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GCN Circular 36106

EP240413a: Upper limits from GECAM-B Observation
2024-04-15T04:55:17Z (a month ago)
Yue Wang <>
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Yue Wang, Shao-Lin Xiong, Chen-wei Wang, Wen-long Zhang, Cheng-kui Li and Chao Zheng, report on behalf of the GECAM team:

GECAM-B was observing normally and covered the sky region of EP240413a (Lian et al., GCN 36086) at event time 2024-04-13T14:39:37 (UTC). The smallest incident angle of GECAM-B GRD detectors is about 21.3 deg for the WXT location (RA=228.794 deg, Dec=-18.8 deg).

There was no GECAM-B in-flight trigger around the event time of EP240413a. An automated, blind search for gamma-ray bursts of GECAM-B data found no burst candidates. The targeted search was run within -50 s ~ 250 s around event time, and also identified no counterpart candidates.

With the three typical GRB spectral models, integration time of 10 s 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):   7.5e-6 erg cm^-2
Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV):  6.6e-6 erg cm^-2
Band model 3 (alpha=0.0, beta=-1.5, Ep=1000 keV):   3.5e-6 erg cm^-2

All measurements above are made with all GRD detectors.

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).
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