Capabilities of the GAMMA-400 gamma-ray telescope to detect gamma-ray bursts from lateral directions

The currently developing space-based gamma-ray telescope GAMMA-400 will measure the gamma-ray and electron + positron fluxes using the main top-down aperture in the energy range from -20 MeV to several TeV in a highly elliptic orbit (without shading the telescope by the Earth and outside the radiation belts) continuously for a long time. The instrument will provide fundamentally new data on discrete gamma-ray sources, gamma-ray bursts (GRBs), sources and propagation of Galactic cosmic rays and signatures of dark matter due to its unique angular and energy resolutions in the wide energy range. The gamma-ray telescope consists of the anticoincidence system (AC), the converter-tracker (C), the time-of-flight system (S1 and S2), the position-sensitive and electromagnetic calorimeters (CC1 and CC2), scintillation detectors (S3 and S4) located above and behind the CC2 calorimeter and lateral detectors (LD) located around the CC2 calorimeter. In this paper, the capabilities of the GAMMA-400 gamma-ray telescope to measure fluxes of GRBs from lateral directions of CC2 are analyzed using Monte-Carlo simulations. The analysis is based on off-line second-level trigger construction using signals from S3, CC2, S4 and LD detectors. For checking the numerical algorithm the data from space-based GBM and LAT instruments of the Fermi experiment are used, namely, three long bursts: GRB 080916C, GRB 090902B, GRB 090926A and one short burst GRB 090510A. The obtained results allow us to conclude that from lateral directions the GAMMA-400 space-based gamma-ray telescope will reliably measure the spectra of bright GRBs in the energy range from similar to 10 to similar to 100 MeV with the on-axis effective area of about 0.13 m(2) for each of the four sides of CC2 and total field of view of about 6 sr. (c) 2021 COSPAR. Published by Elsevier B.V. All rights reserved.

Automated summary

The space-based gamma-ray telescope GAMMA-400 is designed to measure gamma-ray and electron + positron fluxes in a highly elliptic orbit continuously for a long time, providing new data on various astrophysical phenomena. The telescope consists of multiple systems for detecting and measuring gamma-ray sources, GRBs, and Galactic cosmic rays. Through Monte-Carlo simulations, it has been shown that GAMMA-400 can reliably measure the spectra of bright GRBs from lateral directions.