Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Cygnus”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

SAS 3 observations of Cygnus X-1 - The intensity dips

In general, the dips are observed to occur near superior conjunctions of the X-ray source, but one pair of 2-minute dips occurs when the X-ray source is closer to the observer than is the supergiant companion. The dips are analyzed spectrally with the aid of seven energy channels in the range 1.2-50 keV. Essentially, there is no change in the spectral index during the dips. Reductions in the count rates are observed at energies exceeding 6 keV for some of the dips, but the dip amplitude is always significantly greater in the 1.2-3 keV band. It is believed that absorption by partially ionized gas may best explain these results, since the observations of Pravdo et al. (1980) rule out absorption by unionized material. Estimates for the intervening gas density, extent, and distance from the X-ray source are presented. Attention is also given to the problems confronting the models for the injection of gas through the line of sight, believed to be inclined by approximately 30 deg from the binary pole.

Remillard, R. A.↗
NASA NTRS1984

Cygnus X-2 - Neutron star or degenerate dwarf?

Some conflicting models have been proposed for Cyg X-2: a degenerate dwarf model which predicts a distance of 250 + or 50 pc; and a neutron star model which implies a distance of about 8000 pc. Based on a reddening study, it is found that the distance to Cyg X-2 is greater than 1100 pc, which rules strongly against the degenerate dwarf model. This conclusion is based on observations of the 2200 A feature in the spectrum of Cyg X-2 made with the International Ultraviolet Explorer (IUE), and UBV and spectroscopic observations of 38 field stars. For the reddening of Cyg X-2 values of E(B-V) = 0.40 + or - 0.07 (1 sigma) are found and are consistent with the reddening to infinity in that direction inferred from radio data. Consequently, Cyg X-2 may be located in the halo at about 8 kpc as proposed in 1979 by Cowley, Crampton, and Hutchings.

Mcclintock, J. E.↗
NASA NTRS1985

Muon content of gamma ray induced EAS from Cygnus X-3

During 1984 the Leeds group (Lambert et al, OG 2,1-6) have observed emission above 5 times 10 to the 14th power eV in July, September and October at phi approximately 0.6. These observations were made with an array which included the Nottingham 10 sq m muon detector. A search for muons in events at the phase peak and off source has yielded the following results: (1) for 42 on source events we find an average muon density of 0.63 muons m(-2) at a mean core distance Bar R = 32 m and mean primary energy approximately 25 times 10 to the 15th power eV; (2) for 21 off source events average muon density = 1.6 m(-2), Bar R = 32 m with mean primary energy approximately 2.0 x 10 to the 15th power eV; (3) for 11 of the 42 on source events, zero muons were recorded in the 10 sq ms. For these events Bar R = 41 m and mean primary energy approximately 1.5 x 10 to the 15th power eV; (4) for 8 of the 21 off source events, zero muons were recorded in the 10 sq ms. For these events Bar R = 37 m and mean primary energy approximately 1.5 times 10 to the 15th power eV. For all the events the mean zenith angle was approximately 16 deg. A more detailed comparison of on source and further off source events will be presented.

Blake, P. R.↗
NASA NTRS1985

Evidence for long-term variability in the ultra high energy photon flux from Cygnus X-3

A time-correlation analysis of atmospheric Cerenkov pulses by a wide-angle photomultiplier system was previously shown to have present in it a nonrandom component which seemed associated with the Right Ascension (RA) range approx. 20+or-04h. A recent examination of multi-muon events recorded by a photon-decay detector shows a similar time-dependent effect, closely matching the previous results, supporting the suggestion that the effect is of cosmic origin. However, even though Cyg. X-3 lies well inside the region of peak intensity, it does not seem possible to ascribe to it the whole effect, for the implied photon flux appears too large to be reconciled to various gamma-ray measurements of Cyg. X-3. The original data were subjected to a phase-histogram analysis and it as found that only 2.5% of overall recorded data are compatible with a phase-dependent emission from Cyg. X-3. Assuming these events to be gamma rays yields a detected flux of (2.6 + or - 0.3) x 10 to the minus 12th power gamma cm -2s-1 above 5 x 10 to the 14th power eV. Comparing this value with more recent ultra high energy (UHE) photon data from the same source, it is suggested that the available data generally favor a long-term reduction in the Cyg. X-3 inferred luminosity ( 10 to the 13th power eV) by a factor of (1.8 + or - 0.3) per year.

Bhat, C. L.↗
NASA NTRS1985

Low-energy gamma rays from Cygnus X-1

The Cyg X-1 was observed by the balloonborne telescope OPALE, in June 1976. The high energy spectrum of the source, which was in its superlow state, was seen to extend well beyond 1 MeV. The observed low energy gamma ray component of Cyg X-1 is compared with the predictions of recent models involving accretion onto a stellar black hole, and including a possible contribution from the pair annihilation 511 keV gamma ray line.

