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At least 199 records · Page 11
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NASA NTRS1984

Einstein Observations of the Cygnus Loop

The imaging instruments on the Einstein Observatory were used to study the detailed X-ray structure of the Cygnus Loop. An arc minute resolution map of the 0.1-4.0 keV emission from the entire remnant was obtained with the imaging proportional counter (IPC). The bright northeastern and western limbs were mapped with the high resolution imager (HRI). The large-scale structure of the Loop is well modeled as a limb-brightened shell of hot gas at 2 x 10 to the 6th K created by the expansion of a blast wave into an inhomogeneous interstellar medium. The pulse-height data from the IPC indicate that the center of the remnant is generally hotter than the limb with temperatures as high as 4 x 10 to the 6th K. The X-ray maps show good general correlation with large-scale radio and optical structure, and in some cases good detailed correlation with faint optical filaments dominated by hydrogen line emission.

Ku, W. H.-M.↗
NASA NTRS1984

The S201 far-ultraviolet imaging survey. II - A field in Cygnus

Far-ultraviolet imagery of a region in Cygnus, a 20 deg diameter field centered near (1950) R. A. 21 h 31.2 m decl. +37 deg 25 arcmin, was obtained by the S201 far-ultraviolet camera during the Apollo 16 mission. In a 10 minute exposure covering the 1250-1600 A wavelength range (effective wavelength 1400 A), 730 star images can be detected, corresponding to a limiting ultraviolet magnitude of about m (1400) = 10. Assuming nominal interstellar extinction values in this region near the galactic plane, this result corresponds to the detection of A0 V stars to a distance of 300 pc and of B0 V stars to 1500 pc. Uncertainties in spectral classification and interstellar extinction for individual objects are probably more significant than calibration or measurement errors. Most of the objects detected are identified with stars in the Smithsonian Astrophysical Observatory Star Catalog (1966), or the Catalog of Stellar Identifications (1979) or both, but 87 objects remain unidentified (or are identified with late-type stars).

Carruthers, G. R.↗
NASA NTRS1984

Evidence for weak X-ray burst emission from Cygnus X-2 and GX 17 + 2

Events resembling weak X-ray bursts have been detected from the two strong persistent sources, Cygnus X-2 and GX 17 + 2. Both events exhibit rise times less than 2.56 s and 1.2-14.4 keV decay times of approximately 5-10 s. The event from Cyg X-2 is similar to a type-I burst in terms of blackbody temperature and peak luminosity, and it can be plausibly interpreted as a thermonuclear flash from an accreting neutron star. The GX 17 + 2 event exhibits a considerably harder X-ray spectrum which makes it unlikely to be a thermonuclear flash. It is suggested that this event arises from an accretion instability as in type-II bursts.

Kahn, S. M.↗
NASA NTRS1984

Cygnus X-1 revisited

The X- and gamma-ray observations of Cygnus X-1 and their theoretical interpretations are reviewed, with emphasis on new developments since the mid-1970s. The overall data base at present is most consistent with the inverse Compton model by hot thermal electrons of T(e) of about 10 billion K, for the hard X-ray luminosity (10-200 keV). However, the origin of the soft X-rays (not greater than 10 keV) in high states and gamma rays (greater than 200 keV) remain unsettled.

Liang, E. P.↗
NASA NTRS1985

Observations of Cygnus X-3 above 10(15) eV from 1979 - 1984

The ultra high energy gamma-ray source, cygnus X-3, has been observed more or less continuously with an array sensitive to 10 to the 15th power ev primaries between 1 Jan. 1979 and 31 Dec. 1984. There is evidence for time variability in the phase of gamma-ray emission over this period.

Lambert, A.↗
NASA NTRS1985

1000 GeV gamma rays from Cygnus X-3: An update

Measurements of 1000 GeV gamma-rays from Cygnus X-3 made with the University of Durham facility at Dugway, Utah in 1981/82 are reviewed. The light curve of the 4.8 hour modulated emission is updated and shows evidence significant at the 4.4 sigma level for strong emission (9% of the cosmic ray rate) at phase 0.625 and less significant (1.4 sigma level) indications of weaker emission (3% of the cosmic ray rate) at phase 0.125. The effect constituting the excess on the few nights showing the strongest emission appears to arise from the smallest Cerenkov light signals suggesting a steep gamma-ray spectrum. The 1982 data have been searched unsuccessfully for evidence of emission at phase 0.2, in coincidence with the results from the ultra-high energy (extensive Air Showers (EAS) measurements in 1979-1982. A systematic investigation of a long term variation in the strength of the peak of the 4.8 hr modulated 1000 GeV gamma-ray emission has been made. We find that in addition to the approximately 34 d variation reported by us previously, a stronger effect exists at around 19d.

