Source In Cygnus Research Articles

DeeperChandraFollow‐up of Cygnus TeV Source Perpetuates Mystery

A 50 ks Chandra observation of the unidentified TeV source in Cygnus reported by the HEGRA collaboration reveals no obvious diffuse X-ray counterpart. However, 240 pointlike X-ray sources are detected within or nearby the extended TeV J2032+4130 source region, of which at least 36 are massive stars and two may be radio emitters. That the HEGRA source is a composite, having as a counterpart the multiple pointlike X-ray sources we observe, cannot be ruled out. Indeed, the distribution of pointlike X-ray sources appears nonuniform and concentrated broadly within the extent of the TeV source region. We offer a hypothesis for the origin of the very high energy gamma-ray emission in Cyg OB2 based on the local acceleration of TeV-range cosmic rays and the differential distribution of OB versus less massive stars in this association.

The unidentified TeV source (TeV J2032+4130) and surrounding field: Final HEGRA IACT-System results

The unidentified TeV source in Cygnus is now confirmed by follow-up observations from 2002 with the HEGRA stereoscopic system of Cherenkov Telescopes. Using all data (1999 to 2002) we confirm this new source as steady in flux over the four years of data taking, extended with radius 6.2 arcmin (+-1.2 arcmin (stat) +-0.9 arcmin (sys)) and exhibiting a hard spectrum with photon index -1.9. It is located in the direction of the dense OB stellar association, Cygnus OB2. Its integral flux above energies E>1 TeV amounts to \~5% of the Crab assuming a Gaussian profile for the intrinsic source morphology. There is no obvious counterpart at radio, optical nor X-ray energies, leaving TeVJ2032+4130 presently unidentified. Observational parameters of this source are updated here and some astrophysical discussion is provided. Also included are upper limits for a number of other interesting sources in the FoV, including the famous microquasar Cygnus X-3.

Gamma-ray line emission from OB associations and young open clusters

Gamma-ray and microwave observations of the Cygnus region reveal an intense signal of 1.809 MeV line emission, attributed to radioactive decay of 26Al, that is closely correlated with 53 GHz free-free emission, originating from the ionised interstellar medium. We modelled both emissions using a multi-wavelength evolutionary synthesis code for massive star associations that we applied to the known massive star populations in Cygnus. For all OB associations and young open clusters in the field, we determined the population age, distance, and richness as well as the uncertainties in all these quantities from published photometric and spectroscopic data. We propagate the population uncertainties in model uncertainties by means of a Bayesian method. The young globular cluster Cyg OB2 turns out to be the dominant 26Al nucleosynthesis and ionisation source in Cygnus. Our model reproduces the ionising luminosity of the Cygnus region very well, yet it underestimates 26Al production by about a factor of 2. We attribute this underestimation to shortcomings of current nucleosynthesis models, and suggest the inclusion of stellar rotation as possible mechanism to enhance 26Al production. We also modelled 60Fe nucleosynthesis in the Cygnus region, yet the small number of recent supernova events suggests only little 60Fe production. Consequently, a detection of the 1.137 MeV and 1.332 MeV decay lines of 60Fe from Cygnus by the upcoming INTEGRAL observatory is not expected.

G74.5+0.9: A New Bipolar Source in Cygnus

Viewed at 1' resolution at 1420 MHz, the source G74.5+0.9 appears as a double lobe structure of total length 20' with a moderately strong compact source located slightly off-center. Although its morphology is reminiscent of a typical extragalactic radio source with a central jet-core source, its infrared-to-radio ratio is more typical of an H II region. Furthermore, neutral hydrogen observations show the presence of an H I cavity at an LSR velocity of about -70 km s-1. Combining continuum radio, infrared, and optical observations, as well as H I data, we show that the source is compatible with the model of a bipolar H II region. If at its kinematic distance (about 12 kpc), the bipolar source has an overall length of about 60 pc and is powered by an O6 star. The possibility that the source is at a much closer distance of about 2 kpc, associated with material expanding toward us and away from the Cyg OB1/OB3 association, is also considered, in which case its overall dimension is only 12 pc and a B0 star is sufficient to power it. The nature of the central source is also discussed.

X-ray properties of the nuclear source in Cygnus A

From a ROSAT HRI observation of Cygnus A (66 ks), we find a complex emission region whose peak brightness coincides with the radio core source. We examine the relation of the source morphology to the radio emission and evaluate the “obscured quasar” hypothesis for the nuclear emission on the basis of source intensity and limits to the variability.

