TITLE: GCN CIRCULAR NUMBER: 34448 SUBJECT: GRB 230815B: GECAM-B and GECAM-C detection of a burst DATE: 23/08/16 14:16:52 GMT FROM: Yunfei Du at IHEP Shaolin Xiong, Yanqiu Zhang, Yue Huang report on behalf of the GECAM team: GECAM-B and GECAM-C were triggered in-flight by a long burst, GRB 230815B, at 2023-08-15T16:07:29.150 UTC and 2023-08-15T16:07:29.350 UTC, respetively, which was also observed by INTEGRAL/SPI-ACS and Konus-Wind. According to the realtime alert data of GECAM-B and GECAM-C, this burst mainly consists of a bright short pulse followed by a broad pulse with a total duration (T90) of about ~30 sec (15-1000 keV). Using the automatic on-ground localization pipeline with the realtime alert data, GECAM-B localized this burst to the following position (J2000): RA: 325.9 deg DEC: 13.2 deg Err: 5.1 deg (1-sigma, statistical only) The systematic error of this location is estimated to be several degrees. The time-averaged spectrum of GECAM-B realtime data shows that it could be adequately fit by a Band function with a fluence about 1.6E-5 erg/cm^2 in 20-1000 keV. We note that these results are based on realtime alert data and thus very preliminary. Refined analysis will be reported later. Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two microsatellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).