Search

Fast radio bursts (FRBs) are short (millisecond) radio pulses originating from enigmatic sources at extragalactic distances so far lacking a detection in other energy bands. Magnetized neutron stars (magnetars) have been considered as the sources powering the FRBs, but the connection is controversial because of differing energetics and the lack of radio and X-ray detections with similar characteristics in the two classes. We report here the detection by the AGILE satellite on April 28, 2020 of an X-ray burst in coincidence with the very bright radio burst from the Galactic magnetar SGR 1935+2154. The burst detected by AGILE in the hard X-ray band (18-60 keV) lasts about 0.5 seconds, it is spectrally cutoff above 80 keV, and implies an isotropically emitted energy ~ $10^{40}$ erg. This event is remarkable in many ways: it shows for the first time that a magnetar can produce X-ray bursts in coincidence with FRB-like radio bursts; it also suggests that FRBs associated with magnetars may emit X-ray bursts of both magnetospheric and radio-pulse types that may be discovered in nearby sources. Guided by this detection, we discuss SGR 1935+2154 in the context of FRBs, and especially focus on the class of repeating-FRBs. Based on energetics, magnetars with fields B ~ $10^{15}$ G may power the majority of repeating-FRBs. Nearby repeating-FRBs offer a unique occasion to consolidate the FRB-magnetar connection, and we present new data on the X-ray monitoring of nearby FRBs. Our detection enlightens and constrains the physical process leading to FRBs: contrary to previous expectations, high-brightness temperature radio emission coexists with spectrally-cutoff X-ray radiation., Submitted to Nature Astronomy, May 18, 2020

The origin of cosmic neutrinos is still largely unknown. Using data obtained by the gamma-ray imager on board of the AGILE satellite, we systematically searched for transient gamma-ray sources above 100 MeV that are temporally and spatially coincident with ten recent high-energy neutrino IceCube events. We find three AGILE candidate sources that can be considered possible counterparts to neutrino events. Detecting 3 gamma-ray/neutrino associations out of 10 IceCube events is shown to be unlikely due to a chance coincidence. One of the sources is related to the BL Lac source TXS 0506+056. For the other two AGILE gamma-ray sources there are no obvious known counterparts, and both Galactic and extragalactic origin should be considered., 21 pages, 15 figures, 4 tables. Accepted for publication in ApJ

In 2008 AGILE and Fermi detected gamma-ray flaring activity from the unidentified EGRET source 3EG J1236+0457, recently associated with a flat spectrum radio quasar GB6 J1239+0443 at z=1.762. The optical counterpart of the gamma-ray source underwent a flux enhancement of a factor 15-30 in 6 years, and of ~10 in six months. We interpret this flare-up in terms of a transition from an accretion-disk dominated emission to a synchrotron-jet dominated one. We analysed a Sloan Digital Sky Survey (SDSS) archival optical spectrum taken during a period of low radio and optical activity of the source. We estimated the mass of the central black hole using the width of the CIV emission line. In our work, we have also investigated SDSS archival optical photometric data and UV GALEX observations to estimate the thermal-disk emission contribution of GB6 J1239+0443. Our analysis of the gamma-ray data taken during the flaring episodes indicates a flat gamma-ray spectrum, with an extension of up to 15 GeV, with no statistically-relevant sign of absorption from the broad line region, suggesting that the blazar-zone is located beyond the broad line region. This result is confirmed by the modeling of the broad-band spectral energy distribution (well constrained by the available multiwavelength data) of the flaring activity periods and by the accretion disk luminosity and black hole mass estimated by us using archival data.

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 g-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 g rays. A tagged g-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 g-rays through bremsstrahlung in a position-sensitive target. The g-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 g-ray tagging, the probability of fake tagging, the energy resolution and Contents lists available at SciVerse ScienceDirect

The well known Crab Nebula is at the center of the SN1054 supernova remnant. It consists of a rotationally-powered pulsar interacting with a surrounding nebula through a relativistic particle wind. The emissions originating from the pulsar and nebula have been considered to be essentially stable. Here we report the detection of strong gamma-ray (100 MeV-10 GeV) flares observed by the AGILE satellite in September, 2010 and October, 2007. In both cases, the unpulsed flux increased by a factor of 3 compared to the non-flaring flux. The flare luminosity and short timescale favor an origin near the pulsar, and we discuss Chandra Observatory X-ray and HST optical follow-up observations of the nebula. Our observations challenge standard models of nebular emission and require power-law acceleration by shock-driven plasma wave turbulence within a ~1-day timescale., Comment: 23 pages (including Supporting On-line Material), 8 figures, 1 table. Version published in Science Express on January 6, 2011 (available at http://www.sciencemag.org/content/early/2011/01/05/science.1200083)

During its first 2 years of operation, the gamma-ray AGILE satellite almost completed a full study of the gamma-ray sky. This paper presents the preliminary results of the systematic study performed on the AGILE data to search for GeV counterparts and to derive flux upper limits of the TeV sources detected by various instruments (MAGIC, HESS, VERITAS, Cangaroo, MILAGRO, ARGO, … .).