Far-infrared sources in Cygnus X - an extended emission complex at DR 21 and unresolved sources at S106 and ON 2

A new map of 90 micron emission with 15 arcmin resolution is presented of a complex of sources approximately centered on DR 21. The emission is primarily from diffuse sources. Comparison of the 90 micron map with maps at 20 microns and 2.7 GHz leads to a model for diffuse sources in which there are at least two components of interstellar dust, one at 40 K and one at 165 K, responsible for the 90 micron and 20 micron emission respectively. Both components and the ionized gas must be mixed together; dust in an outer neutral shell is relatively unimportant for these sources. The diffuse sources have small infrared excesses and weak temperature gradients. Unresolved, probably compact, sources were observed at S106 and ON 2 and are briefly discussed.

POSITRON ANNIHILATION RADIATION FROM THE GALACTIC CENTER REGION*

Measurements of 0.511 MeV radiation from the vicinity of the galactic center performed by the high resolution gamma ray spectrometer aboard the HEAO 3 spacecraft are discussed. The spectrometer is described and an exploded view of it exhibited, and scans in the 50-244 keV region as well as 0.511 MeV are shown. The intensity from the Crab nebula remained constant while that of the Cygnus source increased considerably, and there was a decrease in the radiation from the vicinity of the galactic center. The flux emanating from the center implies an annihilation rate of 10 to the 43rd per second. The apparent time variation and the spatial extent observed tend to limit the source to a single object and the annihilation region to a size less than about one light year.

The X-ray polarization of the Cygnus sources

Multiple observations of Cygnus X-1, Cygnus X-2, and Cygnus X-3 were carried out with the Bragg crystal polarimeters aboard OSO 8. Of these sources, an unambiguous detection of the time-averaged polarization was obtained only for Cygnus X-1, which has a polarization of 2.4% plus or minus 1.1% at 2.6 keV and 5.3% plus or minus 2.5% at 5.2 keV. While statistically significant evidence for polarization of Cygnus X-2 of 4.9% at 2.6 keV was obtained in a 1975 observation, this result was not confirmed in later observations. For Cygnus X-3, modulation of the observed flux at twice the rotation frequency of the satellite, the signature of polarization, was also detected, but spurious modulation due to the presence of additional sources in the field of view cannot be ruled out.

Long-term studies with the Ariel 5 ASM. II - The strong Cygnus sources

The three bright 3-6 keV X-ray sources in Cygnus are examined for regular temporal variability with a 1300-day record from the Ariel 5 All Sky Monitor. The only periods consistently observed are 5.6 days for Cyg X-1, 11.23 days for Cyg X-2, and 4.8 hours for Cyg X-3.

Spectrophotometry of CRL 2688 from 2 to 24 microns

view Abstract Citations (17) References (2) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectrophotometry of CRL 2688 from 2 to 24 microns. Forrest, W. J. ; Merrill, K. M. ; Russell, R. W. ; Soifer, B. T. Abstract Infrared spectrophotometric observations (2 to 24 microns) are reported for CRL 2688, an IR source in Cygnus associated with twin symmetric reflection nebulae. The entire spectrum from 3 to 24 microns is shown to be a generally featureless continuum and to be too broad to be fit by a single blackbody. No evidence is found for ice absorption near 3.1 microns, and the data suggest a possible emission feature near 3.3 microns. Publication: The Astrophysical Journal Pub Date: August 1975 DOI: 10.1086/181879 Bibcode: 1975ApJ...199L.181F Keywords: Astronomical Photometry; Astronomical Spectroscopy; Infrared Astronomy; Nebulae; Black Body Radiation; Cygnus Constellation; Ice; Astronomy full text sources ADS | data products SIMBAD (1)

A New Variable Radio Source in Cygnus

A New Variable Radio Source in Cygnus

X-Ray Spectra of Discrete Sources in Cygnus

X-ray spectral data from a rocket-borne proportional counter exposure to discrete sources in Cygnus are presented. The data from Cyg x-1, Cyg X-2, and Cyg X-S have sufficient statistical significance to clearly indicate mutually exclusive spectral forms for the three. Upper limits are presented for X-ray intensities above 2 keV for Cyg X-4 and Cyg X-5 (Cygnus Loop).

