Aims. We report the detection by the AGILE satellite of a rapid γ-ray flare from the source 1AGL J1511-0908, associated with the powerful γ-ray quasar PKS 1510-089, during a pointing centered on the ...Galactic center region from 1 March to 30 March 2008. This source has been continuosly monitored in the radio-to-optical bands by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT). Moreover, the γ-ray flaring episode triggered three ToO observations by the $S\!wift$ satellite in three consecutive days, starting from 20 March 2008. The quasi-simultaneous radio-to-optical, UV, X-ray and γ-ray coverage allows us to make a detailed study of the multifrequency time evolution, the spectral energy distribution of this source, and its theoretical interpretation based on the synchrotron and inverse Compton (IC) emission mechanisms. Methods. During the radio-to-optical monitoring provided by the GASP-WEBT, AGILE observed the source with its two co-aligned imagers, the gamma-ray imaging detector (GRID) and the hard X-ray imager (SuperAGILE), which are sensitive in the 30 MeV–30 GeV and 18–60 keV energy bands, respectively. Results. In the period 1–16 March 2008, AGILE detected γ-ray emission from PKS 1510-089 at a significance level of 6.2-σ with an average flux over the entire period of $(84 \pm 17) \times 10^{-8}$ photons cm-2 s-1 for photon energies above 100 MeV. After a predefined satellite re-pointing, between 17 and 21 March 2008, AGILE detected the source at a significance level of 7.3-σ, with an average flux ($E > 100$ MeV) of $(134 \pm 29) \times 10^{-8}$ photons cm-2 s-1 and a peak level of $(281 \pm 68) \times 10^{-8}$ photons cm-2 s-1 with daily integration. During the observing period January-April 2008, the source also showed an intense and variable optical activity, with several flaring episodes and a significant increase in the flux was observed at millimetric frequencies. Moreover, in the X-ray band, the $S\!wift$/XRT observations seem to show a harder-when-brighter behavior of the source spectrum. Conclusions. The flat spectrum radio quasar PKS 1510-089 showed strong activity between January and April 2008, with episodes of rapid variability from radio to γ-ray energy bands, in particular with a rapid γ-ray flaring episode. The spectral energy distribution of mid-March 2008 is modeled with a homogeneous one-zone synchrotron self Compton (SSC) emission plus contributions from inverse Compton scattering of external photons from both the accretion disk and the broad line region. Indeed, some features in the optical-UV spectrum seem to indicate Seyfert-like components such as the little and the big blue bumps.
AGILE is an ASI (Italian Space Agency) Small Space Mission for high energy astrophysics in the range 30 MeV - 50 GeV. The AGILE satellite is currently in the C phase and is planned to be launched in ...2005. The Payload shall consist of a Tungsten-Silicon Tracker, a CsI Minicalorimeter, an anticoincidence system and a X-Ray detector sensitive in the 10-40 KeV range. The purpose of the Minicalorimeter (MCAL) is twofold. It shall work in conjunction with the Tracker in order to evaluate the energy of the interacting photons, and it shall operate autonomously in the energy range 250KeV-250 MeV for detection of transients and gamma ray burst events and for the measurement of gamma ray background fluctuations. We present the architecture of the Test Equipment we have designed and developed in order to test and verify the MCAL Simplified Electrical Model prototype which has been manufactured in order to validate the design of the MCAL Proto Flight Model.
We report on the second Astrorivelatore Gamma a Immagini Leggero (AGILE) multiwavelength campaign of the blazar 3C 454.3 during the first half of 2007 December. This campaign involved AGILE, Spitzer, ...Swift, Suzaku, the Whole Earth Blazar Telescope (WEBT) consortium, the Rapid Eye Mount (REM), and the Multicolor Imaging Telescopes for Survey and Monstrous Explosions (MITSuME) telescopes, offering a broadband coverage that allowed for a simultaneous sampling of the synchrotron and inverse Compton (IC) emissions. The two-week AGILE monitoring was accompanied by radio to optical monitoring by WEBT and REM, and by sparse observations in mid-infrared and soft/hard X-ray energy bands performed by means of Target of Opportunity observations by Spitzer, Swift, and Suzaku, respectively. The source was detected with an average flux of ~250 X 10-8 photons cm-2 s-1 above 100 MeV, typical of its flaring states. The simultaneous optical and Delta *g-ray monitoring allowed us to study the time lag associated with the variability in the two energy bands, resulting in a possible one-day delay of the Delta *g-ray emission with respect to the optical one. From the simultaneous optical and Delta *g-ray fast flare detected on December 12, we can constrain the delay between the Delta *g-ray and optical emissions within 12 hr. Moreover, we obtain three spectral energy distributions (SEDs) with simultaneous data for 2007 December 5, 13, and 15, characterized by the widest multifrequency coverage. We found that a model with an external Compton on seed photons by a standard disk and reprocessed by the broad-line regions does not describe in a satisfactory way the SEDs of 2007 December 5, 13, and 15. An additional contribution, possibly from the hot corona with T = 106 K surrounding the jet, is required to account simultaneously for the softness of the synchrotron and the hardness of the IC emissions during those epochs.
