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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

X-ray spectrum of the entire Cygnus Loop.

The spectrum of the entire Cygnus Loop has been obtained using gas-filled proportional counters and filters flown on a Nike-Aerobee rocket. The results indicate an average spectral temperature of (2.8 plus or minus 0.2) x 1,000,000 K and the presence of excess emission in the energy range from 0.530 to 0.693 keV. If the excess emission originates in a single line at 0.658 keV, the intensity at the earth corresponds to 1.8 plus or minus 0.7 photons per sq cm per sec, or about 10% of the total energy received from the Loop. The spectrum of the entire Loop is found to be attenuated by an average of (4.8 plus or minus 0.2) x 10 to the 20th hydrogen atoms per sq cm.

Stevens, J. C.↗
NASA NTRS1973

On the distance to Cygnus X-1

Interstellar extinction of 50 stars in the immediate vicinity of Cyg X-1 is compared with color excess of HDE 226868. The fact that HDE 226868 has extinction drastically exceeding that of all stars in the field at less than 1 kpc is believed to be in conflict with the model of Trimble et al. (1973) in which the primary is a luminous undermassive star and with other similar models. Uniform extrapolation of the reddening yields a distance estimate of (2.5 plus or minus 0.4) kpc for Cygnus X-1, in agreement with the spectroscopic modulus for an O9 star.

Margon, B.↗
NASA NTRS1974

Long-term observations of Cygnus X-2 from OSO-7

Results of observations of Cygnus X-2 are reported that were made with an X-ray telescope on board the OSO-7 satellite during the three intervals of January 9-16 and 21-26, 1972, and July 8-11, 1972. Random factor-of-two variations were found in the data. No statistically significant periodic variations were found in the range from 10 hours to 2 days.

Ulmer, M. P.↗
NASA NTRS1974

Correlation analysis of X-ray emission from Cygnus X-1

Normalized autocorrelation and cross-correlation coefficients have been calculated for the X-ray emission of Cygnus X-1 in two energy bins, 2.1-5.1 keV and 5.1-12 keV. The analysis shows a strong correlation between the pulsations in the two energy bins, with the low-energy pulsations lagging behind the high-energy ones, or alternatively a shorter duration of the pulse trains in the high-energy bin. The power spectral density derived from the autocorrelation functions indicates a larger contribution of the high-frequency components for the higher-energy X-rays.

Brinkman, A. C.↗
NASA NTRS1974

Distance to Cygnus X-1

An evaluation of the nature of the X-ray source Cygnus X-1 depends on distance relations. The validity of distance estimates provided by Margon et al. (1973) and Bregman et al. (1973) is considered. It is concluded that the possibility of a determination of the distance of HDE 226868 to the required accuracy on the basis of reddening measurements appears unlikely. It is, therefore, thought to be premature to suggest that the X-ray source is a black hole.

Cheng, C.-C.↗
NASA NTRS1974

X-ray structure of the Cygnus loop

An X-ray surface brightness map of the Cygnus Loop in the energy range 0.15-0.85 keV is presented. The X-ray distribution is compared with the optical and radio pictures of the Loop. The location of the center of the supernova shell as derived from the X-ray data is in excellent agreement with the apparent optical and radio centers. We obtain a mean diameter for the X-ray shell of 2.75 (+ or - 0.2) deg. The X-ray spectral data yield a characteristic thermal temperature averaged over the Loop of 2.9 million (+ or - 1.5 million) K. We have calculated anew X-ray parameters for adiabatic blast waves using X-ray production spectra which include line radiation. These parameters are compared with the results of the present experiment. An age of 18,000 years, initial blast energy equal to 3 times 10 to the 50-th power ergs, and ambient interstellar density of 0.25 per cu cm are found.

Rappaport, S.↗
NASA NTRS1974

An upper limit to an X-ray point source at the center of the Cygnus Loop

The Cygnus Loop was observed with a one-dimensional X-ray telescope. Data from two orthogonal scans showed no evidence for a pointlike remnant of the supernova at the center of the Loop. We set an upper limit to the presence of such a source of 2.9% (at 99.9% confidence) of the total emission in the bandwidth from 400 eV to 850 eV. The pulsed component at 62.31 msec suggested by Rappaport et al. (1973) was not observed.

Weisskopf, M. C.↗
NASA NTRS1975

Further joint X-ray, infrared and radio observations of Cygnus X-3

Observations of Cygnus X-3 were carried out at 2.5 - 7.5 keV, 2.2 micron, 8.1 GHz and 2.7 GHz over a two week period. The X-ray data show the periodic structure which is typical of Cyg X-3. At times the X-ray and infrared measurements show very similar periodic structure, both in phase and shape, while at other times the infrared data show no periodic variability. The radio fluxes were usually low during the period of observation; both the daily average radio flux levels and spectral index remained nearly constant.

