Observations Of Cygnus Research Articles

A stochastic propagation model to the energy dependent rapid temporal behaviour of Cygnus X-1 as observed by AstroSat in the hard state

Abstract We report the results from analysis of six observations of Cygnus X-1 by Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) onboard AstroSat, when the source was in the hard spectral state as revealed by the broad-band spectra. The spectra obtained from all the observations can be described by a single-temperature Comptonizing region with disc and reflection components. The event mode data from LAXPC provides unprecedented energy dependent fractional root mean square (rms) and time-lag at different frequencies which we fit with empirical functions. We invoke a fluctuation propagation model for a simple geometry of a truncated disc with a hot inner region. Unlike other propagation models, the hard X-ray emission (>4 keV) is assumed to be from the hot inner disc by a single-temperature thermal Comptonization process. The fluctuations first cause a variation in the temperature of the truncated disc and then the temperature of the inner disc after a frequency dependent time delay. We find that the model can explain the energy dependent rms and time-lag at different frequencies.

Observations of Cygnus X-1 in the MeV band by the INTEGRAL imager

The spectrum of the MeV tail detected in the black-hole candidate Cygnus X-1 remains controversial as it appeared much harder when observed with the INTEGRAL Imager IBIS than with the INTEGRAL spectrometer SPI or CGRO. We present an independent analysis of the spectra of Cygnus X-1 observed by IBIS in the hard and soft states. We developed a new analysis software for the PICsIT detector layer and for the Compton mode data of the IBIS instrument and calibrated the idiosyncrasies of the PICsIT front-end electronics. The spectra of Cygnus X-1 obtained for the hard and soft states with the INTEGRAL imager IBIS are compatible with those obtained with the INTEGRAL spectrometer SPI, with CGRO, and with the models that attribute the MeV hard tail either to hybrid thermal/non-thermal Comptonisation or to synchrotron emission.

AstroSat/LAXPC Observation of Cygnus X-1 in the Hard State

Abstract We report the first analysis of data from AstroSat/LAXPC observations of Cygnus X-1 in 2016 January. LAXPC spectra reveals that the source was in the canonical hard state, represented by a prominent thermal Comptonization component having a photon index of ∼1.8 and high temperature of kT e > 60 keV along with weak reflection and possible disk emission. The power spectrum can be characterized by two broad lorentzian functions centered at ∼0.4 and ∼3 Hz. The rms of the low-frequency component decreases from ∼15% at around 4 keV to ∼10% at around 50 keV, while that of the high-frequency one varies less rapidly from ∼13.5% to ∼11.5% in the same energy range. The time lag between the hard (20–40 keV) and soft (5–10 keV) bands varies in a step-like manner being nearly constant at ∼50 milliseconds from 0.3 to 0.9 Hz, decreasing to ∼8 milliseconds from 2 to 5 Hz and finally dropping to ∼2 milliseconds for higher frequencies. The time lags increase with energy for both the low and high-frequency components. The event mode LAXPC data allows for flux resolved spectral analysis on a timescale of 1 s, which clearly shows that the photon index increased from ∼1.72 to ∼1.80 as the flux increased by nearly a factor of two. We discuss the results in the framework of the fluctuation propagation model.

Corroboration of Dynamic Black Hole Gravitational Physics from Observations of Cygnus X-1

The compact black hole primary in the X-ray binary Cygnus X-1, has recently been characterised by observation. This data can be analysed to test models of black hole gravitational physics. Using the optimum observational data with the least fit parameters, the average of 3 spectral data sets revealed an averaged inner rim accretion disc radius Rin = 2.24 GM/c2. Using the Kerr spinning black hole model results in a theoretical apparent reduction in Rin = 1.41 GM/c2, which also results in an extremely relativistic spin parameter a* > 0.97 c. Here the data is analysed using a dynamic gravitational model. Utilizing this model Rin = 2.24 GM/c2, which is equivalent to the observed Rin = 2.24 GM/c2. In this case the spin parameter does not reach such extreme relativistic speeds, at a* = 0.76 c. These results using dynamic black hole physics are in very good agreement with direct observations of Cygnus X-1. Importantly, this model offers further testable predictions of black hole gravitational physics.

