X-Ray::Tomography

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Ptychographic X-ray computed tomography analysis of cement pastes

Ptychographic X-ray computed tomography analysis of cement pastes

micrometer-sized calcium silicate hydrate (C-S-H) gel (Deboodt et al., 2019) which should result in wrong volume-content analyses. Ptychographic X-ray computed tomography (PXCT) allows a non- invasive assessment of electron (and mass) density at the meso and microscales (Diaz et al., 2012). PXCT is a non-destructive scanning imaging technique which uses the coherence properties of synchrotron radiation (Dierolf et al., 2010). PXCT replaces the post-sample X-ray optics by phase retrieval algorithms which, combined with the ptychographic approach, make the technique very reliable and robust (Faulkner & Rodenburg, 2004; Rodenburg et al., 2007). This technique allows quantitatively distinguishing between different components with very similar absorption contrast, which is not possible with standard (absorption-based) synchrotron X-ray tomography. Moreover, PXCT (Dierolf et al., 2010) combines ptychography and tomography to simultaneously provide two 3D volumes of the difference from one of the real part of the refractive index, δ(r), and the imaginary part of the refractive index, β(r). Consequently, the complete complex-valued refractive index of the sample can be obtained (da Silva et al., 2015) as follows:
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Structural characterization of solid cellular polymers by X-ray tomography and light scattering

Structural characterization of solid cellular polymers by X-ray tomography and light scattering

The X-ray system of CellMat laboratory was built as part of a previous PhD. Thesis [54]. The critical elements are the X-ray tube (microfocus L10101 from Hamamatsu photonics, Japan) and flat panel detector (C7940DK-02 also from Hamamatsu). Both elements were carefully selected since polymers are low absorbing materials. To overcome this constraint, low energy X-rays are required in order to guarantee enough contrast in the images. For this reason, the spectral response of the selected detector should be focused on the low energy range to maximize the sensibility and efficiency. Moreover, dimensions of cellular structure are in the order of microns and therefore high spatial resolution is also relevant, needing small focus spot size and small pixel size in the detector. In addition, tomography experiments are carried out by locating a high precision rotation stage (DT-65 N from PI miCos, Germany) between source and detector.
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In situ hydration imaging study of a ye'elimite paste by ptychographic x-ray computed tomography

In situ hydration imaging study of a ye'elimite paste by ptychographic x-ray computed tomography

Here, we report the results of a ptychographic X-ray computed tomography (PXCT) study on the in situ hydration of ye'elimite with gypsum at different early ages. PXCT is a nondestructive X-ray imaging technique which provides 3D electron density and attenuation coefficient distributions of cement pastes with an isotropic resolution close to 100 nm allowing distinguishing between component phases with very similar contrast in more conventional absorption-based X-ray tomography. The sample was prepared by hydrating ye'elimite with gypsum. Four datasets were recorded at 48, 53, 58 and 63 hours of hydration. The main aim of this imaging study was to quantify the microstructure evolution, within this time interval, with submicrometer spatial resolution. The different component phases were identified and their mass densities determined. Furthermore, the tomograms were segmented and the volume percentage of each component were determined and compared at the four hydrating ages.
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Quantitative disentanglement of nanocrystalline phases in cement pastes by synchrotron ptychographic X-ray tomography

Quantitative disentanglement of nanocrystalline phases in cement pastes by synchrotron ptychographic X-ray tomography

One step forward in X-ray computed tomography involves the use of the diffraction signal (Birkbak et al., 2015). This technique combines the merits of diffraction with computed tomography to allow imaging of the interior of materials, for instance determining the distributions of polymorphs in complex mixtures, by using a focused synchrotron beam and measuring the diffraction or scattering signal arising from the nano- or atomic structure of the specimen in a raster-scanning approach. This technique has also been widely applied to cements (Artioli et al., 2010; Valentini et al., 2011, 2012; Voltolini et al., 2013), e.g. to unravel the change of nucleation mechanism in cements when adding polycarboxylate ether superplasticizers (Artioli et al., 2015) and to better understand the microstructural signature of carbonation in blended cement pastes (Claret et al., 2018). Unfortunately, the best spatial resolution attainable today with this technique, 4 m m, does not allow the hierarchical arrangement of the component phases in the key 100–5000 nm mesoscale range to be understood.
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TítuloAn integrative approach to the anatomy of Syllis gracilis Grube, 1840 (Annelida) using micro computed X ray tomography