Since its early phases of operation, the AGILE mission is successfully observing Gamma Ray Bursts (GRBs) in the hard X-ray band with the SuperAGILE imager and in the MeV range with the Mini-Calorimeter. Up to now, three firm GRB detections were obtained above 25 MeV and some bursts were detected with lower statistical confidence in the same energy band. When a GRB is localized, either by SuperAGILE or Swift/BAT or INTEGRAL/IBIS or Fermi/GBM or IPN, inside the field of view of the Gamma Ray Imager of AGILE, a detection is searched for in the gamma ray band or an upper limit is provided. A promising result of AGILE is the detection of very short gamma ray transients, a few ms in duration and possibly identified with Terrestrial Gamma-ray Flashes. In this paper we show the current status of the observation of Gamma Ray Bursts and Terrestrial Gamma-ray Flashes with AGILE., Four pages and four figures

During the month of 2009 December, the blazar 3C 454.3 became the brightest gamma-ray source in the sky, reaching a peak flux F 2000 × 10 -8 photons cm-2 s-1 for E > 100 MeV. Starting in 2009 November intensive multifrequency campaigns monitored the 3C 454 gamma-ray outburst. Here, we report on the results of a two-month campaign involving AGILE, INTEGRAL, Swift/XRT, Swift/BAT, and Rossi XTE for the high-energy observations and Swift/UVOT, KANATA, Goddard Robotic Telescope, and REM for the near-IR/optical/UV data. GASP/WEBT provided radio and additional optical data. We detected a long-term active emission phase lasting 1 month at all wavelengths: in the gamma-ray band, peak emission was reached on 2009 December 2-3. Remarkably, this gamma-ray super-flare was not accompanied by correspondingly intense emission in the optical/UV band that reached a level substantially lower than the previous observations in 2007-2008. The lack of strong simultaneous optical brightening during the super-flare and the determination of the broadband spectral evolution severely constrain the theoretical modeling. We find that the pre- and post-flare broadband behavior can be explained by a one-zone model involving synchrotron self-Compton plus external Compton emission from an accretion disk and a broad-line region. However, the spectra of the 2009 December 2-3 super-flare and of the secondary peak emission on 2009 December 9 cannot be satisfactorily modeled by a simple one-zone model. An additional particle component is most likely active during these states. © 2010. The American Astronomical Society. All rights reserved.

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., 7 pages, 2 figures. A&A accepted for publication

We present the AGILE gamma-ray observations of the field containing the puzzling gamma-ray source 3EG J1835+5918. This source is one of the most remarkable unidentified EGRET sources. An unprecedentedly long AGILE monitoring of this source yields important information on the positional error box, flux evolution, and spectrum. 3EG J1835+5918 has been in the AGILE field of view several times in 2007 and 2008 for a total observing time of 138 days from 2007 Sept 04 to 2008 June 30 encompassing several weeks of continuous coverage. With an exposure time approximately twice that of EGRET, AGILE confirms the existence of a prominent gamma-ray source (AGL J1836+5926) at a position consistent with that of EGRET, although with a remarkably lower average flux value for photon energies greater than 100 MeV. A 5-day bin temporal analysis of the whole data set of AGL J1836+5926 shows some evidence for variability of the gamma-ray flux. The source spectrum between 100 MeV and 1 GeV can be fitted with a power law with photon index in the range 1.6-1.7, fully consistent with the EGRET value. The faint X-ray source RX J1836.2+5925 that has been proposed as a possible counterpart of 3EG J1835+5918 is well within the AGILE error box. Future continuous monitoring (both by AGILE and GLAST) is needed to confirm the gamma-ray flux variability and to unveil the source origin, a subject that is currently being pursued through a multiwavelength search for counterparts., Comment: accepted for publication by Astron. & Astrophys, 4 pages, 2 figures, 2 tables

AGILE is an Italian Space Agency mission dedicated to the exploration of the gamma-ray Universe. The AGILE, very innovative instrument, combines for the first time a gamma-ray imager (sensitive in the range 30 MeV–50 GeV) and a hard X-ray imager (sensitive in the range 18–60 keV). An optimal angular resolution and very large fields of view are obtained by the use of state-of-the-art Silicon detectors integrated in a very compact instrument. AGILE was successfully launched on April 23, 2007 from the Indian base of Sriharikota and was inserted in an optimal low-particle background equatorial orbit. AGILE will provide crucial data for the study of Active Galactic Nuclei, Gamma-Ray Bursts, unidentified gamma-ray sources, galactic compact objects, supernova remnants, TeV sources, and fundamental physics by microsecond timing. 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 first blazar detection by the AGILE satellite. AGILE detected 3C 454.3 during a period of strongly enhanced optical emission in July 2007. AGILE observed the source with a dedicated repointing 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-50 GeV and 18-60 keV, respectively. Over the entire period, AGILE detected gamma-ray emission from 3C 454.3 at a significance level of 13.8-$\sigma$ with an average flux (E$>$100 MeV) of $(280 \pm 40) \times 10^{-8}$ photons cm$^{-2}$ s$^{-1}$. The gamma-ray flux appears to be variable towards the end of the observation. No emission was detected by Super-AGILE in the energy range 20-60 keV, with a 3-$\sigma$ upper limit of $2.3 \times 10^{-3}$ photons cm$^{-2}$ s$^{-1}$. The gamma-ray flux level of 3C 454.3 detected by AGILE is the highest ever detected for this quasar and among the most intense gamma-ray fluxes ever detected from Flat Spectrum Radio Quasars., Comment: Accepted by Astrophysical Journal Letters; 14 pages, 3 EPS Figures, 1 Table

