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TOPIC: Cygnus X-1 Bubble


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RE: Cygnus X-1 Bubble
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In The Heart Of Cygnus, NASA's Fermi Reveals A Cosmic-ray Cocoon

The constellation Cygnus, now visible in the western sky as twilight deepens after sunset, hosts one of our galaxy's richest-known stellar construction zones. Astronomers viewing the region at visible wavelengths see only hints of this spectacular activity thanks to a veil of nearby dust clouds forming the Great Rift, a dark lane that splits the Milky Way, a faint band of light marking our galaxy's central plane.
Located in the vicinity of the second-magnitude star Gamma Cygni, the star-forming region was named Cygnus X when it was discovered as a diffuse radio source by surveys in the 1950s. Now, a study using data from NASA's Fermi Gamma-ray Space Telescope finds that the tumult of star birth and death in Cygnus X has managed to corral fast-moving particles called cosmic rays.

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Cosmic ray factory observed in stellar superbubble

New images link cosmic rays to an enormous bubble of gas blown by hot, young stars, implying that these mysterious high-energy particles may be made in the same factories where stars are born.
Cosmic rays have puzzled astronomers since they were discovered nearly a century ago. Most are protons and other atomic nuclei. They bombard our planet from all directions, travelling at close to the speed of light.
Where cosmic rays come from is unknown. Astronomers suspect that supernova explosions boost them to such high speeds. Supernovae happen most often in dense clouds of gas and dust where stars between 10 and 50 times the mass of the sun are born and die - so those could be a good place to look.

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Cygnus X-1
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Title: The fate of Cyg X-1: an empirical limit on BH-NS merger rate
Authors: Krzysztof Belczynski, Tomasz Bulik, Charles Bailyn

The recent distance determination allowed precise estimation of the orbital parameters of Cyg X-1, which contains a massive 14.8 Msun BH with a 19.2 Msun O star companion. This system appears to be the clearest example of a potential progenitor of a BH-NS system. We follow the future evolution of Cyg X-1, and show that it will soon encounter a Roche lobe overflow episode, followed shortly by a Type Ib/c supernova and the formation of a NS. It is demonstrated that in majority of cases (>70%) the supernova and associated natal kick disrupts the binary due to the fact that the orbit expanded significantly in the Roche lobe overflow episode. In the reminder of cases (<30%) the newly formed BH-NS system is too wide to coalesce in the Hubble time. Only sporadically (1%) a Cyg X-1 like binary may form a coalescing BH-NS system given a favourable direction and magnitude of the natal kick. If Cyg X-1 like channel (X-ray active phase shorter than 10 Myr) is the only or dominant way to form BH-NS binaries in the Galaxy we can estimate the empirical BH-NS merger rate in the Galaxy at the level of 0.001 per Myr. This rate is so low that the detection of BH-NS systems in gravitational radiation is highly unlikely, generating Advanced LIGO/VIRGO detection rates at the level of only 1 per century. If BH-NS inspirals are in fact detected, it will indicate that the formation of these systems proceeds via some alternative and yet unobserved channels.

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Cygnus X-1 Black Hole
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Title: The Extreme Spin of the Black Hole in Cygnus X-1
Authors: Lijun Gou, Jeffrey E. McClintock, Mark J. Reid, Jerome A. Orosz, James F. Steiner, Ramesh Narayan, Jingen Xiang, Ronald A. Remillard, Keith A. Arnaud, Shane W. Davis

The compact primary in the X-ray binary Cygnus X-1 was the first black hole to be established via dynamical observations. We have recently determined accurate values for its mass and distance, and for the orbital inclination angle of the binary. Building on these results, which are based on our favoured (asynchronous) dynamical model, we have measured the radius of the inner edge of the black hole's accretion disk by fitting its thermal continuum spectrum to a fully relativistic model of a thin accretion disk. Assuming that the spin axis of the black hole is aligned with the orbital angular momentum vector, we have determined that Cygnus X-1 contains a near-extreme Kerr black hole with a spin parameter a/M>0.97 (3 \sigma). For a less probable (synchronous) dynamical model, we find a/M>0.91 (3 \sigma). Our results take into account all significant sources of observational and model-parameter uncertainties, which are dominated by the uncertainties in black hole mass, orbital inclination angle and distance. The uncertainties introduced by the thin-disk model we employ are particularly small in this case, given the disk's low luminosity (L/L_{Edd} ~ 0.02).

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Cygnus X-1
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Since its discovery 45 years ago, Cygnus X-1 has been one of the most intensively studied cosmic X-ray sources. About a decade after its discovery, Cygnus X-1 secured a place in the history of astronomy when a combination of X-ray and optical observations led to the conclusion that it was a black hole, the first such identification.
The Cygnus X-1 system consists of a black hole with a mass about 10 times that of the Sun in a close orbit with a blue supergiant star with a mass of about 20 Suns. Gas flowing away from the supergiant in a fast stellar wind is focused by the black hole, and some of this gas forms a disk that spirals into the black hole. The gravitational energy release by this infalling gas powers the X-ray emission from Cygnus X-1.

