询到20条相似文献，搜索用时 31 毫秒
1.
A. A. Stepanian 《Astrophysics and Space Science》1982,84(2):347-361
According to the proposed model of the Cyg X-3, it should be recognized as a binary system consisting of a pulsar and an usual star. The plasma with the frozen-in field flows out from the star. The electromagnetic continuous spectrum in the range from radio to gamma radiation owes its origin to the interaction of electrons accelerated by a pulsar with the magnetic field of the stream. The influence of the inverse Compton effect on the spectral distribution of radiation has been considered by the numerical calculations of a system of kinetic equations. The calculations show remarkable agreement with the measurements, if the particle energy spectrum is expressed as dN/dE=AE
–2.2. The lower limit of the accelerated particle energy equals approximately 10–2 erg.The situation of the peak of gamma-quantum radiation of very high energy in respect to the minimum in the X-ray radiation can be explained in terms of the suggested model. 相似文献
2.
The statistical equilibrium equations for the continuum and first 10 levels of a hydrogen atom show that the radiation of a bright prominence (the brightness of the H line has attained 56 mÅ of the disc centre spectrum) is completely due to scattering of the Sun radiation. The basic unknowns are separated with certainty: electron concentration (n
e = 3.0 × 1010 cm–3), effective thickness (l = 4.2 × 108 cm) and electron temperature (T
e = 5000 K).Radiation of a very bright prominence (A
(H) = 213 mÅ; T
e = 7300 K; n
e = 5.0 × 1011 cm–3; l = 1.3 × 107 cm) is on account of electron impacts (40%) and the Sun radiation scattering (60%).The parameters are shown to depend greatly on the prominence optical thickness in the lines of the first subordinate series of a hydrogen atom. In the course of determination all the parameters and 100 interconnected integral equations of the radiation diffusion have been thickness-averaged; the population of levels has been calculated by observations using the self-absorption factors. 相似文献
3.
We report on our results of modelling the physical processes in the uppermost layers of strongly irradiated atmospheres of
low mass unevolved companions in Precataclysmic Binaries (PCBs). Reprocessing of Lyman continuum L
c
radiation from the hot subdwarf (sdw) primary is studied in detail. We solve explicitly a set of equations of hydrostatic,
ionization and thermal equilibrium to calculate the intensity of the reprocessed emergent radiation in recombinations for
an optically thin plasma. We consider contributions from free-free and bound-free transitions. Diffuse radiation is taken
into account, but the effects of self-absorption of the re-emitted radiation are neglected.
For a purely hydrogenic atmosphere and typical values of incident fluxes, densities, gas pressures for the irradiated upper
atmospheric layers, we find that the L
c
radiation will be absorbed and re-emitted in recombinations within a column of effective thickness (106–108) cm of HII, depending on the electron density, the effective temperature of the sdw and the separation between the components. One of
the non-trivial results of our model computations lies in the overheating of the uppermost layers of the irradiated atmosphere:
the equilibrium temperature of the gas turns out to be considerably higher than the blackbody temperature following from the
diluted incoming radiation of sdw. Energy balance considerations reveal that roughly 25–50% of the L
c
flux is expended on the ionization of H and is re-emitted subsequently in recombinations. The remaining portion of the L
c
flux is spent on readjustment of the uppermost layers of the irradiated atmosphere. One of the consequences is the onset
of thermal instability in these layers. 相似文献
4.
The propagation of an instantaneous burst of isotropic radiation from the time of its onset at some redshift z 0 to the time of its detection at the present epoch (at z = 0) is considered within the framework of a flat Universe. Thomson scattering by free electrons and scattering in primordial hydrogen lines (Hα, Hβ, Pα, and Pβ) are believed to be the sources of opacity, with the single-scattering albedo in the lines being calculated by taking into account the deexcitation of the upper levels of the transitions being considered under the action of background blackbody radiation. The profiles of these lines in the burst spectrum at the present epoch have been constructed for various z0 at various distances from the burst center. To a first approximation, these profiles do not depend on the burst radiation spectrum and intensity. It is shown that the lines are purely absorption ones at a sufficiently large distance, but an emission component can appear with decreasing distance, which strengthens as the distance decreases, while the absorption component weakens. The absorption depth in the combined profile can reach 2 ×10?4 for the Hα and Hβ lines and 7 × 10?6 for the Pα and Pβ lines. In this case, the relative amplitude of the temperature fluctuations lies within the range 10?7?10?9. The calculations have been performed for bursts with different characteristic initial sizes. At the same z 0, the hydrogen line profiles essentially coincide for sizes smaller than some value, and the contrast of the lines decreases with increasing burst size for greater ones.
相似文献5.
