VizieR Online Data Catalog: MeV-GeV counterparts of TeV sources (Rappoldi+, 2016)

The analysis described in this paper has been applied to a reference sample of TeV sources extracted from the online TeVCat catalog (http://tevcat.uchicago.edu/ (Wakely S., and Horan D.). This online catalog is continuously updated with new sources detected by TeV experiments, and for each source it provides many parameters such as coordinates, source type, flux, and estimated distance (when available). The analysis has been performed using the data collected by the main AGILE instrument, the Gamma-Ray Imaging Detector (GRID). (2 data files). <P /

AGILE Observations of the LIGO-Virgo Gravitational-wave Events of the GWTC-1 Catalog

We present a comprehensive review of AGILE follow-up observations of the Gravitational Wave (GW) events and the unconfirmed marginal triggers reported in the first LIGO-Virgo (LV) Gravitational Wave Transient Catalog (GWTC-1). For seven GW events and 13 LV triggers, the associated 90% credible region was partially or fully accessible to the AGILE satellite at the T 0; for the remaining events, the localization region was not accessible to AGILE due to passages into the South Atlantic Anomaly, or complete Earth occultations (as in the case of GW170817). A systematic search for associated transients, performed on different timescales and on different time intervals about each event, led to the detection of no gamma-ray counterparts. We report AGILE MCAL upper limit fluences in the 400 keV-100 MeV energy range, evaluated in a time window of T 0 ± 50 s around each event, as well as AGILE GRID upper limit (UL) fluxes in the 30 MeV-50 GeV energy range, evaluated in a time frame of T 0 ± 950 s around each event. All ULs are estimated at different integration times and are evaluated within the portions of GW credible region accessible to AGILE at the different times under consideration. We also discuss the possibility of AGILE MCAL to trigger and detect a weak soft-spectrum burst such as GRB 170817A

AGILE TGFS AND GLOBAL LIGHTNING ACTIVITY

[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

TGF DETECTION BY AGILE

We report the detection by the Astrorivelatore Gamma a Immagini Leggero (AGILE) satellite of terrestrial gamma ray flashes (TGFs) obtained with the minicalorimeter (MCAL) detector operating in the ..

The AGILE Mission

AGILE is an Italian Space Agency mission dedicated to observing the gamma-ray Universe. The AGILE's very innovative instrumentation for the first time combines a gamma-ray imager (sensitive in the energy range 30 MeV-50 GeV), a hard X-ray imager (sensitive in the range 18-60 keV), a calorimeter (sensitive in the range 350 keV-100 MeV), and an anticoincidence system. AGILE was successfully launched on 2007 April 23 from the Indian base of Sriharikota and was inserted in an equatorial orbit with very low particle background. Aims. AGILE provides crucial data for the study of active galactic nuclei, gamma-ray bursts, pulsars, unidentified gamma-ray sources, galactic compact objects, supernova remnants, TeV sources, and fundamental physics by microsecond timing. Methods. An optimal sky angular positioning (reaching 0.1 degrees in gamma- rays and 1-2 arcmin in hard X-rays) and very large fields of view (2.5 sr and 1 sr, respectively) are obtained by the use of Silicon detectors integrated in a very compact instrument. Results. AGILE surveyed the gamma- ray sky and detected many Galactic and extragalactic sources during the first months of observations. Particular emphasis is given to multifrequency observation programs of extragalactic and galactic objects. Conclusions. AGILE is a successful high-energy gamma-ray mission that reached its nominal scientific performance. The AGILE Cycle-1 pointing program started on 2007 December 1, and is open to the international community through a Guest Observer Program

An X-ray burst from a magnetar enlightening the mechanism of fast radio bursts

Fast radio bursts (FRBs) are millisecond radio pulses originating from powerful enigmatic sources at extragalactic distances. Neutron stars with large magnetic fields (magnetars) have been considered as the sources powering the FRBs, but the connection requires further substantiation. Here we report the detection by the AGILE satellite on 28 April 2020 of an X-ray burst in temporal coincidence with a bright FRB-like radio burst from the Galactic magnetar SGR 1935+2154. The burst observed in the hard X-ray band (18-60 keV) lasted about 0.5 s, it is spectrally cut off above 80 keV and implies an isotropically emitted energy of about 1040 erg. This event demonstrates that a magnetar can produce X-ray bursts in coincidence with FRB-like radio bursts. It also suggests that FRBs associated with magnetars can emit X-ray bursts. We discuss SGR 1935+2154 in the context of FRBs with low-intermediate radio energies in the range 1038-1040 erg. Magnetars with magnetic fields B ≈ 1015 G may power these FRBs, and new data on the search for X-ray emission from FRBs are presented. We constrain the bursting X-ray energy of the nearby FRB 180916 to be less than 1046 erg, smaller than that observed in giant flares from Galactic magnetars

The 2009 december gamma-ray flare of 3C 454.3: The multifrequency campaign

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

AGILE detection of a rapid γ-ray flare from the blazar PKS 1510-089 during the GASP-WEBT monitoring

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 1510-089 at a significance level of 6.2-sigma with an average flux over the entire period of (84 +/- 17) x 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-sigma, with an average flux (E > 100 MeV) of (134 +/- 29) x 10^{-8} photons cm^{-2} s^{-1} and a peak level of (281 +/- 68) x 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 of the flux was observed at millimetric frequencies. Moreover, in the X-ray band the Swift/XRT observations seem to show an harder-when-brighter behaviour of the source spectrum. The spectral energy distribution of mid-March 2008 is modelled with a homogeneous one-zone synchrotron self Compton emission plus contributions from inverse Compton scattering of external photons from both the accretion disc and the broad line region. Indeed, some features in the optical-UV spectrum seem to indicate the presence of Seyfert-like components, such as the little blue bump and the big blue bump

AGILE detection of extreme γ -ray activity from the blazar PKS 1510-089 during March 2009: Multifrequency analysis

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