Roques, J. P.↗
NASA NTRS1984

Self-absorption of high-energy Gamma-rays in Cygnus X-3

Absorption of high-energy gamma-rays from Cyg X-3 in its own photon field by the reaction gamma + gamma yields e(+) + e(-) is considered. It is found that gamma rays with an energy around 10 to the 12th eV are attenuated, and the observed flux has to be corrected. Gamma rays with energy greater than 10 to the 15th eV which are observed are not affected by the photon field.

Apparao, K. M. V.↗
NASA NTRS1984

Transient dips of Cygnus X-1 observed from Tenma

The transient intensity dips of the binary system Cyg X-1 have been observed, using the gas scintillation proportional counter (GSPC) array onboard the Tenma X-ray astronomy satellite. The duration of the dips was in the range from several seconds to 10 minutes, with several dips occurring as much as 15 h before the superior conjunction. Within the dips, complex structures were observed with time scales of several seconds, and, in at least one case, shorter than two seconds. For a dip lasting longer than 10 minutes, a high-quality spectrum was obtained which reveals the K-absorption edge of iron at 7.18 + or - 0.18 keV. On the basis of the observed absorption, it is suggested that the dips are caused by absorption due to relatively cool matter (less than about 30,000 k); the low-energy excess observed during the dips is due either to an extended soft X-ray emitting corona or to partial obscuration of the X-ray source by multiple blobs. From the time structure of the dip, a blob size of the order of 10 to the 9th cm is derived.

Kitamoto, S.↗
NASA NTRS1985

VLBI observations of the jet in Cygnus A

The luminous radio galaxy Cyg A was observed with a five-station US VLBI array at 5 GHz at epoch 1983.25. The jet can be followed from the core to a distance of 9 milliarcsec (mas). Within the limited dynamic range of these observations, it is one-sided (jet:counterjet ratio greater than 12:1). If this one-sidedness is due to Doppler boosting, then (1) the jet must decelerate to a mildly relativistic velocity on a kiloparsec scale, (2) the source cannot lie with 30 deg of the plane of the sky. The jet points directly at the base of the kpc-scale jet seen by Perley, Dreher, and Cowan (1984); the curvature occurs primarily or entirely on a scale of 10-100 kpc. The jet brightness falls off more slowly inside 1 kpc than in other powerful sources. A search for compact structure in the three bright hot spots revealed no structure lower than 3 mas in size with flux greater than 6 mJy.

Linfield, R.↗
NASA NTRS1985

Search for scattered X-ray halos around variable sources - The X-ray halo of Cygnus X-1

The results of a program to search for the presence of halos due to X-ray scattering by interstellar grains in the line-of-sight to variable X-ray sources are reported. As part of this program, four Einstein HRI images of Cyg X-1 were examined. The analysis technique exploits the intrinsic aperiodic variability of this source to map the point response function of the optics. Any scattered halo present will not reflect short-term central source time variability, since such variability is smoothed by differential time delays of order days. Thus, a residual, nonvariable component to the surface brightness distribution (comprising about 12 percent or more of the source flux) is interpreted as a scattered halo. The Cyg X-1 halo is consistent with those of other sources found in previous studies using different techniques. Comparison is also made with a scattering model and, despite uncertainties in source spectrum and distance, reasonable agreement with the observatons is found using a standard interstellar grain model. The potential of X-ray scattering as a probe of the properties of interstellar grains is demonstrated.

Bode, M. F.↗
NASA NTRS1986

Polarization in massive X-ray binaries. I - A low-inclination model for Cygnus X-1

The possibility that variable linear polarization in massive X-ray binaries is produced by electron scattering in an asymmetric stellar wind is investigated. The stellar wind is asymmetric because of the gravitational field of the secondary (X-ray source). The degree of asymmetry and the magnitude of the linear polarization are controlled by the degree to which the primary star fills its Roche lobe. For the well-observed X-ray binary Cyg X-1, the present model can produce the correct magnitude for the polarization. Provided that the inclination of the system is less than about 20 deg, the present model should also predict the correct phase dependence of the polarization. Modifications to the model are described which would enable it to apply to systems with higher inclination.