TítuloAn integrative approach to the anatomy of Syllis gracilis Grube, 1840 (Annelida) using micro computed X ray tomography

The micro-computed X-ray tomography (micro-CT) has been demonstrated to be a powerful, fast, complementary and novel tool for exploring internal anatomy across many metazoan taxa, including terrestrial and marine vertebrates and invertebrates (Metscher & Müller, 2011; Handschuh et al., 2013; Fernández et al., 2014; Sombke et al., 2015). For instance, its usefulness in studying Annelida anatomy has recently been tested (see Dinley et al., 2010; Faulwetter et al., 2013a; Faulwetter et al., 2013b; Paterson et al., 2014; Parapar et al., 2017a) and increasingly used in descriptions of new taxa (e.g., Parapar, Moreira & Helgason, 2015; Parapar et al., 2016; Parapar et al., 2017b). However, none of these works compares their results with those obtained with other techniques, such as the examination of histological sections (but, see Parapar et al., 2018). This would be necessary to truly assess the strengths and limitations of this novel technique when used in taxonomy and systematics. On the other hand, micro-CT per se is a non-invasive technique and, therefore, seems suitable for studying the anatomy of preserved material (including type specimens) stored in museums and other collections, thus avoiding any significant alteration.
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Geometrical characterization of undisturbed soil samples using X-ray computed tomography image analysis. Effect of soil management on soil structure

Geometrical characterization of undisturbed soil samples using X-ray computed tomography image analysis. Effect of soil management on soil structure

Raw data from tomography correspond to a stack of 1706 two-dimensional 16-bit grayscale images with a pixel size of 50 µm . These horizontal sections are disks of 7.5 cm diameter, 50- µm apart from one another. Thus the three- dimensional image is made up of voxels of 50 µm . They can be pictured as being situated at the center of each pixel. Light values of the grayscale designate voxels corresponding to low densities of the soil column, whereas high values indicate voxels of high density parts of the column. The original two-dimensional projections were ltered by a 3 by 3 median lter before recon- struction to reduce random noise from the detector. It is a nonlinear smoothing method to reduce isolated noise without blurring sharp edges [Wang and Lai, 2009]. This kind of noise contains random occurrences of white pixels (see Fig. 5.2a). When performing a 3 by 3 median lter, a square neighborhood window of 3 by 3 pixels is chosen. This window is centered at each pixel of the image. Let us call this pixel the reference pixel. Then, the median of the grayscale values of the pixels of the window is evaluated. And the original value of the grayscale of the reference pixel is replaced by the median value. This operation is repeated for each pixel of the image.
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Cutting Edge Technologies in Postharvest Research: Journey to the Centre of the Fruit

Cutting Edge Technologies in Postharvest Research: Journey to the Centre of the Fruit

The European FP7 project InsideFood focuses on integrated sensing and imaging devices for designing, monitoring and controlling microstructure of foods. The non- invasive sensors for characterising microstructure studied in the project are either based on tomography (X-ray nano- and microtomography, nuclear magnetic resonance spectroscopy, magnetic resonance imaging, optical coherence tomography) or spectroscopy (time- and space-resolved reflectance spectroscopy). The techniques are correlated to understand the effect of microstructure on water and solute status, texture and optical properties and internal defects of food. To this end, data analysis algorithms are developed, including image processing, modelling and multivariate statistics. The research is aimed to bring closer to the market on-line sensors for microstructure analysis and to provide tools for process design and optimization.
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Preparation of Specimens for Lightand Electron

Preparation of Specimens for Lightand Electron

Rotary Platinum Shadowing 367 Negative Staining 373 Single Particle Analysis of Frozen Macromolecules by Cryoelectron Microscopy 374 Electron Microscope Tomography 378 X-Ray and Electron[r]