GRB 070724B is the first Gamma Ray Burst localized by SuperAGILE, the hard X-ray monitor aboard the AGILE satellite. The coordinates of the event were published $\sim 19$ hours after the trigger. The Swift X-Ray Telescope pointed at the SuperAGILE location and detected the X-ray afterglow inside the SuperAGILE error circle. The AGILE gamma-ray Tracker and Minicalorimeter did not detect any significant gamma ray emission associated with GRB 070724B in the MeV and GeV range, neither prompt nor delayed. Searches of the optical afterglow were performed by the Swift UVOT and the Palomar automated 60-inch telescopes without any significant detection. Similarly the Very Large Array did not detect a radio afterglow. This is the first GRB event with a firm upper limit in the 100 MeV -- 30 GeV energy range, associated with an X-ray afterglow., Comment: 7 pages, 4 figures (of which 2 in color), contains online material. Accepted for publication by Astronomy & Astrophysics Letters

We present all the publicly available data, from optical/UV wavelengths (UVOT) to X-rays (XRT, BAT), obtained from Swift observations of the blazar PKS 2155-304, performed in response to the rapid alert sent out after the strong TeV activity (up to 17 Crab flux level at E > 200 GeV) at the end of July 2006. The X-ray flux increased by a factor of 5 in the 0.3-10 keV energy band and by a factor of 1.5 at optical/UV wavelengths, with roughly one day of delay. The comparison of the spectral energy distribution built with data quasi-simultaneous to the TeV detections shows an increase of the overall normalization with respect to archival data, but only a small shift of the frequency of the synchrotron peak that remains consistent with the values reported in past observations when the TeV activity was much weaker., 13 pages, 3 figures. ApJ Letters, accepted for publication

Context: AGILE is a gamma-ray astrophysics mission which has been in orbit since 23 April 2007 and continues to operate reliably. The gamma-ray detector, AGILE-GRID, has observed Galactic and extragalactic sources, many of which were collected in the first AGILE Catalog. Aims: We present the calibration of the AGILE-GRID using in-flight data and Monte Carlo simulations, producing Instrument Response Functions (IRFs) for the effective area A_eff), Energy Dispersion Probability (EDP), and Point Spread Function (PSF), each as a function of incident direction in instrument coordinates and energy. Methods: We performed Monte Carlo simulations at different gamma-ray energies and incident angles, including background rejection filters and Kalman filter-based gamma-ray reconstruction. Long integrations of in-flight observations of the Vela, Crab and Geminga sources in broad and narrow energy bands were used to validate and improve the accuracy of the instrument response functions. Results: The weighted average PSFs as a function of spectra correspond well to the data for all sources and energy bands. Conclusions: Changes in the interpolation of the PSF from Monte Carlo data and in the procedure for construction of the energy-weighted effective areas have improved the correspondence between predicted and observed fluxes and spectra of celestial calibration sources, reducing false positives and obviating the need for post-hoc energy-dependent scaling factors. The new IRFs have been publicly available from the Agile Science Data Centre since November 25, 2011, while the changes in the analysis software will be distributed in an upcoming release.

The Medium Energy Gamma-ray Astronomy (MEGA) telescope concept will soon be proposed as a MIDEX mission. This mission would enable a sensitive all-sky survey of the medium-energy gamma-ray sky (0.4–50 MeV) and bridge the huge sensitivity gap between the COMPTEL and OSSE experiments on the Compton Gamma Ray Observatory and the visionary Advanced Compton Telescope (ACT) mission. The scientific goals include compiling a much larger catalog of sources in this energy range, performing far deeper searches for supernovae, better measuring the galactic continuum and line emissions, and identifying the components of the cosmic diffuse gamma-ray emission. MEGA records and images gamma rays by completely tracking Compton and pair creation events in a stack of double-sided Si strip detectors surrounded by a pixellated CsI calorimeter. A prototype instrument has been developed and calibrated in the laboratory and at a gamma-ray beam facility. We present calibration results from the prototype and describe the proposed satellite mission.

著者人数：11名, Accepted: 2005-06-13, 資料番号: SA1000579000

We report on observations of the X-ray pulsar IGR J16320-4751 (a.k.a. AX J1631.9-4752) performed simultaneously with INTEGRAL and XMM-Newton. We refine the source position and identify the most likely infrared counterpart. Our simultaneous coverage allows us to confirm the presence of X-ray pulsations at ~1300 s, that we detect above 20 keV with INTEGRAL for the first time. The pulse fraction is consistent with being constant with energy, which is compatible with a model of polar accretion by a pulsar. We study the spectral properties of IGR J16320-4751 during two major periods occurring during the simultaneous coverage with both satellites, namely a flare and a non-flare period. We detect the presence of a narrow 6.4 keV iron line in both periods. The presence of such a feature is typical of supergiant wind accretors such as Vela X-1 or GX 301-2. We inspect the spectral variations with respect to the pulse phase during the non-flare period, and show that the pulse is solely due to variations of the X-ray flux emitted by the source and not to variations of the spectral parameters. Our results are therefore compatible with the source being a pulsar in a High Mass X-ray Binary. We detect a soft excess appearing in the spectra as a blackbody with a temperature of ~0.07 keV. We discuss the origin of the X-ray emission in IGR J16320-4751: while the hard X-rays are likely the result of Compton emission produced in the close vicinity of the pulsar, based on energy argument we suggest that the soft excess is likely the emission by a collisionally energised cloud in which the compact object is embedded., Accepted for publication in MNRAS, 10 pages, 8 figures

In this paper, we present the timing and spectral analysis of several observations of the Crab pulsar with INTEGRAL. All these observations, when summed together provide an high-statistics data set which can be used for accurate phase resolved spectroscopy of the pulsed emission over the energy range 3–350 keV. In particular, we present the light curves in several energy ranges and phase-resolved spectral analysis of the pulsed emission.

