scholarly journals X-Ray and UV Emission from VV Puppis

1983 ◽  
Vol 6 ◽  
pp. 653-653
Author(s):  
J. Patterson ◽  
K. Beuermann ◽  
G. Fabbiano ◽  
D.Q. Lamb ◽  
J. C. Raymond ◽  
...  
Keyword(s):  
Small Region ◽  
Light Curves ◽  
Line Of Sight ◽  
X Rays ◽  
Magnetic Pole ◽  
X Ray ◽  
Opposite Case ◽  
Uv Emission ◽  
Optical Light Curve ◽  
The Mean

We have discovered hard and soft X-ray emission from W Puppis, the last of the four classical AM Her stars to be detected in X-rays. The orbital light curves in both soft and hard X-rays are in excellent agreement with the mean optical light curve, indicating that essentially all of the accretion luminosity originates from a very small region at the white dwarf’s magnetic pole. An X-ray dip occurs once per binary period, when the magnetic pole lies closest to our line of sight, and is probably due to absorption. The X-ray data and optical spectroscopy constrain fairly well the geometry of the system, dictating an inclina-tion angle i < 70º and a mass for the white dwarf in excess of 1.1 Mʘ. X-ray and UV observations constrain the temperature of the soft X-ray component to lie in the range 20–45 eV, while the hard X-ray component has a temperature in excess of 6 keV. The observed flux of soft X-rays is much larger than that of hard X-rays. However, when the energy band-passes of the observations are taken into account, the ratio of the soft and hard X-ray luminosities Ls/Lh = 0.5-50. The ratio is unity for Tbb = 30 eV and Tbr = 50 keV; ifc is smaller if Tbb and/or Tbr are larger and is larger in the opposite case. These results, taken together with those for AM Her using the Einstein OGS, suggest that the famous “soft X-ray problem” in the AM Her stars may have gone away.

scholarly journals An Evaluation of Cellular Neural Networks for the Automatic Identification of Cephalometric Landmarks on Digital Images

2009 ◽  
Vol 2009 ◽  
pp. 1-12 ◽  
Author(s):  
Rosalia Leonardi ◽  
Daniela Giordano ◽  
Francesco Maiorana
Keyword(s):  
Neural Networks ◽  
Cellular Neural Networks ◽  
Automatic Identification ◽  
Cephalometric Analysis ◽  
X Rays ◽  
X Ray ◽  
Automatic Location ◽  
Landmark Identification ◽  
The Mean ◽  
Analogue To Digital

Several efforts have been made to completely automate cephalometric analysis by automatic landmark search. However, accuracy obtained was worse than manual identification in every study. The analogue-to-digital conversion of X-ray has been claimed to be the main problem. Therefore the aim of this investigation was to evaluate the accuracy of the Cellular Neural Networks approach for automatic location of cephalometric landmarks on softcopy of direct digital cephalometric X-rays. Forty-one, direct-digital lateral cephalometric radiographs were obtained by a Siemens Orthophos DS Ceph and were used in this study and 10 landmarks (N, A Point, Ba, Po, Pt, B Point, Pg, PM, UIE, LIE) were the object of automatic landmark identification. The mean errors and standard deviations from the best estimate of cephalometric points were calculated for each landmark. Differences in the mean errors of automatic and manual landmarking were compared with a 1-way analysis of variance. The analyses indicated that the differences were very small, and they were found at most within 0.59 mm. Furthermore, only few of these differences were statistically significant, but differences were so small to be in most instances clinically meaningless. Therefore the use of X-ray files with respect to scanned X-ray improved landmark accuracy of automatic detection. Investigations on softcopy of digital cephalometric X-rays, to search more landmarks in order to enable a complete automatic cephalometric analysis, are strongly encouraged.

scholarly journals X-ray spectra and light curves of cooling novae and a nova like