Jet disc coupling in black hole binaries

In the last decade multi-wavelength observations have demonstrated the importance of jets in the energy output of accreting black hole binaries. The observed correlations between the presence of a jet and the state of the accretion flow provide important information on the coupling between accretion and ejection processes. After a brief review of the properties of black hole binaries, I illustrate the connection between accretion and ejection through two particularly interesting examples. First, an INTEGRAL observation of Cygnus X-1 during a ‘mini-’ state transition reveals disc jet coupling on time scales of orders of hours. Second, the black hole XTEJ1118+480 shows complex correlations between the X-ray and optical emission. Those correlations are interpreted in terms of coupling between disc and jet on time scales of seconds or less. Those observations are discussed in the framework of current models.

Dramatic Variability of X‐Ray Absorption Lines in the Black Hole Candidate Cygnus X‐1

We report results from a 30 ks observation of Cygnus X-1 with the High Energy Transmission Grating Spectrometer (HETGS) on board the Chandra X-Ray Observatory. Numerous absorption lines were detected in the HETGS spectrum. The lines are associated with highly ionized Ne, Na, Mg, Al, Si, S, and Fe, some of which have been seen in earlier HETGS observations. Surprisingly, however, we discovered dramatic variability of the lines over the duration of the present observation. For instance, the flux of the Ne X line at 12.14 A was about 5 × 10-3 photons cm-2 s-1 in the early part of the observation but became subsequently undetectable, with a 99% upper limit of 0.06 × 10-3 photons cm-2 s-1 on the flux of the line. This implies that the line weakened by nearly 2 orders of magnitude on a timescale of hours. The overall X-ray flux of the source did also vary during the observation but only by 20%-30%. For Cyg X-1, the absorption lines are generally attributed to the absorption of X-rays by ionized stellar wind in the binary system. Therefore, they may provide valuable diagnostics on the physical condition of the wind. We discuss the implications of the results.

Power spectra of ionospheric scintillations obtained from observations of Cygnus A on the radio telescope URAN-4

There are many records of Cygnus A passages through the direction pattern obtained on the radio telescope URAN-4 during 1998–2004. Most of these show fluctuations in the flux density caused by ionospheric scintillations. The power spectrum is an important characteristic of the stochastic process and such processes are the main reason for the nature of scintillations. In this paper, estimations of the power spectra of ionospheric scintillations are made from the observations of Cyg A on the radio telescope URAN-4. Examples of the spectra are presented for observations under different circumstances and for several scintillation activity levels.

Very high energy gamma-quanta 1–65 TeV from the Cygnus X-3 binary

The results of almost ten-year observation of Cygnus X-3 point source by SHALON mirror Cherenkov telescope are presented. The galactic source Cygnus X-3, known for more than 10 years as a source with variable intensity 10 −11 − 5 • 10 −12 c m −2 s −1 , was regularly observed since 1995 with average gamma-quantum flux F ( E O > 0.8 T e V ) = ( 6.8 ± 0.7 ) • 10 −13 c m −2 s −1 . The flux in 2003 was ( 1.79 ± 0.33 ) • 10 −12 c m −2 s −1 . Earlier, in 1997, an increase in the flux was also observed ( 1.2 ± 0.5 ) • 10 −12 c m −2 s −1 . The limits on gamma-rays from Cygnus X-3, the source that results stimulated the construction of many new detectors are presented. These upper limits and SHALON fluxes are now more than a factor 100 less than the fluxes originally reported.

