# Gamma-ray Bursts: 50 Years and Counting!
## 7 The High-Energy (AGILE and Fermi) Era (2007-Ongoing)
### AGILE (2007-Ongoing)  
AGILE (\"Astro rivalore Gamma a Immagini LEggero\", Italian for \"Lightweight imaging gamma astro detector\") [111] is an Italian high-energy astrophysics mission launched on 23 April 2007 dedicated to the observation of the high-energy gamma-ray sky. With a weight of just \(\sim\)100 kg and the dimensions of a cube with sides of about 60 cm, AGILE is the lightest and most compact instrument for high-energy astrophysics flying today. AGILE combines, for the first time, a silicon-tungsten tracker gamma-ray imager (\"GRID\", sensitive in the 30 MeV-30 GeV range) [112] with a hard X-ray imager (\"SuperAGILE\", sensitive in the 18-60 keV energy range) [113] with a large FoV (\(\sim\)1-2.5 steradians) and optimal angular resolution. AGILE is also equipped with a non-imaging gamma-ray scintillation mini-calorimeter (MCAL) sensitive between 350 keV and 100 MeV and a plastic scintillator anticoincidence system. AGILE operated in \"pointing\" mode until April 2009 when, following the failure of the inertial pointing system, the satellite was placed in \"Sun Pointing Spinning\" (scanning) mode to continue operations despite the failure. Since then, AGILE has operated in this scanning mode, rotating at a speed of \(\sim\)1\({}^{\circ}\) s\({}^{-1}\) and thus sweeping approximately 70% of the sky every day. This operating mode was found to be optimal for studying the variability of celestial sources. Central to AGILE's success is its world's fastest gamma-ray alarm monitoring system. AGILE is, in fact, equipped with two independent pipelines for monitoring gamma-ray alarms that process data with different data-quality results in order to optimize the response time [114].  
Using data from the AGILE mini-calorimeter (MCAL), it was possible to publish two GRB catalogs, the first in 2013 [115] and the second, more recently, in 2022 [116]. The amount of data obtained made it possible to calculate the counts and flux upper limits pertaining to GRB high-energy emissions between 30 MeV and 3 GeV (the AGILE-GRID energy range), thereby imposing strong constraints on high-energy radiation originating from both the afterglow emission and synchrotron self-Compton emission within internal shocks [117].  
Two exemplary GRBs seen by AGILE were GRB080514B and GRB090510. The first, GRB080514B [118], was the first GeV-bright GRB observed after EGRET. This event also had an afterglow phase, the observation of which allowed a photometric redshift measurement (z\(\sim\)1.8). Remarkably, the high-energy tail of the spectrum of this GRB fell right on the continuation of the Band spectrum used at lower energies, extending it from 20 keV up to \(\sim\)50 MeV. GRB090510 was first localized by _[PERSON]_ and then detected both by AGILE [119] and by _[PERSON]_/LAT [120]. This nearby burst (estimated redshift z\(\sim\)0.903) was unprecedented, as it was the first time that a short GRB was observed simultaneously by three different instruments, managing to extend its spectrum up to more than 300 GeV. The light curve was also anomalous compared to those observed up to that point for short GRBs, as it presented a delayed emission at high energies compared to the prompt phase and a substantial spectral evolution. This temporal behavior and the evolution of the power-law spectrum challenged the models based on synchrotron emission/synchrotron self-Compton in external shocks and on the hadronic models [121].  
More recently, AGILE has had huge success in the application of modern machine-learning techniques for the identification of GRB signals in data from both the gamma-ray imaging detector (GRID) [122] and the anticoincidence system (ACS) [123], leading to the identification of 72 GRB signals with significance \(\geq\)3\(\sigma\), 15 of which are not present in the second MCAL GRB catalog, as they were not identified before when using traditional methods for the data analysis.