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1.
SIXE (Spanish Italian X-ray Experiment) is an X-ray detector withgeometric area of 2300 cm2, formed by four identical gas-filledMulticell Proportional Counters, and devoted to study the long termspectroscopy of selected X-ray sources in the energy range 3–50 keV. Themain characteristics of SIXE are: time accuracy of 1 microsecond,spectral resolution of 5% for E > 35 keV and 46/E% for E <35 keV, continuum sensitivity (3 in 105 s) of 2 ×10-6 ph cm-2 s-1 keV-1, and line sensitivity (3in 105 s) of 8 × 10-6 ph cm-2 s-1. The size of theinstruments and the requirements of the payload (weight 103 kg, fulldimensions 660 × 660 × 450 mm3, power budget < 60 W,on-board memory 2 Gbits, telemetry rate < 100 kbps) make this experimentfully compatible with the MINISAT platform.The main scientific goal of SIXE is the study of short and long termvariability of some of the most important X-ray sources. To do that a fewselected extragalactic and galactic X-ray sources will be selected toperform a dedicated and extensive monitoring program. The mission willprovide in this way the unique opportunity for the study of X-ray sourceswith a temporal accuracy of 1 microsecond all through the time range10-5 :107 s.  相似文献   

2.
The effect of X-ray irradiation on the line-driven stellar wind in X-ray binary systems is studied. The product of the X-ray luminosityL x and the densityn in the wind is a measure to distinguish between the optically thin and thick wind regimes. For an X-ray source of the radiation temperature of 10 keV, the critical value(L x n) c , is of the order of 1037 erg s–1 cm–3; hence, most of wind-fed X-ray sources lie in the optically thick wind regime because ofL x n>(L x n) c . Then the wind structure is determined not only by the parameter =(L x /nR 2),R the distance from the X-ray source, but also by the optical thickness due to helium. The formation of fully ionized helium region depends onL x andn in a way different from that of the Strömgren sphere. In such an optically thick wind, the region behind the He II ionization boundary is little affected by X-ray irradiation and the trace elements remain to be responsible for wind acceleration. Thus, its location is important for the structure of the wind and the interpretation of various phenomena in objects such as wind-fed X-ray pulsars.  相似文献   

3.
H. Zirin 《Solar physics》1976,50(2):399-404
A large surge was observed on September 17, 1971, part of which, after travelling 200 000 km through the corona, returned to the surface to form a filament. The filament lasted about 30 min, then rose up and returned to the source of the surge. We interpret this as the filling of a semi-stable magnetic trap.The energetics of radio, X-ray, and surge expulsion are estimated. The radio spectrum and flux correspond to a thermal source of area 4 (arcmin)2, T 190 000 K, N e 2 V 7 × 1048, which is optically deep at 8800 MHz.The soft X-ray source has T 12 × 106 K, N e 2 V 3 × 1048; and if an equal mass is expelled in the surge, the kinetic energy of the surge is similar to the thermal energy of the X-ray source.  相似文献   

4.
The radio properties ofUhuru X-ray sources with fairly certain extragalactic identifications are described briefly. Radio to X-ray flux ratios are low for rich clusters of galaxies and high for double radio sources. There is some evidence from the Abell 426 (Perseus) and Abell 1367 clusters that a radio galaxy in a rich cluster may be the centre of extended X-ray emission. Nuclei of galaxies have an enormous range in X-ray luminosity; the known range is from 1030 W for our galaxy to 3×1038 W for 3C 273. Unidentified X-ray sources at high galactic latitudes may include new classes of objects with very low radio to X-ray flux ratios or hard X-ray emission.  相似文献   

