X-ray Source Cyg Research Articles

Results of observation of Cyg γ-2, BL Lac, 3C66A, Mk 501, and the Crab nebula by the GT-48 gamma-ray telescope in 2006

The active galactic nuclei BL Lac, 3C66A, and Mk501, as well as the Crab nebula and the Cyg γ-2 source were observed in 2006 at the Crimean Astrophysical Observatory using the GT-48 gamma-ray telescope. Very high energy (VHE) gamma-ray fluxes at a high confidence level (Q > 4) were detected from the active galactic nuclei and the Crab nebula. VHE gamma-ray fluxes from the unidentified gamma-ray source Cyg γ-2 and the X-ray source Cyg X-3 were recorded during observations of Cyg γ-2.

Correlation between break frequency and power-density spectrum slope for the X-ray source Cygnus X-2: RXTE/PCA data

We present RXTE observations of the X-ray source Cyg X-2 during 1996–1999. Its power-density spectra in the 0.1–128-Hz band are fitted by a model that takes into account the power-law spectral behavior at frequencies below and above the break frequency, with an introduction of one or more Lorenz lines to describe the peaks of quasi-periodic oscillations that correspond to the horizontal branch of the Z track. The RXTE observations revealed a positive correlation between the break frequency and the indices of the two parts of the spectrum. The spectrum steepens with increasing break frequency both above and below the break frequency.

On the possible nature of the source of x-ray radiation in quasars

The possible nature of the source responsible for X-rays in quasars is discussed. High luminosity accretion disks around supermassive black holes are considered according to the approach which is somewhat different from the standard accretion disk theory. X-ray spectra of quasars are known to be like the X-ray spectrum of the galactic X-ray source Cyg X-1 (Pozdnyakov L. A. et al., 1983, Inoue, H., 1989). It points to the similarity of the physical conditions in the radiating plasma of these objects. We shall show that in the framework of the a-disks theory (Shakura N. & Sunyaev R., 1973) there exist high (-lO'K) temperature solutions, being independent of the central object's mass. We shall consider high luminosity (-&dd) accretion disks around supermassive (-109Ma) black holes in the zone where radiation pressure is dominant. Our approach differs from the standard accretion disks theory in the following points: 1. Radiation pressure is considered exactly, and it is not considered the LTE approximation: Prad # bT4. 2. Radiation transfer is considered in the Eddington approximation with the Compton effect included, and it is not considered in the diffusion approximation. These differences lead to modification of the temperature structure of accretion disks only, and two high temperature solutions may appear under certain conditions, in addition to the known solution. They exist because a cooling function A( T) has a local minimum at T - lo6 K, and when the energy generation rate becomes greater than the cooling rate at T - lo6 K on the given disk radius, two additional solutions appear. We may write the balance of thermal energy equation for these high temperature states: Using Tuker's (1975) analytical approximation for A( T), we find two solutions: T, = 1.47~109a20--1~~ ~-3~2 (2)

Observations of steady flux of PeV-energy extensive air showers from Cygnus X-3 during 1984-1986

view Abstract Citations (22) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Steady Flux of PeV--Energy Extensive Air Showers from Cygnus X-3 during 1984--1986 Tonwar, S. C. ; Gopalakrishnan, N. V. ; Rajeev, M. R. ; Sreekantan, B. V. Abstract Data taken with a 24-detector extensive-air-shower (EAS) array, operating at Ooty since June, 1984, have been used to search for excess of EASs of energy greater than 250 TeV from the direction of binary X-ray source Cyg X-3. The data show a time-averaged excess in the number of showers from this direction, over the background determined from other regions of the sky having the same declination. The excess is most prominent among older showers having a flatter lateral distribution. A part of this excess shows up significantly in the phase region, 0.6-0.8 in the 4.8-hr periodicity analysis. These observations correspond to an integral flux of (7.16 + or - 3.15) x 10 to the -13th/sq cm sec at energies greater than 250 TeV and of (1.04 + or - 0.44) x 10 to the -13th/sq cm sec at energies greater than 2.5 PeV. The observations confirm, for the first time, results reported by the Kiel group (Samorski and Stamm, 1983) of a directional excess from the direction of Cyg X-3, without requiring the 4.8-hr periodicity analysis as was necessary in many of the other experiments reporting positive signals. This emphasizes the advantage of good angular resolution for such studies. Publication: The Astrophysical Journal Pub Date: July 1988 DOI: 10.1086/185215 Bibcode: 1988ApJ...330L.107T Keywords: Cosmic Ray Showers; Gamma Rays; Neutron Stars; Particle Flux Density; X Ray Binaries; Angular Resolution; Electron Emission; Electron Energy; Histograms; Light Curve; Relativistic Particles; Space Radiation; GAMMA RAYS: GENERAL; X-RAYS: SOURCES full text sources ADS | data products SIMBAD (1)

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.