2020 ◽  
Vol 499 (2) ◽  
pp. 3006-3018
Author(s):  
Bangzheng Sun ◽  
Marina Orio ◽  
Andrej Dobrotka ◽  
Gerardo Juan Manuel Luna ◽  
Sergey Shugarov ◽  
...  
Keyword(s):  
Light Curve ◽  
Accretion Rate ◽  
High Energy ◽  
Gravitational Energy ◽  
Light Curves ◽  
Clear Correlation ◽  
X Rays ◽  
High State ◽  
X Ray ◽  
Low X

ABSTRACT We present X-ray observations of novae V2491 Cyg and KT Eri about 9 yr post-outburst of the dwarf nova and post-nova candidate EY Cyg, and of a VY Scl variable. The first three objects were observed with XMM–Newton, KT Eri also with the Chandra ACIS-S camera, V794 Aql with the Chandra ACIS-S camera and High Energy Transmission Gratings. The two recent novae, similar in outburst amplitude and light curve, appear very different at quiescence. Assuming half of the gravitational energy is irradiated in X-rays, V2491 Cyg is accreting at $\dot{m}=1.4\times 10^{-9}{\!-\!}10^{-8}\,{\rm M}_\odot \,{\rm yr}^{-1}$, while for KT Eri, $\dot{m}\lt 2\times 10^{-10}{\rm M}_\odot \,{\rm yr}$. V2491 Cyg shows signatures of a magnetized WD, specifically of an intermediate polar. A periodicity of  39 min, detected in outburst, was still measured and is likely due to WD rotation. EY Cyg is accreting at $\dot{m}\sim 1.8\times 10^{-11}{\rm M}_\odot \,{\rm yr}^{-1}$, one magnitude lower than KT Eri, consistently with its U Gem outburst behaviour and its quiescent UV flux. The X-rays are modulated with the orbital period, despite the system’s low inclination, probably due to the X-ray flux of the secondary. A period of  81 min is also detected, suggesting that it may also be an intermediate polar. V794 Aql had low X-ray luminosity during an optically high state, about the same level as in a recent optically low state. Thus, we find no clear correlation between optical and X-ray luminosity: the accretion rate seems unstable and variable. The very hard X-ray spectrum indicates a massive WD.

Isoelastic Cementless Total Hip Replacement in Rheumatoid Arthritis. Long-Term Results

1992 ◽  
Vol 2 (2) ◽  
pp. 43-46
Author(s):  
U. Fusco ◽  
R. Capelli ◽  
A. Avai ◽  
M. Gerundini ◽  
L. Colombini ◽  
...  
Keyword(s):  
Rheumatoid Arthritis ◽  
Hip Replacement ◽  
The Other ◽  
Long Term Results ◽  
X Rays ◽  
X Ray ◽  
The Mean ◽  
Cementless Total Hip Replacement

Between 1980 and 1987 we have implanted 46 isoelastic cementless THR in 40 patients affected with rheumatoid arthritis. We have reviewed 38 hips clinically and by X-ray. The mean follow-up was 8,5 years. Harris hip scores ranged from 30.6 preoperatively to 73,4 post-operatively when reviewed. While on the other hand Merle D'Aubigné hip scores ranged from 7,06 pre-operatively to 15,59 post-operatively. All patients have been satisfied, and X-rays showed an improvement for both Charnely and Gruen X-ray score.

scholarly journals Pair Production in AGN

1989 ◽  
Vol 134 ◽  
pp. 194-196
Author(s):  
C. Done ◽  
A. C. Fabian
Keyword(s):  
Pair Production ◽  
Compton Scattering ◽  
Energy Flux ◽  
Large Fraction ◽  
Small Region ◽  
X Rays ◽  
X Ray ◽  
Electron Positron ◽  
Γ Rays ◽  
Radiant Power

