The AGILE Mission Barbiellini, G.; Argan, A.; Boffelli, F. ...
Astronomy and astrophysics (Berlin),
08/2009, Letnik:
502, Številka:
3
Journal Article
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Context. AGILE is an Italian Space Agency mission dedicated to observing the gamma-ray Universe. The AGILE's very innovative instrumentation for the first time combines a gamma-ray imager (sensitive ...in the energy range 30 MeV–50 GeV), a hard X-ray imager (sensitive in the range 18–60 keV), a calorimeter (sensitive in the range 350 keV–100 MeV), and an anticoincidence system. AGILE was successfully launched on 2007 April 23 from the Indian base of Sriharikota and was inserted in an equatorial orbit with very low particle background. Aims. AGILE provides crucial data for the study of active galactic nuclei, gamma-ray bursts, pulsars, unidentified gamma-ray sources, galactic compact objects, supernova remnants, TeV sources, and fundamental physics by microsecond timing. Methods. An optimal sky angular positioning (reaching 0.1 degrees in gamma-rays and 1–2 arcmin in hard X-rays) and very large fields of view (2.5 sr and 1 sr, respectively) are obtained by the use of Silicon detectors integrated in a very compact instrument. Results. AGILE surveyed the gamma-ray sky and detected many Galactic and extragalactic sources during the first months of observations. Particular emphasis is given to multifrequency observation programs of extragalactic and galactic objects. Conclusions. AGILE is a successful high-energy gamma-ray mission that reached its nominal scientific performance. The AGILE Cycle-1 pointing program started on 2007 December 1, and is open to the international community through a Guest Observer Program.
We report the detection by the Astrorivelatore Gamma a Immagini Leggero (AGILE) satellite of terrestrial gamma ray flashes (TGFs) obtained with the minicalorimeter (MCAL) detector operating in the ...energy range 0.3–100 MeV. We select events typically lasting a few milliseconds with spectral and directional selections consistent with the TGF characteristics previously reported by other space missions. During the period 1 June 2008 to 31 March 2009 we detect 34 high‐confidence events showing millisecond durations and a geographical distribution peaked over continental Africa and Southeast Asia. For the first time, AGILE‐MCAL detects photons associated with TGF events up to 40 MeV. We determine the cumulative spectral properties of the spectrum in the range 0.5–40 MeV, which can be effectively described by a Bremsstrahlung spectrum. We find that both the TGF cumulative spectral properties and their geographical distribution are in good agreement with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) results.
Aims. Supernova remnants (SNRs) are believed to be the main sources of Galactic cosmic rays. Molecular clouds associated with SNRs can produce gamma-ray emission by means of the interaction of ...accelerated particles with the concentrated gas. The middle-aged SNR W28, because of its associated system of dense molecular clouds, provides an excellent opportunity to test this hypothesis. Methods. We present the AGILE/GRID observations of SNR W28, and compare them with observations at other wavelengths (TeV and 12CO (J=1$\rightarrow$0) molecular line emission). Results. The gamma-ray flux detected by AGILE from the dominant source associated with W28 is (14 ± 5) × 10-8 ph cm-2 s-1 for E > 400 MeV. This source is positionally well correlated with the TeV emission observed by the HESS telescope. The local variations in the GeV to TeV flux ratio imply that there is a difference between the CR spectra of the north-west and south molecular cloud complexes. A model based on a hadronic-induced interaction and diffusion with two molecular clouds at different distances from the W28 shell can explain both the morphological and spectral features observed by both AGILE in the MeV-GeV energy range and the HESS telescope in the TeV energy range. The combined set of AGILE and H.E.S.S. data strongly support a hadronic model for the gamma-ray production in W28.
AGILE is a mission of the Italian Space Agency (ASI) Scientific Program dedicated to γ-ray astrophysics, and has operated in a low Earth orbit since 2007 April 23. It is designed to be a very light ...and compact instrument, capable of simultaneously detecting and imaging photons in the 18-60 keV X-ray energy band and in the 30 MeV-50 GeV γ-ray energy range with a good angular resolution ( 1◦ @ 1 GeV). The core of the instrument is the Silicon Tracker, supplemented by a CsI calorimeter and an AntiCoincidence system, which form the Gamma Ray Imaging Detector (GRID). Before launch, the GRID needed on-ground calibration with a tagged γ-ray beam to estimate its performance and validate the Monte Carlo simulation. The GRID was calibrated using a tagged γ-ray beam with energy up to 500 MeV at the Beam Test Facilities at the INFN Laboratori Nazionali di Frascati. These data are used to validate a GEANT 3-based simulation by comparing the data and the Monte Carlo simulation by measuring the angular and energy resolutions. The GRID angular and energy resolutions obtained using the beam agree well with the Monte Carlo simulation. Therefore the simulation, can be used to simulate the same performance on-flight with high reliability.
