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Search Results: 1 - 10 of 580001 matches for " A. G. Cocco "
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BeppoSAX average spectra of Seyfert galaxies
A. Malizia,L. Bassani,J. B. Stephen,G. Di Cocco,F. Fiore,A. J. Dean
Physics , 2003, DOI: 10.1086/375712
Abstract: We have studied the average 3-200 keV spectra of Seyfert galaxies of type 1 and 2, using data obtained with BeppoSAX. The average Seyfert 1 spectrum is well-fitted by a power law continuum with photon spectral index Gamma~1.9, a Compton reflection component R~0.6-1 (depending on the inclination angle between the line of sight and the reflecting material) and a high-energy cutoff at around 200 keV; there is also an iron line at 6.4 keV characterized by an equivalent width of 120 eV. Seyfert 2's on the other hand show stronger neutral absorption (NH=3-4 x 10^{22} atoms cm-2) as expected but are also characterized by an X-ray power law which is substantially harder (Gamma~1.75) and with a cut-off at lower energies (E_c~130 keV); the iron line parameters are instead substantially similar to those measured in type 1 objects. There are only two possible solutions to this problem: to assume more reflection in Seyfert 2 galaxies than observed in Seyfert 1 or more complex absorption than estimated in the first instance. The first possibility is ruled out by the Seyfert 2 to Seyfert 1 ratio while the second provides an average Seyfert 2 intrinsic spectrum very similar to that of the Seyfert 1. The extra absorber is likely an artifact due to summing spectra with different amounts of absorption, althought we cannot exclude its presence in at least some individual sources. Our result argues strongly for a very similar central engine in both type of galaxies as expected under the unified theory.
3EG J2027+3429 another Blazar behind the Galactic Plane
V. Sguera,A. Malizia,L. Bassani,J. B. Stephen,G. Di Cocco
Physics , 2003, DOI: 10.1051/0004-6361:20031612
Abstract: We report on the association of an X-ray source (WGA J2025.1+3342), serendipitously found with BeppoSAX in two separate observations, with the unidentified EGRET source 3EG J2027+3429. The source is detected from 1 keV up to about 100 keV, has a flat (0.6-1.5) spectrum and is highly variable both in intensity and shape. The data indicate marginal evidence for an iron line in the source rest frame. The overall X-ray luminosity is 4 10^{45} erg s^{-1} typical of a quasar. The X-ray source is coincident in radio with a bright object characterized by a flat spectrum over the band 0.3-10 GHz while in optical it is identified with a quasar at redshift 0.22. All available data indicate a SED compatible with a low frequency peaked or red blazar type object. This identification is interesting because this is the second blazar found behind the galactic plane in the direction of the Cygnus region.
Performance of a SensL-30035-16P Silicon Photomultiplier array at liquid argon temperature
S. Catalanotti,A. G. Cocco,G. Covone,M. D Incecco,G. Fiorillo,G. Korga,B. Rossi,S. Walker
Physics , 2015,
Abstract: Next generation multi-ton scale noble liquid experiments have the unique opportunity to discover dark matter particles at the TeV scale, reaching the sensitivity of 10^-48 cm2 in the WIMP nucleon scattering cross-section. A prerequisite will be the reduction of radiogenic background sources to negligible levels. This is only possible if ultra pure high efficiency photosensors are available for the scintillation light readout. Current experiments (e.g. Xenon, LUX, Darkside, ArDM) use cryogenic PMTs as photosensors. An attractive alternative is represented by silicon photomultiplier arrays (SiPM arrays), which show unrivalled performances in single photon detection. This paper reports on the performance of the SensL-30035-16P SiPM array and a custom made cryogenic front-end board at the liquid argon temperature.
BeppoSAX/PDS identification of the true counterpart of the Piccinotti source H0917-074
A. Malizia,G. Malaguti,L. Bassani,M. Cappi,A. Comastri,G. Di Cocco,E. Palazzi,C. Vignali
Physics , 2002, DOI: 10.1051/0004-6361:20021202
Abstract: High energy emission has been discovered serendipitously by the BeppoSAX/PDS telescope in the ~1.3 degree field of view around the Piccinotti source H0917-074. A re-pointing of BeppoSAX/NFI has allowed the association of this emission with the Seyfert 2 galaxy MCG-1-24-12 which lies within the original HEAO1/A2 error box of H0917-074. This is the first PDS serendipitous discovery of a Seyfert 2 galaxy and the first detection of MCG-1-24-12 in the X-ray domain. The measured 2-10 keV flux of MCG-1-24-12 is ~1 x 10^(-11) erg cm^(-2) s^(-1) compatible with the Piccinotti HEAO-1/A2 observation. This is a factor of ~6 greater than that observed from EXO0917.3-0722, originally suggested as the counterpart of the Piccinotti source. The 2-10 keV spectrum of MCG-1-24-12 shows the presence of Fe K_alpha emission together with an absorption feature at ~8.7 keV. At high energies, the Seyfert 2 still dominates and the observed 20-100 keV flux is ~4 x 10^(-11)erg cm^(-2) s^(-1).
