TITLE:   GCN CIRCULAR
NUMBER:  44964
SUBJECT: GRB 260616A: GECAM-B observation
DATE:    26/06/17 14:27:22 GMT
FROM:    guohx@ihep.ac.cn

Hao-Xuan Guo, Zheng-Hang Yu, Chen-Wei Wang, Chao Zheng, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:

GECAM-B was triggered in-flight by GRB 260616A, at 2026-06-16T03:21:40.040 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi/GBM team, GCN #44948), BALROG (T. Preis et al., GCN #44949), Fermi/LAT (S. Lopez et al., GCN #44960).

According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 117 +/-3 s.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb260616A.png

Using the localization reported by Fermi/LAT (R.A. = 93.53 deg, Dec = -32.07 deg, Err = 0.54 deg, GCN #44960) , the time-averaged spectrum from T0-77.5 s to T0+133.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.35 +0.08/-0.07 and the cutoff energy, parameterized as Epeak, is 679 +141/-121 keV. The event fluence (10-1000 keV) in this time interval is (2.02 +0.05/-0.06)E-04 erg/cm^2.

The 'Amati' relation diagram of GRB 260616A is shown at:
https://www.bursthub.cn//admin/static/gecambgrb260616A_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).