We present the results of new AGILE observations of PSR B1509 -- 58 performed over a period of ~2.5 years following the detection obtained with a subset of the present data. The modulation ...significance of the light curve above 30 MeV is at a 5 Delta *s confidence level and the light curve is similar to those found earlier by COMPTEL up to 30 MeV: a broad asymmetric first peak reaching its maximum 0.39 ? 0.02 cycles after the radio peak plus a second peak at 0.94 ? 0.03. The gamma-ray spectral energy distribution of the pulsed flux detected by COMPTEL and AGILE is well described by a power law (photon index Delta *a = 1.87 ? 0.09) with a remarkable cutoff at Ec = 81 ? 20 MeV, representing the softest spectrum observed among gamma-ray pulsars so far. The pulsar luminosity at E > 1 MeV is L Delta *g = 4.2+0.5 --0.2 X 1035 erg s--1, assuming a distance of 5.2 kpc, which implies a spin-down conversion efficiency to gamma rays of ~0.03. The unusual soft break in the spectrum of PSR B1509 -- 58 has been interpreted in the framework of polar cap models as a signature of the exotic photon-splitting process in the strong magnetic field of this pulsar. In this interpretation, our spectrum constrains the magnetic altitude of the emission point(s) at 3 km above the neutron star surface, implying that the attenuation may not be as strong as formerly suggested because pair production can substitute photon splitting into regions of the magnetosphere where the magnetic field becomes too low to sustain photon splitting. In the case of an outer-gap scenario or the two-pole caustic model, better constraints on the geometry of the emission would be needed from the radio band in order to establish whether the conditions required by the models to reproduce AGILE light curves and spectra match the polarization measurements.
At the core of the AGILE scientific instrument, designed to operate on a satellite, there is the Gamma Ray Imaging Detector (GRID) consisting of a Silicon Tracker (ST), a Cesium Iodide ...Mini-Calorimeter and an Anti-Coincidence system of plastic scintillator bars. The ST needs an on-ground calibration with a γ-ray beam to validate the simulation used to calculate the energy response function and the effective area versus the energy and the direction of the γ rays. A tagged γ-ray beam line was designed at the Beam Test Facility (BTF) of the INFN Laboratori Nazionali of Frascati (LNF), based on an electron beam generating γ-rays through bremsstrahlung in a position-sensitive target. The γ-ray energy is deduced by difference with the post-bremsstrahlung electron energy 1,2. The electron energy is measured by a spectrometer consisting of a dipole magnet and an array of position sensitive silicon strip detectors, the Photon Tagging System (PTS). The use of the combined BTF-PTS system as tagged photon beam requires understanding the efficiency of γ-ray tagging, the probability of fake tagging, the energy resolution and the relation of the PTS hit position versus the γ-ray energy. This paper describes this study comparing data taken during the AGILE calibration occurred in 2005 with simulation.
Context. We report the detection by the AGILE (Astro-rivelatore Gamma a Immagini LEggero) satellite of an intense gamma-ray flare from the source AGL J1511-0909, associated with the powerful quasar ...PKS 1510-089, during ten days of observations from 23 August to 1 September 2007. Aims. During the observation period, the source was in optical decrease following a flaring event monitored by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT). The simultaneous gamma-ray, optical, and radio coverage allows us to study the spectral energy distribution and the theoretical models based on the synchrotron and inverse Compton (IC) emission mechanisms. Methods. AGILE observed the source with its two co-aligned imagers, the Gamma-Ray Imaging Detector and the hard X-ray imager Super-AGILE sensitive in the 30 MeV $\div$ 50 GeV and 18 $\div$ 60 keV bands, respectively. Results. Between 23 and 27 August 2007, AGILE detected gamma-ray emission from PKS 1510-089 when this source was located ~$50^\circ$ off-axis, with an average flux of $(270 \pm 65)$ $\times$ 10-8 photons cm-2 s-1 for photon energy above 100 MeV. In the following period, 28 August-1 September, after a satellite re-pointing, AGILE detected the source at ~$35^\circ$ off-axis, with an average flux (E > 100 MeV) of $(195 \pm 30)$ $\times$ 10-8 photons cm-2 s-1. No emission was detected by Super-AGILE, with a 3-σ upper limit of 45 mCrab in 200 ks. Conclusions. The spectral energy distribution is modelled with a homogeneous one-zone synchrotron self Compton (SSC) emission plus contributions by external photons: the SSC emission contributes primarily to the X-ray band, whereas the contribution of the IC from the external disc and the broad line region match the hard gamma-ray spectrum observed.
The AGILE scientific instrument has been calibrated with a tagged
γ
-ray beam at the Beam Test Facility (BTF) of the INFN Laboratori Nazionali di Frascati (LNF). The goal of the calibration was the ...measure of the Point Spread Function (PSF) as a function of the photon energy and incident angle and the validation of the Monte Carlo (MC) simulation of the silicon tracker operation. The calibration setup is described and some preliminary results are presented.