5.
The Crosa and Boynton (1980) empirical model for discrete mass transfer in Her X-1 is further developed. The photometric features of the light curve (peaks of an hour duration and 0.3–0.7 m amplitude, steps near orbital phase =0); and the linear polarization bursts are assumed to be due to the formation and eclipses of the plasma blobs produced by discrete transfer of matter from optical star surface and its interaction with the accretion disc rim. The long lifetime (20h) of the cold (3×104 K) blob extending up to 1011 cm above the disc plane, as well as the deep X-ray flickerings (300 s) during the X-ray absorption dips are assumed to arise from a dispersal of accreting matter by the Rayleigh-Taylor instability in a blob moving through a hot corona of the disk atT c =3×106 K andn c =3×1011 cm–3. Thermal equilibrium in the corona and in the blobs are supported by X-ray flux. Within the first few hours after its formation a blob disintegrates into drops withr=5×109 cm,T=3×104 K, andn=3×1013 cm–3 which move then along Keplerian orbits. Frictional interactions of the drops with the corona destroy them on a 20h time-scale. The proposed model makes it possible to interpret the diverse observational facts and to predict numerous observational displays in the optical, UV, and X-ray bands. The first results of our optical-spectrum observations of blobs are briefly described.  相似文献   

6.
Using measurements of EUV and X-ray spectral lines we derive the differential emission measure vs electron temperature T from the transition region to the corona of an active region (105 T <5 × 106 K). The total emission measure and radiative losses are of order 3 × 1048 cm–3 and 4 × 1026 ergss–1 respectively. The emission measure at T > 106 K (i.e. that mainly responsible for the X-ray emission) is about 75% of the total. We also examine the use of Mg x 625 Å as an indicator of coronal electron density. A set of theoretical energy balance models of coronal loops in which the loop divergence is a variable parameter is presented and compared with the observations. Particular attention is given to the limitations inherent in any such comparison.  相似文献   

7.
Saku Tsuneta 《Solar physics》1982,113(1-2):35-48
Some X-class flares (hot thermal flares, HTF) observed with the Hinotori satellite show unique behavior: slow time variability, a compact hard X-ray source containing dense (n > 1011 cm–3) and hot (T > 3 × 107 K) plasma, and unusually weak microwave emission in spite of the intense magnetic field (B > 330 G) required theoretically to sustain the hot plasma. These observations show that HTF's have essentially thermal characteristics throughout the flare evolution, while in impulsive flares, there is a transition in the energy release mode from particle acceleration (impulsive phase) to plasma heating (gradual phase). This behavior can be explained in a unified manner by employing parallel DC electric field acting over large distances.  相似文献   

8.
One-hundred fifty-six large-scale enhancements of X-ray emission from solar active regions were studied on full-disk filterheliograms to determine characteristic morphology and expansion rates for heated coronal plasma. The X-ray photographs were compared with H observations of flares, sudden filament disappearances, sprays and loop prominence systems (LPS). Eighty-one percent of the X-ray events were correlated with H filament activity, but only forty-four percent were correlated with reported H flares. The X-ray enhancements took the form of loops or arcades of loops ranging in length from 60 000 km to 520 000 km and averaging 15 000 km in width. Lifetimes ranged from 3 hr to >24 hr. Event frequency was 1.4 per day. X-ray loop arcades evolved from sharp-edged clouds in cavities vacated by rising H filaments. Expansion velocities of the loops were 50 km s-1 immediately after excitation and 1–10 km s-1 several hours later. These long-lived loop arcades are identified with LPS, and it is suggested that the loops outlined magnetic fields which were reconnecting after filament eruptions. Another class of X-ray enhanced loops stretched outside active regions and accompanied sprays or lateral filament ejections. H brightenings occurred where these loops intersected the chromosphere. Inferred excitation velocities along the loops ranged between 300 and 1200 km s-1. It is suggested that these loops outlined closed magnetic fields guiding slow mode shocks from flares and filament eruptions.  相似文献   

9.
We compare solar X-ray observations from the UCSD experiment aboard OSO-7 with high resolution energetic electron observations from the UCAL experiment on IMP-6 for a small solar flare on 26 February 1972. A proportional counter and NaI scintillator covered the X-ray energy range 5–300 keV, while a semiconductor detector telescope covered electrons from 18 to 400 keV. A series of four non-thermal X-ray spikes were observed from 1805 to 1814 UT with average spectrum dJ/d (hv) (hv)–4.0 over the 14–64 keV range. The energetic electrons were observed at 1 AU beginning 1840 UT with a spectrum dJ/dE E –3.1. If the electrons which produce the X-ray emission and those observed at 1 AU are assumed to originate in a common source, then these observations are consistent with thin target X-ray production at the Sun and inconsistent with thick target production. Under a model consistent with the observed soft X-ray emission, we obtain quantitative estimates of the total energy, total number, escape efficiency, and energy lost in collisions for the energetic electrons.  相似文献   