X-Ray Observation of a New Soft Source in Cygnus

The location of the new X-ray source, designated Cygnus X-6, is discussed. The polycarbonate window counter detected Cyg X-6 only in the pulse-height interval from 0.5 to 1.3 keV. A total of 44 counts was acquired from the source above a diffuse X-ray and non-X-ray background of 18 plus or minus 3 counts. The polycarbonate pulse-height spectrum for Cyg X-6 is presented together with the calculated counter response to three different model source spectra.

New OH Radio Emission Sources in Cygnus

ALL radio observational work on OH has so far been concentrated on previously known astronomical objects. Initially the OH microwave radiation was found absorbed in the spectra of strong continuum sources1, but in the search for more OH absorption lines weaker and weaker continuum sources were investigated. The guide in this search was the source catalogue made by Westerhout2, which contains sources around the galactic plane measured at the frequency 1,390 MHz. Many of these sources have a thermal spectrum and therefore are associated with H II regions. Because the first OH emission sources were found in or near some of these H II regions3,4, the search for more OH emission was carried out chiefly on thermal radio sources. Many new OH emission sources were found in this way and theories of maser action in OH associated with H II regions were produced5,6.

The Spectra of Several X-Ray Sources in Cygnus and Scorpio

X ray spectra from sources in Cygnus and Scorpio, noting three strongest in Cygnus and six at low galactic longitude

High-Resolution Observations of the Radio Sources in Cygnus and Cassiopeia

High-Resolution Observations of the Radio Sources in Cygnus and Cassiopeia

An experimental investigation of the scintillation of radio stars observed at frequencies of 223 and 456 megacycles per second from a location close to the auroral zone

This paper describes a study of the amplitude and angular scintillations of the Cygnus and Cassiopeia sources at College, Alaska. Phase-switch and phase-sweep interferometers were used at frequencies of 223 and 456 Mc/s for one year centered at about the peak of the recent sunspot cycle. The scintillation effects were found to be of much greater magnitude than at temperate latitudes, and they showed clear evidence of geomagnetic and auroral control. The solar time dependence was considerably less than is observed at temperate latitudes. The zenith-angle dependence of the scintillation amplitude was different for the two sources; for both, the zenith-angle dependence was much less than would be predicted for the case of spherical diffracting irregularities. The relative absence of a zenith-angle effect is attributed to the compensating effect of magnetic field alignment of anisotropic irregularities. The difference between the zenith-angle curves for the two sources, as well as the greater magnitude of the Cygnus scintillations relative to the Cassiopeia scintillations, is attributed to the fact that the Cassiopeia source subtends a larger solid angle than the Cygnus source. The occasional occurrence of long-duration fades on the interferometer records (of periods up to 1 hour) is interpreted in terms of irregularities that on these occasions subtended less than the solid angle of the source and resulted in a diffraction pattern on the ground having autocorrelation distance less than 100 meters.

Cosmological Significance of Angular Measurements of Distant Radio Sources

THE programme of interferometric observations of distant radio sources at present being carried out by H. P. Palmer et al. at Jodrell Bank may prove to be of great significance for cosmology. The preliminary results recently published1 indicate that out of 91 sources 38 were of sufficiently small angular diameter to produce measurable interference fringes at the long base line used (32,000 λ at λ = 1.89 m.), and at least 7 had a diameter between half-power points less than 3 sec. of arc. Furthermore, these 7 were described as having “an extremely high surface brightness which is comparable with that of the intense radio source in Cygnus I.A.U. 19 N4A”.

A Spectral Analysis of the Radio Sources in Cygnus X at 1390 Mc/s and 408 Mc/s

A high resolution survey of the Cygnus X region was made at 408 Mc/s using the 250 ft paraboloid at Jodrell Bank. The results were combined with the high resolution surveys at 1390 Mc/s of Drake and Westerhout to investigate the spectral characteristics of the individual radio sources in Cygnus X. The results support the previous conclusions that the emission is from optically thin H II regions except for the strongest source in the region, the γ Cygni source, which was found to have a non-thermal component.

LXXV. The low frequency spectrum of the cygnus (19N4A) and cassiopeia (23N5A) radio sources

Abstract The intensities of the radio sources in Cygnus (19N4A) and Cassiopeia (23N5A) have been measured at frequencies of 16·5, 19·0, 22·6 and 30·0 Mc/s by using the 218-foot aperture transit radio telescope at Jodrell Bank. The main feature of the results is the abrupt fall in intensity of both sources at frequencies below 22 Mc/s. Possible causes of this behaviour are discussed and it is shown that the effect is probably due to absorption of the radiation in an interstellar HII region of average density and extent.