Results of Light Curve Analysis of the Massive Binary Cyg X-1/V1357 Cyg in Primary Minimum

The results of new UBV photometric observations of V1357 Cyg in primary minimum are presented. Observations were carried out from 1996 up to now with 60 cm telescope in Crimea with the goal to study additional radiation that was detected in the mean light curve of this system near orbital phase 0.0. The properties of this additional radiation are also considered.     

Very High Energy Emission from the Binary System Cyg X-3

Cyg X-3 is actively studied in the entire range of the electromagnetic spectrum from the radio band to ultrahigh energies. Based on the detection of ultrahigh-energy gamma-ray emission, it has been suggested that Cyg X-3 could be one of the most powerful sources of charged cosmic-ray particles in the Galaxy. We present the results of long-term observations of the Cygnus Х-3 region at energies 800 GeV–100 TeV by the SHALON mirror Cherenkov telescope. In 1995 the SHALON observations revealed a new Galactic source of very high energy gamma-ray emission coincident in its coordinates with the microquasar Cyg X-3. To reliably identify the detected source with Cyg X-3, an analysis has been performed and an orbital period of 4.8 h has been found, which is a signature of Cyg X-3. A series of flares in Cyg X-3 at energies >800 GeV and their correlation with the activity in the X-ray and radio bands have been observed. The results obtained in a wide energy range for Cyg X-3, including those during the periods of relativistic jet events, are needed to find the connection and to understand the different components of an accreting binary system.     

A Photometric Study of EB-type eclipsing binary GO CYG

Two colour (B and V) photoelectric observations of EB-type eclipsing binary GO Cyg were carried out for 15 nights during October and December 1996. Three new times of minimum lights have been derived. With these and previously published times of minimum lights, a continuous period increase of dP/dt = 1.51 × 10^-7 d yr^-1 was estimated from the quadratic light element. B and V light curves have been analyzed by the method of the Wilson and Devinney Differential Correction. GO Cyg is confirmed to belong to the group of near contact systems based on light curve analysis and its absolute dimensions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Properties of X-ray shots of Cyg X-1 in high state

Temporal variations in the high-energy radiation of Cyg X-1 can be represented by the properties of its X-ray short bursts (shots). The properties of the X-ray shots of Cyg X-1 have been studied extensively, especially for the Cyg X-1 in its typical low/hard state. In this paper, we study the shot properties when Cyg X-1 is in its high/soft state, using direct superposition of shots and the autocorrelation function. Our result shows that when Cyg X-1 is in the high state, the shot structure is qualitatively similar to that of the low state, and that the full-width at half-maximum (FWHM) of the shot decreases with increasing energy, which is inconsistent with the prediction of the Comptonization model. In addition, the evolution of the shot energy spectrum and the asymmetry of the shot structure can explain the observed time lag in Cyg X-1.     

Energy spectrum and time variations of hard X-rays from Cyg X-1

Experimental results on the intensity, energy spectrum and time variations in hard X-ray emission from Cyg X-1 based on a balloon observation made on 1971, April 6 from Hyderabad (India) are described. The average energy spectrum of Cyg X-1 in the 22–154 keV interval on 1971 April 6 is best represented by a power law dN/dE=(5.41±1.53)E ^{–(1.92±0.10)} photons cm^–2s^–1 keV^–1 which is in very good agreement with the spectrum of Cyg X-1 derived from an earlier observation made by us on 1969 April 16 in the 25–151 keV band and given by dN/dE=(3.54±2.44)E ^{–(1.89±0.22)} photons cm^–2s^–1 keV^–1. A thermal bremsstrahlung spectrum fails to give a good fit over the entire energy range for both the observations. Comparison with the observations of other investigators shows that almost all balloon experiments consistently give a spectrum of E ^–2, while below 20 keV the spectrum varies fromE ^–1.7 toE ^–5. There is some indication of a break in the Cyg X-1 spectrum around 20 keV. Spectral analysis of data in different time intervals for the 1971 April 6 flight demonstrates that while the source intensity varies over time scales of a few minutes, there is no appreciable variation in the spectral slope. Analysis of various hard X-ray observations for long term variations shows that over a period of about a week the intensity of Cyg X-1 varies upto a factor of four. The binary model proposed by Dolan is examined and the difficulties in explaining the observed features of Cyg X-1 by this model are pointed out.     