10.
This paper summarizes and analyzes the results of radio optical, infrared, and X-ray observations of a large sector of the sky in the constellation Cygnus (19h20m-22h, =30–50°;l II=65–90°, |b II|10°). This region is associated with an extended X-ray source referred to as the Cygnus superbubble. About a quarter of the superbubble region is occupied by the extensively investigated multicomponent thermal radio source Cyg X. The region contains eight OB-associations which, when projected on the sky, duplicate the outline of the X-ray superbubble. These associations contains 110 stars of high luminosity (about 40 Wolf-Rayet and Of stars). The observations suggest that the X-ray superbubble is not a single object. Between 50 and 75% of its X-ray emission can be ascribed to discrete sources, the rest being probably due to regions of coronal gas about 100 pc in diameter, created by stellar winds and, possibly, supernova explosions in individual associations. The objects that produce the X-ray and optical radiation of the presumed superbubble are located at distances from 0.5 to 2.5 kpc from the Sun in the Carina-Cygnus spiral arm. The eastern portion of the region presumed superbubble contains the associations Cyg OB7 and Cyg OB4 and is generally less than 1 kpc distant, while the western portion contains the associations Cyg OB1, 2, 3, 8, and 9 and is 1 to 2 kpc distant.  相似文献   

11.
Simulation calculations have been made to examine the modification effect of a hot X-ray photon field on a-ray spectrum by the photon-photon pair production and inverse Compton scattering processes. The Cyg X-3 system was used as a paradigm. It is shown that a-ray spectrum can change significantly when passing through the ambient keV X-ray photon field of an accretion binary source. For Cyg X-3, a significant amount of r-rays originated near the central source in the range of 102-104 MeV could be absorbed by the extended X-ray photons from accretion disk corona in a high X-ray luminosity state and, on the other hand, the inverse Compton effect of secondary electrons could cause a considerable increase in intensity of-rays between ~ 10 MeV and ~ 50 MeV. The relevance of the absorption effect for observations is discussed.  相似文献   

12.
I find that a one-dimensional strong coronal shock (M s 3) will grow outward until the Mach number (M s ) ceases to increase with height (dM s /dh = 0). The shock is driven by the pressure gradient and it is damped by gravity and by energy losses (radiative and conductive). The driving and damping terms reach equilibrium for M s - 4.Standard shock jump conditions for M s - 4 lead to post-shock temperatures in the corona in the range 107 to 1.8 × 107K and emission measures from 3.8 × 1047 to 3.8 × 1048 cm-3. For isolated simple events, I predict an exponential decay of the emission measure with decay times in the range 1 6.5 min.In a detailed study of over 4000 X-ray bursts, Drake (1970) compares 1 to 6 keV X-ray data with 7.7 to 12.5 keV X-ray data (the thermal component) and finds ranges for the temperatures of 1.2 × 107 to 1.8 × 107K, for the emission measures of 5.1 × 1047 to 3.8 x 1048 cm-3 and for the decay times 0.5 20 min. He also finds that the emission measure varies ... both from event to event and within the event, by more than a factor of two.The agreement between the predictions and the observations makes it appear that a strong shock in the corona will produce a post-shock state that yields the observed characteristics of the soft component of X-ray bursts (the thermal X-rays).I give several examples where sprays and fast eruptive prominences 1} \right)$$ " align="middle" border="0"> , that are not associated with solar flares, are associated with thermal X-ray bursts. There were two slow eruptive prominences (M 1) in the sample, and neither of them yielded a detectable X-ray burst.Now at the Dept. of Physics and Astronomy (NASA), Univ. of New Mexico; Albuquerque, N.M. 87106.  相似文献   