AGILE is an ASI space mission for high energy astrophysics in the gamma ray energy range 30MeV-50GeV, and in the X-ray band (10keV-40keV). AGILE is composed of three detecting systems: a Tungsten-Silicon Tracker, a Csl Mini-Calorimeter and a Silicon based X-ray detector (Super-Agile), plus an anticoincidence system for background rejection. The satellite will have good imaging performances (with angular resolution of a few arc-minutes in the gamma ray band), good timing resolution and a large field of view (about 1/5 of the sky). AGILE high energy detector is composed of a Silicon Tracker, a Mini-Calorimeter, the Anticoincidence and the Data Handling system The Mini-Calorimeter can also work as a stand-alone gamma ray detector in the energy range 250keV-250MeV, with no imaging capabilities, for the detection of transients and gamma ray burst events and for the evaluation of gamma ray background fluctuations. The Mini-Calorimeter is made of 30 independent elements of 37.5 × 2.3 × 1.5 cm stacked in two layers. Each detector scintillator signal is read out via two photodiodes glued on the small surfaces of the bar. The characteristics of the engineering model detectors has been deeply investigated and will be reported.

The Seyfert 1 galaxy MCG-6-30-15 (z≃0.008, L B ∼4×10 44 erg/s) was observed by XMM-Newton on 2000 June 11-12, for a total of 95 ks. The source shows high flux and spectral variability down to timescales of t ∼300 s. This work presents the results of the time-resolved spectral analysis of the brightest flare (a factor of 2 variation in ∼1000 s) which occurred during the observation. The analysis of such flare indicates: 1) a softening of the X-ray spectrum in phase with the flux, and 2) a soft-to-hard time lag of about ∼ 600 s. A strong and complex Fe-Kαemission feature is detected ∼ 3000 s after the flare. The same feature was not present before and during the flare. This may indicate that the Fe line was produced as a consequence of the flare. The present analysis allows the formulation of a different hypothesis for the physical mechanisms responsible for the X-ray emission.

The project of a new calorimeter module for Compton telescopes based on an array of silicon drift detectors (SDD) coupled to thallium activated cesium iodide (CsI(Tl)) scintillating crystals is presented. Because of their low output capacitance and the possibility to have the first amplifying stage directly integrated on chip, SDDs show better noise performances than traditional p-intrinsic-n (PIN) photodiodes. For this reason, SDDs coupled to scintillators show a higher energy resolution than similar systems based on PIN photodiodes. The detectors will be integrated in an array with read-out based on custom made ASIC’s built to match with the SDDs electrical properties. Shaped signals are digitally converted by a Digital Front-End Electronic Board which also takes care of ASICs handshaking. The system architecture is based on the PICsIT instrument on board the INTEGRAL satellite, at present fully operative. In this paper an overview of the instrument will be given and the status of the project will be reported.

AGILE is an ASI (Italian Space Agency) small space mission for high energy astrophysics in the gamma ray energy range 30MeV–50GeV, and in the X-ray band 10keV–40keV. AGILE is composed of three scientific detectors: a TungstenSilicon Tracker, a CsI Mini-Calorimeter and a Silicon based X-ray detector (Super-Agile), moreover an anticoincidence system carries out background rejection. The satellite’s payload will have good imaging performances (with angular resolution of a few arc-minutes in the gamma ray band), good timing resolution and a large field of view (about 1/5 of the sky). AGILE detection principle is based on the pair production process that arises from the interaction between high energy photons and the Tungsten layers of the Silicon Tracker. The Silicon Tracker is designed to determine the direction of the incoming radiation, while the Mini-Calorimeter evaluates the energy of the interacting photons. The Mini-Calorimeter can also work as a stand-alone gamma ray detector in the energy range 250keV–250MeV, with no imaging capabilities, for the detection of transients and gamma ray burst events (in cooperation with Super-Agile) and for the evaluation of gamma ray background fluctuations. In this paper a description of the Mini-Calorimeter is done.

PICsIT (Pixellated Imaging CaeSium Iodide Telescope) is the high energy detector of the IBIS telescope on-board the INTEGRAL satellite. PICsIT operates in the gamma-ray energy range between 175 keV and 10 MeV, with a typical energy resolution of 10% at 1 MeV, and an angular resolution of 12 arcmin within a \~100 square degree field of view, with the possibility to locate intense point sources in the MeV region at the few arcmin level. PICsIT is based upon a modular array of 4096 independent CsI(Tl) pixels, ~0.70 cm^2 in cross-section and 3 cm thick. In this work, the PICsIT on-board data handling and science operative modes are described. This work presents the in-flight performances in terms of background count spectra, sensitivity limit, and imaging capabilities., 8 pages, 4 figures. Accepted for publication on A&A, special issue on First Science with INTEGRAL

PICsIT is the high-energy detector layer of the IBIS Imager, composed of 4096 CsI(Tl) scintillator detectors 8:4 8:4 300 mm in size with PhotoDiode readout. The detector operates in the 175 keV 20.4 MeV range and its data generation modes make it possible to collect information from single events and multiple coincident events. PICsIT is surrounded by the active BGO VETO and is located about 3 metres below the coded mask. The entire PICsIT plane is physically divided into 8 modules and logically divided into smaller units. The overall performance of the plane is directly related to the behaviour of each individual pixel, including its electronics, the system interconnection logic, and interaction with the other sub-systems. Pixels and electronic parameters were monitored constantly during instrument assembly. The following report describes PICsIT design and contains a summary of on-ground test results.

