Systematic study of the simultaneous events detected by GECAM

¹ School of Physical Science and Technology, Southwest Jiaotong University, Chengdu Sichuan 611756, China
² State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquan Road, Beijing 100049, China
³ School of Science, Xizang University, Lhasa 850001, China
⁴ University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100049, China
⁵ Department of Nuclear Science and Technology, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an, China
⁶ School of Physics and Electronic Science, Guizhou Normal University, Guiyang 550001, China
⁷ Guizhou Provincial Key Laboratory of Radio Astronomy and Data Processing, Guizhou Normal University, Guiyang 550001, China
⁸ College of Physics and Hebei Key Laboratory of Photophysics Research and Application, Hebei Normal University, Shijiazhuang, Hebei 050024, China
⁹ Shijiazhuang Key Laboratory of Astronomy and Space Science, Hebei Normal University, Shijiazhuang, Hebei 050024, China
¹⁰ Institute of Astrophysics, Central China Normal University, Wuhan 430079, China
¹¹ School of Physics and Optoelectronics, Xiangtan University, Xiangtan 411105, China
¹² Key Laboratory of Lithium Battery New Energy Materials and Devices of Jiangxi Education Department, College of Intelligent Manufacturing and Materials & Chemical Engineering, Yichun University, Yichun, Jiangxi Province 336000, China
¹³ Computing Center, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquan Road, Beijing 100049, China
¹⁴ College of Electronic and Information Engineering, Tongji University, Shanghai 201804, China
¹⁵ School of Physics and Physical Engineering, Qufu Normal University, Qufu, Shandong 273165, China
¹⁶ School of Computer and Information, Dezhou University, Dezhou Shandong 253023, China

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Received: 3 December 2025
Accepted: 11 February 2026

Abstract

Gravitational-wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is a constellation of all-sky monitors in hard X-ray and gamma-ray bands, primarily observing high-energy transients such as gamma-ray bursts, soft gamma-ray repeaters, solar flares, and terrestrial gamma-ray flashes. As GECAM has the highest temporal resolution (0.1 μs) among instruments of its kind, it can identify the so-called simultaneous events (STEs) that deposit signals in multiple detectors nearly at the same time (with a time window of 0.3 μs). However, the properties and origin of STEs have not yet been explored. In particular, STEs may impact the observation of high-energy transients. In this work, we present the first systematic study of the properties of STEs detected by GECAM, including the morphology, energy deposition, and the dependence on the geomagnetic latitude. Based on their properties, we suggest that these STEs probably result from direct interactions between high-energy charged cosmic rays and the satellite. GEANT4 Monte Carlo simulations using the GECAM spacecraft mass model were carried out to provide additional support for this interpretation. Our result indicates that GECAM could potentially detect and characterize the high-energy cosmic rays through STEs, thereby extending its scientific capability.