TITLE: GCN CIRCULAR NUMBER: 39261 SUBJECT: LIGO/Virgo/KAGRA S250206dm: Upper limits from GECAM Observations DATE: 25/02/10 03:19:49 GMT FROM: yqzhang_cl@163.com

Ce Cai (HEBNU), Shao-Lin Xiong, Yan-Qiu Zhang, Wen-Jun Tan, Chen-Wei Wang, Yue Wang and Jin-Peng Zhang (IHEP) report on behalf of the GECAM team:

At the event time 2025-02-06T21:25:30.439 (UTC) of S250206dm (GCN 39175; GCN 39178; GCN 39231), GECAM-C was observing normally and monitored 66.9% of the localization probability region of this GW event, while GECAM-A and GECAM-B detectors were turned off.

There was no GECAM-C in-flight trigger around the event time of S250206dm. The routine blind search of GECAM-C data also found no burst candidate. Thus, we implemented a targeted search [1] within +/-30 s around the event time, and identified no candidate above 3 sigma.

Considering three typical GRB spectral models (i.e. soft, normal and hard Band functions), three timescales and the center region of GW localization (RA= 38.21°, Dec = 53.47°), the 3 sigma upper limits of the GRB energy flux (10 keV-1000 keV, in units of 10^-7 erg/s/cm^2) are reported below:

Timescale (s) Soft Normal Hard 0.1 1.84 2.33 4.10 1 0.58 0.73 1.29 10 0.18 0.23 0.41

With the median luminosity distance of 373 Mpc from the GW detection (GCN 39231), we further calculate the following upper limits of the GRB intrinsic luminosity (1 keV-10 MeV, in units of 10^49 erg/s):

Timescale (s) Soft Normal Hard 0.1 0.46 0.55 3.39 1 0.14 0.17 1.06 10 0.05 0.05 0.33

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

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).

[1] C. Cai et al. MNRAS 508, 3910–3920 (2021) https://doi.org/10.1093/mnras/stab2760

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