The PICsIT instrument is the high-energy imaging detector of IBIS on board INTEGRAL and comprises 4096 individual scintillator elements each working in the energy range from about 175 keV to 10 MeV. Images of the sky are created using the coded aperture technique wherein each point in the detection plane contributes to the final image. For this reason the sensitivity at any point in the image is highly dependent on both the total background and its spatial and temporal uniformity. Herein we describe the PICsIT in-flight background, for the principal modes of operation, from the point of view of total count rate and spectrum, and discuss both the spatial and temporal stability. Based on observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation of Russia and the USA.

The ESA observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory) is dedicated to the fine spectroscopy (2.5 keV FWHM @ 1 MeV) and fine imaging (angular resolution: 12 arcmin FWHM) of celestial gamma-ray sources in the energy range 15 keV to 10 MeV with concurrent source monitoring in the X-ray ( keV) and optical (V -band, 550 nm) energy ranges. INTEGRAL carries two main gamma-ray instruments, the spectrometer SPI (Vedrenne et al. [CITE]) – optimized for the high-resolution gamma-ray line spectroscopy (20 keV–8 MeV), and the imager IBIS (Ubertini et al. [CITE]) – optimized for high-angular resolution imaging (15 keV–10 MeV). Two monitors, JEM-X (Lund et al. [CITE]) in the () keV X-ray band, and OMC (Mas-Hesse et al. [CITE]) in optical Johnson V -band complement the payload. The ground segment includes the Mission Operations Centre at ESOC, ESA and NASA ground stations, the Science Operations Centre at ESTEC and the Science Data Centre near Geneva. INTEGRAL was launched on 17 October 2002. The observing programme is well underway and sky exposure (until June 2003) reaches ~1800 ks in the Galactic plane. The prospects are excellent for the scientific community to observe the high energy sky using state-of-the-art gamma-ray imaging and spectroscopy. This paper presents a high-level overview of INTEGRAL.

The IBIS telescope is the high angular resolution gamma-ray imager on-board the INTEGRAL Observatory, successfully launched from Baikonur (Kazakhstan) the 17th of October 2002. This medium size ESA project, planned for a 2 year mission with possible extension to 5, is devoted to the observation of the gamma-ray sky in the energy range from 3 keV to 10 MeV (Winkler 2001). The IBIS imaging system is based on two independent solid state detector arrays optimised for low ( 15-1000 keV) and high ( 0.175-10.0 MeV) energies surrounded by an active VETO System. This high efficiency shield is essential to minimise the background induced by high energy particles in the highly excentric out of van Allen belt orbit. A Tungsten Coded Aperture Mask, 16 mm thick and ~1 squared meter in dimension is the imaging device. The IBIS telescope will serve the scientific community at large providing a unique combination of unprecedented high energy wide field imaging capability coupled with broad band spectroscopy and high resolution timing over the energy range from X to gamma rays. To date the IBIS telescope is working nominally in orbit since more than 9 month. Reglero Velasco, Victor, Victor.Reglero@uv.es

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., 12 pages, 4 figures, to be published in ApJ Letters

Position sensitive detectors coupled to coded masks are used for imaging in high energy astronomy. PICsIT is the γ-ray position sensitive detector of the IBIS telescope to be flown onboard the INTEGRAL satellite in 2001. PICsIT detector functionalities and scientific performances as a whole are described in details elsewhere in this Conference (Labanti et al. (Nucl. Instr. and Meth. A, this conference)). In this work, we present the aim, methodology, and results of the tests and calibrations performed on the first qualification lot of 136 PICsIT pixels carried out at SCIONIX laboratories in The Netherlands, in April 1999. Before being accepted for PICsIT, each detection unit has in fact to be fully characterized in terms of energy resolution and lower energy threshold. The principal aim of PICsIT pixel qualification campaign described in this work has been to measure the key parameters of each CsI(Tl)+photodiode detection unit: CsI(Tl) crystals light output, gain variation with temperature, energy resolution degradation due to scintillation light production and collection, inhomogeneity in the crystal, and the variation of these quantities after a thermo-vacuum stress treatment.

The CLAIRE collaboration is presently preparing the first astronomical observation of a gamma-ray lens. In June 2000, the instrument is to be flown on a stratospheric balloon by the French Space Agency CNES. CLAIRE features a Laue diffraction lens, a detector module with a 3×3 germanium array, and a balloon gondola stabilized to 15″ pointing accuracy. The instruments lens focuses gamma-ray photons from its 526 cm 2 area onto a small solid-state detector, with only 18 cm 3 equivalent volume for background noise. Hence, for the first time in gamma-ray astronomy, the statistics will be dominated by the signal. Besides its excellent sensitivity, the telescope has outstanding angular and spectral resolution. The primary objective for the first balloon flight of CLAIRE is to detect the Crab nebula and measure its extend at 170 keV with an angular resolution of about 1 arcmin. Scientific objectives for further flights include collapsed objects, SNRs, and broad class annihilators.