The X-ray luminosity and variability of many AGN are sufficiently extreme that any hard γ-rays produced in the source will collide with the X-rays and create electron-positron pairs, rather than escape. A small region where vast amounts of energy are produced, such as an AGN, is an ideal place to accelerate particles to relativistic energies and so produce γ-rays by Compton scattering. The observed X-ray spectra of AGN are hard and indicate that most of the luminosity is at the highest energies so that absorption of the γ-rays represents a large fraction of the energy flux, which can then be re-radiated at lower energies. Pairs can thus effectively reprocess much of the radiant power in an AGN.

scholarly journals Glimpses of the past activity of Sgr A★ inferred from X-ray echoes in Sgr C

2018 ◽  
Vol 610 ◽  
pp. A34 ◽  
Author(s):  
D. Chuard ◽  
R. Terrier ◽  
A. Goldwurm ◽  
M. Clavel ◽  
S. Soldi ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Black Hole ◽  
Monte Carlo Model ◽  
Line Of Sight ◽  
X Rays ◽  
X Ray ◽  
Supermassive Black Hole ◽  
The Past ◽  
Sgr A ◽  
Past Activity

Context. For a decade now, evidence has accumulated that giant molecular clouds located within the central molecular zone of our Galaxy reflect X-rays coming from past outbursts of the Galactic supermassive black hole. However, the number of illuminating events as well as their ages and durations are still unresolved questions. Aims. We aim to reconstruct parts of the history of the supermassive black hole Sgr A★ by studying this reflection phenomenon in the molecular complex Sgr C and by determining the line-of-sight positions of its main bright substructures. Methods. Using observations made with the X-ray observatories XMM-Newton and Chandra and between 2000 and 2014, we investigated the variability of the reflected emission, which consists of a Fe Kα line at 6.4 keV and a Compton continuum. We carried out an imaging and a spectral analysis. We also used a Monte Carlo model of the reflected spectra to constrain the line-of-sight positions of the brightest clumps, and hence to assign an approximate date to the associated illuminating events. Results. We show that the Fe Kα emission from Sgr C exhibits significant variability in both space and time, which confirms its reflection origin. The most likely illuminating source is Sgr A★. On the one hand, we report two distinct variability timescales, as one clump undergoes a sudden rise and fall in about 2005, while two others vary smoothly throughout the whole 2000–2014 period. On the other hand, by fitting the Monte Carlo model to the data, we are able to place tight constraints on the 3D positions of the clumps. These two independent approaches provide a consistent picture of the past activity of Sgr A★, since the two slowly varying clumps are located on the same wavefront, while the third (rapidly varying) clump corresponds to a different wavefront, that is, to a different illuminating event. Conclusions. This work shows that Sgr A★ experienced at least two powerful outbursts in the past 300 yrs, and for the first time, we provide an estimation of their age. Extending this approach to other molecular complexes, such as Sgr A, will allow this two-event scenario to be tested further.

scholarly journals Evidence for variability time-scale-dependent UV/X-ray delay in Seyfert 1 AGN NGC 7469

2020 ◽  
Vol 494 (3) ◽  
pp. 4057-4068
Author(s):  
Mayukh Pahari ◽  
I M McHardy ◽  
Federico Vincentelli ◽  
Edward Cackett ◽  
Bradley M Peterson ◽  
...  
Keyword(s):  
Light Curve ◽  
Time Lag ◽  
Accretion Disc ◽  
Light Curves ◽  
X Rays ◽  
X Ray ◽  
Cross Correlation Analysis ◽  
Optical Continuum ◽  
Delay Prediction ◽  
Ngc 7469

