TITLE: GCN CIRCULAR NUMBER: 33406 SUBJECT: GRB 230307A: GECAM detection of an extremely bright burst DATE: 23/03/07 16:53:45 GMT FROM: Dong Xu at NAOC/CAS Shaolin Xiong, Chenwei Wang, Yue Huang, report on behalf of the GECAM team: GECAM-B was triggered in-flight by the extremely bright long burst at 2023-03-07T15:44:06.650 UTC (T0), which was also observed by Fermi/GBM (GCN 33405). The GECAM-B ground calculated location (J2000) is: R.A.: 28.03 [deg] Dec.: -81.51 [deg] Error: 1 [deg] (1-sigma, statistical only) The systematic error of this location is estimated to be ~2 degrees. This GECAM location is consistent with the Fermi/GBM one within error. The GECAM-B light curve shows a roughly FRED shape with a possible precursor, with a total duration of ~100 sec. The time-averaged spectrum analysis on the trigger alert data shows this burst has a fluence of about 1E-3 erg/cm2 in 20-1000 keV, which is notably high, and comparable to GRB 130427A. We caution that this analysis is very preliminary. Refined analysis will be reported later. Follow-up observations are encouraged.