TITLE:   GCN CIRCULAR
NUMBER:  40922
SUBJECT: GRB 250702A: GECAM-B detection
DATE:    25/07/03 16:26:33 GMT
FROM:    Chenwei Wang at IHEP <cwwang@ihep.ac.cn>

Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:

GECAM-B was triggered in-flight by the long burst GRB 250702A at 2025-07-02T09:54:07.850 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#40881). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 24.0 +2.5/-4.5 s.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecamgrb250702A.png

This burst is incident from the back of satellite platform and the on-ground localization is subject by the Earth shadow of Fermi/GBM. With the localization from Fermi/GBM (RA=317.8, DEC=48.1, GCN#40881). The time-averaged spectrum from T0-2 s to T0+31 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.91 +0.20/-0.16 and the cutoff energy, parameterized as Epeak, is 417 +136/-93 keV. The event fluence (10-1000 keV) in this time interval is (3.85 +0..35/-0.41)E-05 erg/cm^2. 

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (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).