Preliminary results obtained from BeppoSAX observation of the starburst galaxy NGC253 are presented. X-ray emission from the object is clearly extended but most of the emission is concentrated on the optical nucleus. Preliminary analysis of the LECS and MECS data obtained using the central 4' region indicates that the continuum is well fitted by two thermal components at 0.9 keV and 7 keV. Fe K line at 6.7 keV is detected for the first time in this galaxy; the line has an equivalent width of ~300eV. The line energy and the shape of the 2-10 keV continuum strongly support thermal origin of the hard X-ray emission of NGC253. From the measurement of the Fe K line the abundances can be unambiguously constrained to ~0.25 the solar value. Other lines clearly detected are Si, S and Fe XVIII/Ne, in agreement with ASCA results., 4 pages, LateX, 2 figures (included). Uses espcrc2.sty (included) To appear in The Active X-ray Sky: Results from BeppoSAX and Rossi-XTE, Rome, Italy, 21-24 October, 1997. Eds.: L. Scarsi, H. Bradt, P. Giommi and F. Fiore

AGILE is a Scientific Mission dedicated to high‐energy astrophysics supported by ASI with scientific participation of INAF and INFN. The AGILE instrument is designed to simultaneously detect and image photons in the 30 MeV – 50 GeV and 15 – 45 keV energy bands with excellent imaging and timing capabilities, and a large field of view covering ∼ 1/5 of the entire sky at energies above 30 MeV. A CsI calorimeter is capable of GRB triggering in the energy band 0.3–50 MeV. The broadband detection of GRBs and the study of implications for particle acceleration and high energy emission are primary goals of th emission. AGILE can image GRBs with 2–3 arcminutes error boxes in the hard X‐ray range, and provide broadband photon‐by photon detection in the 15–45 keV, 03–50 MeV, and 30 MeV–30 GeV energy ranges. Microsecond on‐board photon tagging and a ∼ 100 microsecond gamma‐ray detection deadtime will be crucial for fast GRB timing. On‐board calculated GRB coordinates and energy fluxes will be quickly transmitted to the ground by an ORBCOMM transceiver. AGILE have recently (December 2005) completed its gamma‐ray calibration. It is now (January 2006) undergoing satellite integration and testing. The PLSV launch is planned in early 2006. AGILE is then foreseen to be fully operational during the summer of 2006. It will be the only mission entirely dedicated to high‐energy astrophysics above 30 MeV during the period mid‐2006/mid‐2007.

The analysis of an INTEGRAL AO2 observation of the error contours of the EGRET source 3EG J1621+8203 is presented. The only source found inside the error contours for energies between 20 and 30 keV at 5 sigma detection significance is the FR I radio galaxy NGC 6251. This supports the identification of NGC 6251 with 3EG J1621+8203. The observed flux is higher and softer than observed in the past, but consistent with a variable blazar-like spectral energy distribution., 5 pages, 2 figures. Accepted for publication on A&A Main Journal

Cadmium telluride is a semiconductor material which is now widely used in both spectroscopic and imaging applications. Among its properties, the most advantageous is its ability to operate at room-temperatures, so as to avoid the need for bulk cooling devices. Nevertheless, a quantitative evaluation of the temperature dependance of the detectors response is needed in order to establish a temperature range for safe operation. In this paper, some parameters are evaluated at temperatures ranging from -35/spl deg/C up to 40/spl deg/C with an energy source of 511 keV for a set of three spectroscopy grade CdTe detectors. The data obtained seem to indicate a significant temperature independence below O/spl deg/C, while at temperatures over 10/spl deg/C spectra degradations occur. >

Context. The detection and the characterization of the high energy emission component from individual gamma-ray bursts (GRBs) is one of the key science objectives of the currently operating gamma-ray satellite AGILE, launched in April 2007. In its first two years of operation AGILE detected three GRBs with photons of energy larger than 30 MeV. One more GRB was detected in AGILE third operation year, while operating in spinning mode. Aims. For the 64 other GRBs localized during the period July 2007 to October 2009 in the field of view of the AGILE Gamma-Ray Imaging Detector (GRID), but not detected by this instrument, we estimate the count and flux upper limits on the GRB high energy emission in the AGILE-GRID energy band (30 MeV-3 GeV). Methods. To calculate the count upper limits, we adopted a Bayesian approach. The flux upper limits are derived using several assumptions on the high-energy spectral behavior. For 28 GRBs with available prompt spectral information, a flux upper limit and the comparison with the expected flux estimated from spectral extrapolation of the Band spectrum to the 30 MeV-3 GeV band are provided. Moreover, upper limits on the flux under the assumption of an extra power law component dominating the 30 MeV-3 GeV band are calculated for all GRBs and considering four different values for the spectral photon index. Finally, we performed a likelihood upper limit on the possible delayed emission up to 1 h after the GRB. Results. The estimated flux upper limits range between 1 x 10(-4) and similar to 2 x 10(-2) photons cm(-2) s(-1) and generally lie above the flux estimated from the extrapolation of the prompt emission in the 30 MeV-3 GeV band. A notable case is GRB 080721, where the AGILE-GRID upper limit suggests a steeper spectral index or the presence of a cut-off in the high energy part of the Band prompt spectrum. The four GRBs detected by AGILE-GRID show high-energy (30 MeV-3 GeV) to low-energy (1 keV-10 MeV) fluence ratios similar to those estimated in this paper for the 64 GRBs without GRID detection, favoring the possibility that AGILE-GRID detected only high-fluence, hard GRBs. From the flux upper limits derived in this work we put some constraint on high-energy radiation from the afterglow emission and from synchrotron self Compton emission in internal shocks.