Mason, K. O.↗
NASA NTRS1976

Observations of Cygnus X-3 by ANS

The hard X-ray experiment (1 - 28 keV) on ANS observed Cygnus X-3 in November 1974, and in May 1975. The average flux intensities for these time periods were found to be 22.4 + or - 0.5 cts/sec and 12.8 + or - 0.3 cts/sec (1.3 - 7.1 keV), the former being the highest average value ever observed. The spectrum studies show an excess in the flux above the fitted continuum which can be interpreted as a line emission of FeXXIV and/or FeXXV, at approximately 6.5 keV. The strength of this feature varied in phase with the 4.8 hr X-ray modulation, and remained at a constant relative intensity. The period of the X-ray modulation is refined to 0.1996813 + or - 0.0000006 day and obtained at a 2 sigma upper limit to a continuous change in the period of 50 to the minus 13th power/sec. This new limit places serious constraints on several models for this object.

Parsignault, D. R.↗
NASA NTRS1976

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.↗
NASA NTRS1976

Observations of Cygnus X-1 in its two intensity states by ANS

The hard X-ray experiment (1 - 28 keV) on ANS, observed Cygnus X-1 in November 1974, and in May 1975, putting in evidence the two dramatically different states of this object. The average intensity in November was 15 cts/sec, and the observations showed remarkable features in the X-ray light curve and in the spectrum, which were correlated with the 5.6 days period of HDE226868. The May observations showed a count rate of approximately 80-100 cts/sec, with fluctuations up to approximately 130 cts/sec, uncorrelated with the spectroscopic binary. The May X-ray spectrum was much softer than the November one, and possibly was made up of two components.

Parsignault, D. R.↗
NASA NTRS1976

Optical observations of HDE 226868 = Cygnus X-1: A review

The present state of knowledge of the binary system HDE226868 = Cygnus X-1 is summarized, including system dimensions, nature of the secondary X-ray source, and mass transfer properties. Some deficiencies in the optical observations are pointed out; these deficiencies make interpretation of the system difficult, but can be corrected.

Bolton, C. T.↗
NASA NTRS1976

The long term variability of HDE 226868 = Cygnus X-1

Investigation of blue-sensitive photographs of HDE 226868 = Cygnus X-1 reveal no (+ or - 0.06 mag) long-term changes in brightness since the beginning of the century nor any abrupt intensity changes similar to what was observed at X-ray and radio frequencies. From the double sinusoidal fluctuation with 5.6 day period, an attempt is made to derive a more precise value for the orbital period, but problems are encountered and discussed. There exists evidence that the amplitude of the orbital fluctuations is increasing slowly with time.

Liller, W.↗
NASA NTRS1975

Soft X-ray search of centre of Cygnus Loop

Equipment on the Copernicus satellite has been used to search for evidence of a compact object in the center of the Cygnus Loop supernova remnant. Rocket measurements reported by Rappaport et al. (1973) indicate that a central object exists. However, the study conducted with the aid of the satellite was negative. This negative result could indicate that the X-ray source was simply not in its high-intensity mode at the time of observation, or could arise because the source is at some other location in the Loop.

Snyder, W. A.↗
NASA NTRS1976

Evidence for an 11.2 day periodicity from Cygnus X-2

Evidence is reported for a periodicity of 11.17 (+ or - 0.10) days in the emission from Cygnus X-2. The data were obtained quasi-continuously over a period of more than one year with the Ariel-5 All-Sky Monitor. It is noted that this period is more than an order of magnitude larger than the 0.787-day binary period of Sco X-1 and is not a simple alias of a similarly short period. It is suggested that the 11.17-day modulation might be precessionally induced; otherwise, it would be rather unusual since the Cyg X-2 candidate is assumed to have a low-mass primary and periods in excess of about 2 days are usually associated with high-mass primaries.

Holt, S. S.↗
NASA NTRS1976

ANS observations of Cygnus X-1

Cygnus X-1 was observed from 3 November until 9 November 1974, using the hard X-ray (1-28 keV) and soft X-ray (1-8 keV) experiment on board the Astronomical Netherlands Satellite. On three occasions, on 4 and 5 November, the X-ray spectrum was observed to be harder, while the flux intensity in the 1-7 keV ranges decreased by about 50% from its quiescent value. These events occurred near and following the time of superior conjunction of the likely optical counterpart HDE 226 868. These events appear to be the same as previously reported absorption dips and reveal this phenomenon to be more complex than had been believed. A systematic study of the X-ray spectral variations in these energy bands, on a time scale of 64 seconds over the period of the spectroscopic binary, is presented.

Parsignault, D. R.↗
NASA NTRS1976

Further joint X-ray, infrared, and radio observations of Cygnus X-3

Observations of Cygnus X-3 have been carried out at 2.5-7.5 keV, 2.2 micrometers, 8.1 GHz, and 2.7 GHz over a two week period. The X-ray data show the periodic structure which is typical of Cyg X-3. At times the X-ray and infrared measurements show very similar periodic structure, both in phase and in shape, while at other times the infrared data show no periodic variability. The radio fluxes were unusually low during the period of observation; both the daily average radio flux levels and the spectral index remained nearly constant.

Mason, K. O.↗