13.
The burst component of the solar X-ray flux in the soft wavelength range 2 < < 12 Å observed from Explorer 33 and Explorer 35 from July 1966 to September 1968 was analyzed. In this period 4028 burst peaks were identified.The differential distributions of the temporal and intensity parameters of the bursts revealed no separation into more than one class of bursts. The most frequently observed value for rise time was 4 min and for decay time was 12 min. The distribution of the ratio of rise to decay time can be represented by an exponential with exponent -2.31 from a ratio of 0.3 to 2.7; the maximum in this distribution occurred at a ratio of 0.3. The values of the total observed flux, divided by the background flux at burst maximum, can be represented by a power law with exponent -2.62 for ratios between 1.5 and 32. The distribution of peak burst fluxes can be represented by a power law with exponent - 1.75 over the range 1–100 milli-erg (cm2 sec)–1. The flux time integral values are given by a power law with exponent -1.44 over the range 1–50 erg cm–2.The distribution of peak burst flux as a function of H importance revealed a general tendency for larger peak X-ray fluxes to occur with both larger H flare areas and with brighter H flares. There is no significant dependence of X-ray burst occurrence on heliographic longitude; the emission thus lacks directivity.The theory of free-free emission by a thermal electron distribution was applied to a composite quantitative discussion of hard X-ray fluxes (data from Arnoldy et al., 1968; Kane and Winckler, 1969; and Hudson et al., 1969) and soft X-ray fluxes during solar X-ray bursts. Using bursts yielding measured X-ray intensities in three different energy intervals, covering a total range of 1–50 keV, temperatures and emission measures were derived. The emission measure was found to vary from event to event. The peak time of hard X-ray events was found to occur an average of 3 min before the peak time of the corresponding soft X-ray bursts. Thus a changing emission measure during the event is also required. A free-free emission process with temperatures of 12–39 × 106K and with an emission measure in the range 3.6 × 1047 to 2.1 × 1050 cm–3 which varies both from event to event and within an individual event is required by the data examined.Now at Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey.  相似文献   

14.
The birth and early evolution of a solar active region has been investigated using X-ray observations from the Lockheed Mapping X-Ray Heliometer on board the OSO-8 spacecraft. X-ray emission is observed within three hours of the first detection of H plage. At that time, a plasma temperature of 4 × 106 K in a region having a density of the order of 1010 cm–3 is inferred. During the fifty hours following birth almost continuous flares or flare-like X-ray bursts are superimposed on a monotonically increasing base level of X-ray emission produced by plasma with a temperature of the order 3 × 106 K. If we assume that the X-rays result from heating due to dissipation of current systems or magnetic field reconnection, we conclude that flare-like X-ray emission soon after active region birth implies that the magnetic field probably emerges in a stressed or complex configuration.  相似文献   

15.
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16.
We have investigated the influence of X-ray irradiation on the vertical structure of the outer accretion disk in low-mass X-ray binaries by performing a self-consistent calculation of the vertical structure and X-ray radiation transfer in the disk. Penetrating deep into the disk, the field of scattered X-ray photons with energy E ≳ 10 keV exerts a significant influence on the vertical structure of the accretion disk at a distance R ≳ 1010 cm from the neutron star. At a distance R ∼ 1011 cm, where the total surface density in the disk reaches Σ0 ∼ 20 g cm−2, X-ray heating affects all layers of an optically thick disk. The X-ray heating effect is enhanced significantly in the presence of an extended atmospheric layer with a temperature T atm ≈ (2–3) × 106 K above the accretion disk. We have derived simple analytic formulas for the disk heating by scattered X-ray photons using an approximate solution of the transfer equation by the Sobolev method. This approximation has a ≲10% accuracy in the range of X-ray photon energies E < 20 keV.  相似文献   

