THEAGILEALERT SYSTEM FOR GAMMA-RAY TRANSIENTS

Abstract

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 γ-ray transients of galactic and extragalactic origins. This work presents the AGILE innovative approach to fast γ-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 Gamma-Ray Alert System, (2) a new algorithm for blind search identification of transients within a short processing time, (3) the AGILE procedure for γ-ray -2transient alert management, and (4) the likelihood of ratio tests that are necessary to evaluate the post-trial statistical significance of the results. Special algorithms and an optimized sequence of tasks are necessary to reach our goal. Data are automatically analyzed at every orbital downlink by an alert pipeline operating on different timescales. As proper flux thresholds are exceeded, alerts are automatically generated and sent as SMS messages to cellular telephones, e-mails, and push notifications of an application for smartphones and tablets. These alerts are crosschecked with the results of two pipelines, and a manual analysis is performed. Being a small scientificclass mission, AGILE is characterized by optimization of both scientific analysis and ground-segment resources. The system is capable of generating alerts within two to three hours of a data downlink, an unprecedented reaction time in γ-ray astrophysics.

AGILE Detection of Gamma-Ray Sources Coincident with Cosmic Neutrino Events

“…upper limit on the gamma-ray emission above 100 MeV over an interval of 1 week just before T 0 . Similar cases of AGILE sources, both transients and steady, not confirmed by FERMI-LAT have been detected in the past (Pittori et al 2009;Verrecchia et al 2013;Bulgarelli et al 2018). Several reasons can explain these discrepancies: source variability; different spectral response of the instruments; source visibility/exposure due to the different observing modes; event classification algorithms; background model (especially important for sources near the Galactic plane).…”

The AGILE data center and its legacy

“…The AGILE-GRID ground segment alert system is distributed among ADC and the AGILE Team Institutes and it combines the ADC quick-look with the AGILE Science Alert System developed by the AGILE Team [2]. GRID Alerts are sent via email (and sms) both on a contact-by-contact basis and on a daily timescale.…”

AGILE: ten years after

“…The very fast AGILE ground segment alert system [25,26] has been recently further optimized for the search of electromagnetic counterparts of gravitational waves, allowing the AGILE Team to perform a full data reduction and the preliminary Quick Look scientific analysis only 25/30 minutes after the telemetry download from the spacecraft.…”