We give an overview of the AGILE gamma-ray satellite scientific highlights. AGILE is an Italian Space Agency (ASI) mission devoted to observations in the 30 MeV - 50 GeV gamma-ray energy range, with simultaneous X-ray imaging in the 18-60 keV band. Launched in April 2007, the AGILE satellite has completed its tenth year of operations in orbit, and it is substantially contributing to improve our knowledge of the high-energy sky. Emission from cosmic sources at energies above 100 MeV is intrinsically non-thermal, and the study of the wide variety of observed Galactic and extragalactic gamma-ray sources provides a unique opportunity to test theories of particle acceleration and radiation processes in extreme conditions.
Context. Known TeV sources detected by major Cerenkov telescopes are investigated to identify possible MeV-GeV gamma-ray counterparts. Aims. A systematic study of the known sources in the web-based TeVCat Catalog has been performed to search for possible gamma-ray counterpart on the AGILE data collected during the first period of operations in observing pointing mode. Methods. For each TeV source, a search for a possible gamma-ray counterpart based on a multi-source Maximum Likelihood algorithm is performed on the AGILE data taken with the GRID instrument from July 2007 to October 2009. Result…
We present a study of the Angular Resolution of the AGILE gamma-ray imaging detector (GRID) that is operational in space since April 2007. The AGILE instrument is made of an array of 12 planes each equipped with a Tungsten converter and Silicon micros trip detectors and is sensitive in the energy range 50 MeV - 10 GeV. Among the space instruments devoted to gamma-ray astrophysics, AGILE uniquely exploits an analog readout system with dedicated electronics coupled with Silicon detectors. We show the results of Monte Carlo simulations carried out to reproduce the gamma-ray detection by the GRID,…
The AGILE satellite, in orbit since 2007, localized up to October 2009 about 1 Gamma Ray Burst (GRB) per month with the hard X-ray imager SuperAGILE (18 - 60 keV) (with a rate reduced by a factor 2-3 in spinning mode) and is detecting around 1 GRB per week with the non-imaging Mini-Calorimeter (MCAL, 0.35 - 100 MeV). Up to October 2011 the AGILE Gamma Ray Imaging Detector firmly detected four GRBs in the energy band between 20 MeV and few GeV. In this paper we review the status of the GRBs observation with AGILE and discuss the upper limits in the gamma-ray band of the non-detected events.
We report on a systematic search for hard X-ray and gamma-ray emission in coincidence with fast radio bursts (FRBs) observed by the AGILE satellite. We used 13 years of AGILE archival data searching for time coincidences between exposed FRBs and events detectable by the MCAL (0.4-100 MeV) and GRID (50 MeV-30 GeV) detectors at timescales ranging from milliseconds to days/weeks. The current AGILE sky coverage allowed us to extend the search for high-energy emission preceding and following the FRB occurrence. We considered all FRBs sources currently included in catalogues, and identified a sub-sa…
AGILE pointed observations performed from July 9, 2007 to October 30, 2009 cover a very large time interval, with a γ-ray dataset useful to perform studies of medium to high brightness galactic sources in the 30 MeV -- 50 GeV energy range. We present a study of the 1AGL galactic sources in the E > 100 MeV band, over the complete Agile pointed Observation Blocks (OBs) archive. The first AGILE Gamma-Ray Imaging Detector (GRID) catalog included a sample of 47 sources (1AGL; Pittori et al. 2009), detected with a conservative analysis over the first year of operations dataset. In the analysis here …
We focus on two repeating fast radio bursts (FRBs) recently detected by the CHIME/FRB experiment in 2018--2019 (Source 1: 180916.J0158+65, and Source 2: 181030.J1054+73). These sources have low excess dispersion measures (DMs) ($ < 100 \rm \, pc \, cm^{-3}$ and $ < 20 \rm \, pc \, cm^{-3}$, respectively), implying relatively small maximal distances. They were repeatedly observed by AGILE in the MeV--GeV energy range. We do not detect prompt emission simultaneously with these repeating events. This search is particularly significant for the submillisecond and millisecond integrations obtainable…
We will review the crucial AGILE gamma-ray SNR observations focusing on the evidence of hadronic cosmic-ray acceleration that has been obtained so far. We discuss data on SNR IC443, W28 and W44. We show that in all cases a consistent model of hadronic acceleration and interaction with gaseous surroundings can be used to successfully explain the quite complex morphology and spectral characteristics of the sources. AGILE, with its crucially important sensitivity near 100 MeV, is equipped to prove the existence of pi-zero emission.