ABSTRACT Using a month-long X-ray light curve from RXTE/PCA and 1.5 month-long UV continuum light curves from IUE spectra in 1220–1970 Å, we performed a detailed time-lag study of the Seyfert 1 galaxy NGC 7469. Our cross-correlation analysis confirms previous results showing that the X-rays are delayed relative to the UV continuum at 1315 Å by 3.49 ± 0.22 d, which is possibly caused by either propagating fluctuation or variable Comptonization. However, if variations slower than 5 d are removed from the X-ray light curve, the UV variations then lag behind the X-ray variations by 0.37 ± 0.14 d, consistent with reprocessing of the X-rays by a surrounding accretion disc. A very similar reverberation delay is observed between Swift/XRT X-ray and Swift/UVOT UVW2, U light curves. Continuum light curves extracted from the Swift/GRISM spectra show delays with respect to X-rays consistent with reverberation. Separating the UV continuum variations faster and slower than 5 d, the slow variations at 1825 Å lag those at 1315 Å by 0.29 ± 0.06 d, while the fast variations are coincident (0.04 ± 0.12 d). The UV/optical continuum reverberation lag from IUE, Swift, and other optical telescopes at different wavelengths are consistent with the relationship: τ ∝ λ4/3, predicted for the standard accretion disc theory while the best-fitting X-ray delay from RXTE and Swift/XRT shows a negative X-ray offset of ∼0.38 d from the standard disc delay prediction.

scholarly journals X-Rays from Wolf-Rayet Stars Observed by the Einstein Observatory

1982 ◽  
Vol 99 ◽  
pp. 589-595
Author(s):  
W. T. Sanders ◽  
J. P. Cassinelli ◽  
K. A. van der Hucht
Keyword(s):  
Mean Value ◽  
Spectral Energy ◽  
X Rays ◽  
X Ray ◽  
Total Luminosity ◽  
Hydrogen Emission Lines ◽  
Flux Level ◽  
The Mean ◽  
Einstein Observatory ◽  
Thin Source

Preliminary results of three X-ray surveys are presented. Out of a sample of 20 stars, X-rays were detected from four Wolf-Rayet stars and two 08f+ stars. The detected stars have about the same mean value as 0 stars for the X-ray to total luminosity ratio, LX/L = 10−7, but exhibit a much larger variation about the mean. The spectral energy distributions are also found to be like that of 0 stars in that they do not exhibit large attenuation of X-rays softer than 1 keV. This indicates that for both the 0 stars and WR stars much of the X-ray emission is coming from hot wisps or shocks in the outer regions of the winds and not from a thin source at the base of the wind. The general spectral shape and flux level place severe restrictions on models that attribute the lack of hydrogen emission lines to extremely high temperatures of the gas in the wind.

scholarly journals Non-equilibrium chemistry and destruction of CO by X-ray flares

2019 ◽  
Vol 486 (1) ◽  
pp. 1094-1122 ◽  
Author(s):  
Jonathan Mackey ◽  
Stefanie Walch ◽  
Daniel Seifried ◽  
Simon C O Glover ◽  
Richard Wünsch ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Thermal Evolution ◽  
Galactic Nuclei ◽  
Galactic Centre ◽  
X Rays ◽  
X Ray ◽  
Uv Emission ◽  
Sgr A ◽  
X Ray Binaries ◽  
Fractal Cloud

ABSTRACT Sources of X-rays such as active galactic nuclei and X-ray binaries are often variable by orders of magnitude in luminosity over time-scales of years. During and after these flares the surrounding gas is out of chemical and thermal equilibrium. We introduce a new implementation of X-ray radiative transfer coupled to a time-dependent chemical network for use in 3D magnetohydrodynamical simulations. A static fractal molecular cloud is irradiated with X-rays of different intensity, and the chemical and thermal evolution of the cloud are studied. For a simulated $10^5\, \mathrm{M}_\odot$ fractal cloud, an X-ray flux &lt;0.01 erg cm−2 s−1 allows the cloud to remain molecular, whereas most of the CO and H2 are destroyed for a flux of ≥1 erg cm−2 s−1. The effects of an X-ray flare, which suddenly increases the X-ray flux by 105×, are then studied. A cloud exposed to a bright flare has 99 per cent of its CO destroyed in 10–20 yr, whereas it takes &gt;103 yr for 99 per cent of the H2 to be destroyed. CO is primarily destroyed by locally generated far-UV emission from collisions between non-thermal electrons and H2; He+ only becomes an important destruction agent when the CO abundance is already very small. After the flare is over, CO re-forms and approaches its equilibrium abundance after 103–105 yr. This implies that molecular clouds close to Sgr A⋆ in the Galactic Centre may still be out of chemical equilibrium, and we predict the existence of clouds near flaring X-ray sources in which CO has been mostly destroyed but H is fully molecular.