Lars Wåhlin 《Astrophysics and Space Science》1981,76(1):259-260
In a closed gravitationally-bound Universe we are subject to an inward accelerationa
0. One consequence of this acceleration is that matter will radiate and create a black-body spectrum throughout the Universe. Using the valuea
0=7.623×10–12 ms–2 and a radiation formula from a previously-described cosmological model (Wåhlin, 1981), we obtain a black-body temperature of 2.766 K. 相似文献
6.
Cyclotron microwave emission from magnetic stars is considered, assuming that they have coronae with the temperatureT107 K and the emission measureEM1054 cm–3. It has been shown that the cyclotron radiation from a star with a dipole magnetic field has a specific spectrum with a maximum in the frequency rangesv
o/2 >v >sv
o/2 (s being the number of cyclotron harmonic, andv
o the gyrofrequency corresponding to the polar magnetic field) and radiation flux decreasing towards lower frequencies asv
4/3. The frequency of the spectrum maximum depends on the angle between the line-of-sight and the magnetic axis of the star. The observed radiation from a rotating magnetic star can be modulated with a modulation depth of about 0.2 at frequencies near maximum. The radiation is partially circularly-polarized in the sense of an extraordinary mode. The degree of polarization is almost constant at frequenciesv >sv
o/2 and increases with frequency atv >sv
o/2. The estimation of cyclotron radio fluxes of the nearest magnetic stars shows that they are observable in microwaves by means of modern radio astronomy. 相似文献
7.
Using slab model atmospheres that are irradiated from both sides by photospheric, chromospheric, and coronal radiation fields we have determined the ionization and excitation equilibrium for hydrogen.The model atom consists of two bound levels (n = 1 and n = 2) and a continuum. Ly- was assumed to be optically thick with the transition in detailed radiative balance. The Balmer continuum was assumed to be optically thin with the associated radiative ionization dominated by the photospheric radiation field (T
rad = 5940 K). The ionization equilibrium was determined from an exact treatment of the radiative transfer problem for the internally generated Ly-c field and the impressed chromospheric and coronal field (characterized by T
rad = 6500K).Our calculations corroborate the hypothesis that N2, the n = 2 population density, is uniquely determined by the electron density N
e. We also present ionization curves for 6000K, 7500K, and 10000K models ranging in total hydrogen density from 1 × 1010/cm3 to 3 × 1012/cm3. Using these curves it is possible to obtain the total hydrogen density from the n = 2 population density in prominences and spicules.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
8.
We show results of numerical simulations of a three component plasma consisting of electrons, ions and dust with external
gravitation and radiation fields. We perform simulation runs, starting from an analytic halo equilibrium, balancing pressure,
gravitational, and radiative forces. Within these the equilibrium is perturbed by the radiation of a typical OB-star association.
The perturbation has a total energy input of 107
L
⊙ and a duration of 30 Myrs. After switching off the perturbation, the simulations are continued to further investigate the
dynamics induced. We start with a self consistent one-fluid MHD model without background magnetic field and show for an asymmetric
case that the system approaches a new equilibrium after switching on the perturbation. Later it relaxes into the starting
configuration again, when the additional radiation is turned off. We then show, first by including a disk-parallel magnetic
field and then by redoing the simulations with a full three-fluid code, the influence of magnetic fields and species separation
on the plasma dynamics. With our computations we demonstrate that these features can be important for the explanation of the
structures of galactic halos and large scale mass flows.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
D. S. Davis 《Astrophysics and Space Science》1985,116(1):89-96
Spherical accretion onto black holes at high accretion rates leads to temperatures and optical depths for which Comptonization of the emerging radiation plays an important role, altering both the plasma temperature and the emergent spectrum. In this paper the nonlocal effects of Comptonization are accounted for by numerically modeling the scattering process with Monte Carlo techniques. Calculations are performed for black hole masses ranging from 101–109
M
and are compared with the local scattering model of Ipser and Price (1983). It is found that the local scattering approximation underestimates the energy in the X-ray portion of the spectrum. Monte Carlo calculations shows that the spectrum flattens and the spectral index decreases to values about 20% below those obtained by using the local scattering approximation. 相似文献
10.
The ionization conditions in coronal loops are investigated in the temperature range 2 × 105–2 × 106K, assuming velocity, density and temperature distributions computed for a siphon model of a pure hydrogen plasma. Use is made of the set of the carbon ions as an example of the general behaviour of the ions characteristic of that temperature range. It is found that the deviation from equilibrium ionization is large for subsonic-supersonic flow if the density is less than 5 × 109cm–-3, with the exception of the lower part of the first leg of very cool loops (T 2 × 10 K). With this exception cooler loops, given their larger density drop along the axis, show deviations from ionization equilibrium more easily than hotter ones, in spite of their lower flow velocity. We conclude that the possibility of a non-equilibrium state must be taken into account when deducing from measurements of line intensities the temperature of loops in which a flow may occur.Now at Institute for Plasma Research, Stanford University, as an E.S.A. Fellow. 相似文献
11.
