1,720,990 research outputs found
The X-ray Pulsar A0535+26: Pulse profile and its Time variability in Hard X-rays
No full textA hard X-ray observation 8400 s long of the recurrent transient X-ray pulsar A0535 + 26 has been performed. The data were obtained with a balloon-borne experiment in the energy range 27-190 keV when the source was near the maximum of the 1980 October transient outburst. Results from the pulse shape analysis show that the time-averaged pulse profile in the hard X-ray range is quite different from that measured by other observers at different epochs. It exhibits a double-peaked structure fairly stable with energy, with the greatest variation seen in the intensity ratio between the two peaks. In addition, the pulsed fraction shows a clear increase at higher energies, which converges to 100 percent at about 100 keV. A timing analysis has shown significant pulse period variations (up to an absolute value of Delta P/P of about 0.007) on time scales of thousands of seconds. Finally, a high variability in pulse shape and intensity was discovered on time scales varying from the order of seconds to few tens of minutes. The short time scale variability was studied using Power Spectral Density estimates and direct inspection of the data. This variability appears to be chaotic, and shot-like events with typical duration of 10 s and mean frequency of one every 25 s have been observed.
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Beppo-SAX observation of the Coma Cluster
No full textWe present first results of the BeppoSAX observation of the Coma Cluster. Thanks to the unprecedented sensitivity of the PDS instrument, the source has been detected up to similar to 80 keV. There is clear evidence for emission in excess to the thermal one above similar to 25 keV, very likely of non-thermal origin. We have therefore, for the first time, detected the long sought Inverse Compton emission on CMB photons predicted in clusters, like Coma, with radio halos. Combining X and radio observations, a value of 0.16 mu G for the volume-averaged intracluster magnetic field is derived. (C) 2000 COSPAR. Published by Elsevier Science Ltd
Clinical analysis of the diagnostic accuracy and time of execution of a transillumination caries detection method compared to bitewing radiographs
Get PDFPurposes: this clinical study evaluated the accuracy and execution time of a digital imaging fiber-optic transillumination (DIFOTI) technique for the detection of approximal caries in posterior teeth compared to intra-oral examination associated with bitewing radiographs. Methods: one hundred patients were selected and submitted to clinical inspection and bitewing radiographs. The outcomes of this process were converted into scores, according to the International Caries Detection and Assessment System (ICDAS): 0—sound tooth; 1, 2, and 3—carious lesion confined within enamel; 4, 5, and 6—dentin carious lesion. Subsequently, an independent investigator acquired digital images of the same teeth using a DIFOTI device (DIAGNOcam, Kavo Dental), which were also converted into ICDAS scores. The time required for executing diagnostic procedures was measured. The clinical sensitivity and specificity of DIFOTI were analyzed by receiver operating characteristic (ROC) curves. The time necessary to perform the diagnostic methods was evaluated by Mann–Whit-ney U (alfa = 0.05). Results: the overall test accuracy for the DIFOTI-based device ranged from 0.717 to 0.815 (area under the ROC curve) with p < 0.0001 for all ICDAS scores. Bitewing radiographs took almost twice the time required by DIFOTI (p < 0.001). Conclusions: the DIFOTI-based device DI-AGNOcam provided accurate detection of approximal caries in posterior teeth, even at early stages. The technique employed for transillumination caries diagnosis by the same device took less time than conventional bitewing radiographs. Clinical Relevance: transillumination devices, such as DI-AGNOcam, can be accurately used for caries diagnosis in approximal surfaces of posterior teeth, demanding less clinical time and without radiation-related risks
Effects of iron overload on bile secretion and hepatic porphyrin metabolism in ethinyl estradiol-treated rats
No full textEffects of iron overload on bile secretion and hepatic porphyrin metabolism in ethinyl estradiol-treated rats
No full textThe complex 0.1-200 keV spectrum of the Seyfert 1 Galaxy NGC 4593
No full textWe report on the first observation of the Seyfert 1 galaxy NGC 4593 in the 0.1-200 keV band, performed with the BeppoSAX observatory. Its spectral components are for the first time simultaneously! measured: a power-law with photon spectral index Gamma similar or equal to 1.9; the Compton-reflection of the primary power-law; a moderately broad (sigma > 60 eV) K-alpha fluorescent line from neutral iron; and an absorption edge, whose threshold energy is consistent with K-shell photoionization from OVII. The amount of reflection and the iron line properties are consistent with both being produced in a plane-parallel, X-ray illuminated relativistic accretion disc surrounding the nuclear black hole, seen at an inclination of similar or equal to 30 degrees. Any cutoff of the intrinsic continuum is constrained to lap above 150 keV. The claim for a strongly variable soft excess is dismissed by our data and by a reanalysis of archival ASCA and ROSAT data
Hard X-ray radiation in the Coma Cluster spectrum
No full textHard X-ray radiation has been detected for the first time in the Coma Cluster by BeppoSAX. Thanks to the unprecedented sensitivity of the Phoswich Detection System (PDS) instrument, the source has been detected up to similar to 80 keV. There is clear evidence (4.5 sigma) for nonthermal emission in excess of thermal emission above similar to 25 keV. The hard excess is very unlikely to be the result of X Comae, the Seyfert 1 galaxy that is present in the field of view of the PDS. A hard spectral tail that is due to inverse Compton scattering on cosmic microwave background photons is predicted in clusters, like Coma, with radio halos. Combining the present results with radio observations, a volume-averaged intracluster magnetic field of similar to 0.15 mu G is derived, while the electron energy density of the emitting electrons is similar to 7 x 10(-14) ergs cm(-3)
The high energy instrument PDS on-board the BeppoSAX X-ray astronomy Satellite
No full textBeppoSAX/PDS experiment is one of four narrow field instruments of the BeppoSAX payload, that also includes two wide field cameras. The goal of PDS is to extend the energy range of BeppoSAX to hard X-rays. The operative energy range of PDS is 15 to 300 keV, where the experiment can perform sensitive spectral and temporal studies of celestial sources. The PDS detector is composed of 4 actively shielded NaI(Tl)/CsI(Na) phoswich scintillators with a total geometric area of 795 cm2 and a field of view of 1°.3 (FWHM). In this paper we describe the experiment design and discuss its functional performance and calibration data analysis system
A look with
No full textA pointed observation of the low-luminosity galactic source
4U 2206+54 was carried out in November 1998 with BeppoSAX. The light
curve of 4U 2206+54 shows erratic variability on a timescale of ~1 h; neither hardness variations nor time periodicities are detected
throughout this 67 ks long observation. Thanks to the wide spectral
coverage capabilities of BeppoSAX we could observe the source X-ray
continuum over three energy decades, from 0.6 to 60 keV.
The spectrum could be equally well fitted either with a blackbody plus
Comptonization or with a high energy cutoff power law. No iron emission
around 6.5 keV was detected, while a tentative detection of a cyclotron
resonant feature in absorption is presented. Comparison of the present
BeppoSAX data with the information available in the literature for
this source suggests that 4U 2206+54 is a close binary system in which a
(possibly magnetized) NS is accreting from the companion star wind.
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