Exosat Observations of H2252−035: Pulse Phase and Orbital Phase Dependent Low Energy Absorption and Iron Line Emission

1987 ◽  
Vol 93 ◽  
pp. 281-292
Author(s):  
W. Pietsch ◽  
W. Voges ◽  
E. Kendziorra ◽  
M. Pakull
Keyword(s):  
Energy Absorption ◽  
Line Emission ◽  
Low Energy ◽  
Gas Absorption ◽  
X Rays ◽  
Medium Energy ◽  
Iron Line ◽  
X Ray ◽  
Low Energies ◽  
Optical Light Curve

AbstractThe 805 sec pulsing X-ray source H2252−035 has been observed for 7 h on September 14/15 and on September 17, 1983 in X-rays with the low energy telescope and the medium energy detectors of EXOSAT. While below 2 keV the semiamplitude of the 805 s pulses is ~ 100% in the 2.3–7.9 keV band it is only ~ 40%. X-ray dips that are more pronounced in low energies occur simultaneously with the orbital minimum of the optical light curve. The medium energy spectra during dips with respect to the non dip spectrum can be explained by just enhanced cold gas absorption of an additional absorbing column of 2 1022 cm−2. Model spectra for the 805 s minimum have to include a strong iron emission line at 6.55 keV with an equivalent width of 3 keV in addition to a reduced continuum intensity (radiating area) and enhanced low energy absorption.

The Utility of Preoperative Magnetic Resonance Imaging for Determining the Flexibility of Sagittal Imbalance

Neurosurgery ◽  
2017 ◽  
Vol 83 (3) ◽  
pp. 465-470
Author(s):  
Akshay Sharma ◽  
Sina Pourtaheri ◽  
Jason Savage ◽  
Iain Kalfas ◽  
Thomas E Mroz ◽  
...  
Keyword(s):  
Lumbar Lordosis ◽  
Surgical Planning ◽  
Pelvic Incidence ◽  
Sagittal Imbalance ◽  
X Rays ◽  
Resonance Imaging ◽  
Patient Counseling ◽  
X Ray ◽  
Preoperative Magnetic Resonance ◽  
The Mean

Abstract BACKGROUND Scoliosis X-rays are the gold standard for assessing preoperative lumbar lordosis; however, particularly for flexible lumbar deformities, it is difficult to predict from these images the extent of correction required, as standing radiographs cannot predict the thoracolumbar alignment after intraoperative positioning. OBJECTIVE To determine the utility of preoperative MRI in surgical planning for patients with flexible sagittal imbalance. METHODS We identified 138 patients with sagittal imbalance. Radiographic parameters including pelvic incidence and lumbar lordosis were obtained from images preoperatively. RESULTS The mean difference was 2.9° between the lumbar lordosis measured on supine MRI as compared to the intraoperative X-rays, as opposed to 5.53° between standing X-rays and intraoperative X-ray. In patients with flexible deformities (n = 24), the lumbar lordosis on MRI measured a discrepancy of 3.08°, as compared to a discrepancy of 11.46° when measured with standing X-ray. CONCLUSION MRI adequately determined which sagittal deformities were flexible. Furthermore, with flexible sagittal deformities, lumbar lordosis measured on MRI more accurately predicted the intraoperative lumbar lordosis than that measured on standing X-ray. The ability to preoperatively predict intraoperative lumbar lordosis with positioning helps with surgical planning and patient counseling regarding expectations and risks of surgery.

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