We present the results of 2.5 years AGILE observations of PSR B1509-58. The modulation significance of the light-curve above 30 MeV is at a sigma confidence level and the light-curve is similar to those found earlier up to 30 MeV by \comp: 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 pulsed flux is well described by a power-law (photon index alpha=1.87 +/-0.09) with a remarkable cutoff at E_c=81+/- 20 MeV, representing the softest spectrum observed among gamma-ray …
AGILE (Astrorivelatore Gamma a Immagini LEggero) is an Italian Space Agency (ASI) mission launched on April 23rd, 2007. The AGILE-GRID instrument onboard of the AGILE satellite is devoted to gamma-ray astrophysics in the 30 MeV - 50 GeV energy range. This paper presents the results of a systematic study performed on the first three years of AGILE-GRID data to search for GeV and sub-GeV counterparts (or derive flux upper limits) of sources detected at very high-energy by TeV experiments. Many of the TeV sources are still unidentified and deep observations at lower energies are needed to identif…
We present the results of new AGILE observations of PSR B1509-58 performed over a period of $\sim$2.5 years following the detection obtained with preliminary data. The modulation significance of the lightcurve above 30 MeV is at a 5$σ$ confidence level and the lightcurve is similar to those found earlier up to 30 MeV by COMPTEL: a broad asymmetric first peak reaching its maximum $0.39 \pm 0.02$ cycles after the radio peak plus a second peak at $0.94 \pm 0.03$. The $γ$-ray spectral energy distribution of pulsed flux is well described by a power-law (photon index $α=1.87\pm0.09$) with a remarkab…
Strong gamma-ray flares from the Crab Nebula have been recently discovered by AGILE and confirmed by Fermi-LAT. We study here the spectral evolution in the gamma-ray energy range above 50 MeV of the September 2010 flare that was simultaneously detected by AGILE and Fermi-LAT. We revisit the AGILE spectral data, and present an emission model based on rapid (within 1 day) acceleration followed by synchrotron cooling. We show that this model successfully explains both the published AGILE and Fermi-LAT spectral data showing a rapid rise and a decay within 2-3 days. Our analysis constrains the acce…
We present a study on the gamma-ray emission detected by the AGILE-GRID from the region of the SNR G78.2+2.1 (Gamma Cygni). In order to investigate the possible presence of gamma rays associated with the SNR below 1 GeV, it is necessary to analyze the gamma-ray radiation underlying the strong emission from the pulsar PSR J2021+4026, which totally dominates the field. An "off-pulse" analysis has been carried out, by considering only the emission related to the pulsar off-pulse phase of the AGILE-GRID light curve. We found that the resulting off-pulsed emission in the region of the SNR - detecte…
We present the results of 2.5 years of AGILE observations of PSR B1509-58 and of the same interval of Fermi observations. The modulation significance of AGILE light curve above 30 MeV is at a 5 sigma confidence level and the light curve shows a broad asymmetric first peak reaching its maximum $0.39 \pm 0.02$ cycles after the radio peak plus a second peak at$0.94 \pm 0.03$. The gamma-ray spectral energy distribution of pulsed flux is well described by a power-law (photon index $α=1.87\pm0.09$) with a remarkable cutoff at below 100 MeV, representing the softest spectrum observed among gamma-ray …
We present the results of multi-year gamma-ray observations by the AGILE satellite of the black hole binary system Cygnus X-1. In a previous investigation we focused on gamma-ray observations of Cygnus X-1 in the hard state during the period mid-2007/2009. Here we present the results of the gamma-ray monitoring of Cygnus X-1 during the period 2010/mid-2012 carried out for which includes a remarkably prolonged `soft state' phase (June 2010 -- May 2011). Previous 1--10 MeV observations of Cyg X-1 in this state hinted at a possible existence of a non-thermal particle component with substantial mo…
Short gamma-ray bursts (GRBs), typically lasting less than 2 s, are a special class of GRBs of great interest. We report the detection by the AGILE satellite of the short GRB 090510 which shows two clearly distinct emission phases: a prompt phase lasting ~ 200 msec and a second phase lasting tens of seconds. The prompt phase is relatively intense in the 0.3-10 MeV range with a spectrum characterized by a large peak/cutoff energy near 3 MeV, in this phase, no significant high-energy gamma-ray emission is detected. At the end of the prompt phase, intense gamma-ray emission above 30 MeV is detect…