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HDE 226868
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Title: Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system. I. The non-dip spectrum in the low/hard state
Authors: Manfred Hanke, Joern Wilms, Michael A. Nowak, Katja Pottschmidt, Norbert S. Schulz, Julia C. Lee
(Version v2)

We present analyses of a 50 ks observation of the supergiant X-ray binary system Cygnus X-1/HDE 226868 taken with the Chandra High Energy Transmission Grating Spectrometer (HETGS). Cyg X-1 was in its spectrally hard state and the observation was performed during superior conjunction of the black hole, allowing for the spectroscopic analysis of the accreted stellar wind along the line of sight. A significant part of the observation covers X-ray dips as commonly observed for Cyg X-1 at this orbital phase, however, here we only analyse the high count rate non-dip spectrum. The full 0.5-10 keV continuum can be described by a single model consisting of a disk, a narrow and a relativistically broadened Fe Kalpha line, and a power law component, which is consistent with simultaneous RXTE broad band data. We detect absorption edges from overabundant neutral O, Ne and Fe, and absorption line series from highly ionised ions and infer column densities and Doppler shifts. With emission lines of He-like Mg XI, we detect two plasma components with velocities and densities consistent with the base of the spherical wind and a focused wind. A simple simulation of the photoionisation zone suggests that large parts of the spherical wind outside of the focused stream are completely ionised, which is consistent with the low velocities (<200 km/s) observed in the absorption lines, as the position of absorbers in a spherical wind at low projected velocity is well constrained. Our observations provide input for models that couple the wind activity of HDE 226868 to the properties of the accretion flow onto the black hole.

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Posts: 131433
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Cygnus X-1
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Title: An unusually bright and long outburst of Cygnus X-1 observed with INTEGRAL
Authors: J. Malzac, P. Lubinski, A. A. Zdziarski, M. Cadolle Bel, M. Turler, P. Laurent

We present INTEGRAL light curves and spectra of the black-hole binary Cyg X-1 during a bright event that occurred in 2006 September, and which was simultaneous with a detection at 0.1-1 TeV energies by the MAGIC telescope. We analyse the hard X-ray emission from 18 to 700 keV with the INTEGRAL data taken on 2006 September 24-26 by the IBIS and SPI instruments. These data are complemented with RXTE All Sky Monitor data at lower energy. We present the light curves and fit the high energy spectrum with various spectral models. Despite variations in the flux by a factor of 2 in the the 20-700 keV energy band, the shape of the energy spectrum remained remarkably stable. It is very well represented by an e-folded power law with the photon index 1.4 and a high energy cut-off at 130-140 keV. The spectrum is also well described by thermal Comptonisation including a moderate reflection component, with a reflection amplitude R around 0.4. The temperature of the hot Comptonising electrons is about 70 keV and their Thomson optical depth is about 2.5. These spectral properties are typical of those observed in the low/hard state. This shows that Cyg X-1 may stay in the low hard state at least up to the flux level of 2 Crab, which corresponds to 2-3 per cent of the Eddington luminosity. It is the first time a persistent high-mass black-hole binary is observed at a few percent of the Eddington luminosity with a stable low/hard state spectrum over a period of a few days. Such state has so far been observed only during the rising phase of transient low-mass black-hole binaries.

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HDE 226868/Cygnus X-1 binary system
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Title: On the orbital and physical parameters of the HDE 226868/Cygnus X-1 binary system
Authors: Lorenzo Iorio
(Version v2)

In this paper we explore the consequences of the recent determination of the mass m=(8.7 +/- 0.8)M_Sun of Cygnus X-1, obtained from the Quasi-Periodic Oscillation (QPO)-photon index correlation scaling, on the orbital and physical properties of the binary system HDE 226868/Cygnus X-1. By using such a result and the latest spectroscopic optical data of the HDE 226868 supergiant star we get M=(24 +/- 5)M_Sun for its mass. It turns out that deviations from the third Kepler law significant at more than 1-sigma level would occur if the inclination i of the system's orbital plane to the plane of the sky falls outside the range 41-56 deg: such deviations cannot be due to the first post-Newtonian (1PN) correction to the orbital period because of its smallness; interpreted in the framework of the Newtonian theory of gravitation as due to the stellar quadrupole mass moment Q, they are unphysical because Q would take unreasonably large values. By conservatively assuming that the third Kepler law is an adequate model for the orbital period we obtain i=(48 +/- 7) deg which yields for the relative semimajor axis a=(42 +/- 9)R_Sun. Our estimate for the Roche's lobe of HDE 226868 is r_M = (21 +/- 6)R_Sun.

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Title: Observations of microquasars with the MAGIC telescope
Authors: J. Rico, M. Rissi, P. Bordas, V. Bosch-Ramon, J. Cortina, J. M. Paredes, M. Ribo, D. F. Torres, R. Zanin

We report on the results from the observations in very high energy band (VHE, E_gamma > 100GeV) of the black hole X-ray binary (BHXB) Cygnus X-1. The observations were performed with the MAGIC telescope, for a total of 40 hours during 26 nights, spanning the period between June and November 2006. We report on the results of the searches for steady and variable gamma-ray signals, including the first experimental evidence for an intense flare, of duration between 1.5 and 24 hours.

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Title: A dark jet dominates the power output of the stellar black hole Cygnus X-1
Authors: E. Gallo (Amsterdam), R. Fender, C. Kaiser, D. Russell (Southampton), R. Morganti, T. Oosterloo (ASTRON), S. Heinz (MIT)

Accreting black holes are thought to emit the bulk of their power in the X-ray band by releasing the gravitational potential energy of the in-falling matter.
At the same time, they are capable of producing highly collimated jets of energy and particles flowing out of the system with relativistic velocities. Here researchers show that the 10 solar mass black hole in the X-ray binary Cygnus X-1 is surrounded by a large-scale (about 5 pc in diameter) ring-like structure that appears to be inflated by the inner radio jet.
They estimate that in order to sustain the observed emission of the ring, the jet of Cygnus X-1 has to carry a kinetic power that can be as high as the bolometric X-ray luminosity of the binary system.
This result may imply that low-luminosity stellar mass black holes as a whole dissipate the bulk of the liberated accretion power in the form of `dark', radiatively inefficient relativistic outflows, rather than locally in the X-ray emitting inflow.

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