17 research outputs found
Study of the performance of standard RPC chambers as a function of bakelite temperature
A systematic study of the performance of the Resistive Plate Chambers as a function of the bakelite temperature is presented. The current, the rate and the efficiency were measured in the temperature range 22-40degreesC. The values of the relative humidity during the data taking were in the range 40-60%. Measurements show a strong dependence of the efficiency on bakelite temperature. (C) 2003 Elsevier Science B.V. All rights reserved
The LOFT mission concept: a status update
The Large Observatory For x-ray Timing (LOFT) is a mission concept which was proposed to ESA as M3 and M4 candidate in the framework of the Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument and the uniquely large field of view of its wide field monitor, LOFT will be able to study the behaviour of matter in extreme conditions such as the strong gravitational field in the innermost regions close to black holes and neutron stars and the supra-nuclear densities in the interiors of neutron stars. The science payload is based on a Large Area Detector (LAD, >8m2 effective area, 2-30 keV, 240 eV spectral resolution, 1 degree collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g., GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the current technical and programmatic status of the mission
AGILE detection of extreme Îł -ray activity from the blazar PKS 1510-089 during March 2009: Multifrequency analysis
We report on the extreme gamma-ray activity from the FSRQ PKS 1510-089
observed by AGILE in March 2009. In the same period a radio-to-optical
monitoring of the source was provided by the GASP-WEBT and REM. Moreover,
several Swift ToO observations were triggered, adding important information on
the source behaviour from optical/UV to hard X-rays. We paid particular
attention to the calibration of the Swift/UVOT data to make it suitable to the
blazars spectra. Simultaneous observations from radio to gamma rays allowed us
to study in detail the correlation among the emission variability at different
frequencies and to investigate the mechanisms at work. In the period 9-30 March
2009, AGILE detected an average gamma-ray flux of (311+/-21)x10^-8 ph cm^-2
s^-1 for E>100 MeV, and a peak level of (702+/-131)x10^-8 ph cm^-2 s^-1 on
daily integration. The gamma-ray activity occurred during a period of
increasing activity from near-IR to UV, with a flaring episode detected on
26-27 March 2009, suggesting that a single mechanism is responsible for the
flux enhancement observed from near-IR to UV. By contrast, Swift/XRT
observations seem to show no clear correlation of the X-ray fluxes with the
optical and gamma-ray ones. However, the X-ray observations show a harder
photon index (1.3-1.6) with respect to most FSRQs and a hint of
harder-when-brighter behaviour, indicating the possible presence of a second
emission component at soft X-ray energies. Moreover, the broad band spectrum
from radio-to-UV confirmed the evidence of thermal features in the optical/UV
spectrum of PKS 1510-089 also during high gamma-ray state. On the other hand,
during 25-26 March 2009 a flat spectrum in the optical/UV energy band was
observed, suggesting an important contribution of the synchrotron emission in
this part of the spectrum during the brightest gamma-ray flare, therefore a
significant shift of the synchrotron peak
Multiwavelength observations of 3C 454.3. III. Eighteen months of agile monitoring of the "crazy diamond"
We report on 18 months of multiwavelength observations of the blazar 3C 454.3 (Crazy Diamond) carried out in the period 2007 July-2009 January. In particular, we show the results of the AGILE campaigns which took place on 2008 May-June, 2008 July-August, and 2008 October-2009 January. During the 2008 May-2009 January period, the source average flux was highly variable, with a clear fading trend toward the end of the period, from an average Îł-ray flux F E>100 MeV âł 200 Ă 10-8photonscm -2s-1 in 2008 May-June, to F E>100 MeV 80 Ă 10-8photonscm-2s-1 in 2008 October-2009 January. The average Îł-ray spectrum between 100 MeV and 1 GeV can be fit by a simple power law, showing a moderate softening (from ÎGRID ⌠2.0 to ÎGRID ⌠2.2) toward the end of the observing campaign. Only 3Ï upper limits can be derived in the 20-60 keV energy band with Super-AGILE, because the source was considerably off-axis during the whole time period. In 2007 July-August and 2008 May-June, 3C 454.3 was monitored by Rossi X-ray Timing Explorer (RXTE). The RXTE/Proportional Counter Array (PCA) light curve in the 3-20 keV energy band shows variability correlated with the Îł-ray one. The RXTE/PCA average flux during the two time periods is F 3-20 keV = 8.4 Ă 10-11ergcm-2s -1, and F 3-20 keV = 4.5 Ă 10 -11ergcm-2s-1, respectively, while the spectrum (a power law with photon index ÎPCA = 1.65 0.02) does not show any significant variability. Consistent results are obtained with the analysis of the RXTE/High-Energy X-Ray Timing Experiment quasi-simultaneous data. We also carried out simultaneous Swift observations during all AGILE