During its first 2 years of operation, the gamma-ray AGILE satellite accumulated an extensive dataset for the Galactic plane. The data have been monitored for transient sources and several gamma-ray sources were detected. Their variability and possible association were studied. In this talk we will focus on the results of extensive observations of the Carina Region during the time period 2007 July - 2009 January, for a total livetime of ~130 days. The region is extremely complex, hosting massive star formation, with the remarkable colliding wind binary Eta Carinae, massive star clusters and HII regions (e.g. NGC 3324, RCW49, Westerlund II) and a giant molecular cloud extending over 150 pc (between l=284.7 and l=289). The Carina Nebula itself is the largest and IR highest surface brightness nebula of the Southern emisphere. We monitored several gamma ray sources in the Carina Region. In particular we detect a gamma ray source (1AGL J1043-5931) consistent with the position of Eta Carinae and report a remarkable 2-days gamma-ray flaring episode from this source on 2008 Oct 11-13. If 1AGL J1043-5931 is associated with the Eta Car system, our data provides the long sought first detection above 100 MeV of a colliding wind binary., 5 pages, 5 figures, proceedings of RICAP 2009

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 the 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.

We present a prototype of an X- and γ-ray camera based on a semiconductor crystal of mercuric iodide (HgI 2 ) having a cross-sectional area of 10 × 10 mm 2 and a thickness of 0.5 mm. Two orthogonal sets of 20 charge-collecting μstrips are deposited on the two opposite surfaces of the detector giving a pixel size of 0.5 × 0.5 mm 2 . Using commercial hybrid preamplifiers several experimental tests have been performed in order to assess the performance of this device. Preliminary results on the spectroscopic capabilities together with an evaluation of the attainable spatial resolution are presented.

Cygnus X-3 (Cyg X-3) is a well-known microquasar producing variable emission at all wavelengths. Cyg X-3 is a prominent X-ray binary producing relativistic jets, and studying its high energy emission is crucial for the understanding of the fundamental acceleration processes in accreting compact objects. Aims. Our goal is to study extreme particle acceleration and {\gamma}-ray production above 100 MeV during special spectral states of Cyg X- 3 usually characterized by a low hard X-ray flux and enhanced soft X-ray states. We observed Cyg X-3 with the AGILE satellite in extended time intervals from 2009 Jun.-Jul., and 2009 Nov.-2010 Jul. We report here the results of the AGILE {\gamma}-ray monitoring of Cyg X-3 as well as the results from extensive multiwavelength campaigns involving radio (RATAN-600, AMI-LA and Mets\"{a}hovi Radio Observatories) and X-ray monitoring data (XTE and Swift). We detect a series of repeated {\gamma}-ray flaring activity from Cyg X-3 that correlate with the soft X-ray states and episodes of decreasing or non-detectable hard X-ray emission. Furthermore, we detect {\gamma}-ray enhanced emission that tends to be associated with radio flares greater than 1 Jy at 15 GHz, confirming a trend already detected in previous observations. The source remained active above 100 MeV for an extended period of time (almost 1.5 months in 2009 Jun.-Jul. and 1 month in 2010 May). We study in detail the short timescale {\gamma}-ray flares that occurred before or near the radio peaks. Our results confirm the transient nature of the extreme particle acceleration from the microquasar Cyg X-3. A series of repeated {\gamma}-ray flares shows correlations with radio and X-ray emission confirming a well established trend of emission. We compare our results with Fermi-LAT and MAGIC TeV observations of Cyg X-3., Comment: 16 pages, 8 figures, 7 tables; A&A (2011)

The multi-purpose INTEGRAL mission is continuously contributing to Gamma Ray Burst (GRB) science, thanks to the performances of its two main instruments, IBIS and SPI, operating in the hard X-ray/soft gamma-ray domain. We investigate the possibilities offered to the study of GRBs by PICsIT, the high-energy detector of the IBIS instrument. We searched for transient episodes in the PICsIT light curves archive from May 2006 to August 2009, using stringent criteria optimized for the detection of long events. In the time interval under examination PICsIT provides an energy coverage from 208 to 2600 keV, resolved in eight energy channels, combined with a fine time resolution of 16 ms. PICsIT successfully observes GRBs in the 260-2600 keV energy range with an incoming direction spread over half the sky for the brightest events. We compiled a list of 39 bursts, most of which are confirmed GRBs or simultaneous to triggers from other satellites/instruments. We produced light curves with a time sampling down to 0.25 s in three energy intervals for all events. Because an adequate response matrix is not yet available for the PICsIT burst sample, we obtained a calibration coefficient in three selected energy bands by comparing instrumental counts with physical fluences inferred from observations with different satellites. The good time resolution provided by the PICsIT data allows a spectral variability study of our sample through the hardness ratio., 20 pages, 48 figures. Accepted for publication in A&A

The observation of Gamma Ray Bursts (GRBs) in the gamma-ray band has been advanced by the AGILE and Fermi satellites after the era of the Compton Gamma-Ray Observatory. AGILE and Fermi are showing that the GeV-bright GRBs share a set of common features, particularly the high fluence from the keV up to the GeV energy bands, the high value of the minimum Lorentz factor, the presence of an extended emission of gamma-rays, often delayed with respect to lower energies, and finally the possible presence of multiple spectral components. GRB 100724B, localised in a joint effort by Fermi and the InterPlanetary Newtork, is the brightest burst detected in gamma-rays so far by AGILE. Characteristic features of GRB 100724B are the simultaneous emissions at MeV and GeV, without delayed onset nor time lag as shown by the analysis of the cross correlation function, and the significant spectral evolution in hard X-rays over the event duration. In this paper we show the analysis of the AGILE data of GRB 100724B and we discuss its features in the context of the bursts observed so far in gamma-rays and the recently proposed models., 8 pages, 5 figures. Accepted for publication by A&A. Final version after the correction by the language editor