Chadwick, P. M.↗
NASA NTRS1985

High-resolution spectrum of Cygnus X-1

A high resolution spectrum of Cygnus X-1 in the 45 to 600 keV range is presented. The measurement was made by the HEAO 3 gamma ray spectrometer during 82 days in the fall of 1979 and spring of 1980, when the source was in its normal low state. Results of a search for narrow emission lines from the source are reported. The spectrum shows no significant narrow features. The 3 delta upper limit to a narrow 511 keV annihilation line is 3 x 0.0001 photons/sq cm/s. There is also no evidence in HEAO 3 broadband data above 500 keV for the broad annihilation feature observed by HEAO 1.

Ling, J. C.↗
NASA NTRS1985

A two-dimensional spectrum of a nonradiative shock filament in the Cygnus Loop

A two-dimensional spectrum of a nonradiative filament in the Cygnus Loop covering the spectral region 4600-7500 A is presented and discussed. Emission lines of H, He II, and forbidden O III, as well as extremely faint N II and S II forbidden lines, were detected. Small spatial differences for some of the filament's emission lines and a possible velocity gradient across the filament's western edge were also observed. Measured relative line intensities are combined with previous nonradiative data and are compared to new nonradiative shock models which treat one, two, and three postshock temperature distributions. It is found that two- and three-temperature models provide a good fit to the observed relative line intensities. The observed weak N II and S II forbidden line emissions are interpreted as due to either radiative shock emissions produced by small density fluctuations in the shocked cloud (e.g., cloud cores), or faint dust grain reflection of the remnant's bright radiative filament emission.

Fesen, R. A.↗
NASA NTRS1985

Anatomy of a cosmic-ray neutrino source and the Cygnus X-3 system

The effects of an intense beam of ultra-high energy cosmic rays from a compact object in the Cygnus X-3 binary system hitting the companion star, and of the subsequent production of secondary neutrinos, are examined. A maximum allowable beam luminosity of about 10 to the 42nd erg/s is found for a system containing a 1-10 solar mass main sequence target star. The proton beam must heat a relatively small area of the target star to satisfy observational constraints on the resulting stellar wind. With such a model, the neutrino to gamma-ray flux ratio of about 1000 can result from a combination of gamma-ray absorption and a large neutrino to gamma-ray duty cycle ratio. It is found that the high density of the atmosphere resulting from compression by the beam leads to pion cascading and a neutrino spectrum peaking at 1-10 GeV energies.

Stecker, F. W.↗
NASA NTRS1986

Observation of muons from Cygnus X-3 in the NUSEX experiment

Ground based observations by means of Cerenkov light detectors and air shower arrays have established that Cyngus X-3 is a powerful source of high energy particles. The detection of a 10 to the 15th power eV signal was first reported by the Kiel experiment. Air showers with large age parameter were accepted in order to select those generated by primary gamma rays. At variance with the expectation, the muon density associated with these events was found to be surprisingly high. This puzzling result stimulated a temporal analysis of the muons recorded in Nucleon Stability Experiment (NUSEX) coming from the region around the source. A positive signal was found suggesting the presentation of this result. The analysis of the data recorded during the 2.4 years of effective working time is presented with a fine tuning of the period and the energy spectrum of the muons from the Cygnus X-3 direction derived assuming consistency between NUSEX and SOUDAN results.

Piazzoli, B. D.↗
NASA NTRS1986

The Cygnus loop - A detailed comparison of X-ray and optical emission

A comparison at a resolution of 17 arcsec is presented between optical emission from forbidden O III and forbidden S II and the thermal X-ray emission for a field on the southeast edge of the Cygnus Loop SNR. The relationship between optical and X-ray emission in the field is described, generalizing to the Loop as a whole when possible. Several possible explanations for the presence of bright X-ray emission in the vicinity of optical emission are presented and evaluated based on the data. These mechanisms involve evaporation, gradual variations and gradients in the density of the preshock intercloud medium, and additional compression of material which has already been heated to X-ray temperatures by the adiabatic blast wave. The additional compression could result from rapid deceleration of the blast wave itself or from reshocking by reflected or bow shocks around dense clouds. Implications of the observations for models of SNR evolution and the interstellar medium are discussed.