Probing the Precession of the Inner Accretion Disk in Cygnus X‐1

We show that changes in the orientation of the inner accretion disk of Cygnus X-1 affect the shape of the broad Fe K$\alpha$ emission line emitted from this object, in such a way that eV-level spectral resolution observations (such as those that will be carried out by the {\it ASTRO-E2} satellite) can be used to analyze the dynamics of the disk. We here present a potential diagnostic tool, supported by numerical simulations, by which a few observations of Cygnus X-1, separated in time, can determine whether its accretion disk actually precesses, and if so, determine its period and precession angle. This approach could also be used for similar studies in other microquasar systems.

Simultaneous ASCA and Hubble Space Telescope/GHRS Observations of Cygnus X‐2/V1341 Cygni11Based partially on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5‐26555.

ABSTRACTWe present results from ultraviolet and X‐ray observations of the low‐mass X‐ray binary Cygnus X‐2. The simultaneous Hubble Space Telescope/GHRS and ASCA observations took place during the low state of an 82 day cycle. We compare our observations as well as archival IUE and RXTE data with models that predict ultraviolet and optical continuum emission from an X‐ray–heated disk and a Roche lobe–filling star. The model predictions are consistent with observed optical, ultraviolet, and X‐ray variations over both orbital and long‐term periods. The X‐ray spectral state, the luminosities implied by fits to the X‐ray data, the ultraviolet continuum and line fluxes, and the mass accretion rates obtained from fits to the ultraviolet continuum are consistent with location of our observations on the normal and horizontal branches of the Z‐shaped X‐ray color‐color diagram. A combination of changes to mass accretion rate and obstruction by a warped disk can be invoked as a possible explanation for the motion of the “Z” in the color‐color plane. The GHRS/G160M measurements concentrated on N v (λ1238.8; λ1242.8) and He ii (λ1640.5). The low‐resolution (GHRS/G140L) observations captured Si iv (λ1393.8; λ1402.8), N iv (λ1486.5), and C iv (λ 1548); absorption lines detected in the spectra are interstellar. Although the relative line fluxes are consistent with emission from an X‐ray–heated accretion disk corona, predictions from models of line emission from simple disks do not fit the observed emission‐line profiles. The lack of double peaks suggests that most of the line emission is from the surface of the companion and the radial velocities (80–130 km s−1) are consistent with emission from the optical star at the orbital phase (0.70–0.74) of our observations.

X‐Ray Spectral and Timing Observations of Cygnus X‐2

We report on a joint BeppoSAX/RXTE observation of the Z-type low-mass X-ray binary Cyg X-2. The source was in the so-called high overall intensity state and in less than 24 hr went through all three branches of the Z track. The continuum X-ray spectrum could be described by the absorbed sum of a soft thermal component, modeled as either a blackbody or a multicolor disk blackbody, and a Comptonized component. The timing power spectrum showed several components, including quasi-periodic oscillations in the range 28-50 Hz while the source was on the horizontal branch (horizontal branch oscillation; HBO). We found that the HBO frequency was well correlated with the parameters of the soft thermal component in the X-ray spectrum. We discuss implications of this correlation for models of the HBO.

ITAL]Chandra[/ITAL] Observations of Cygnus A: Magnetic Field Strengths in the Hot Spots of a Radio Galaxy

We report X-ray observations of the powerful radio galaxy Cygnus A with the Chandra X-Ray Observatory. This Letter focuses on the radio hot spots, all four of which are detected in X-rays with a very similar morphology to their radio structure. X-ray spectra have been obtained for the two brighter hot spots (A and D). Both are well described by a power law with photon index Γ = 1.8 ± 0.2 absorbed by the Galactic column in the direction of Cygnus A. Thermal X-ray models require too high gas densities and may be ruled out. The images and spectra strongly support synchrotron self-Compton models of the X-ray emission, as proposed by Harris, Carilli, & Perley on the basis of ROSAT imaging observations. Such models indicate that the magnetic field in each of the brighter hot spots is 1.5 × 10-4 G, with an uncertainty of a few tens of percent. This value is close to the equipartition field strengths assuming no protons are present. The possibility that the X-rays are synchrotron radiation is briefly discussed but not favored. We speculate that production of the γ ~ 107 electrons necessary for X-ray synchrotron radiation from hot spots is inhibited when the external gas density is high, as is the case when the radio galaxy is within a cooling flow.