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Near Infrared Counterparts to Chandra X Ray Sources Toward the Galactic Center  I  Statistics and a Catalog of Candidates

Near Infrared Counterparts to Chandra X Ray Sources Toward the Galactic Center I Statistics and a Catalog of Candidates

them are expected to be accidental, and the average probabil- ity among these matches is 7%. In benefit to the pursuit of counterparts, the data in Table 3 provide the means to priori- tize spectroscopic targets based on their relative probabilities. In general, the highest probabilities are associated with the bright- est infrared matches to the X-ray sources with the smallest positional uncertainties. Most of the sources with σ X 0. 5 are in the central field near Sgr A ∗ , owing to the large num- ber of observations and high photon statistics in that particular region. Repeated deep Chandra observations of the extended survey area could feasibly localize the majority of the current catalog of X-ray sources to the level of accuracy achieved in the central field around Sgr A ∗ , which would eliminate a large number of spurious infrared matches. Such observations would complement data from the United Kingdom Infrared Digital Sky Survey (UKIDSS; Lawrence et al. 2007), which will pro- duce a deeper catalog, down to K s 17–18 mag. UKIDSS will
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Luminosity functions of LMXBs in different stellar environments

Luminosity functions of LMXBs in different stellar environments

Although the above picture is attractive in its simplicity, there is a plausible alternative scenario: the entire population of LMXBs in galaxies, including those in the field may have been produced dynamically in GCs and later expelled into the field. Although the debate is still going on (White et al. 2002; Kundu et al. 2002, 2007; Irwin 2005; Juett 2005; Humphrey & Buote 2008), several strong arguments have been presented which sug- gest a (significant) fraction of field LMXBs formed in situ via primordial binary formation. These include the difference in spa- tial distributions of field LMXBs and GCs (e.g. Kundu et al. 2007) and the lack of correlation between the specific frequency of field LMXBs and that of GCs (e.g. Juett 2005). At the same time, Humphrey & Buote (2008) came to the opposite conclu- sion. The recently found evidence that the X-ray luminosity function (XLF) of GC-LMXBs may di ff er from that of field LMXBs (Voss & Gilfanov 2007a; Voss et al. 2009; Woodley et al. 2008; Kim et al. 2009) adds to this debate. Although some
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WEAK HARD X RAY EMISSION FROM TWO BROAD ABSORPTION LINE QUASARS OBSERVED WITH NuSTAR: COMPTON THICK ABSORPTION OR INTRINSIC X RAY WEAKNESS?

WEAK HARD X RAY EMISSION FROM TWO BROAD ABSORPTION LINE QUASARS OBSERVED WITH NuSTAR: COMPTON THICK ABSORPTION OR INTRINSIC X RAY WEAKNESS?

this observed ratio and the column density was calibrated using the MYTorus model (Murphy & Yaqoob 2009) 34 im- plemented in XSPEC. The MYTorus model computes the transmitted and scattered X-ray spectra from a toroidal-shaped absorber/reprocessor in a physical and self-consistent way, and it was designed to model X-ray spectra in the Compton-thick regime. The model was calculated for neutral material. However, for our purpose of constraining the basic absorption column den- sity in these BAL quasars, the model is likely also applicable to ionized material, as high-energy X-ray attenuation is domi- nated by Compton scattering (not photoelectric absorption) in the Compton-thick regime. Two important geometrical param- eters of the MYTorus model are the half-opening angle of the obscuring medium and the inclination angle (0 ◦ corresponds to a face-on viewing angle). The default half-opening angle was set to 60 ◦ (corresponding to a covering factor of 0.5), and we assumed an inclination angle of 80 ◦ (large inclination angles are generally expected for BAL quasars; see Section 1.1). We also explored the effects of different inclination angles and a differ- ent geometry with a half-opening angle of 37 ◦ (corresponding to a covering factor of 0.8). The other parameters of the model, such as the relative cross-normalization factors of different com- ponents, were set as the default values (see Section 8.2 of the MYTorus manual).
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SPECTRAL PROPERTIES OF X RAY BINARIES IN CENTAURUS A