Cox, D. P.↗
NASA NTRS1986

Origin of ultra-high-energy gamma-rays from Cygnus X-3 and related sources

Diffusive shock acceleration of ions is examined as the mechanism responsible for the ultrahigh energy (UHE) gamma ray emission observed from Cygnus X-3 and several other binary X-ray sources at energies of 10 to the 15th eV and higher. The shock acceleration can under reasonable assumptions be sufficiently short to allow acceleration of ions to energies near 10 to the 16th eV. It is proposed that the subsequent proton-proton collisions and photodissociation of He-4 can produce a flux of neutrons that escapes from the acceleration site despite high magnetic fields. These neutrons, by interacting with the binary companion, produce the observed UHE radiation.

Kazanas, D.↗
NASA NTRS1986

A deep H-alpha image of faint Balmer-line filaments in the northeast Cygnus Loop supernova remnant

A deep H-alpha image of a field outside the optically bright northeast limb of the Cygnus Loop supernova remnant is presented. Two filaments which are just visible on the red POSS print form part of two long and unbroken lines of filaments which generally bound a region of diffuse emission and fainter filaments. However, the diffuse emission extends out to a newly detected line of extremely faint filaments 3 arcmin to the northeast. The brightest filaments are resolved into multiple components with widths less than 2 arcsec. Comparison with the POSS print leads to a rough estimate of the proper motion of 6 arcsec per century, although temporal variations in the relative brightnesses of the components of a filament could confuse attempts to more accurately measure the true proper motion. The morphology of the emission strongly suggests that it arises in a single large sheet. No direct evidence is found favoring the existence of the dense cloud cores which have been hypothesized as a way of evaporatively enhancing the X-ray emissivity and producing forbidden line emission in the filaments.

Hester, J. J.↗
NASA NTRS1986

A comparison of high-resolution radio and optical data for the northeast region of the Cygnus Loop

Radio observations of the northeastern part of the Cygnus Loop obtained with the VLA at 18 cm with a resolution of 4.7 arcsec are presented and discussed. In general, the brightest radio filaments match the brightest optical filaments very well, particularly those which are bright in H-alpha. The agreement in position, morphology, and relative brightness is particularly good where all four optical species are bright. However, a few bright radio features have no bright optical counterparts. The general radio and optical structure of the region can be explained by a model in which shocked interstellar clouds form filaments due to unstable cooling and compression. The features appear to be ropelike, although it is not possible to rule out that they are irregular sheets seen edge-on. A large gradation in cooling on a scale of parsecs is evidenced by the sequence of the optical species in emission, with a corresponding increase in density generally evidenced by the continuum radio emission.

Straka, W. C.↗
NASA NTRS1985

Ultra-high-energy gamma-rays from Cygnus X-3

Ultrahigh-energy gamma-ray emission with photon energies up to 20 PeV has been detected from the galactic X-ray source Cygnus X-3, implying acceleration of charged particles to even greater energies. A model for acceleration of particles to such energies in a binary containing an accreting neutron star with a magnetic field of about 100 MG is presented. The acceleration occurs in an accretion disk surrounding the neutron star, by an unipolar-inductor mechanism.

Chanmugam, G.↗
NASA NTRS1987

Theoretical interpretation of the HEAO-3 observations of Cygnus X-3 under the HEAO-3 Guest Investigator Program

A model of the galactic X-ray source Cygnus X-3 (Cyg X-3) is presented which deviates from previous models by positing that the X-rays originate in a jet rather than a binary system consiting of an ordinary star and a collapsed object. In the new model, the 4.8 hour period of Cyg X-3 is caused by variable absorption which occurs as the jet precesses. The primary role of the accretion disk corona (ADC) in modulating Cyg X-3 radiation is to make the observed intensity of a blob of material in a jet appear dimmer by absorption. The needed derivation of the positional dependence of the density of the ADC is freed of some complications by assuming that only the inner regions of the disk are precessing, with a period shorter than 4.8 hours. This model permits the secondary star to be a supergiant, as indicated by the luminosity of the system. The model is especially helpful in interpreting production of radio outbursts and very high energy gamma rays.

Marscher, Alan P.↗
NASA NTRS1986

High-resolution X-ray spectroscopic evidence of nonequilibrium conditions in the Cygnus Loop

High-resolution spectroscopic X-ray observations of a portion of the Cygnus Loop made with the Focal Plane Crystal Spectrometer aboard the Einstein Observatory are reported. Emission lines for O VII, O VIII, and Ne IX are measured, and upper limits are set to other transitions in O VII and O VIII. The detected emission line fluxes are consistent with emission from an equilibrium plasma with an electron temperature of about 3 x 10 to the 6th K, a value similar to that obtained by numerous previous observers. The absence of any O VII forbidden line emission strongly suggests that the emitting plasma is not in collisional ionization equilibrium. This is shown to be the case using several line diagnostics formed from the observed emission lines and a simple model describing the X-ray emission from an ionizing nonequilibrium plasma.

Vedder, P. W.↗