[1] The AGILE satellite detects Terrestrial Gamma-ray Flashes (TGFs) in the 0.35–100 MeV energy range using its Mini-Calorimeter (MCAL) instrument with an average detection rate of 10 TGFs/month. Thanks to its Low Earth Orbit with only 2.5 degree of inclination, AGILE guarantees an unprecedented exposure above the equator, where both lightning activity and TGF detection peak. Here we report the comparison between the AGILE TGFs detected between March 2009 and February 2010 and full climatology lightning worldwide distribution based on satellite optical observations from LIS (Lightning Imaging Sensor) and OTD (Optical Transient Detector) instruments. This approach is complementary to the one-to-one TGF/lightning correlations by ground-based sferics measurements. Based on mono and bi-dimensional Kolmogorov-Smirnov tests, we show that the AGILE TGFs and time-averaged global lightning in the equatorial area are not drawn from the same distribution. However, we find significant regional differences in the degree of correlation as well as in the TGF/lightning ratio. In the case of south east Asia we find a 87% probability for the TGF and lightning being samples of the same distribution. This result supports the idea that the physical conditions at play in TGF generation can have strong geographical and climatological modulation. Based on the assumption that the observed range of TGF/flash ratio holds at all latitudes we can estimate a global rate of ≃ 220 ÷ 570 TGFs per day. The observed TGF/flash geographical modulation as well as the TGF global rate estimate are in agreement with previous observations.

We report the AGILE γ -ray observations and the results of the multiwavelength campaigns on seven flaring blazars detected by the mission: During two multiwavelength campaigns, we observed γ -ray activity from two Flat Spectrum Radio Quasars of the Virgo region, e.g. 3C 279 and 3C 273 (the latter being the first extragalactic source simultaneously observed with the γ -ray telescope and the hard X ray imager of the mission). Due to the large FOV of the AGILE/GRID instrument, we achieved an almost continuous coverage of the FSRQ 3C 454.3. The source showed flux above 10 −6 photons/cm 2 /s ( E > 100 MeV ) and showed day by day variability during all the AGILE observing periods. In the EGRET era, the source was found in high γ -ray activity only once. An other blazar, PKS 1510-089 was frequently found in high γ -ray activity. S5 0716+71, an intermediate BL Lac object, exhibited a very high γ -ray activity and fast γ -ray variability during a period of intense optical activity. We observed high γ -ray activity from W Comae, a BL Lac object, and Mrk 421, a high energy peaked BL Lac object. For this source, a multiwavelength campaign from optical to TeV has been performed.

The AGILE satellite, in orbit since 2007, is localizing about 0.5 GRBs per month with the hard X‐ray imager SuperAGILE (18–60 keV) and is detecting around 1 GRB per week with the non‐imaging Minicalorimeter (0.35–100 MeV). Up to now the AGILE Gamma Ray Imaging Detector firmly detected four GRBs in the energy band between 20 MeV and few GeV. In this presentation we review the status of the GRBs observation with AGILE, we discuss the upper limits in the gamma‐ray band of the non‐detected events and we show some interesting bursts, especially GRB 090618 (bright in soft and hard‐X rays, optical and radio but lacking GeV emission) and GRB 100724B (with a bright GeV emission simultaneous to hard‐X rays without delayed onset).

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., 13 pages, 7 figures, 3 tables. Accepted for publication in Astronomy and Astrophysics

The Imager proposed for the gamma-ray satellite project INTEGRAL is based on a multilayer two-dimensional array of CsI(TI) elements viewed by Si photodiodes. The total active area is ≈2500 cm2. The operative energy interval ranges from 0.05 to 10 MeV. A prototype version of this instrument, ready to be tested on a ballon-borne experiment, has been realized. In this article the expected performances of the instrument are presented, toghether with the first calibration results of the prototype.

The low energy balloon-borne gamma-ray telescope ZEBRA is capable of producing images of the sky with a resolution of 1° and a point source location accuracy of a few arcminutes. In order to fully exploit the sensitivity of this instrument, a platform stabilised in three axes to this precision has been developed, which however has an absolute pointing accuracy of 30′-1°. Therefore there is a need to have on board a system which will allow post facto reconstruction of the absolute pointing direction of the telescope as a function of time, for observations in both day- and night-time conditions. An independently steerable starsensor has been constructed, based on a CCD imaging system, for this purpose. The results obtained with this device during the first flight of the ZEBRA telescope in May 1989 from the NASA balloon base in Palestine, Texas are presented.

Identification of gamma-ray-emitting Galactic sources is a long-standing problem in astrophysics. One such source, 1AGL J2022+4032, coincident with the interior of the radio shell of the supernova remnant Gamma Cygni (SNR G78.2+2.1) in the Cygnus Region, has recently been identified by Fermi as a gamma-ray pulsar, LAT PSR J2021+4026. We present long-term observations of 1AGL J2022+4032 with the AGILE gamma-ray telescope, measuring its flux and light curve. We compare the light curve of 1AGL J2022+4032 with that of 1AGL J2021+3652 (PSR J2021+3651), showing that the flux variability of 1AGL J2022+4032 appears to be greater than the level predicted from statistical and systematic effects and producing detailed simulations to estimate the probability of the apparent observed variability. We evaluate the possibility that the gamma-ray emission may be due to the superposition of two or more point sources, some of which may be variable, considering a number of possible counterparts. We consider the possibility of a nearby X-ray quiet microquasar contributing to the flux of 1AGL J2022+4032 to be more likely than the hypotheses of a background blazar or intrinsic gamma-ray variabilty of LAT PSR J2021+4026., 7 pages, 7 figures, accepted for publication in Astronomy & Astrophysics