SPECTRAL PROPERTIES OF X RAY BINARIES IN CENTAURUS A

LMXBs) and we identify three transient black hole (BH) LMXB candidates coincident with the dust lane, which is the remnant of a small late-type galaxy. Our results also provide tentative support for the apparent “gap” in the mass distribution of compact objects between ∼2–5 M . We propose that BH LMXBs are preferentially found in the dust lane, and suggest this is because of the younger stellar population. The majority (∼70%–80%) of potential Roche lobe filling donors in the Cen A halo are 12 Gyr old, while BH LMXBs require donors 1 M to produce the observed peak luminosities. This requirement for more massive donors may also explain recent results that claim a steepening of the X-ray luminosity function with age at L x 5 × 10 38 erg s −1 for the XB population of
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X ray spectral constraints for z approximate to 2 massive galaxies: the identification of reflection dominated active galactic nuclei

X ray spectral constraints for z approximate to 2 massive galaxies: the identification of reflection dominated active galactic nuclei

The lack of a flat X-ray spectral slope for the IR-excess galaxies appears to suggest that we have now individually de- tected many of the heavily obscured AGNs that were origi- nally contributing to the stacked data in Daddi et al. (2007a). However, we must be careful when interpreting X-ray stack- ing analyses of X-ray undetected source populations since the effects of Eddington bias and source variability (see §3.1.1) can dominate over the X-ray signal produced by the major- ity of the source population. For example, in going from the 1 Ms Chandra data to the 4 Ms Chandra data, the same number of heavily obscured AGNs were identified in the IR- excess (three of the 13 X-ray detected sources) and IR-normal (three of the 14 X-ray detected sources) galaxy populations despite there being little evidence for heavily obscured AGNs in the IR-normal galaxies from the 1 Ms stacked data of Daddi et al. (2007a). It is therefore likely that further heavily ob- scured AGNs will be identified with deeper Chandra data but we cannot provide direct X-ray constraints from the current dataset.
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Searching for supergiant fast X ray transients with Swift

Searching for supergiant fast X ray transients with Swift

The information collected so far on IGR J17407−2808 is therefore di ffi cult to interpret. In the framework of the HMXB/SFXT nature of IGR J17407 − 2808, pro factors are the light curve flaring, which is characterized by at leat two or- ders of magnitude during the flare and the overall dynamic range of about four orders of magnitude. The spectral proper- ties are also reminiscent of what is usually observed from these systems, even though the broadband properties of these sys- tems are not always a distinctive feature (Romano et al. 2014a). Against the HMXB / SFXT hypothesis is the low LOS absorp- tion, making it unlikely to hide a supergiant behind the F star, even when the F star is only a foreground source. The X-ray flares displayed by IGR J17407−2808 are also quite short com- pared to those of the SFXTs, which typically last a few thou- sands of seconds. The broadband spectral properties and the op- tical counterpart could be roughly consistent with those of a LMXB but the short flares displayed by IGR J17407−2808 and the fast variability are not commonly observed in LMXBs. The latter typically undergo weeks- to months-long outbursts regu- lated by the accretion disk instability (Lasota 2001) and might show additional flaring activity on top of this (see, for exam- ple, McClintock & Remillard 2006, for a review). The variabil- ity recorded by Swift and shown in Figs. 6 and 7 is thus not closely reminiscent of that displayed by either black holes or NS LMXBs in outburst. We note that the profiles and durations of the short flares emitted from IGR J17407−2808 do not resem- ble those of type-I X-ray bursts, thus also excluding the associ- ation between this object and the so-called burst only sources (Cornelisse et al. 2004). Given the relatively high luminosities recorded by Swift (L ∼ 10 33 −10 37 erg s −1 ) for any reasonable es-
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Modificación de superficies de vidrio y nanoparticulas de sílica con complejos carbenos de Fischer : aplicaciones en nanociencia

Modificación de superficies de vidrio y nanoparticulas de sílica con complejos carbenos de Fischer : aplicaciones en nanociencia