We have calculated the distortions of the cosmic microwave background (CMB) spectrum in the wavelength range 2–50 cm due to the superposition of the CMB hydrogen recombination radiation in subordinate lines. The level populations were determined by numerically solving the equation of recombination kinetics together with the statistical equilibrium equations for a 60-level model hydrogen atom. The relative distortions are ≈10?7–10?6, with their wavelength dependence having a low-contrast, wavy pattern. However, the contrast increases severalfold and becomes pronounced when passing to the differential distortion spectrum. We study the dependence of the distortions on cosmological parameters. 相似文献
12.
On the basis of Sobolev's method, the population of 30 levels of hydrogen atom is determined allowing for the radiative and collision processes of the heating and ionization of the medium with velocity gradient gradv=10–9–10–11s–1, electron temperatureT
e=104 K-2×104 K and electron densityN
e=1010 cm–3–1011 cm–3. The central source radiation is characterized by a power spectrum with spectral indices varying from 0 to 2. A region of possible physical conditions is found where the thermal diffuse radiation of the envelope exceeds the emission in the Balmer H line. 相似文献
13.
The continuum spectrum of OJ 287, like most other BL Lac objects, is featureless- no emission or absorption lines are observed. However, OJ 287 shows variations at different timescales in flux and polarization at various wavelength bands. Using the available variability data one can estimate the sizes of the emission regions in the source from light travel time arguments. We assume the emission mechanism to be synchrotron radiation by high energy electrons with single power law energy distribution. Theoretical synchrotron spectrum in the frequency range 1011–1017
H
z
is compared with the observed spectral shape, obtained from new multifrequency quasi-simultaneous observations, to estimate the lower and upper cut off frequencies. These frequencies are used to obtain theoretical values of the variability timescales and magnetic field in the emission region. We obtain a value of 0.93 G for the magnetic field and 5.184×104
sec for the cooling time from the quiescent continuum spectrum. The shock-in-jet model explains the spectrum where shocks accelerate the particles and amplify the magnetic field in the jet. This timescale is compared with the one obtained from observed short timescale variability (20 minutes) with proper beaming correction. The short timescale variations (200 minutes in the source frame), possibly caused by an additional, flaring, component of the source, are also used to calculate compressed magnetic field. The observed and theoretically estimated variability timescales and the shape of the spectrum suggest that there are more than one emission components in OJ 287. 相似文献
14.
TeV Gamma Rays From the Galactic Center Direct and Indirect Links to the Massive Black Hole in Sgr A
The recent detection of TeV gamma-radiation from the direction of the Galactic Center within several arc-minutes around Sgr
A* is the first model-independent evidence of existence of high-energy particle accelerator(s) in the central 10 pc region of
our Galaxy. This is an extraordinary site that harbours many remarkable objects with the compact radio source Sgr A* – a hypothetical super-massive black hole (SMBH) – in the dynamical center of the Galaxy. Here we explore the possible direct and indirect links of the reported TeV emission to the SMBH. We show that at least three γ-ray production scenarios that take place close
to the event horizon of the SMBH can explain the reported TeV fluxes. An alternative (or additional) channel of TeV radiation
is related to the run-away protons accelerated in Sgr A*. Quasi-continuous injection of relativistic protons into the surrounding dense gas environment initiates detectable high-energy
gamma-ray emission. The absolute flux and the energy spectrum of this radiation component strongly depend on the history of
particle injection and the character of diffusion of protons during the last 105 yr. For a reasonable combination of a few model parameters, one can explain the detected gamma-ray flux solely by this diffuse
component. 相似文献
15.
In this paper, we suggest that a solar flare may be triggered by a lack of thermal equilibrium rather than by a magnetic instability. The possibility of such a thermal nonequilibrium (or catastrophe) is demonstrated by solving approximately the energy equation for a loop under a balance between thermal conduction, optically thin radiation and a heating source. It is found that, if one starts with a cool equilibrium at a few times 104 K and gradually increases the heating or decreases the loop pressure (or decreases the loop length), then, ultimately, critical metastable conditions are reached beyond which no cool equilibrium exists. The plasma heats up explosively to a new quasi-equilibrium at typically 107 K. During such a thermal flaring, any magnetic disruption or particle acceleration are secondary in nature. For a simple-loop (or compact) flare, the cool core of an active-region loop heats up and the magnetic tube of plasma maintains its position. For a two-ribbon flare, the material of an active-region (or plage) filament heats up and expands along the filament; it slowly rises until, at a critical height, the magnetic configuration becomes magnetohydrodynamically unstable and erupts violently outwards. In this case thermal nonequilibrium acts as a trigger for the magnetic eruption and subsequent magnetic energy release as the field closes back down. 相似文献
16.