17.
On 23 May 1967 energetic (10–50 keV) solar flare X-rays were observed by the OGO-III ion chamber during the period 1808–2100 UT. The time-intensity profile for the X-ray event showed three distinct peaks at 1810, 1841 and 1942 UT. The second peak, which is equivalent to 2.9 × 10–3 ergs cm–2sec–1 above 20 keV, is the largest X-ray burst observed so far by the OGO-I and OGO-III ion chambers. The soft (2–12 Å) X-ray observations reported by Van Allen (1968) also show similar peaks, roughly proportional in magnitude to the energetic X-ray peaks. However, the intensity of energetic X-rays peaked in each case 5–10 min earlier than the soft X-ray intensity indicating a relatively hard photon energy spectrum near the peak of the energetic X-ray emission. The corresponding time-intensity profile for the solar radio emission also showed three peaks in the microwave region nearly coincident with the energetic X-ray peaks. The third radio peak was relatively rich in the metric emission. Beyond this peak both the energetic X-rays and the microwave emission decayed with a time constant of 8 min while the corresponding time constant for the soft X-rays was 43 min. In view of the earlier findings about the energetic X-rays it is indicated that the 23 May solar X-ray event was similar to those observed earlier. During the 23 May event the integral energy flux spectrum at the time of peak intensity is found to be consistent with the form e –E/E 0, E 0 being about 3.4 and 3.7 keV for the peaks at 1841 and 1942 UT, respectively. Assumption of a similar spectrum during the decay phase indicates that the spectral index E 0 decreased nearly exponentially with time.The OGO-III ion chamber, which is also sensitive to protons 12 MeV, observed a solar particle event starting at 2100 UT on 23 May. It could not be determined uniquely which of the two principal X-ray peaks was associated with the particle event, and in fact both may have contributed. The particle intensity reached its maximum value at 1003 UT on 25 May 1967. The equivalent peak radiation dosage was 24 R/hour behind the 0.22 g cm–2 thick aluminum wall of the chamber. This peak radiation dosage was considerably smaller than the maximum dosage (60 R/hour) during the 2 September 1966 solar particle event, the largest event observed so far by the OGO-I and OGO-III satellites. The temporal relationship between the solar X-ray and particle events on 23 May 1967 was similar to that observed in the solar flare events on 7 July 1966, 28 August 1966 and 27 February 1967.  相似文献   

18.
A survey of soft X-ray images from Skylab has revealed a class of large-scale transient X-ray enhancements in the lower corona which are typically associated with the disappearance of H filaments away from active regions. Contemporary with the H filament disappearance, X-ray emitting structures appeared at or near the filament location with shape and size resembling the filament. Eventually these structures faded, but the filament cavity was no longer obvious. Typically the peak of the X-ray event lagged the end of the filament disappearance by tens of minutes. The durations of the coronal X-ray enhancements were considerably longer than the associated H filament disappearances. Major flare effects, such as chromospheric brightenings, typically were not associated with these X-ray events.One event analyzed quantitatively had a peak temperature between 1.8 and 2.7 × 106 K, achieved a peak density of 109 cm–3 and resulted in an enhancement in the plasma pressure over the conditions of the preexisting coronal cavity of at least a factor of 7. The mass of the coronal X-ray emitting material was about 10% that of the preexisting filament and the thermal energy of the coronal event was on the order of 1029 erg, about 10% of the mechanical energy of the H filament eruption. The event appeared to cool by radiative losses and not by thermal conduction. It is likely that the coronal enhancements are caused by heating of an excess of previously cooler material, either from the filament itself, or by compression of coronal material by a changing magnetic field.  相似文献   

19.
Simultaneous observations of a solar limb flare in the X-ray and ultraviolet regions of the spectrum are presented. Temporal and spectral X-ray observations were obtained for the 25–300 keV range while temporal, spectral, and spatial X-ray observations were obtained for the 30–0.3 keV range. The ultraviolet observations were images with a 10 spatial resolution in the lines of O v (T e 2.5 × 105 K) and Fe xxi (T e 1.1 × 107 K). The hard X-ray and O v data indicate that the impulsive phase began in the photosphere or chromosphere and continued for several minutes as material was ejected into the corona. Impulsive excitation was observed up to 30 000 km above the solar surface at specific points in the flare loop. The Fe xxi observations indicate a preheating before the impulsive phase and showed the formation of hot post-flare loops. This later formation was confirmed by soft X-ray observations. These observations provide limitations for current flare models and will provide the data needed for initial conditions in modeling the concurrent coronal transient.  相似文献   

20.
A study of the expected intensities of the stronger solar neon-like ion emission lines, some not yet observed, is carried out to compare with the observational situation. The potential usefulness of the 2p 5 3s(3 P 2) - 2p 6 forbidden line as a density diagnostic is discussed and new electric quadrupole lines in the soft X-ray range are noted. Observability diagrams are presented as a convenient overview of the known and unobserved lines. The S vii resonance lines appear to have anomalous intensities.  相似文献   

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