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1.
The short-term X-ray variability distinguishes Cyg X-1, which is the most likely candidate for a black hole, from other X-ray sources. The present status of our knowledge on this short-term variation, mainly from the UHURU, the MIT and the GSFC observations, is reviewed. The nature of impulsive variations which compose the time variation exceeding the statistical fluctuation is discussed. There are indications that the energy spectrum of large pulses is harder than the average spectrum, or that the large pulses are the characteristics of the hard component of the spectrum if it is composed of two, soft and hard, components. Features of the variations may be partly simulated by the superposition of random shot-noise pulses with a fraction of a second duration. However, the autocorrelation analysis and the dynamic spectrum analysis indicate that the correlation lasts for several seconds and in the variation are buried some regularities which exhibit power concentrations in several frequency bands; 0.2–0.3, 0.4–0.5, 0.8, 1.2–1.5 Hz. There are several possible interpretations of these results in terms of; e.g. (a) a mixture of shot-noise pulses with two or more constant durations, (b) the shape of the basic shot-noise pulse, (c) bunching of the pulses, (d) superposition of wave-packets or temporal oscillations. But we have not yet reached any definite understandings in the nature of the variabilities. The substructure of the fluctuations on a time scale of milliseconds suggested by two investigations is also discussed.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975. 相似文献
2.
Y. Ogawara 《Solar physics》1982,113(1-2):361-370
The Institute for Space and Astronautical Sciences (ISAS) is developing a satellite dedicated to high-energy observations of solar flares. The Solar-A will be launched in August–September, 1991, from the Kagoshima Space Center on board a M3S-II vehicle. The instrument complement emphasizes hard X-ray and soft X-ray imaging, and contains instruments supplied in part by U.S. and U.K. experimenters. This paper describes the instrumentation and the tentative observing program. 相似文献
3.
The Soft X-ray Telescope for the SOLAR-A mission 总被引：6，自引：0，他引：6
S. Tsuneta L. Acton M. Bruner J. Lemen W. Brown R. Caravalho R. Catura S. Freeland B. Jurcevich M. Morrison Y. Ogawara T. Hirayama J. Owens 《Solar physics》1991,136(1):37-67
The Soft X-ray Telescope (SXT) of the SOLAR-A mission is designed to produce X-ray movies of flares with excellent angular and time resolution as well as full-disk X-ray images for general studies. A selection of thin metal filters provide a measure of temperature discrimination and aid in obtaining the wide dynamic range required for solar observing. The co-aligned SXT aspect telescope will yield optical images for aspect reference, white-light flare and sunspot studies, and, possibly, helioseismology. This paper describes the capabilities and characteristics of the SXT for scientific observing.After the launch the name of SOLAR-A has been changed to YOHKOH. 相似文献
4.
M. Yoshimori K. Okudaira Y. Hirasima T. Igarashi M. Akasaka Y. Takai K. Morimoto T. Watanabe K. Ohki J. Nishimura T. Yamagami Y. Ogawara I. Kondo 《Solar physics》1991,136(1):69-88
The SOLAR-A spacecraft has spectroscopic capabilities in a wide energy band from soft X-rays to gamma-rays. The Wide Band Spectrometer (WBS), consisting of three kinds of spectrometers, soft X-ray spectrometer (SXS), hard X-ray spectrometer (HXS) and gamma-ray spectrometer (GRS), is installed on SOLAR-A to investigate plasma heating, high-energy particle acceleration, and interaction processes. SXS has two proportional counters and each counter provides 128-channel pulse height data in the 2–30 keV range every 2 s and 2-channel pulse count data every 0.25 s. HXS has a NaI scintillation detector and provides 32-channel pulse height data in the 20–400 keV range every 1 s and 2-channel pulse count data every 0.125 s. GRS has two identical BGO scintillation detectors and each detector provides 128-channel pulse height data in the 0.2–10 MeV range every 4 s and 4-channel pulse count data (0.2–0.7, 0.7–4, 4–7, and 7–10 MeV) every 0.25–0.5 s. In addition, each of the BGO scintillation detectors provides 16-channel pulse height data in the 8–100 MeV range every 4 s and 2-channel pulse count data (8–30 and 30–100 MeV) every 0.5 s. The SXS observations enable one to study the thermal evolution of flare plasma by obtaining time series of electron temperatures and emission measures of hot plasma; the HXS observations enable one to study the electron acceleration and heating mechanisms by obtaining time series of the electron spectrum; and the GRS observations enable one to study the high-energy electron and ion acceleration and interaction processes by obtaining time series of electron and ion spectra.After the launch the name of SOLAR-A has been changed to YOHKOH. 相似文献
5.