Results from the short baseline experiments at CERN
Alfredo G. Cocco
Physics , 2001,
Abstract: Considerations based on particle physics (in particular the so-called see-saw mechanism) and on cosmology, in relation to the Dark Matter question, motivated the search for numu nutau oscillation in the region of small mixing angles. We present here the outcome of the short-baseline programme carried out at CERN by the CHORUS and NOMAD experiments. Both experiments are about to publish their final results. At values of squared mass difference greater than 1 eV2 oscillations between numu and nutau are excluded at 90% C.L. down to mixing angles values of O(10^{-4}).
3D dynamic simulations of spontaneous rupture propagation governed by different constitutive laws with rake rotation allowed
A. Bizzarri,M. Cocco
Annals of Geophysics , 2005, DOI: 10.4401/ag-3201
Abstract: In this work we present a 3D Finite Difference numerical method to model the dynamic spontaneous propagation of an earthquake rupture on planar faults in an elastic half-space. We implement the Traction-at-Split-Nodes fault boundary condition for a system of faults, either vertical or oblique, using different constitutive laws. We can adopt both a slip-weakening law to prescribe the traction evolution within the breakdown zone or rate- and state-dependent friction laws, which involve the choice of an evolution relation for the state variable. Our numerical procedure allows the use of oblique and heterogeneous distribution of initial stress and allows the rake rotation. This implies that the two components of slip velocity and total dynamic traction are coupled together to satisfy, in norm, the adopted constitutive law. The simulations presented in this study show that the rupture acceleration to super-shear crack speeds occurs along the direction of the imposed initial stress; the rupture front velocity along the perpendicular direction is slower than that along the pre-stress direction. Depending on the position on the fault plane the orientation of instantaneous total dynamic traction can change with time with respect to the imposed initial stress direction. These temporal rake rotations depend on the amplitude of initial stress and on its distribution on the fault plane. They also depend on the curvature and direction of the rupture front with respect to the imposed initial stress direction: this explains why rake rotations are mostly located near the rupture front and within the cohesive zone.
Prevalence of periprosthetic osteolysis after total hip replacement in patients with rheumatic diseases
Perez Alamino R, Casellini C, Baňos A, Schneeberger EE, Gagliardi SA, Maldonado Cocco JA, Citera G
Open Access Rheumatology: Research and Reviews , 2012, DOI: http://dx.doi.org/10.2147/OARRR.S31736
Abstract: evalence of periprosthetic osteolysis after total hip replacement in patients with rheumatic diseases Original Research (1303) Total Article Views Authors: Perez Alamino R, Casellini C, Baňos A, Schneeberger EE, Gagliardi SA, Maldonado Cocco JA, Citera G Published Date June 2012 Volume 2012:4 Pages 57 - 62 DOI: http://dx.doi.org/10.2147/OARRR.S31736 Received: 13 March 2012 Accepted: 28 March 2012 Published: 06 June 2012 Rodolfo Perez Alamino, Carolina Casellini, Andrea Banos, Emilce Edith Schneeberger, Susana Alicia Gagliardi, José Antonio Maldonado Cocco, Gustavo Citera Section of Rheumatology, Instituto de Rehabilitación Psicofísica, Buenos Aires, Argentina Abstract: Periprosthetic osteolysis (PO) is a frequent complication in patients with joint implants. There are no data regarding the prevalence of PO in patients with rheumatoid arthritis (RA), juvenile chronic arthritis (JCA), ankylosing spondylitis (AS), and osteoarthritis (OA). Objectives: To evaluate the prevalence of PO in patients with RA, JCA, AS, and OA, who have undergone total hip replacement (THR), and to identify factors associated with its development. Methods: The study included patients diagnosed with RA (ACR 1987), AS (modified New York criteria), JCA (European 1977 criteria), and osteoarthritis (OA) (ACR 1990 criteria) with unilateral or bilateral THR. Demographic, clinical, and therapeutic data were collected. Panoramic pelvic plain radiographs were performed, to determine the presence of PO at acetabular and femoral levels. Images were read by two independent observers. Results: One hundred twenty-two hip prostheses were analyzed (74 cemented, 30 cementless, and 18 hybrids). The average time from prosthesis implantation to pelvic radiograph was comparable among groups. PO was observed in 72 hips (59%). In 55% of cases, PO was detected on the femoral component, with a lower prevalence in RA (53%) vs AS (64.7%) and JCA (76.5%). Acetabular PO was more frequent in JCA patients (58.8%), compared with RA (11.6%) and OA (28.5%) patients (P = 0.0001 and P = 0.06, respectively). There was no significant association between the presence of PO and clinical, functional, or therapeutic features. Conclusion: The prevalence of PO was 59%, being more frequent at the femoral level. Larger studies must be carried out to determine the clinical significance of radiologic PO.