Friend, D. B.↗
NASA NTRS1986

Observations of quasi-periodic oscillations from GX 5 - 1 and Cygnus X-2 with the Einstein (HEAO 2) Observatory

The bright galactic bulge X-ray source GX 5 - 1 was observed in April 1979 with the Monitor Proportional Counter on board the Einstein (HEAO 2) Observatory. Analysis of the high time resolution data from the Time Interval Processor confirms the recent Exosat discovery of quasi-periodic oscillations in the X-ray emission from GX 5 - 1. In addition, the summed 0.4 s power spectrum shows the low-frequency red noise component also discovered in the Exosat data. Low-frequency structure is also clearly present in data taken from the bright galaxtic X-ray source Cyg X-2 in December 1978. The expected power spectrum for quasi-periodic oscillations was calculated, including the low-frequency red noise component, using a simple shot noise model with oscillating shots.

Elsner, R. F.↗
NASA NTRS1987

The complex cross-spectra of Cygnus X-2 and GX 5-1

The intensity variations of Cyg X-2 and GX 5-1 are analyzed with a Fourier cross-spectral technique making it possible to measure the frequency dependence of the time lags between the intensity variations in two X-ray spectral bands. In the 20-40 Hz frequency range of the quasi-periodic oscillations (QPO), the hard (about 5-18 keV) signal lags the soft (about 1-5 keV) one, while the reverse is true for the associated red noise. The observed time lags range from 0.4 to 8 ms. For similar QPO parameters, the observed lags are much smaller in GX 5-1 than they are in Cyg X-2. The 'hard lags' previously measured in the cross-correlation functions of these sources are now identified as due to lags in the QPO. It is argued that the 'soft lags' now detected in the red noise are not inconsistent with the interpretation of the hard lags as due to inverse Compton scattering.

Van Der Klis, M.↗
NASA NTRS1987

Long-term gamma-ray spectral variability of Cygnus X-1

Data from HEAO 3 observations of 0.05-10-MeV gamma-ray emission from Cyg X-1 during two 90-d periods (in fall 1979 and spring 1980) are compiled in tables and graphs and analyzed statistically to determine the temporal and spectral variability. It is found that a steady increase in 100-keV emission is accompanied by a decrease (and eventual disappearance) of MeV emission. The mechanisms which could theoretically be responsible for these phenomena are discussed.

Ling, J. C.↗
NASA NTRS1987

Cygnus X-3 and other ultra-high-energy gamma-ray sources

Recently, several binary X-ray sources have been found to be sources of ultrahigh-energy gamma emission. Air-shower observations indicate photon energies above about 1 PeV. Observations from Cyg X-3 are reviewed and compared with data on the sources Her X-1, Vel X-1, and LMC X-4. Current theoretical models for the production of gamma rays and the acceleration of high-energy particles are discussed, and the consequences for the evolution of such systems are examined.

Barnard, John J.↗
NASA NTRS1988

Interpretation of the gamma-ray bump from Cygnus X-1

The strong 0.5-2 MeV gamma-ray bump of Cyg X-1 recently reported by HEAO 3 observers can be interpreted self-consistently as the emission from a hot (kT of about 400 keV) pair-dominated plasma. The emission region parameters are uniquely determined by the spectral fit and observed luminosity via the pair-balance condition, suggesting that the gamma rays are produced in the inner region of the accretion flow at the expense of the normal power-law hard X-rays.

Liang, Edison P.↗
NASA NTRS1988

Long-term temporal variability of Cygnus X-2

Observations of the low-mass binary X-ray source Cyg X-2 taken over a five-year period using instruments on OSO 8, HEAO 1, and Einstein are presented. Irregular changes in intensity of up to 60 percent on time scales ranging from minutes to days are seen. The source appears to have long-term low-luminosity states during which dips lasting about three days occur. When these long dips occur, they always appear at the same phase in the optically determined 9.8-day orbital period. There are three distinct types of short-term dips distinguished by differing correlations between spectral hardness and intensity.

Vrtilek, S. D.↗
NASA NTRS1988

VLBI angular broadening measurements in the Cygnus region

Multiple-frequency VLBI observations of eight compact radio sources with lines of sight which cross the Galactic plane in Cyg are reported. The data are presented in a table and map and analyzed, with a focus on angular broadening (AB) induced by interstellar scattering. AB is confirmed in four of the sources, whereas the structures of the other four appear to be intrinsic. The AB is found to be limited to a region within a few deg of the Galactic plane.

Fey, A. L.↗
NASA NTRS1989

A search for a dynamical attractor in Cygnus X-1

A method used for searching for low-dimensional attractors in fluctuating signals is applied to the aperiodicity observed in Cyg X-1. The analysis technique for determining the dimension of an attractor given its light curve, and the practical limitations in applying the technique, are described. The requirement of large amounts of low-noise data is found to be very important in using the technique. No low-dimensional attractor is found for the set of Cyg X-1 data used, but evidence of an attractor with large dimension may be present.

Lochner, James C.↗