Silicon drift detectors (SDD) of small dimensions (up to 1
cm
2) have been successfully employed in X-ray spectroscopy due to their small anode geometry, which allows to minimize the electronic noise ...due to the readout device. Many applications, however, require large sensitive areas to be covered (e.g. X-ray astronomy), so that these detectors are effectively impractical. We present the spectroscopic performance of a 53
cm
2 sensitive area, multi-anode SDD, measured at room temperature using an eight-channel readout setup. The measurements, taken using
55Fe and
241Am sources, and X-ray tubes generating energies down to 2
keV, show energy resolutions in the range 290–570
eV FWHM, at 20
°C, depending on the number of anodes collecting the signal. Further developments we are carrying out could improve the detector characteristics and allow to approach the performance of small area SDDs.
We report on a multiwavelength observation of the blazar 3C 454.3 (which we dubbed crazy diamond) carried out on November 2007 by means of the astrophysical satellites AGILE, International Gamma-Ray ...Astrophysics Laboratory (INTEGRAL), Swift, the Whole Earth Blazar Telescope (WEBT) Consortium, and the optical-NIR telescope Rapid Eye Mount (REM). Thanks to the wide field of view of the AGILE satellite and its prompt alert dissemination to other observatories, we obtained a long (three weeks), almost continuous gamma -ray coverage of the blazar 3C 454.3 across 14 decades of energy. This broadband monitoring allows us to study in great detail light curves, correlations, time lags, and spectral energy distributions (SEDs) during different physical states. Gamma-ray data were collected during an AGILE pointing toward the Cygnus Region. Target of Opportunity (ToO) observations were performed to follow up the gamma -ray observations in the soft and hard X-ray energy bands. Optical data were acquired continuously by means of a preplanned WEBT campaign and through an REM ToO repointing. 3C 454.3 is detected at a ~19 sigma level during the three-week observing period, with an average flux above 100 MeV of F E > 100 MeV = (170 ± 13) X 10-8 photons cm-2 s-1. The gamma -ray spectrum can be fitted with a single power law with photon index Gamma GRID = 1.73 ± 0.16 between 100 MeV and 1 GeV. We detect significant day-by-day variability of the gamma -ray emission during our observations, and we can exclude that the fluxes are constant at the 99.6% (~2.9 sigma ) level. The source was detected typically around 40 deg off-axis, and it was substantially off-axis in the field of view of the AGILE hard X-ray imager. However, a five-day long ToO observation by INTEGRAL detected 3C 454.3 at an average flux of about F 20-200 keV = 1.49 X 10-3 photons cm-2 s-1with an average photon index of Gamma IBIS = 1.75 ± 0.24 between 20-200 keV. Swift also detected 3C 454.3 with a flux in the 0.3-10 keV energy band in the range (1.23-1.40) X 10-2 photons cm-2 s-1 and a photon index in the range Gamma XRT = 1.56-1.73. In the optical band, both WEBT and REM show an extremely variable behavior in the R band. A correlation analysis based on the entire data set is consistent with no time lags between the gamma -ray and the optical flux variations. Our simultaneous multifrequency observations strongly indicate that the dominant emission mechanism between 30 MeV and 30 GeV is dominated by inverse Compton scattering of relativistic electrons in the jet on the external photons from the broad line region.
We present the results of a series of optical, UV, X-ray and γ-ray observations of the BL Lac object S50716+714 carried out by the Swift and AGILE satellites in late 2007 when the blazar was flaring ...close to its historical maximum at optical frequencies. We have found that the optical through soft X-ray emission, likely due to synchrotron radiation, was highly variable and displayed a different behavior in the optical UV and soft X-ray bands. The 4-10 keV flux, most probably dominated by the inverse Compton component, instead remained constant. The counting statistics in the relatively short AGILE GRID observation was low and consistent with a constant γ-ray flux at a level similar to the maximum observed by EGRET. An estimate of the γ-ray spectral slope gives a value of the photon index that is close to 2, suggesting that the peak of the inverse Compton component in the Spectral Energy Distribution (SED) is within the AGILE energy band. The different variability behavior observed in different parts of the SED exclude interpretations predicting highly correlated flux variability like changes in the beaming factor or the magnetic field in simple SSC scenarios. The observed SED changes may instead be interpreted as due to the sum of two SSC components, one of which is constant while the other is variable and with a systematically higher synchrotron peak energy.