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 promi…
The polarimetry of gamma rays converting to an $e^+e^-$ pair would open a new window on the high-energy gamma-ray sky by, among other things, providing insight into the radiation mechanism in pulsars (curvature or synchrotron) or deciphering the composition of the gamma-ray emitting jets in blazars (leptonic or lepto-hadronic). The performance of polarimeters based on homogeneous active targets (gas detectors (MeV, HARPO) or emulsions (GeV, GRAINE) has been studied both with simulation and by the analysis of data collected with telescope prototypes on linearly-polarised gamma-ray beams, and fo…
The high-fluence GRB131108A at redshift z=2.4, was detected by the Mini-Calorimeter (MCAL, 0.35-100 MeV) and the Gamma- Ray Imaging Detector (GRID, 30 MeV - 30 GeV) onboard the AGILE satellite. The burst emission consisted of a very bright initial peak,lasting 0.1 s, followed by a fainter emission detected for ~25 s with the MCAL and ~80 s with the GRID. The AGILE spectra, when compared with those reported at lower energies, indicate the presence of a prominent high-energy component with peak energy in the 10-20 MeV region. Contrary to other GRBs, this high-energy component is present also dur…
In recent years, a new generation of space missions offered great opportunities of discovery in high-energy astrophysics. In this article we focus on the scientific operations of the Gamma-Ray Imaging Detector (GRID) onboard the AGILE space mission. The AGILE-GRID, sensitive in the energy range of 30 MeV-30 GeV, has detected many gamma-ray transients of galactic and extragalactic origins. This work presents the AGILE innovative approach to fast gamma-ray transient detection, which is a challenging task and a crucial part of the AGILE scientific program. The goals are to describe: (1) the AGILE…
The AGILE satellite, operating since mid 2007 and primarily devoted to high-energy astrophysics, is one of the only three currently operating space instruments capable of detecting Terrestrial Gamma-Ray Flashes (TGFs), together with RHESSI and $Fermi$-GBM. Thanks to the AGILE Mini-Calorimeter instrument energy range extended up to 100MeV and its flexible trigger logic on sub-millisecond time scales, AGILE is detecting more than 10 TGFs/month, adding a wealth of observations which pose severe constrains on production models. The main AGILE discoveries in TGF science during two and a half years …
The Italian gamma-ray satellite AGILE has recently reported the detection of some variable high-energy sources likely of galactic origin. These sources do not have any obvious counterpart at lower energies. We propose that these sources are produced in proton-dominated jets of galactic microquasars. We develop a model for microquasar jets that takes into account both primary leptons and protons and all relevant radiative processes, including secondary particle emission and gamma-ray attenuation due to pair creation in the jet. We obtain spectral energy distributions that correspond to what is …
The AGILE satellite detected transient high-energy gamma-ray emission from the X-ray binary V404 Cygni, during the June 2015 outburst observed in radio, optical, X-ray and soft gamma-ray frequencies. The activity was observed by AGILE in the 50-400 MeV energy band, between 2015-06-24 UT 06:00:00 and 2015-06-26 UT 06:00:00 (MJD 57197.25 - 57199.25), with a detection significance of ${\sim}4.3σ$. The gamma-ray detection, consistent with a contemporaneous observation by Fermi-LAT, is correlated with a bright flare observed at radio and hard X-ray frequencies, and with a strong enhancement of the …
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 lightcurve above 30 MeV is at a 5$σ$ confidence level and the lightcurve 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 …
We report the AGILE observations of GRB 220101A, which took place at the beginning of 1st January 2022 and was recognized as one of the most energetic gamma-ray bursts (GRBs) ever detected since their discovery. The AGILE satellite acquired interesting data concerning the prompt phase of this burst, providing an overall temporal and spectral description of the event in a wide energy range, from tens of keV to tens of MeV. Dividing the prompt emission into three main intervals, we notice an interesting spectral evolution, featuring a notable hardening of the spectrum in the central part of the …