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.
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.
Astro-rivelatore Gamma ad Immagini LEggero (AGILE) is a small gamma-ray astronomy satellite mission of the Italian Space Agency dedicated to high-energy astrophysics launched in 2007 April. Its ~ 1 ...is a subset of s absolute time tagging capability coupled with a good sensitivity in the 30 MeV-30 GeV range, with simultaneous X-ray monitoring in the 18-60 keV band, makes it perfectly suited for the study of gamma-ray pulsars following up on the Compton Gamma Ray Observatory/EGRET heritage. In this paper, we present the first AGILE timing results on the known gamma-ray pulsars Vela, Crab, Geminga, and B1706 - 44. The data were collected from 2007 July to 2008 April, exploiting the mission Science Verification Phase, the Instrument Timing Calibration, and the early Observing Pointing Program. Thanks to its large field of view, AGILE collected a large number of gamma-ray photons from these pulsars (~ 10,000 pulsed counts for Vela) in only few months of observations. The coupling of AGILE timing capabilities, simultaneous radio/X-ray monitoring, and new tools aimed at precise photon phasing, also exploiting timing noise correction, unveiled new interesting features at the submillisecond level in the pulsars' high-energy light curves.
Aims. We report the γ-ray activity from the intermediate BL Lac S5 0716+714 during observations acquired by the AGILE satellite in September and October 2007. These detections of activity were ...contemporaneous with a period of intense optical activity, which was monitored by GASP–WEBT. This simultaneous optical and γ-ray coverage allows us to study in detail the light curves, time lags, γ-ray photon spectrum, and Spectral Energy Distributions (SEDs) during different states of activity. Methods. AGILE observed the source with its two co-aligned imagers, the Gamma-Ray Imaging Detector (GRID) and the hard X-ray imager (Super-AGILE), which are sensitive to the 30 MeV–50 GeV and 18–60 keV energy ranges, respectively. Observations were completed in two different periods, the first between 2007 September 4–23, and the second between 2007 October 24–November 1. Results. Over the period 2007 September 7–12, AGILE detected γ-ray emission from the source at a significance level of 9.6-σ with an average flux (E > 100 MeV) of (97 ± 15) $\times$ 10-8 photons cm-2 s-1, which increased by a factor of at least four within three days. No emission was detected by Super-AGILE for the energy range 18–60 keV to a 3-σ upper limit of 10 mCrab in 335 ks. In October 2007, AGILE repointed toward S5 0716+714 following an intense optical flare, measuring an average flux of (47 ± 11) $\times$ 10-8 photons cm-2 s-1 at a significance level of 6.0-σ. Conclusions. The γ-ray flux of S5 0716+714 detected by AGILE is the highest ever detected for this blazar and one of the most intense γ-ray fluxes detected from a BL Lac object. The SED of mid-September appears to be consistent with the synchrotron self-Compton (SSC) emission model, but only by including two SSC components of different variabilities.
Context. The mini-calorimeter (MCAL) instrument on-board the AGILE satellite is a non-imaging gamma-ray scintillation detector sensitive in the 300 keV–100 MeV energy range with a total on-axis ...geometrical area of 1400 cm2. Gamma-ray bursts (GRBs) are one of the main scientific targets of the AGILE mission and the MCAL design as an independent self-triggering detector makes it a valuable all-sky monitor for GRBs. Furthermore MCAL is one of the very few operative instruments with microsecond timing capabilities in the MeV range. Aims. In this paper the results of GRB detections with MCAL after one year of operation in space are presented and discussed. Methods. A flexible trigger logic implemented in the AGILE payload data-handling unit allows the on-board detection of GRBs. For triggered events, energy and timing information are sent to telemetry on a photon-by-photon basis, so that energy and time binning are limited by counting statistics only. When the trigger logic is not active, GRBs can be detected offline in ratemeter data, although with worse energy and time resolution. Results. Between the end of June 2007 and June 2008 MCAL detected 51 GRBs, with a detection rate of about 1 GRB/week, plus several other events at a few milliseconds timescales. Since February 2008 the on-board trigger logic has been fully active. Comparison of MCAL detected events and data provided by other space instruments confirms the sensitivity and effective area estimations. MCAL also joined the 3rd Inter-Planetary Network, to contribute to GRB localization by means of triangulation.
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