GCN Circular 36058

Chen-Wei Wang, Shao-Lin Xiong, Jia-Cong Liu, Cheng-Kui Li and Chao Zheng, report on behalf of the GECAM team:

GECAM-B was observing normally and covered the sky region of EP240408a at event time 2024-04-08T17:56:30 (UTC). The smallest incident angle of GECAM-B GRD detectors is about 27.3 deg for the WXT location (RA=158.840 deg, Dec=-35.749 deg).

There was no GECAM-B in-flight trigger around the event time of EP240408a. An automated, blind search for gamma-ray bursts of GECAM-B data found no burst candidates. The targeted search was run within +/-150 s around event time, and also identified no counterpart candidates.

With the three typical GRB spectral models, integration time of 10 s (which is the duration of the EP240408a) and the WXT localization, the 3-sigma upper-limits of fluence (15 - 300 keV, incident energy) are reported below:

Band model 1 (alpha=-1.9, beta=-3.7, Ep=70 keV):   2.4e-6erg cm^-2
Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV):  3.5e-6 erg cm^-2
Band model 3 (alpha=0.0, beta=-1.5, Ep=1000 keV):   4.3e-6 erg cm^-2

All measurements above are made with the GRD detector which has the smallest incident angle to this source.

We note that these results are preliminary and refined analysis will be reported later.

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).