The LIGO/Virgo Collaboration (LVC) detected on 2017 January 4, a significant gravitational-wave (GW) event (now named GW170104). We report in this Letter the main results obtained from the analysis of hard X-ray and gamma-ray data of the AGILE mission that repeatedly observed the GW170104 localization region (LR). At the LVC detection time $T_0$ AGILE observed about 36% of the LR. The gamma-ray imaging detector did not reveal any significant emission in the energy range 50 MeV--30 GeV. Furthermore, no significant gamma-ray transients were detected in the LR that was repeatedly exposed over tim…
Aims. We present the second AGILE-GRID Catalog (2AGL) of γ-ray sources in the 100 MeV-10 GeV energy range. Methods. With respect to previous AGILE-GRID catalogs, the current 2AGL Catalog is based on the first 2.3 years of science data from the AGILE mission (the so called 'pointing mode') and incorporates more data and several analysis improvements, including better calibrations at the event reconstruction level, an updated model for the Galactic diffuse gamma-ray emission, a refined procedure for point-like source detection, and the inclusion of a search for extended γ-ray sources. Results. T…
Supernova remnants (SNRs) are believed to be the main sources of Galactic cosmic rays. Molecular clouds associated with SNRs can produce gamma-ray emission through the interaction of accelerated particles with the concentrated gas. The middle aged SNR W28, for its associated system of dense molecular clouds, provides an excellent opportunity to test this hypothesis. We present the AGILE/GRID observations of SNR W28, and compare them with observations at other wavelengths (TeV and 12CO J=1-->0 molecular line emission). The gamma-ray flux detected by AGILE from the dominant source associated wit…
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 t…
The AGILE gamma-ray satellite provides large sky exposure levels ($\geq 10^9$ cm$^2$ s per year on the Galactic Plane) with sensitivity peaking at $E\sim$100 MeV where the bulk of pulsar energy output is typically released. Its $\sim$1 $μ$s absolute time tagging capability makes it perfectly suited for the study of gamma-ray pulsars. AGILE collected a large number of gamma-ray photons from EGRET pulsars ($\geq$40,000 pulsed counts for Vela) in two years of observations unveiling new interesting features at sub-millisecond level in the pulsars' high-energy light-curves, gamma-ray emission from …
During the first two years of observation, AGILE detected several blazars at high significance: 3C 279, 3C 454.3, PKS 1510-089, S5 0716+714, 3C 273, W Comae, Mrk 421 and PKS 0537-441. We obtained long-term coverage of 3C 454.3, for a total of more than three months at energies above 100 MeV. 3C 273 was the first blazar detected simultaneously by the AGILE gamma-ray detector and by its hard X-ray monitor. S5 0716+714, an intermediate BL Lac object, exhibited a very fast and intense gamma-ray transient during an optical high-state phase, challenging the current theoretical models for energy extr…
The AGILE satellite detected several episodes of transient gamma-ray emission from Cygnus X-3. Cross-correlating the AGILE light curve with both X-ray and radio monitoring data, we found that the main events of gamma-ray activity were detected while the system was in soft spectral X-ray states, that coincide with local and often sharp minima of the hard X-ray flux, a few days before intense radio outbursts. This repetitive temporal coincidence between the gamma-ray transient emission and spectral state changes of the source turns out to be the spectral signature of high-energy activity from th…
We present the first catalog of high-confidence gamma-ray sources detected by the AGILE satellite during observations performed from July 9, 2007 to June 30, 2008. Catalogued sources are detected by merging all the available data over the entire time period. AGILE, launched in April 2007, is an ASI mission devoted to gamma-ray observations in the 30 MeV - 50 GeV energy range, with simultaneous X-ray imaging capability in the 18-60 keV band. This catalog is based on Gamma-Ray Imaging Detector (GRID) data for energies greater than 100 MeV. For the first AGILE catalog we adopted a conservative an…