BeppoSAX view of NGC 526A: a Seyfert 1.9 galaxy with a flat spectrum
R. Landi,L. Bassani,G. Malaguti,M. Cappi,A. Comastri,M. Dadina,G. Di Cocco,A. C. Fabian,E. Palazzi,G. G. C. Palumbo,M. Trifoglio
Physics , 2001, DOI: 10.1051/0004-6361:20011182
Abstract: In the present work we report the BeppoSAX observation of the Seyfert 1.9 galaxy NGC 526A in the band 0.1-150 keV. The high energy instrument onboard, PDS, has succeeded in measuring for the first time the spectrum of this source in the 13-150 keV range. The combined analysis of all Narrow Field Instruments provides a power law spectral index of ~ 1.6 and confirms the flat spectral nature of this source. Although NGC 526A varies strongly in the 2-10 keV over period of months/years, its spectral shape remains constant over these timescales. An Fe K-alpha line, characterized by a complex structure, has been detected in the 6-7 keV range. The line, which has an equivalent width of 120 eV, is not compatible with being produced in an absorbing torus with N_H ~ 10^22 cm^-2, but most likely originates by reflection in an accretion disk viewed at an intermediate inclination angle of ~ 42 deg. The reflection component is however small (R < 0.7) and so it is not sufficient to steepen the spectrum to photon index values more typical of AGNs. Instead, we find that the data are more consistent with a flat power law spectrum cut-off at around 100 keV plus a small reflection component which could explain the observed iron line. Thus NGC 526A is the only bona-fide Seyfert 2 galaxy which maintains a "flat spectrum" even when broad band data are considered: in this sense its properties, with respect to the general class of Seyfert 2's, are analogous to those of NGC 4151 with respect to the vast majority of Seyfert 1's.
The changing look of PKS 2149-306
V. Bianchin,L. Foschini,G. Ghisellini,G. Tagliaferri,F. Tavecchio,A. Treves,G. Di Cocco,M. Gliozzi,E. Pian,R. M. Sambruna,A. Wolter
Physics , 2009, DOI: 10.1051/0004-6361/200811128
Abstract: Aims: We study the blazar nature of the high-redshift Flat-Spectrum Radio Quasar PKS 2149-306 (z = 2.345) by investigating its long-term behavior. Methods: We analyzed all publicly available optical-to-X-ray observations performed by XMM-Newton, Swift, and INTEGRAL. Conclusions: PKS 2149-306 is one of four blazars at z>2 that have been observed in the hard-X-ray regime with both the BAT and ISGRI instruments. Observations acquired almost 1 year apart in the 60-300 keV energy band in the object rest frame, exhibit no noticeable change in spectral slope associated with a flux variation of more than a factor of two. Swift data appear to show a roll-off below ~1 keV, which becomes increasingly evident during a ~3-day time-frame, that can be explained as the natural spectral break caused by the Inverse Compton onset. The broad-band spectra allow us to identify two different states. The SED modeling suggests that they can be interpreted by only a change in the bulk Lorentz factor of the jet.
In-flight calibrations of IBIS/PICsIT
G. Malaguti,A. Bazzano,A. J. Bird,G. Di Cocco,L. Foschini,P. Laurent,A. Segreto,J. B. Stephen,P. Ubertini
Physics , 2003, DOI: 10.1051/0004-6361:20031208
Abstract: PICsIT (Pixellated Imaging CaeSium Iodide Telescope) is the high energy detector of the IBIS telescope on-board the INTEGRAL satellite. It consists of 4096 independent detection units, ~0.7 cm^2 in cross-section, operating in the energy range between 175 keV and 10 MeV. The intrinsically low signal to noise ratio in the gamma-ray astronomy domain implies very long observations, lasting 10^5-10^6 s. Moreover, the image formation principle on which PICsIT works is that of coded imaging in which the entire detection plane contributes to each decoded sky pixel. For these two main reasons, the monitoring, and possible correction, of the spatial and temporal non-uniformity of pixel performances, expecially in terms of gain and energy resolution, is of paramount importance. The IBIS on-board 22Na calibration source allows the calibration of each pixel at an accuracy of <0.5% by integrating the data from a few revolutions at constant temperature. The two calibration lines, at 511 and 1275 keV, allow also the measurement and monitoring of the PICsIT energy resolution which proves to be very stable at ~19% and ~9% (FWHM) respectively, and consistent with the values expected analytical predictions checked against pre-launch tests.
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