Outbursts of Cygnus X-3 observed at 1.3 and 3.3 mm wavelengths

The X-ray source Cyg X-3 is associated with a radio source which shows irregular, fast and extremely strong outbursts of radiation. The first such event was seen in September 1972 by many observers over a wide frequency range1; several more events have occurred since then. The main characteristics of the outbursts have been described by the behaviour of an expanding synchrotron source, which undergoes adiabatic and synchrotron losses1,8. However, the detailed physics of the outbursts remains to be understood, in spite of a growing set of observational data. Here we report observations of Cyg X-3 made simultaneously at wavelengths of 1.3 and 3.3 mm, showing outbursts with an intensity of several Janskys and a duration of only a few hours.

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.

On the observations of muons in the direction of Cyg X-3

The binary X-ray source Cyg X-3, a known gamma ray emitter, was recently seen to be emmitting a new type of neutral radiation producing muons detected in deep underground experiments. Here an explanation is offered for the deviation of the observed muon directions from that of Cyg X-3. A new underground experiment is suggested to verify the explanation. The new observations enjoying reduced backgrounds will help establish the phenomenon with enormously improved statistical significance. The nature of the neutral radiation, however, remains obscure.

On the Possible Short-Period Irregular Light Fluctuations of V1357 CYG =CYG X-1

AbstractPhotoelectric observations in U, B, V, were carried out to study the possible rapid (during a night) fluctuations of the close binary system V1357 Cyg, including the X-ray source Cyg X-1. Assuming the existence of irregular fast light fluctuations in the X-ray source Cyg X-1,the conclusion can be drawn that during these observations in 1979 the amplitude of the variations did not exceed 0.04 mag.

γ-Ray observations of Cygnus X-3 at energies of 1012eV

The Crimean Observatory group have detected γ rays from the direction of the X-ray source Cyg X-3 (refs 1–5): rays of energy 1012eV were observed using the atmospheric Cerenkov technique. Measurements with satellite-borne instruments in the 108eV region have shown effects from Cyg X-3 in one case6, but not in another7. Similarly, γ rays have been seen in some balloon flights8, but not in those of McKechnie et al.9 nor of White et al.10. A study using the atmospheric Cerenkov technique at 1011eV showed no effect11, though it has been shown to be compatible with the Crimean result4. We report here observations taken at Mount Hopkins Observatory, Arizona (altitude 2.3 km) in April, May and June 1980 using a similar system to that of Stepanian et al.3, which seem to confirm, at least qualitatively, the Crimean results.

New highly variable radio source, possible counterpart of γ-ray source CG135+1

THE discovery of a highly variable radio source which coincides in position with cosmic γ-ray source CG135+1 (ref. 1) is reported here. The radio source, which we designate GT 0236+610, was discovered during a survey of the galactic plane for a class of highly variable radio sources. The survey was aimed at the detection of sources whose radio emission is normally very weak or absent but which from time to time exhibit short periods of intense radio emission. The prototype of this class of object is the X-ray source Cyg X–3 which was found2 to exhibit giant radio outbursts of duration approximately 1 week at irregular intervals of a few months. The survey consisted of repeatedly mapping an area of approximately 50 deg2 along the galactic plane, every day for 19 d. The daily results were subtracted from the average of the 19 d for evidence of variability.

A search for rapid optical periodicities from Cyg X-l

ACCORDING to the most widely accepted model of the X-ray source Cyg X-1, the X rays are produced in a gas disk surrounding and accreting into a black hole with a mass of about 10M⊙. The accretion disk is maintained by matter transferred from the binary companion of Cyg X-1, the blue supergiant HDE226868. The X-ray luminosity of Cyg X-l is known to vary randomly on a wide range of time scales, from many days to a few milliseconds, with the shortest of these time scales corresponding to the dynamical time scale of the innermost stable orbit around the black hole1,2. The optical luminosity of the Cyg X-l system is also known to vary on time scales of days3, but only one case of extremely rapid optical variability has been reported4,5. The properties of the rapid variations were most unusual. The variations were transient and were detected only four times, but they occurred sufficiently frequently that three of these detections occurred during the total of only 2 h of observations accumulated by Auriemma et al. in July 19754,5. The variations were nearly periodic, with periods of 83.53 ms, 83.71 ms, 83.59 ms, and with |ΔP/P| ∼ 2× 10−4. The periodicities were long lived, lasting at least 6 min and probably over 10 min, so that the pulse trains consisted of over 4,000 pulses. The amplitudes of the pulses were large, up to 0.042 mag. No comparable behaviour has been detected in the X-ray light curve of Cyg X-l, and it is far from clear that this behaviour is consistent with our present conceptions of accretion disks. Thus, the detections of these pulses, if confirmed, would be of some importance since they would require a revision of the models for Cyg X-1. Therefore, we have taken an extensive set of observations of Cyg X-l with the purpose of detecting additional examples of the rapid periodicities.