On July 31st, 2016, the ICECUBE collaboration reported the detection of a high-energy starting event induced by an astrophysical neutrino. We report here about the search for a gamma-ray counterpart of the ICECUBE-160731 event made with the AGILE satellite. No detection was found spanning the time interval of +/- 1 ks around the neutrino event time T0 using the AGILE "burst search" system. Looking for a possible gamma-ray precursor in the results of the AGILE-GRID automatic Quick Look procedure over predefined 48-hours time-bins, we found an excess above 100 MeV between one and two days before…
The gamma-ray energy range from a few hundred keV to a few hundred MeV has remained largely unexplored, mainly due to the challenging nature of the measurements, since the pi- oneering, but limited, observations by COMPTEL on the Compton Gamma-Ray Observatory (1991-2000). This energy range is a transition region between thermal and nonthermal processes, and accurate measurements are critical for answering a broad range of astrophysical questions. We are developing a MIDEX-scale wide-aperture discovery mission, ComPair (Compton-Pair Production Space Telescope), to investigate the energy range f…
The two still unidentified MeV sources EGR J1122-5946 and AGL J2022+3622 are here tentatively associated with soft gamma-ray candidate counterparts detected through INTEGRAL/IBIS observations. On the basis of spatial proximity and/or similar transient behaviour, we propose the supergiant fast X-ray transient (SFXT) IGR J11215-5952 and the candidate SFXT IGR J20188+3647 as possible candidate counterparts of EGR J1122-5946 and AGL J2022+3622, respectively. Our findings possibly suggest that hard fast X-ray transients could represent a new class of galactic transient MeV/TeV emitters. Additional …
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 InterP…
Relativistically expanding sources of X-rays and gamma-rays cover an enormous range of (central) compactness and Lorentz factor. The underlying physics is discussed, with an emphasis on how the dominant dissipative mode and the emergent spectrum depend on these parameters. Photons advected outward from high optical depth are a potentially important source of Compton seeds. Their characteristic energy is bounded below by ~1 MeV in pair-loaded outflows of relatively low compactness, and remains near ~1 MeV at very high compactness and low matter loading. This is compared with the characteristic …
The flat-spectrum radio quasar 4C $+$71.07 is a high-redshift ($z=2.172$), $γ$-loud blazar whose optical emission is dominated by the thermal radiation from accretion disc. 4C $+$71.07 has been detected in outburst twice by the AGILE $γ$-ray satellite during the period end of October - mid November 2015, when it reached a $γ$-ray flux of the order of $F_{\rm E>100\,MeV} = (1.2 \pm 0.3)\times 10^{-6}$ photons cm$^{-2}$ s$^{-1}$ and $F_{\rm E>100\,MeV} = (3.1 \pm 0.6)\times 10^{-6}$ photons cm$^{-2}$ s$^{-1}$, respectively, allowing us to investigate the properties of the jet and of the emission…
We report the results of an extensive search in the AGILE data for a gamma-ray counterpart of the LIGO gravitational wave event GW150914. Currently in spinning mode, AGILE has the potential of covering with its gamma-ray instrument 80 % of the sky more than 100 times a day. It turns out that AGILE came within a minute from the event time of observing the accessible GW150914 localization region. Interestingly, the gamma-ray detector exposed about 65 % of this region during the 100 s time intervals centered at -100 s and +300 s from the event time. We determine a 2-sigma flux upper limit in the …
Recent observations by the Fermi-LAT showed that there are delayed arrivals of GeV photons relative to the onset of MeV photons in some GRBs. In order to avoid a large optical depth, the minimal value of the Lorentz factor has been estimated to be higher than 1000 in some brightest bursts. In this paper, we present a detailed calculation of the time delay between the MeV and GeV photons in the framework of the magnetic-dominated jet model. We find that the time delay strongly depends on the saturated bulk Lorentz factor of the jet. Inspired by this fact, we use this model to calculate the Lore…