Los soportes utilizados fueron en todos los casos, vidrios cubre objeto para microscopios ópticos de 2 x 2 cm conseguidos comercialmente a través de Marienfeld Laboratory GmbH y Co. KG. La limpieza de los sustratos sólidos es de crítica importancia y existen numerosos métodos. En primer lugar se realiza un lavado de los mismos con una solución de detergente no iónico 1:100 % v/v para retirar el polvillo y restos particulados que pudieran contener. Se dejan los mismos en la solución de lavado por media hora y luego se retiran uno a uno y se enjuagan con suciente agua ultrapura, para retirar todo el detergente y se secaron en estufa. Posteriormente, se continúa con el trabajo de activación. Como se explicó en la introducción, es necesario retirar todo el material orgánico que pueda tener la supercie y dejar grupos hidroxilos libres para que la reacción con los organosilanos sea efectiva. Para ello, existen algunas metodologías descriptas en bibliografía que incluyen el uso de ácidos u oxidantes fuertes que dejen una supercie mas hidrofílica que la de partida (Jin et al., 2001) (Fujiwara et al., 2009). Luego de probar algunas de estas técnicas la metodología que se comenta a continuación fue con la que se obtuvieron mejores resultados, además de ser completamente reproducibles y sencilla de llevar a cabo.
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Luminosity functions of LMXBs in centaurus a : globular clusters versus the field

Luminosity functions of LMXBs in centaurus a : globular clusters versus the field

due to intrinsically faint systems that are currently in outburst. Calculations of the luminosity distribution of X-ray binaries ac- counting for these effects appear to be beyond the predictive power of the current generation of population synthesis codes. The problem is further complicated by the fact that the accurate calculation of the formation rates of various types of binaries is insufficient, as the evolution, X-ray lifetimes, and the transient behavior of the binaries should be also considered. Estimates of Voss & Gilfanov (2007b) indicate that He-accreting systems may contribute about ∼1/3 to the LMXB population of globular clusters, in rough agreement with the statistics of globular clus- ter sources in the Milky Way. This may be sufficient to explain the falloff of the GC LF to low luminosities, although modeling would depend on the details of the luminosity distribution of X-ray binaries formed via other formation mechanisms (which may differ from the LF of field sources) and on the fraction of He-accreting systems in outburst. On the other hand, the fact that the value of the critical luminosity limit for persistent He- accreting systems, ∼10 37 erg s − 1 , is in the range where the GC LF falloff begins, gives an indirect support to the proposed sce- nario. A more direct observational test may come from statistics of transient sources in globular clusters in nearby galaxies.
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Heavily Obscured AGN in Star Forming Galaxies at z sime 2

Heavily Obscured AGN in Star Forming Galaxies at z sime 2

For the X-ray-undetected sources, we found a slightly lower average redshift of z ∼ 1.9, based on photometric measure- ments only. We found that in general the X-ray-detected sources are brighter in both the 24 μm and optical bands compared to the undetected ones. Taking advantage of the low Chandra background, we performed X-ray stacking, finding a significant (3σ ) detection in both the soft and hard bands. The average X-ray flux of these sources is ∼ 8 ×10 −17 erg cm −2 s −1 , indicat- ing that in order to detect these sources individually, exposure times of ∼10 Ms with Chandra would be required. Taken at face value, the observed average HR of 0.13 corresponds to a N H of ∼2 × 10 23 cm − 2 . However, this can also be interpreted as the effects of combining a population of 90% CT AGNs and 10% star-forming galaxies, which in general have softer X-ray spec- tra. From this analysis we found marginal evidence for a small dependence of the fraction of AGNs relative to star-forming galaxies on 24 μm flux, going from ∼95% for the brightest sources to ∼ 80% at the lowest flux bin. The spectral fitting analysis performed to these sources indicate that in general there is evidence for substantial young stellar populations, younger than 100 Myr. This suggests that these sources are simulta- neously experimenting significant star formation and heavily obscured AGNs activity. We did not found significant differ- ences in the stellar masses and extinction values for the host galaxies of the X-ray-detected and undetected IR-red excess sources.
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A NuSTAR survey of nearby ultraluminous infrared galaxies