A spherical accretion model of Cyg X-1

THE binary X-ray source Cyg X-1 is widely believed to be a black hole, and most current models for explaining its X-ray spectrum1 assume an accretion disk. The reason for requiring a disk, rather than a spherical accretion flow, is that earlier investigations of the properties of spherically accreting black holes seemed to indicate that, for the mass transfer rates required to give the observed luminosities of 1037–1038 erg s−1, the cooling time of the gas would be so short compared to the freefall time that the gas would arrive essentially cold at the Schwarzschild radius, and there being no solid surface to transform the infall kinetic energy into thermal energy, very little of this would be radiated away2–4.

Another major change in the radio source associated with Cyg X-1

THE sudden appearance1,2 of a faint radio source inside the probable position region for the X-ray source Cyg X-1 was associated with major changes in the X-ray emission observed3 during the period February–May 1971. This coincidence established a probable association with the X-ray source. The accurate position of the radio source led to an identification2,4 with the bright, blue star HDE226868. Subsequent optical investigations have established5,6 this object to be a binary system with a massive, invisible component that may be a black hole.

A search for the Zeeman effect in the X-ray star candidates theta2 ORI and X Per, the X-ray source CYG X-1, and the B2 Ib star HD 31327.

A search for the Zeeman effect in the X-ray star candidates theta2 ORI and X Per, the X-ray source CYG X-1, and the B2 Ib star HD 31327.

Spectroscopic Variations in Cyg X-2

The x-ray source Cyg X-2 was optically identified with a fifteenth magnitude blue object. Initial spectroscopic observations showed the presence of broad Balmer absorption lines, a narrow strong Ca II K line, and a narrow He II lambda 4686 emission line. Radial velocity variations were also evident, confirmed by later spectroscopic observations. Photometric monitoring showed that the object varied erratically on a time scale of minutes. More recent spectroscopic observations showed that the He II emission had developed a P-Cygni profile, and that emission at lambda lambda 4640-50 due to C III-N III was present. The present communication reports the results of additional spectroscopic observations obtained in 1972 and 1973 with the 82 inch and 107 inch reflectors at the McDonald Observatory. The 1972 spectra obtained showed the He II and C III--N III emission features, and P-Cygni structure was evident in the He line. A strong Ca II K line was shown in the 1973 spectra, indicating a spectral type of F5 or later, although the strength of the Balmer absorption lines indicated a spectral type A5 or earlier. The C III-N III emission was no longer seen in the 1973 spectra. The He II emission was present, butmore » with no evidence of P-Cygni structure, and it appears that Cyg X-2 no longer shows large radial velocity variations. Further optical studies are needed. (UK)« less

Periodicity of Cyg X-3

THE discovery of regular pulsations in the X-ray source Cyg X-3 with a period P≃4.8 h was recently announced1–2. The observations were performed in connexion with the detection on September 3, 1972, of a large radio outburst3. The value P≃4.8 h is somewhat in between the period of pulsation of pulsars and pulsating X-ray sources (∼1 s) and the period of occultation of X-ray sources in a binary system (∼2 day), which supposedly coincides with the period of revolution of the system.

Spectroscopic Observations of the Optical Candidate for Cygnus X-1

The spectroscopic binary BD+34 3815 (= HDE 226868) with a period of 5.6 days, which is the brightest object in the position box for the X-ray source Cyg X-1, is studied to determine whether it meets all the requirements for being a black hole. Evidence is presented that the mass of the secondary is larger than the upper limits for white dwarfs or neutron stars, but there is no conclusive evidence that the optical binary is an X-ray source, and that the secondary is a collapsed object.

More Unusual Radio Events in Cygnus X-3

DURING September 2–11, 1972, an unprecedented radio event was observed1, 2 in the X-ray source Cyg X-3. We now report observations of additional outbursts of similar nature during September 18–25, 1972.

HD 152667 and SCO X-2.

The spectroscopic binary P Cygni star HD 152667 lies close in the sky to the X-ray source Sco X-2. We have analysed the existing photometry of this star and find that two solutions are possible. One is a conventional one and predicts that the unseen secondary is a B3 V star. The alternative solution suggests that all photometric variations are due only to one, gravity darkened star filling its Roche lobe and accompanied by what could be a dense, massive companion. HD 152667 has many similarities to HDE 226868 which has been identified with the X-ray source Cyg X-1.