The AGILE satellite discovered the transient source AGL J2241+4454 in 2010 which triggered the study of the associated field allowing for the discovery of the first Be/black hole binary system: MWC 656. This binary was suggested to be the counterpart of AGL J2241+4454, but this is still not a firm association. In this work we explore the archival AGILE and Fermi/LAT data in order to find more transient events originating in the field of AGL J2241+4454 and address the possibility to link them to the accretion/ejection processes of MWC 656. We found a total of 9 other transient events with AGILE…
We report the AGILE gamma-ray observations and the results of the multiwavelength campaigns on seven flaring blazars detected by the mission: During two multiwavelength campaigns, we observed gamma-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 gamma-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 10E-6 photons/cm2/s…
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 γ-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…
Persistent activity of magnetars is associated with electric discharge that continually injects relativistic particles into the magnetosphere. Large active magnetic loops around magnetars must be filled with outflowing particles that interact with radiation via resonant scattering and spawn electron-positron pairs. The outflow energy is processed into copious e+- until the plasma enters outer parts of the loop where the magnetic field is reduced below 10^13 G. In the outer zone, photons scattered by the outflow do not convert to e+- pairs and the outflow radiates its energy away. The escaping …
In the last few years Fermi and AGILE observations have indicated the existence of a possible population of transient MeV-GeV sources located on the Galactic plane and characterized by fast flares lasting only a very few days. Notably, no blazar-like counterparts are known within their error boxes so they could represent a completely new class of Galactic transient high energy emitters. The task of identifying their counterparts at lower energies remains very challenging. Despite this difficulty, INTEGRAL observations have provided intriguing hints that reliable candidate counterparts for thes…
Pulsars are known to power winds of relativistic particles that can produce bright nebulae by interacting with the surrounding medium. These pulsar wind nebulae (PWNe) are observed in the radio, optical, x-rays and, in some cases, also at TeV energies, but the lack of information in the gamma-ray band prevents from 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 …
We report the detection by the AGILE satellite of a rapid gamma-ray flare from the powerful gamma-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 gamma-ray flaring episode triggered three ToO observations by the Swift satellite in three consecutive days, starting from 20 March 2008. In the period 1-16 March 2008, AGILE detected gamma-ray emission from PKS 1510…
We argue that small pitch angle synchrotron emission provides an important dissipation mechanism which has to be taken into account in the models of formation of relativistic magnetized gamma-ray burst (GRB) outflows from the newborn black holes and/or magnetars. We show that if the GRB outflow is proton loaded, spectral energy distribution of this emission is expected to sharply peak in 0.1-1~MeV energy band. If the small pitch angle synchrotron emission efficiently cools relativistic particles of the outflow, its spectrum below the peak energy is a powerlaw with spectral index alpha ~ -1, cl…
GRB 130821A was detected by Fermi-GBM/LAT, Konus-Wind, SPI-ACS/INTEGRAL, RHESSI and Mars Odyssey-HEND. Although the data of GRB 130821A are very limited, we show in this work that the high energy gamma-ray emission (i.e., above 100 MeV) alone imposes tight constraint on the density profile of the circum-burst medium as well as the initial Lorentz factor of the outflow. The temporal behavior of the high energy gamma-ray emission is consistent with the forward shock synchrotron radiation model and the circum-burst medium likely has a constant-density profile. The Lorentz factor is about a few hu…
