A blind search for intraday gamma-ray transients with Fermi-LAT: Detections of GRB and solar emissions

Abstract

We present a search for intraday transient γ-ray signals using 15.4 yr of the Fermi Large Area Telescope data. The search is based on a recently developed variable-size sliding-time-window (VSSTW) analysis and is aimed at studying variable γ-ray emission from gamma-ray bursts (GRBs) and the Sun. We refined the algorithm for searches for transient sources in order to solve the search problem within a reasonable amount of CPU time. These refinements allowed us to increase the number of gamma-ray bursts, solar flares, and quiescent solar events detected with the VSSTW technique by several times compared to the previous VSSTW search. The current search revealed a new γ-ray signal recorded with Fermi-LAT on 2018 January 12. This signal is probably from a GRB and deserves an exploration of the existing archival multiwavelength observations in order to identify it in an unambiguous way. We also report a γ-ray signal from the solar flare on 2023 December 31 that occurred during the 25th solar cycle.