Veniamin Berezinsky 《Astrophysics and Space Science》2007,309(1-4):453-463
Propagation of UHE protons through CMB radiation leaves the imprint on energy spectrum in the form of Greisen–Zatsepin–Kuzmin
(GZK) cutoff, bump (pile-up protons) and dip. The dip is a feature in energy range 1×1018–4×1019 eV, caused by electron-positron pair production on CMB photons. Calculated for power-law generation spectrum with index
γ
g
=2.7, the shape of the dip is confirmed with high accuracy by data of Akeno—AGASA, HiRes, Yakutsk and Fly’s Eye detectors.
The predicted shape of the dip is robust: it is valid for the rectilinear and diffusive propagation, for different discretenesses
in the source distribution, for local source overdensity and deficit etc. This property of the dip allows us to use it for
energy calibration of the detectors. The energy shift λ for each detector is determined by minimum χ
2 in comparison of observed and calculated dip. After this energy calibration the absolute fluxes, measured by AGASA, HiRes
and Yakutsk detectors remarkably coincide in energy region 1×1018–1×1020 eV. Below the characteristic energy E
c
≈1×1018 eV the spectrum of the dip flattens for both diffusive and rectilinear propagation, and more steep galactic spectrum becomes
dominant at E<E
c
. The energy of transition E
tr<E
c
approximately coincides with the position of the second knee E
2kn
, observed in the cosmic ray spectrum. The dip-induced transition from galactic to extragalactic cosmic rays at the second
knee is compared with traditional model of transition at ankle, the feature observed at energy ∼1×1019 eV.
相似文献
17.
George L. Withbroe 《Solar physics》1975,45(2):301-317
A technique for analyzing measurements of XUV spectral line intensities is described. Application of the technique to OSO-4 and OSO-6 spectra indicates that the mean coronal temperature is 2.1 × 106 K in typical active solar regions and that the mean coronal temperature in typical quiet regions ranges from 1.5 × 106 to 2.1 × 106 K. One active region spectrum shows evidence for substantial quantities of coronal material with 2 × 106 < T < 3.5 × 106 K. Measurements from limb spectra show evidence that (1) coronal abundances of N and O are low relative to heavier elements; or (2) that the ionization equilibrium calculations used may contain systematic errors; or (3) that the XUV intensity measurements may be incorrectly calibrated. 相似文献
18.
Elena DzifčÁKOVÁ 《Solar physics》2006,234(2):243-256
Changes in the excitation equilibrium of Feviii – Fe xv in the solar corona due to the electron non-thermal κ-distribution
are studied. The shape of the distribution affects the electron excitation rate and thus the relative intensities of the spectral
lines. Since the shape of the electron distribution function influences also the ionization equilibrium of Fe, both effects
change the final intensities of the lines. Possibilities for diagnostics of the shape of the electron distribution in the
solar corona are discussed. Synthetic spectrum of Fe for T = 1.58× 106 K and ne = 108 cm−3 is shown together with the synthetic spectra computed with DEM for the quiet Sun. 相似文献
19.
The emissivity for the two photons decay from the metastable level 2s has been computed in the case of a gaseous nebula of pure hydrogen, with both radiative and collisional excitation of the states.The populations of 2s and 2p levels are deduced from the condition of equilibrium with other levels. Electron temperatures between 104 and 4×104K and electron densities between 104 and 106 cm–3 have been investigated.For the optically thin case Ly intensity has also been computed.In the case of collisional excitation a much greater efficiency for the two photons process is found, which profoundly affects the appearance of the continuous spectrum. 相似文献
20.
Lars Wåhlin 《Astrophysics and Space Science》1981,74(1):157-167
In a closed expanding-contracting Universe, matter will be subject to an inward acceleration large enough to prevent perpetual expansion. A closed Universe must also perform a simple harmonic motion, which might consist either of one single cycle or of an infinite series of oscillations about a central point. It is the purpose of this study to find the rate ofa
0, the cosmic acceleration, from which the gravitational constantG can be determined. It will be shown from Ampère's equation and Planck's radiation law that it is possible to derivea
0=7.623×10–12 ms–2, a value which also conforms with the uncertainty principle. The relationship betweena
0 and electromagnetic radiation is based on the concept that charges (such as electrons) must emit radiation while accelerating. The rate ofa
0 yields a universal gravitational constant ofG=6.645×10–11 N m2 kg–2. 相似文献