Intense X-ray flares from Aquila X-1 and Circinus X-1
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Buff, J.↗
Engineering topics
Buff, J.
Publications and source records attributed to Buff, J..
The transient X-ray source A0620-00 - Intensity variations and evidence for an 8 day periodicity
The X-ray intensity of the transient source A0620-00 has been measured frequently with the SAS-3 X-ray Observatory from August 8, 1975 to February 13, 1976. This brightest of all known X-ray transients shows intensity variations on a time scale of days superposed on a general decline. Intensity data for the period from January 7 to February 13, 1976, show evidence of an approximate 7.8-day periodicity that may be the result of binary motion.
Matilsky, T.↗
Discovery of X-ray bursts from two sources in Aquila
Two X-ray burst sources have been discovered in Aquila with the aid of the SAS 3 X-ray Observatory; MXB 1906 + 00 and Aql MXB. The present paper reports on source positions, spectra, time structure, and burst energy. Five bursts were detected from MXB 1906 + 00, and the data are shown to be consistent with the assumption that there was a burst about every 8.9 hr. A comparison of raw counting data for three bursts indicates that the bursts were detected in the energy range from 1.3 to 19 keV and that the spectrum softened during burst decay. The spectrum of the one burst observed from Aql MXB is found not to soften during burst decay. It is suggested that MXB 1906 + 00 and the previously known 'steady' source A 1905 + 00 are very likely to be the same source and that the ratio of time-averaged 'steady' luminosity to time-averaged burst luminosity would be approximately 80.
Lewin, W. H. G.↗
Transfer of X-rays through a spherically symmetric gas cloud
Approximate solutions are presented for the transfer of radiation through spherically symmetric gas clouds surrounding a point source of X-rays. The approach is similar to that of Tarter and Salpeter (1969) except that heating by Compton scattering and the Auger effect is included. The temperature and ionization structure are sensitive to the source spectrum, and the solutions are not unique if soft X-rays are deficient. The emergent spectrum is rich in optical, ultraviolet, and X-ray emission lines. The radiation force due to photoelectric absorption of X-rays may exceed the force due to Compton scattering by a factor of order 10 for the radiation fields and densities likely to be encountered in galactic binary X-ray sources.
Hatchett, S.↗
A fast transient source of hard X-rays at high galactic latitude
An extremely short-lived transient X-ray source has been detected with the SAS-3 satellite at a high galactic latitude (about -51 deg). The source, designated MX 2346-65, had a duration of between 45 s and 2200 s as well as a very hard spectrum. This source had not been detected in previous sky surveys and was not seen again by SAS-3 in 7 days of further periodic observations. Possible explanations of this type of event are discussed.
Rappaport, S.↗
Discovery of a 283-second periodic variation in the X-ray source 3U 0900-40
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Mcclintock, J. E.↗
Search for X-ray emission from Nova Cygni 1975
A search for X-rays from Nova Cygni 1975 was carried out before, during, and after the time of optical maximum. No X-rays were detected over the spectral range 0.1-50 keV. On the basis of these results a strong upper limit of .0001 has been placed on the ratio of X-ray to optical luminosity for this nova, consistent with effective temperatures of about 10,000 K. If Nova Cygni 1975 is a virgin nova, its low mass exchange rate would imply that any associated X-ray emission would not be detectable by present techniques.
Hoffman, J. A.↗
The transient periodic X-ray source in Taurus, A0535+26
Eighteen X-ray light curves of the 104-sec periodicity in the Taurus X-ray nova A 0535+26 are analyzed which were obtained by SAS-3 in six energy intervals between 1 and 35 keV during the period from May 30 to June 2, 1975. It is shown that the pulse structure is relatively simple at energies above 19 keV, but develops a complex series of five irregularly spaced maxima at lower energies. The energy spectrum averaged over the 104-sec period is found to be extremely hard, with a best-fit temperature of about 30 keV for the exponential spectrum, an excess at about 15 keV, and a steepening above 20 keV. It is suggested that A 0535+26 may be a compact object in a binary system containing the peculiar Be star HDE 245770. The transient behavior could arise due to episodic mass loss by the primary or because the compact object is in a highly eccentric orbit about the companion, with appreciable mass transfer occurring only at periastron.
Bradt, H.↗
SAS-3 observations of an X-ray flare from Cygnus X-1
Preliminary results are presented for the SAS-3 observation of an X-ray flare from Cygnus X-1. The 1.5 to 6 keV intensity rose by a factor of four and exhibited variability on several time scales from seconds to hours. The 6 to 15 keV intensity showed less activity. The event is similar to that observed by ANS and Ariel 5, but lasted less than two weeks.
Canizares, C. R.↗
X-ray nova A0620-00 - Celestial position and low-energy flux
The X-ray nova A0620-00 (Nova Monocerotis 1975) has been observed with the SAS-3 satellite. The 1-10 keV intensity was observed to increase by a factor of 2.3 from August 8 to August 11, 1975. It reached and maintained a constant intensity of 1.7 by 10 to the -6 power erg/sq cm/sec from August 11 to August 13. Limits on periodicities of not more than 2 per cent of the power were obtained for periods from 0.2 ms to 435 s. A precise position was obtained with the SAS-3 modulation collimators on August 15. This led directly to optical and radio identifications. Observations with the SAS-3 low-energy concentrator system on August 27 showed an intense 0.4-0.8 keV flux emanating from the nova. A hydrogen column density of 3.5 (plus or minus 0.3) by 10 to the 21st power per sq cm was inferred from these data.
Doxsey, R.↗
Isothermal blast wave model of supernova remnants
The validity of the 'adiabatic' assumption in supernova-remnant calculations is examined, and the alternative extreme of an isothermal blast wave is explored. It is concluded that, because of thermal conductivity, the large temperature gradients predicted by the adiabatic model probably are not maintained in nature. Self-similar solutions to the hydrodynamic equations for an isothermal blast wave have been found and studied. These solutions are then used to determine the relationship between X-ray observations and inferred parameters of supernova remnants. A comparison of the present results with those for the adiabatic model indicates differences which are less than present observational uncertainties. It is concluded that most parameters of supernova remnants inferred from X-ray measurements are relatively insensitive to the specifics of the blast-wave model.
Solinger, A.↗