Context. We report the results of a 3-week multi-wavelength campaign targeting the flat spectrum radio quasar 3C 273 carried out with the AGILE gamma-ray mission, covering the 30 MeV–50 GeV and ...18–60 keV, the REM observatory (covering the near-IR and optical), Swift (near-UV/Optical, 0.2–10 keV and 15–50 keV), INTEGRAL (3–200 keV) and Rossi XTE (2–12 keV). This is the first observational campaign including gamma-ray data, after the last EGRET observations, more than 8 years ago. Aims. This campaign has been organized by the AGILE team with the aim of observing, studying and modelling the broad band energy spectrum of the source, and its variability on a week timescale, testing the emission models describing the spectral energy distribution of this source. Methods. Our study was carried out using simultaneous light curves of the source flux from all the involved instruments, in the different energy ranges, to search for correlated variability. Then a time-resolved spectral energy distribution was used for a detailed physical modelling of the emission mechanisms. Results. The source was detected in gamma-rays only in the second week of our campaign, with a flux comparable to the level detected by EGRET in June 1991. We found an indication of a possible anti-correlation between the emission at gamma-rays and at soft and hard X-rays, supported by the complete set of instruments. Instead, optical data do not show short term variability, as expected for this source. Only in two preceding EGRET observations (in 1993 and 1997) 3C 273 showed intra-observation variability in gamma-rays. In the 1997 observation, flux variation in gamma-rays was associated with a synchrotron flare. The energy-density spectrum with almost simultaneous data partially covers the regions of synchrotron emission, the big blue bump, and the inverse-Compton. We adopted a leptonic model to explain the hard X/gamma-ray emissions, although from our analysis hadronic models cannot be ruled out. In the adopted model, the soft X-ray emission is consistent with combined synchrotron-self Compton and external Compton mechanisms, while hard X and gamma-ray emissions are compatible with external Compton from thermal photons of the disk. Under this model, the time evolution of the spectral energy distribution is well interpreted and modelled in terms of an acceleration episode of the electron population, leading to a shift in the inverse Compton peak towards higher energies.
Context. We report the detection by the AGILE satellite of an intense gamma-ray flare from the gamma-ray source 3EG J1255-0549, associated with the Flat Spectrum Radio Quasar 3C 279, during the AGILE ...pointings towards the Virgo Region on 2007 July 9-13. Aims. The simultaneous optical, X-ray and gamma-ray covering allows us to study the spectral energy distribution (SED) and the theoretical models relative to the mid-July flaring episode. Methods. AGILE observed the source during its Science Performance Verification Phase with its two co-aligned imagers: the Gamma-Ray Imaging Detector (GRID) and the hard X-ray imager (Super-AGILE) sensitive in the 30 MeV-50 GeV and 18-60 keV respectively. During the AGILE observation the source was monitored simultaneously in the optical band by the REM telescope and in the X-ray band by the Swift satellite through 4 target of opportunity observations. Results. During 2007 July 9-13, AGILE-GRID detected gamma-ray emission from 3C 279, with the source at ~2° from the center of the field of view, with an average flux of (210 ± 38) $\times$ 10-8 ph cm-2 s-1 for energy above 100 MeV. No emission was detected by Super-AGILE, with a 3-σ upper limit of 10 mCrab. During the observation, which lasted about 4 days, no significative gamma-ray flux variation was observed. Conclusions. The Spectral Energy Distribution is modelled with a homogeneous one-zone Synchrotron Self Compton emission plus the contributions by external Compton scattering of the direct disk radiation and, to a lesser extent, by external Compton scattering of photons from the Broad Line Region.
Characterization of a tagged beam line at the Beam Test Facility Cattaneo, P W; Argan, A; Boffelli, F ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2012, Letnik:
674
Journal Article
Recenzirano
At the core of the AGILE scientific instrument, designed to operate on a satellite, there is the Gamma Ray Imaging Detector (GRID) consisting of a Silicon Tracker (ST), a Cesium Iodide ...Mini-Calorimeter and an Anti-Coincidence system of plastic scintillator bars. The ST needs an on-ground calibration with a gamma - ray beam to validate the simulation used to calculate the energy response function and the effective area versus the energy and the direction of the gamma rays. A tagged gamma - ray beam line was designed at the Beam Test Facility (BTF) of the INFN Laboratori Nazionali of Frascati (LNF), based on an electron beam generating gamma - rays through bremsstrahlung in a position-sensitive target. The gamma - ray energy is deduced by difference with the post-bremsstrahlung electron energy 1,2. The electron energy is measured by a spectrometer consisting of a dipole magnet and an array of position sensitive silicon strip detectors, the Photon Tagging System (PTS). The use of the combined BTF-PTS system as tagged photon beam requires understanding the efficiency of gamma - ray tagging, the probability of fake tagging, the energy resolution and the relation of the PTS hit position versus the gamma - ray energy. This paper describes this study comparing data taken during the AGILE calibration occurred in 2005 with simulation.
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