Apparent superluminal expansion in Cygnus X-3

The Galactic radio-emitting X-ray binary Cygnus X-3 is known to be a source of large-scale radio jets associated with periods of intense radio flaring. These jets have been found to have an expansion velocity of ∼0.3c and are believed (on kinematic grounds) to lie close to the plane of the sky. We present new observations of Cygnus X-3 using the VLBA at 15 GHz. These observations, which included the detection of two small flares, show an additional kind of behaviour with apparent superluminal expansion along both major and minor axes. Evidence for superluminal activity has been found in a number of X-ray binary systems such as GRS 1915+105 and GRO J1655−40 with their superluminal radio jets. Apparently similar morphologies of the Galactic and extragalactic jet sources have led to the X-ray binaries being described as ‘micro-quasars’. The superluminal expansion seen in our results appears to be different in nature from these other two sources, and a number of mechanisms are presented and discussed.

ITAL]ASCA[/ITAL] Observation of Cygnus X-1 in the Soft State: Mass of the Compact Object

We describe the ASCA observation of the black hole candidate Cyg X-1 in the soft state of 1996 May and report the mass estimation of the central object from X-ray spectral analysis. The energy spectrum in 0.7-10 keV can be described by the sum of a power law (Γ = 2.3 ± 0.1) and an ultrasoft component; the latter is most probably the emission from an optically thick accretion disk. Through the spectral analysis of the ultrasoft component, we estimated the size of the accretion disk, which is closely related to the Schwarzschild radius and, hence, to the mass of the central object. Taking the general relativistic effects into account, the most probable mass of the compact object is estimated as 12+ 3−1M☉. This value is independent of, yet consistent with, the mass estimate based on the orbital kinematics information.

Simultaneous millimetre and radio observations of Cygnus X-3 in a quiescent radio state

Observations of Cygnus X-3 at 2.0 and 1.1 mm with the JCMT, partially simultaneous with radio flux measurements at 2 cm and 18 cm, are presented. These are the first known observations of Cyg X-3 at millimetre wavelengths whilst the source was in a quiet radio state. The observed millimetre fluxes are several times greater than those expected for the synchrotron tail of emission extrapolated from the radio, and the 2-mm flux exceeds that at 1.1 mm, suggesting a peak in the region of a few mm. The observations are interpreted using an extension of the model of Marti, Paredes & Estalella to repeated short injections of relativistic electrons in a region in the Cyg X-3 stellar wind which is optically thin to millimetre-wave photons, but optically thick at centimetre wavelengths. Centimetre-wavelength emission is not observed until the ejecta have travelled further out in the wind. A MERLIN radio map at 18 cm reveals the same elliptical asymmetry in the scattering medium around Cyg X-3 as found by Wilkinson, Narayan & Spencer.