T. Kosugi K. Makishima T. Murakami T. Sakao T. Dotani M. Inda K. Kai S. Masuda H. Nakajima Y. Ogawara M. Sawa K. Shibasaki 《Solar physics》1991,136(1):17-36
The Hard X-ray Telescope (HXT) is a Fourier-synthesis imager; a set of spatially-modulated photon count data are taken from 64 independent subcollimators and are Fourier-transformed into an image by using procedures such as the maximum entropy method (MEM) or CLEAN. The HXT takes images of solar flares simultaneously in four energy bands, nominally 15 (or 19)–24, 24–35, 35–57, and 57–100 keV, with an ultimate angular resolution as fine as 5 arc sec and a time resolution 0.5 s. Each subcollimator has a field of view wider than the solar disk. The total effective area of the collimator/detector system reaches 70 cm2, about one order of magnitude larger than that of the HINOTORI hard X-ray imager. Thanks to these improvements, HXT will for the first time enable us to take images of flares at photon energies above 30 keV. These higher-energy images will be compared with lower-energy ones, giving clues to the understanding of nonthermal processes in solar flares, i.e., the acceleration and confinement of energetic electrons. It is of particular importance to specify the acceleration site with regard to the magnetic field figuration in a flaring region, which will be achieved by collaborative observations between HXT and the Soft X-ray Telescope on board the same mission.After the launch the name of SOLAR-A has been changed to YOHKOH. 相似文献
6.
M. Matsuoka M. Fujii S. Miyamoto J. Nishimura M. Oda Y. Ogawara S. Hayakawa I. Kasahara F. Makino Y. Tanaka P. C. Agrawal B. V. Sreekantan 《Astrophysics and Space Science》1972,18(2):472-490
Simultaneous hard X-ray and optical observations of Sco X-1 were carried out on 1971 May 1 at Hyderabad, India, when Sco X-1 was optically bright. The X-ray intensity observed by balloon-borne counter telescopes increased in coincidence with optical enhancements, while the plasma temperature derived by fitting the X-ray spectrum in the energy range 20–40 keV to the thermal bremsstrahlung spectrum did not appreciably change over the whole period of observation. 相似文献
7.
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
8.
T. Takakura K. Ohki N. Shibuya M. Fujii M. Matsuoka S. Miyamoto J. Nishimura M. Oda Y. Ogawara S. Ota 《Solar physics》1971,16(2):454-464
The location and size of a solar impulsive hard X-ray burst have been determined in one dimension to a considerable precision with a balloon-borne X-ray modulation collimator. The center of the X-ray source is on the line passing through the center of a big H flare region of 3 arc min. The size of the X-ray source is remarkably smaller and may be one arc min or less. 相似文献
9.
S. Tsuneta T. Takakura N. Nitta K. Ohki K. Makishima T. Murakami M. Oda Y. Ogawara 《Solar physics》1983,86(1-2):313-321
This paper presents studies of the vertical structure of hard X-ray flares for two contrasting examples. The 1981 May 13 flare contained a coronal hard X-ray source which was located above 50000 km above the photosphere. On the other hand, the 1981 July 20 flare had a chromospheric double source structure in the initial phase. Electrons in this case were able to stream freely from the corona to the chromosphere. 相似文献
10.
The Institute for Space and Astronautical Sciences (ISAS) is developing a satellite dedicated to high-energy observations of solar flares. The Solar-A will be launched in August–September, 1991, from the Kagoshima Space Center on board a M3S-II vehicle. The instrument complement emphasizes hard X-ray and soft X-ray imaging, and contains instruments supplied in part by U.S. and U.K. experimenters. This paper describes the instrumentation and the tentative observing program.
相似文献