High-energy phenomena in the cosmos, and in particular processes leading to the emission of gamma- rays in the energy range 10 MeV - 100 GeV, play a very special role in the understanding of our Universe. This energy range is indeed associated with non-thermal phenomena and challenging particle acceleration processes. The technology involved in detecting gamma-rays is challenging and drives our ability to develop improved instruments for a large variety of applications. GAMMA-LIGHT is a Small Mission which aims at an unprecedented advance of our knowledge in many sectors of astrophysical and E…
Cygnus X-1 is the archetypal black hole (BH) binary system in our Galaxy. We report the main results of an extensive search for transient gamma-ray emission from Cygnus X-1 carried out in the energy range 100 MeV - 3 GeV by the AGILE satellite, during the period 2007 July - 2009 October. The total exposure time is about 300 days, during which the source was in the "hard" X-ray spectral state. We divided the observing intervals in 2 or 4 week periods, and searched for transient and persistent emission. We report an episode of significant transient gamma-ray emission detected on 2009, October 16…
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 HI…
We present a variability study of a sample of bright gamma-ray (30 MeV -- 50 GeV) sources. This sample is an extension of the first AGILE catalogue of gamma-ray sources (1AGL), obtained using the complete set of AGILE observations in pointing mode performed during a 2.3 year period from July 9, 2007 until October 30, 2009. The dataset of AGILE pointed observations covers a long time interval and its gamma-ray data archive is useful for monitoring studies of medium-to-high brightness gamma-ray sources. In the analysis reported here, we used data obtained with an improved event filter that cover…
The middle-aged supernova remnant (SNR) W44 has recently attracted attention because of its relevance regarding the origin of Galactic cosmic-rays. The gamma-ray missions AGILE and Fermi have established, for the first time for a SNR, the spectral continuum below 200 MeV which can be attributed to neutral pion emission. Confirming the hadronic origin of the gamma-ray emission near 100 MeV is then of the greatest importance. Our paper is focused on a global re-assessment of all available data and models of particle acceleration in W44, with the goal of determining on a firm ground the hadronic …
Photons of energy larger than 100 MeV from long-GRBs arrive a few seconds after <10 MeV photons do. We show that this delay is a natural consequence of a magnetic dominated relativistic jet. The much slower acceleration of a magnetic jet with radius (compared with a hot baryonic outflow) results in high energy gamma-ray photons to be converted to electron-positron pairs out to a larger radius whereas lower energy gamma-rays of energy less than ~10 MeV can escape when the jet crosses the Thomson-photosphere. The resulting delay for the arrival of high energy photons is found to be similar to th…
We study the spectrum of high frequency radiation emerging from mildly dissipative photospheres of long-duration gamma-ray burst outflows. Building on the results of recent numerical investigations, we assume that electrons are heated impulsively to mildly relativistic energies by either shocks or magnetic dissipation at Thomson optical depths of several and subsequently cool by inverse Compton, scattering off the thermal photons of the photosphere. We show that even in the absence of magnetic field and non-thermal leptons, inverse Compton scattering produces power-law tails that extend from t…
We study the spectra of photospheric emission from highly relativistic gamma-ray burst outflows using a Monte Carlo (MC) code. We consider the Comptonization of photons with a fast cooled synchrotron spectrum in a relativistic jet with photon to electron number ratio $N_γ/N_e = 10^5$. For all our simulations, we use mono-energetic protons which interact with thermalised electrons through the Coulomb interaction. The photons, electrons and protons are cooled adiabatically as the jet expands outwards. We find that the initial energy distribution of the protons and electrons do not have any appre…
We report on the second AGILE multiwavelength campaign of the blazar 3C 454.3 during the first half of December 2007. This campaign involved AGILE, Spitzer, Swift,Suzaku,the WEBT consortium,the REM and MITSuME telescopes,offering a broad band coverage that allowed for a simultaneous sampling of the synchrotron and inverse Compton (IC) emissions.The 2-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,…