The spectrum of Cyg X-1 — A theoretical model

We have calculated the spectrum of Cyg X-1 under the assumption that the radiation orginates in a disk around a 11M black-hole. Supersonic turbulence prevails in the outer parts of the disk and electron-electron bremsstrahlung appears to be resonsible for the maintenance of the temperature at a level less than 10¹⁰ K near the inner edge of the disk. The theoretical spectrum gives the best fit with the observations if the Reynolds number is about 1200.     

Clumped structure of WR wind derived from IR observations of WR+O binaries: some comments on the light curve solution for V444 Cygni

Strong increasing of the width and the depth of the secondary minimum of the light curve of V444 Cyg Wolf-Rayet eclipsing binary discovered by Cherepashchuk and Khaliullin (1973, 1975) from simultaneous narrow band continuum observations (4244–7512 Å) have been confirmed by new quasi-simultaneous UJK observations. This increasing of the width and the depth of the secondary minimum implies strong increasing of the radius of the extended atmosphere of the WN5 star with wavelength, which cannot be explained be the theory of homogeneous WR wind. These data can be understood in the model of WR wind proposed by Cherepashchuk et al. (1984). New data, supporting the reliability of the light curve solution for V444 Cyg of Cherepashchuk (1975) are presented.     

The bipolar jets associated with the planetary nebulae NGC 2392 and NGC 6543

TheUBV-photometry of a well-known X-ray binary Her X-1/HZ Her over 16 years is presented. The mean light curves of this system were constructed, using our and published data. Based on our observations in primary minimum the colour behaviour of Her X-1/HZ Her was investigated. An additional radiation during total eclipse of accretion disk is found at the ascending branch of the light curve.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Cyg X-1高态中短暴性质的研究

CygX-1高能辐射的时变特征可以通过短暴(shot)的性质反映．因此CygX-1的短暴性质，特别是处于低态时的性质曾被广泛研究,利用直接叠加短暴和自相关函数，对CygX-1高态时短暴的性质进行了研究．结果表明，当CygX-1处于高态时，其短暴的结构类似于低态时所具有的性质，短暴的半高宽随能量的增加按指数下降．此结果和康普顿化模型不一致．另外，短暴的能谱演化及结构的非对称性可以解释CygX-1中的时延现象．     

On the origin of soft gamma-rays from Cyg X-1

A hypothesis is suggested that the observed excess atE300 keV in the spectrum of Cyg X-1 has a nonthermal origin and is associated with the development of a relativistic electromagnetic cascade, initiated by accelerated particles in the accretion plasma, surrounding a black hole.     

The time lag of high-energy photons of Cyg X-1 in hard state

The time lag between hard and soft X-rays is an important aspect of the study of high-energy emission. Fourier cross spectrum, often used in calculating the time lag, is unable to measure statistically significant fast light variation above Fourier frequency 30 Hz from the measurements of Cyg X-1. The method of cross correlation function in time domain, developed by Li Ti-pei, can be effectively used in measuring time lags on different time scales. Using Li's method we discuss the properties of the time lag of high-energy photons of Cyg X-1 in hard state at different times. The results show that there is a significant time lap on short times scales (< 0.1 s). We confront different models of hard-state Cygnus X-1 with the observed time lag.     

Observations of variable and transient X-ray sources with the Ariel V sky survey experiment

Results obtained during the first six months in orbit of Ariel V with the Leicester Sky Survey are reviewed. Among 80 sources found by a scan of the Milky Way, 16 are new, and 11 UHURU sources in the scanned region are not detected. Some of these sources may be transient. The light curve of Cen X-3 in a binary cycle shows a dip between phase 0.5, and 0.75, and a secondary maximum at the centre of the dip. The dip and the maximum get progressively weaker in the succeeding cycles. These features are interpreted in terms of the stellar wind accretion model. Cyg X-1 observation for 14 days gives a broad minimum around superior conjuction. Four bright transient sources of nova-like light curves have been observed. The light curves and the spectra are given for TrA X-1 (A1524-62) and Tau X-T (A0535+26).Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

High energy gamma-rays from cygnus X-3

Simultaneous observations by the ESA satellite COS-B show that the 2–12 keV X-rays and 150–5000 MeV gamma-rays of Cyg X-3 are negatively correlated. A clear gamma-ray image of Cyg X-3 can be obtained between June 1977 and June 1980, when the X-ray emission was low, to yield a flux of P(E > 100MeV) ~ 1 × 10⁻⁶cm⁻²s⁻¹.     

