Cross-calibration of the energy response of the gamma-ray detectors on board GECAM-B

¹ State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
² University of Chinese Academy of Sciences, Beijing 100049, China
³ College of Physics and Hebei Key Laboratory of Photophysics Research and Application, Hebei Normal University, Shijiazhuang, Hebei 050024, China
⁴ Shijiazhuang Key Laboratory of Astronomy and Space Science, Hebei Normal University, Shijiazhuang, Hebei 050024, China
⁵ Guizhou Provincial Key Laboratory of Radio Astronomy and Data Processing, Guizhou Normal University, Guiyang 550001, PR China
⁶ School of Physics and Electronic Science, Guizhou Normal University, Guiyang 550001, PR China
⁷ School of Computer and Information, Dezhou University, Dezhou 253023, Shandong, China
⁸ School of Physics and Optoelectronics, Xiangtan University, Xiangtan 411105, Hunan, China
⁹ Institute of Astrophysics, Central China Normal University, Wuhan 430079, China

^★ Corresponding authors: xiongsl@ihep.ac.cn; qiaorui@ihep.ac.cn; anzh@ihep.ac.cn

Received: 21 April 2025
Accepted: 26 June 2025

Abstract

Context. The Gravitational-wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) was primarily designed to detect gamma-ray bursts (GRBs), particularly those associated with gravitational-wave events. The energy response of detectors plays a crucial role in detection performance and scientific data analysis.

Aims. We applied the cross-calibration methodology to calibrate and optimize the energy response of the gamma-ray detectors (GRDs) on board GECAM-B, using eight GRBs that were jointly observed by GECAM-B and other well-calibrated instruments. These GRBs enable the comprehensive calibration of all GRDs with different incident angles.

Methods. Cross-calibration using well-calibrated instruments is the most efficient way to verify the energy response of the detectors. The basic approach involves performing a joint spectral analysis and introducing a constant factor to quantify the difference in effective area between instruments. This calibration method has been widely used in the cross-calibration of many high-energy astrophysical instruments.

Results. We completed the cross-calibration of all 25 GRDs, covering two electronics readout channels and different incidence angles. The results of the joint spectral fitting demonstrate that GECAM-B exhibits good consistency with the well-calibrated Fermi/GBM instrument. Furthermore, the GECAM-B energy response matrix accurately reproduces the observational data without requiring any corrections or modifications.

Conclusions. Thanks to the broad energy band, accurate energy response, and anti-saturation design, GECAM-B can constrain spectral models and measure spectral parameters for not only typical bursts but also exceptionally bright events, including GRB 221009A and GRB 230307A, the two brightest GRBs ever detected.