campaigns. Swift/XRT detected 3C 454.3 with an observed flux in the 2-10 keV energy band in the range (0.9-7.5) Ă 10-11ergcm-2s-1 and a photon index in the range ÎXRT = 1.33-2.04. In the 15-150 keV energy band, when detected, the source has an average flux of about 5mCrab. GASP-WEBT monitored 3C 454.3 during the whole 2007-2008 period in the radio, millimeter, near-IR, and optical bands. The observations show an extremely variable behavior at all frequencies, with flux peaks almost simultaneous with those at higher energies. A correlation analysis between the optical and the Îł-ray fluxes shows that the Îł-optical correlation occurs with a time lag of Ï = -0.4+0.6-0.8 days, consistent with previous findings for this source. An analysis of 15 GHz and 43 GHz VLBI core radio flux observations in the period 2007 July-2009 February shows an increasing trend of the core radio flux, anti-correlated with the higher frequency data, allowing us to derive the value of the source magnetic field. Finally, the modeling of the broadband spectral energy distributions for the still unpublished data, and the behavior of the long-term light curves in different energy bands, allow us to compare the jet properties during different emission states, and to study the geometrical properties of the jet on a time-span longer than one year. © 2010. The American Astronomical Society. All rights reserved
Italian Opuntia ficus-indica Cladodes as Rich Source of Bioactive Compounds with Health-Promoting Properties
Natural by-products, especially phenolic compounds, are in great demand by the nutra-pharmaceutical and biomedical industries. An analytical study was performed to investigate, for the first time, the presence of antioxidant constituents and the corresponding in vitro antioxidant activity in the extract of cladodes from Ficodindia di San Cono (Opuntia ficus-indica) protected designation of origin (PDO). The cladode extracts were analysed for target determination of selected constituents, i.e. \u3b2-polysaccharides and total phenolic content. Moreover, the antioxidant activity of hydro-alcoholic extracts was assessed by means of two different methods: \u3b1, \u3b1-diphenyl-\u3b2-picrylhydrazyl (DPPH) free radical scavenging method and ferric reducing antioxidant power (FRAP) assay. An untargeted UHPLC-ESI-QTOF-MS profiling approach was used to depict the phenolic profile of hydro-alcoholic cladode extracts. Interestingly, over 2 g/kg of polyphenols were detected in this matrix, and these compounds were mainly responsible for the antioxidant properties, as shown by the strong correlation between phenolic classes and antioxidant scores. Finally, this study provides basic information on the presence of bioactive compounds and in vitro antioxidant activities in cladode extracts from cactus that might recommend their novel applications at the industrial level in the field of nutraceutical products
The RPC charge read-out in the ARGO-YBJ experiment.
The ARGO-YBJ experiment at the Yangbajing Laboratory (4300 m a.s.l.) is taking data with about 1900 m2 of its carpet. The digital read-out of the RPCs, performed by means of pick-up electrodes 7 x 62 cm2 ('strips'), well suited to detect small size air showers, implies a limitation to the measurable energy of a few hundreds of TeV. In order to extend the energy range up to the knee region an analog read-out of the RPCs has been implemented. Each RPC has been equipped with two large size pads of dimensions 1.40 x 1.25 m2. The analog read-out system has been put in operation on 180 m2 of the detector, allowing a cross-check of digital and analog information. In this paper a brief description of the analog read-out system is given, and preliminary results are discussed
Time calibration of the ARGO-YBJ experiment
The ARGO-YBJ detector has the capability to measure the arrival direction of the primary cosmic rays by means of detailed space-time pictures of the air showers. Therefore the time calibration of the apparatus is crucial for astronomical observations. Here a software procedure for the time-calibration is presented. It has been applied to the portion of the apparatus currently in data-taking (____
First results on the angular resolution of the ARGO-YBJ detector.
A carpet of about 1900 m2 of Resistive Plate Chambers (about 1/3 of the whole ARGO-YBJ detector) has been put in data taking at the Yangbajing High Altitude Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l.). We present the first results on the angular resolution. The comparison of experimental results with MC simulations is discussed
Sky survey with the ARGO-YBJ detector
The ARGO-YBJ experiment is planned to detect gamma ray sources with an energy threshold of a few hundreds of GeV. The large field of view of the detector and its high duty cycle allow the continuous monitoring of a large part of the sky, searching for both unknown stable sources and transient emissions as AGN flares and Gamma Ray Bursts. In this work we present the first data obtained with a subset of the detector (covering _ 1900 m_ ) concerning the search for stable and transient sources in the declination range