The search for hot spots associated with the Cygnus X-3 relativistic jet

We report and shortly discuss here the observational work carried out in order to test the possibility that two previously detected radio sources, in the vicinity of the well known microquasar Cygnus X-3, could be hot spot tracers of interaction between its relativistic jet and the interstellar medium (ISM). The motivation behind this search is in part justified considering recent theoretical models of high energy γ-ray emission which strongly rely on the interaction sites of galactic relativistic jets with nearby ISM clouds. The results presented in this paper include an improved radio exploration of the several arc-minute field around Cygnus X-3 using the Very Large Array (VLA), as well as deep near infrared (NIR) imaging with the Calar Alto 3.5 m telescope. We anticipate here that our observations do not appear to support the initial hot spot hypothesis. Instead, the resulting images suggest that the two radio sources, originally believed to be hot spot candidates, are most likely background or foreground objects.     

On a possible model of the object Cyg X-3

According to the proposed model of the Cyg X-3, it should be recognized as a binary system consisting of a pulsar and an usual star. The plasma with the frozen-in field flows out from the star. The electromagnetic continuous spectrum in the range from radio to gamma radiation owes its origin to the interaction of electrons accelerated by a pulsar with the magnetic field of the stream. The influence of the inverse Compton effect on the spectral distribution of radiation has been considered by the numerical calculations of a system of kinetic equations. The calculations show remarkable agreement with the measurements, if the particle energy spectrum is expressed as dN/dE=AE ^–2.2. The lower limit of the accelerated particle energy equals approximately 10^–2 erg.The situation of the peak of gamma-quantum radiation of very high energy in respect to the minimum in the X-ray radiation can be explained in terms of the suggested model.     

Balloon observations of fast intensity fluctuations and flare-like enhancements of X-ray emission from Cygnus X-1

The paper presents the results of the investigation on the short term X-ray emission characteristics of Cyg X-1 in the 20–150 keV range. The observations were made with balloon-borne oriented scintillation telescope and the flights were conducted from Hyderabad, India. The source was tracked over a duration of 1 hr that enabled detailed observations with time resolution of the order of 1 min. Fluctuations in the intensity of Cyg X-1 with time scales of the order of minutes have been detected besides short-term flare-like enhancements. The spectral characteristics of the flare emission features are discussed and their relationship to the phase of the binary is examined.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

Photometric study of the FUor star V 1735 Cyg (Elias 1-12)

Results from optical photometric observations of the PMS star V 1735 Cyg are reported. The star is located in the IC 5146 dark cloud complex—a region of active star formation. On the basis of observed outburst and spectral properties, V 1735 Cyg was classified as a FUor object. We present data from BVRI CCD photometric observations of the star, collected from March 2003 to January 2009. Plates from the Rozhen Schmidt telescope archive were scanned for a brightness estimation of the star. A sequence of sixteen comparison stars in the field of V 1735 Cyg was calibrated in BVRI bands. The data from photographic observations made from 1986 to 1992 show a strong light variability (ΔV=1_⋅^m2). In contrast, the recent photometric data obtained from 2003 to 2009 show only small amplitude variations (ΔI=0_⋅^m3). The analysis of existing photometric data shows a very slow decrease in star brightness—1_⋅^m8 (R) for a 44 year period. The possibilities for future photometric investigations of V 1735 Cyg using the photographical plate archives is discussed briefly.     

X-ray timing behaviour of Cygnus X-2 at low intensities

It is known that the overall (mean) intensity of the low-mass X-ray binary Cyg X-2 varies on time-scales from a day to months, independently of the variations on time-scales of hours to a day by which the source moves between the horizontal, normal and flaring branches.
We present RXTE PCA observations of Cyg X-2, taken when its overall intensity was near its lowest values, in 1996 October and 1997 September. For the first time we perform a study of the fast timing behaviour at such low intensities. During the 1996 October observations, the source was in the left part of the horizontal branch, and during the 1997 September observations was most likely in the lower parts of the normal branch and flaring branch.
We find that the properties of the very low-frequency noise during the 1997 September observations are consistent with a monotonic decrease in its strength and power-law index as a function of overall intensity. In contrast, the strength of the ∼6 Hz normal branch quasi-periodic oscillations does not vary monotonically with overall intensity. They are strongest at medium overall intensity and weaker both when the overall intensity is low and when the overall intensity is high.