The Agile Alert 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 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 Gamma-Ray Alert System, (2) a new algorithm for blind search identification of transients within a short processing time, (3) the AGILE procedure for gamma-ray transient 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 scientific-class 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 gamma-ray astrophysics.

34 pages, 9 figures, 5 tables

References in corpus (4)

• Discovery of Powerful Gamma-Ray Flares from the Crab Nebula
• Multifrequency monitoring of the blazar 0716+714 during the GASP-WEBT-AGILE campaign of 2007
• The AGILE monitoring of Cygnus X-3: transient gamma-ray emission and spectral constraints
• Calibration of AGILE-GRID with In-Flight Data and Monte Carlo Simulations

Cited by in corpus (13)

• AGILE Observations of the Gravitational Wave Event GW150914
• AGILE detection of a candidate gamma-ray precursor to the ICECUBE-160731 neutrino event
• The Second AGILE Catalog of Gamma-Ray Sources
• AGILE Observations of Two Repeating Fast Radio Bursts with Small Intrinsic Dispersion Measures
• AGILE Observations of the Gravitational Wave Source GW170104
• AGILE Observations of the Gravitational-wave Source GW170817: Constraining Gamma-Ray Emission from a NS-NS Coalescence
• The Bright $\gamma$-ray Flare of 3C 279 in June 2015: AGILE Detection and Multifrequency Follow-up Observations
• AGILE detection of gamma-ray sources coincident with cosmic neutrino events
• AGILE Observations of Fast Radio Bursts
• The AGILE Data Center and its Legacy
• AGILE, Fermi, Swift, and GASP-WEBT multi-wavelength observations of the high-redshift blazar 4C $+$71.07 in outburst
• The AGILE real-time analysis pipelines in the multi-messenger era
• AGILE results on relativistic outflows above 100 MeV