TITLE:   GCN CIRCULAR
NUMBER:  44854
SUBJECT: GRB 260604C: GECAM-B observation
DATE:    26/06/07 12:57:24 GMT
FROM:    Xinghao Luo at IHEP <2952704891@qq.com>

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

GECAM-B was triggered in-flight by GRB 260604C, at 2026-06-04T20:18:44.600 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44822), and SVOM/ECLAIRs (D. Gotz et.al., GCN#44823).

According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 7 +/-0.5 s.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb260604C.png

In addition, the position of this burst, is determined by SVOM/ECLAIRs (RA=224.3461 , DEC=28.6558, with a 90% confidence level raiuds of 9.6 arcmins , D.Gotz et.al., GCN #43647). With this localization, the time-averaged spectrum from T0-0.5 to T0+7.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.41 +0.12/-0.09 and the cutoff energy, parameterized as Epeak, is 759 +342/-210 keV. The event fluence (10-1000keV) in this time interval is (2.88 +0.086/-0.11)E-05 erg/cm^2.

The 'Amati' relation diagram of GRB 260604C is shown at:
https://www.bursthub.cn//admin/static/gecambgrb260604C_amati.png

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).