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

¹ GRAPPA, Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
e-mail: phdmitry@gmail.com
² Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
³ Academia Sinica Institute of Astronomy and Astrophysics, 11F of AS/NTU Astronomy-Mathematics Building, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan
⁴ Jodrell Bank Centre for Astrophysics, University of Manchester, Manchester M13 9PL, UK
e-mail: anthony.moraghan@manchester.ac.uk

Received: 17 January 2024
Accepted: 19 April 2024

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.