GRB 080514B is the first gamma ray burst (GRB), since the time of EGRET, for which individual photons of energy above several tens of MeV have been detected with a pair-conversion tracker telescope. ...This burst was discovered with the Italian AGILE gamma-ray satellite. The GRB was localized by a cooperation between AGILE and the interplanetary network (IPN). The gamma-ray imager (GRID) estimate of the position, obtained before the SuperAGILE-IPN localization, is found to be consistent with the burst position. The hard X-ray emission observed by SuperAGILE lasted about 7 s, while there is evidence that the emission above 30 MeV extends for a longer duration (at least 13 s). Similar behavior has been seen from a few other GRBs observed with EGRET. However, during the brightest phases, the latter measurements were affected by instrumental dead time effects, resulting in only lower limits to the burst intensity. Thanks to the small dead time of the AGILE/GRID we could assess that in the case of GRB 080514B the gamma-ray to X-ray flux ratio changes significantly between the prompt and extended emission phase.
We report on the extremely intense and fast gamma-ray flare above 100 MeV detected by AGILE from the Crab Nebula in mid-April 2011. This event is the fourth of a sequence of reported major gamma-ray ...flares produced by the Crab Nebula in the period 2007/mid-2011. These events are attributed to strong radiative and plasma instabilities in the inner Crab Nebula, and their properties are crucial for theoretical studies of fast and efficient particle acceleration up to 1015 eV. Here we study the very rapid flux and spectral evolution of the event that on 2011 April 16 reached the record-high peak flux of F = (26 ? 5) X 10--6 photons cm--2 s--1 with a rise-time timescale that we determine to be in the range 6-10 hr. The peak flaring gamma-ray spectrum reaches a distinct maximum near 500 MeV with no substantial emission above 1 GeV. The very rapid rise time and overall evolution of the Crab Nebula flare strongly constrain the acceleration mechanisms and challenge MHD models. We briefly discuss the theoretical implications of our observations.
Using gamma-ray data collected by the Astro-rivelatore Gamma ad Immagini LEggero (AGILE) satellite over a period of almost one year (from 2007 July to 2008 June), we searched for pulsed signals from ...35 potentially interesting radio pulsars, ordered according to and for which contemporary or recent radio data were available. AGILE detected three new top-ranking nearby and Vela-like pulsars with good confidence both through timing and spatial analysis. Among the newcomers we find pulsars with very high rotational energy losses, such as the remarkable PSR B1509 - 58 with a magnetic field in excess of 1013 Gauss, and PSR J2229 + 6114 providing a reliable identification for the previously unidentified EGRET source 3EG 2227 + 6122. Moreover, the powerful millisecond pulsar B1821 - 24, in the globular cluster M28, is detected during a fraction of the observations. Four other promising gamma-ray pulsar candidates, among which is the notable J2043 + 2740 with an age in excess of 1 million years, show a possible detection in the timing analysis only and deserve confirmation.
We report the first blazar detection by AGILE. AGILE detected 3C 454.3 during a period of strongly enhanced optical emission in 2007 July. AGILE observed the source with a dedicated repointlng during ...the period 2007 July 24-30 with its two co-aligned imagers, the Gamma-Ray Imaging Detector and the hard X-ray imager Super-AGILE sensitive in the 30 MeV to 50 GeV and 18-60 keV ranges, respectively. Over the entire period, AGILE detected y-ray emission from 3C 454.3 at a significance level of 13.8 a with an average flux (E > 100 MeV) of (280 plus or minus 40) x 10 super(-5) photons cm-2, s-1. The y-ray flux appears to be variable toward the end of the observation. No emission was detected by Super-AGILE in the energy range 20-60 keV, with a 3 o upper limit of 2.3 x 10 super(-3) photons cm-2 S-1. The Y-ray flux level of 3C 454.3 detected by AGILE Is the highest ever detected for this quasar and among the most intense Y-ray fluxes ever detected from fiat-spectrum radio quasars.
Pulsars are known to power winds of relativistic particles that can produce bright nebulae by interacting with the surrounding medium. These pulsar wind nebulae are observed by their radio, optical, ...and x-ray emissions, and in some cases also at TeV (teraelectron volt) energies, but the lack of information in the gamma-ray band precludes drawing a comprehensive multiwavelength picture of their phenomenology and emission mechanisms. Using data from the AGILE satellite, we detected the Vela pulsar wind nebula in the energy range from 100 MeV to 3 GeV. This result constrains the particle population responsible for the GeV emission and establishes a class of gamma-ray emitters that could account for a fraction of the unidentified galactic gamma-ray sources.
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