Observations of Cygnus X-1 COMPTEL during 1991

Observations of Cygnus X-1 COMPTEL during 1991

The Status of Ultra-High-Energy Gamma-Ray Observations

AbstractIn 1983 Samorski and Stamm found evidence of ultra-high-energy (UHE) gamma-ray emission from Cygnus X-3 in archival data from the Kiel air shower array. The emission appeared to be emitted only at one phase in the binary orbit. The Kiel array was sensitive to air showers generated by particles with energies above 3 × 1015 eV. Their discovery led to searches in archival data from other arrays for evidence of UHE emission from Cygnus X-3 and other potential sources in the Galaxy, and to the construction of new air shower arrays dedicated to UHE astronomy.In the mid 1980s many groups around the world claimed detections of Cygnus X-3, Hercules X-1, Vela X-1, and other objects. Cygnus X-3 is strongly variable at all wavelengths, and so it would be surprising if this variability did not extend to UHE gamma-rays also. This indeed appeared to be the case, and in the mid to late 1980s the UHE gamma-ray output showed a steady decline apart from transient UHE emission following giant radio flares. With the exception of possible detections above 1017 eV by the Fly’s Eye and Akeno Array, I am unaware of any statistically compelling claimed detections of this source reported over the past 4 years. The new arrays—CASA-MIA and SPASE—have not detected any of the claimed sources, and it seems likely that at least some of these early claims may have been premature. However, although none of the observations taken alone was of extremely high statistical significance, the observations of Cygnus X-3 by different groups showed a consistency which I feel cannot be ascribed to chance alone. The observations of Cygnus X-3 and the Crab Nebula/Pulsar are reviewed with particular reference to the results published during the last 5 years.Subject headings: gamma rays: observations — pulsars: individual (Crab Nebula) — stars: individual (Cygnus X-3)

Recent observations of VHE gamma rays from Cygnus X-3

The authors' observations of Cygnus X-3 in 1981-88 have suggested that sporadic 12.6 ms pulsed very high energy gamma rays are produced at or near the maximum (phase 0.6) in the 4.8 h X-ray cycle. Cygnus X-3 was observed with the Durham University Mark IV Northern Hemisphere gamma-ray telescope in 1989, shortly after two radio outbursts were detected from the object. An analysis of these data suggests that 12.6 ms pulsar emission may be observed at a phase in the 4.8 h cycle some 1000 s before their prediction from previous measurements. This is in agreement with measurements made at Woomera by the University of Adelaide. More recent observations using the Mark III Southern Hemisphere telescope at large zenith angles have not provided any further evidence for pulsar activity.

Low-flux hard X-ray observation of Cygnus X-1

The black hole candidate Cygnus X-1 was observed at a low flux level on 1985 August 5 with the POKER experiment in the hard X-ray range. During the same flight, the Crab Nebula was also observed as a in-flight calibration source, and the spectral results are reported. The measurements shows a low flux for Cygnus X-1. The photon spectrum is well described by a single power law, with a photon index of α = 1.87 and an intensity of 2.57 × 10 -3 photons/(cm 2 × s × keV) at 50 keV, corresponding to 1.11 Crab.

SMM/HXRBS observations of Cygnus X-1 from 1986 December to 1988 April

view Abstract Citations (12) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS SMM/HXRBS Observations of Cygnus X-1 from 1986 December to 1988 April Schwartz, R. A. ; Orwig, L. E. ; Dennis, B. R. ; Ling, J. C. ; Wheaton, W. A. Abstract The Solar Maximum Mission's Hard X-ray Burst Spectrometer made 30 measurements of Cygnus X-1 from December, 1986 to April, 1988, yielding a data set of broad synoptic coverage but limited duration for each data point. The hard X-ray intensity was found to be between the gamma(2) and gamma(3) levels, with a range of fluctuations about the average intensity level. The shape of the photon spectrum was found to be closest to that reported by Ling et al. (1983, 1987) during the time of the gamma(3) level emission, although the spectral shapes reported for the gamma(2) and gamma(1) levels were not precluded. Publication: The Astrophysical Journal Pub Date: July 1991 DOI: 10.1086/170281 Bibcode: 1991ApJ...376..312S Keywords: Solar Maximum Mission; Stellar Spectra; X Ray Astronomy; X Ray Binaries; X Ray Spectra; Light Curve; Satellite-Borne Instruments; Spaceborne Astronomy; Spectrum Analysis; Astrophysics; STARS: INDIVIDUAL CONSTELLATION NAME: CYGNUS X-1; X-RAYS: BINARIES; X-RAYS: SPECTRA full text sources ADS | data products SIMBAD (1)