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N. Kylafis D. Giannios D. Psaltis 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2810-2812
We propose a jet model for the low/hard state of galactic black-hole X-ray sources which explains the energy spectra from radio to X-rays and a number of timing properties in the X-ray domain such as the time lag spectra, the hardening of the power density spectra and the narrowing of the autocorrelation function with increasing photon energy. The model assumes that (i) there is a magnetic field along the axis of the jet, (ii) the electron density in the jet drops inversely proportional to distance, (iii) the jet is “hotter” near its center than at its periphery, and (iv) the electrons in the jet follow a power-law distribution function. We have performed Monte Carlo simulations of Compton upscattering of soft photons from the accretion disk and have found power-law high-energy spectra with photon-number index in the range 1.5–2 and cutoff at a few hundred keV, power-law time lags versus Fourier frequency with index 0.8, and an increase of the rms amplitude of variability and a narrowing of the autocorrelation function with increasing photon energy as they have been observed in Cygnus X-1. The spectrum at long wavelengths (radio, infrared, optical) is modeled to come from synchrotron radiation of the energetic electrons in the jet. We find flat to inverted radio spectra that extend from the radio up to about the optical band. For magnetic field strengths of the order 105–106 G at the base of the jet, the calculated spectra agree well in slope and flux with the observations. 相似文献
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M. van der Klis 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2675-2679
Some aspects of the rapid X-ray variability of low magnetic-field neutron stars in low-mass X-ray binaries are briefly summarized. 相似文献
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Diane Sonya Wong Ryan Chornock Alexei V. Filippenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2813-2815
We present results of optical follow-up observations of candidate ultra-luminous X-ray sources (ULXs). Using Keck optical spectroscopy, 17 of the candidates from the Colbert and Ptak [Colbert, E.J.M., Ptak, A.F. A catalog of candidate intermediate-luminosity X-ray objects. ApJS 143, 25–45, 2002] catalog have been identified; this is one of the largest sets of optical identifications of such objects thus far. Fifteen are background active galactic nuclei (AGN); two are foreground stars in our Galaxy. These findings are consistent with background and foreground object expectations, as derived from log N–log S relations. Also, the results are briefly discussed in terms of the spiral-galaxy/ULX connection. 相似文献
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R.O. Pacumbaba Jr. C.A. Beyl 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The adaptation of specific remote sensing and hyperspectral analysis techniques for the determination of incipient nutrient stress in plants could allow early detection and precision supplementation for remediation, important considerations for minimizing mass of advanced life support systems on space station and long term missions. This experiment was conducted to determine if hyperspectral reflectance could be used to detect nutrient stress in Lactuca sativa L. cv. Black Seeded Simpson. Lettuce seedlings were grown for 90 days in a greenhouse or growth chamber in vermiculite containing modified Hoagland’s nutrient solution with key macronutrient elements removed in order to induce a range of nutrient stresses, including nitrogen, phosphorus, potassium, calcium, and magnesium. Leaf tissue nutrient concentrations were compared with corresponding spectral reflectances taken at the end of 90 days. Spectral reflectances varied with growing location, position on the leaf, and nutrient deficiency treatment. Spectral responses of lettuce leaves under macronutrient deficiency conditions showed an increase in reflectance in the red, near red, and infrared wavelength ranges. The data obtained suggest that spectral reflectance shows the potential as a diagnostic tool in predicting nutrient deficiencies in general. Overlapping of spectral signatures makes the use of wavelengths of narrow bandwidths or individual bands for the discrimination of specific nutrient stresses difficult without further data processing. 相似文献
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Michael Juntao Yuan Beverley J. Wills 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2599-2603
Changes in Eddington accretion ratios are thought to result in X-ray spectral index changes in Galactic binary black hole systems. Objects with higher Eddington ratios have softer X-ray spectra. Can we apply this result to much more massive black hole systems such as QSOs? If so, X-ray observations will give us valuable insight into the physics of QSOs. Among QSOs, X-ray spectral index is part of a large set of correlated optical and UV observational properties, especially optical Fe II and [O III] strengths in the Hβ region. To investigate whether this set of correlations is related to Eddington ratio, we use as probes, BALQSOs that have been suggested to be youthful super-accretors. We conducted infrared spectroscopy of the Hβ rest wavelength region for a sample of BALQSOs and compared line measurements with those for high and low redshift non-BAL QSOs. Hβ line widths and bolometric luminosity are used to calculate QSO black hole masses and Eddington ratios. Our results support the hypothesis that optical Fe II and [O III] line strengths are Eddington ratio indicators in QSO central engines. A possible explanation is that strong Fe II and weak [O III] indicate abundant cold gas that could fuel near Eddington accretion. 相似文献
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《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013,52(4):732-739
In the last decade, high-resolution X-ray spectroscopy has revolutionized our understanding of the role of accretion disk winds in black hole X-ray binaries. Here I present a brief review of the state of wind studies in black hole X-ray binaries, focusing on recent arguments that disk winds are not only extremely massive, but also highly variable. I show how new and archival observations at high timing and spectral resolution continue to highlight the intricate links between the inner accretion flow, relativistic jets, and accretion disk winds. Finally, I discuss methods to infer the driving mechanisms of observed disk winds and their implications for connections between mass accretion and ejection processes. 相似文献
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H. Sreehari Nirmal Iyer D. Radhika Anuj Nandi Samir Mandal 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(3):1374-1386
We carried out spectro-temporal analysis of the archived data from multiple outbursts spanning over the last two decades from the black hole X-ray binary GX 339-4. In this paper, the mass of the compact object in the X-ray binary system GX 339-4 is constrained based on three indirect methods. The first method uses broadband spectral modelling with a two component flow structure of the accretion around the black hole. The broadband data are obtained from RXTE (Rossi X-ray Timing Explorer) in the range 3.0 to 150.0?keV and from Swift and NuSTAR (Nuclear Spectroscopic Telescope Array) simultaneously in the range 0.5 to 79.0?keV. In the second method, we model the time evolution of Quasi-periodic Oscillation (QPO) frequencies, considering it to be the result of an oscillating shock that radially propagates towards or away from the compact object. The third method is based on scaling a mass dependent parameter from an empirical model of the photon index () – QPO () correlation. We compare the results at 90 percent confidence from the three methods and summarize the mass estimate of the central object to be in the range . 相似文献
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Alexander F. Zakharov Francesco De Paolis Gabriele Ingrosso Achille Nucita Asghar Qadir 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(12):2061-2063
General relativity (GR) can be probed by several tests in the weak gravitational field limit. On the contrary, very poor information exists about GR tests in strong gravitational fields. Here, we focus on the interaction of light rays with the strong gravitational field of a massive black hole and show that relativistic images may form. Hence, we calculate the shapes of shadows (mirages) forming just near BH horizons and discuss the possibility to estimate the black hole parameters (mass, spin and charge) by future astrometric missions. In 2007, the Radioastron space telescope will be launched and it will allow to evaluate those parameters for the black hole hosted at the center of our Galaxy. 相似文献