A NuSTAR survey of nearby ultraluminous infrared galaxies

0.8% of the bolometric luminosity. Our present result is consistent with those from the multiple-epoch fi tting by Teng et al. ( 2009 ) . The large drop in the observed 2 – 10 keV fl ux in the 2006 Suzaku X-ray Imaging Spectrometer ( XIS ) data is likely due to an intervening absorber, since a change by a factor of 30 in intrinsic fl ux is rare in AGNs ( Gibson & Brandt 2012 ) . The incomplete nature of the time series data makes it impossible to precisely determine the timescale of variability. If it is of the order of years, as is consistent with the data, then the Compton-thick absorber responsible for the Suzaku variability must be within a few parsecs of the nucleus. However, a more extreme case of intrinsic variability ( a factor of ∼ 260 ) was observed in the narrow-line Seyfert 1 galaxy PHL  1092 ( Miniutti et al. 2012 ) so we cannot absolutely rule out the possibility of strongly varying intrinsic fl ux. Indeed, our best- fi t model, even in the high state, should not have been detectable by Suzaku PIN in the 2006 observation, which speaks to the much greater sensitivity above 10 keV of NuSTAR compared to Suzaku PIN.
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Globular Clusters and X Ray Point Sources in Centaurus A (NGC 5128)

Globular Clusters and X Ray Point Sources in Centaurus A (NGC 5128)

available metallicity data, closely matching previous studies ( Harris et al. 2004; Woodley et al. 2005). But of the confirmed GCs with X-ray sources, 6 (21%) are metal-poor and 23 (79%) are metal-rich clusters out of the 29 confirmed GC matches with available metallicity data. Of the additional candidate GC LMXBs, 16 (52%) are metal-poor (blue) and 15 (48%) are metal-rich (red) objects from the 32 candidate GCs with available metallicity data. From a straight combination of confirmed and candidate GCs, we therefore find that 22 (37%) of LMXBs match metal- poor GCs and 38 (63%) match metal-rich ones out of the 60 GCs with available data. We note, however, that some fraction of the GC candidates, particularly those with (B V ) < 0:5 (see Fig. 7), might be interlopers or very young clusters, so the frac- tion matched to the metal-rich clusters is probably a lower limit. We conclude therefore that the ratio of metal-rich to metal-poor GCs with associated LMXBs is k 1.7. While previous obser- vations of early-type galaxies gives a ratio of 3, the scatter around this value is very large (Sivakoff et al. 2007) and com- fortably includes our lower limit. If we consider only the con- firmed GCs, the ratio is 3, more in line with the mean of the values found in previous studies.
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Swift monitoring of NGC 5548: X ray reprocessing and short term UV/optical variability

Swift monitoring of NGC 5548: X ray reprocessing and short term UV/optical variability

Lags measured from correlated X-ray/UV/optical monitoring of AGN allow us to determine whether UV/optical variability is driven by reprocessing of X-rays or X-ray variability is driven by UV/optical seed photon variations. We present the results of the largest study to date of the relationship between the X-ray, UV and optical variability in an AGN with 554 observations, over a 750 d period, of the Seyfert 1 galaxy NGC 5548 with Swift. There is a good overall correlation between the X-ray and UV/optical bands, particularly on short time-scales (tens of days). The UV/optical bands lag the X-ray band with lags which are proportional to wavelength raised to the power 1.23 ± 0.31. This power is very close to the power (4/3) expected if short time-scale UV/optical variability is driven by reprocessing of X-rays by a surrounding accretion disc. The observed lags, however, are longer than expected from a standard Shakura–Sunyaev accretion disc with X-ray heating, given the currently accepted black hole mass and accretion rate values, but can be explained with a slightly larger mass and accretion rate, and a generally hotter disc. Some long-term UV/optical variations are not paralleled exactly in the X-rays, suggesting an additional component to the UV/optical variability arising perhaps from accretion rate perturbations propagating inwards through the disc.
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