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Disc Models (disc + models)
Selected AbstractsAn additional soft X-ray component in the dim low/hard state of black hole binariesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2010C. Y. Chiang ABSTRACT We test the truncated disc models using multiwavelength (optical/ultraviolet/X-ray) data from the 2005 hard state outburst of the black hole Swift J1753.5,0127. This system is both fairly bright and has fairly low interstellar absorption, so gives one of the best data sets to study the weak, cool disc emission in this state. We fit these data using models of an X-ray illuminated disc to constrain the inner disc radius throughout the outburst. Close to the peak, the observed soft X-ray component is consistent with being produced by the inner disc, with its intrinsic emission enhanced in temperature and luminosity by reprocessing of hard X-ray illumination in an overlap region between the disc and corona. This disc emission provides the seed photons for Compton scattering to produce the hard X-ray spectrum, and these hard X-rays also illuminate the outer disc, producing the optical emission by reprocessing. However, the situation is very different as the outburst declines. The optical is probably cyclo-synchrotron radiation, self-generated by the flow, rather than tracing the outer disc. Similarly, limits from reprocessing make it unlikely that the soft X-rays are directly tracing the inner disc radius. Instead they appear to be from a new component. This is seen more clearly in a similarly dim low/hard state spectrum from XTE J1118+480, where the 10 times lower interstellar absorption allows a correspondingly better view of the ultraviolet/extreme ultraviolet (EUV) emission. The very small emitting area implied by the relatively high temperature soft X-ray component is completely inconsistent with the much larger, cooler, ultraviolet component which is well fit by a truncated disc. We speculate on the origin of this component, but its existence as a clearly separate spectral component from the truncated disc in XTE J1118+480 shows that it does not simply trace the inner disc radius, so cannot constrain the truncated disc models. [source] Modelling the extreme ultraviolet emission during the low state of Hercules X-1MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003D. A. Leahy ABSTRACT Hercules X-1 was observed for extended periods during its low state by the Extreme Ultraviolet Explorer (EUVE). These observations yield low-state light curves in the extreme ultraviolet (EUV) which are compared with a composite model here. The model includes reflection of soft X-rays off the companion HZ Her, including the shadowing of HZ Her by the accretion disc, and emission from the accretion disc surface. Four different geometries for the accretion disc were adopted, all derived from the RXTE All-Sky Monitor (ASM) 35-day light-curve modelling. Three were thin disc models for different system inclinations, i, and the fourth was a disc with a thick inner ring for i= 85°. With the HZ Her reflection model, with no free parameters except normalization, and a simple model for the disc emission, the models fit the data well. The disc emission accounts for about half of the EUV flux, depending on which accretion disc geometry is used. The disc geometry that best fits the EUV light curves is the disc with a thick inner ring, which is the same model that gives the best fit to the RXTE/ASM light curve. [source] On the accretion geometry of Cyg X-1 in the low/hard stateMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003F. Eugenio Barrio ABSTRACT We fit the broad-band RXTE PCA and HEXTE spectrum of Cyg X-1 from 3,200 keV with reflection models which calculate the vertical ionization structure of an X-ray illuminated disc. We consider two geometries corresponding to a truncated disc/inner hot flow and magnetic flares above an untruncated disc. Both models are able to fit the PCA 3,20 keV data, but with very different spectral components. In the magnetic flare models the 3,20 keV PCA spectrum contains a large amount of highly ionized reflection, while in the truncated disc models the amount of reflection is rather small. The Compton downscattering rollover in reflected emission means that the magnetic flare models predict a break in the spectrum at the high energies covered by the HEXTE bandpass which is not seen. By contrast, the weakly illuminated truncated disc models can easily fit the 3,200 keV spectra. [source] Relativistic ionized accretion disc models of MCG,6-30-15MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001D.R. Ballantyne We present results from fitting of ionized accretion disc models to three long ASCA observations of the Seyfert 1 galaxy MCG,6-30-15. All three data sets can be fitted by a model consisting of ionized reflection from the inner region of the accretion disc (with twice solar Fe abundance) and a separate disc-line component from farther out on the disc. The disc-line is required to fit the height of the observed Fe K, line profile. However, we show that a much simpler model of reflection from a very weakly ionized constant-density disc also fits the data. In this case only a single cold Fe K, line at 6.4 keV is required to fit the observed line. The ionized disc models predict that O viii K,, C vi K,, Fe xvii L, and Fe xviii L, lines will appear in the soft X-ray region of the reflection spectrum, but are greatly blurred as a result of Compton scattering. The equivalent width (EW) of O viii K, is estimated to be about 10 eV and seems to be as strong as the blend of the Fe L lines. This result creates difficulty for the claim of a strong relativistic O viii line in the XMM - Newton grating spectrum of MCG,6-30-15, although we cannot strictly rule it out since MCG,6-30-15 was in an anomalously low state during that observation. We find that increasing the O abundance or breaking the continuum below 2 keV will not significantly strengthen the line. The second Fe K, line component in the ionized disc model may arise from neutral reflection from a flared disc, or from a second illumination event. The data cannot distinguish between the two cases, and we conclude that single-zone ionized disc models have difficulty fitting these hard X-ray data of MCG,6-30-15. [source] Mirror eclipses in the cataclysmic variable IP PegMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001S.P. Littlefair We present time resolved K -band infrared spectra of the dwarf nova (DN) IP Peg in early quiescence. The Brackett , and He i (,2.0581) lines in our data show hitherto unseen behaviour, which we term a mirror eclipse, and interpret as an eclipse of the secondary star by an optically thin accretion disc. Mirror eclipses are a direct probe of the structure and physical conditions of accretion discs. For example, on assuming the relevant level populations to be in local thermal equilibrium, we constrain the temperature and density of the optically thin material, causing the mirror eclipse in IP Peg to be and respectively. In order to match our data, we find that at least the outermost 20 per cent of the disc (in radius) must be entirely optically thin. Implications for time-dependent disc models are examined. [source] Narrow-Line Seyfert 1 Galaxies with high-energy sharp spectral drops: reflection-versus absorption modelsASTRONOMISCHE NACHRICHTEN, Issue 10 2006Th. Boller Abstract With the launch of XMM-Newton in 1999, two Narrow-Line Seyfert 1 Galaxies (NLS1s) have been detected (IRAS 13224,3809 and 1H 0707,495) showing sharp spectral drops at energies equal or above the neutral Fe K edge at 7.1 keV without any narrow Fe K reemission. In this paper I summarize our present knowledge on the observed properties of sharp high-energy spectral drops. I list the problems presently arising from the reflection dominated and the optically thick disc models. Finally, I present an alternative solution which consists of a combination of the accretion disc model and the reflection dominated model. This might solve the problems of the standard accretion disc model. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||