GECAM possible detection of quasi-periodic oscillations from GECAM 221124A/GRB 221124A

ATel #15777; Huang Y., Li X. B, Liu J. C., Zhao Y., Xiong S. L., Ge M. Y., Xiao S., Wang P., Li C. K., Chen Y. P., Li B., Zhang S. N., Lu F. J., Song L. M. report on behalf of the GECAM team
on 25 Nov 2022; 15:59 UT
Credential Certification: Yu-Peng Chen (chenyp@ihep.ac.cn)

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GECAM-B was triggered in-flight by a long burst at 2022-11-24T02:00:25.650 UTC (T0) and 2022-11-24T02:05:49.550 respectively, which was also observed by CALET (GCN #32981) and Konus-Wind.

The GECAM-B ground calculated location (J2000) is:
RA: 313.6 deg
Dec: 34.4 deg
Err: 3.9 (1-sigma, statistical only)
The systematic error of this location is estimated to be ~2 degrees.

The GECAM-B light curve shows a complicated structure with many bumps and peaks, with a total duration of ~470 sec from T0-70 s to T0+400 s. The time-averaged spectrum from this time interval can be fitted by a simple power law with the spectral index of gamma = -1.34+-0.04. The fluence (20-1000 keV) in this time interval is 1.1 E-5 erg/cm^2. The GECAM-B light curve is at "http://twiki.ihep.ac.cn/pub/GECAM/GRBList/GECAM_221124A.png".

We also performed a timing analysis of this burst. There appears to be quasi-periodic oscillations (QPO) at the period of about 3 seconds throughout the burst, with a significance of ~3 sigma. This analysis is based on the 10 ms GECAM-B light curve, from T0 + 300 s to T0 + 370 s. The power spectrum is normlizied to Leahy power. A peak power of ~60 is found at 0.32 Hz, with possible excess power at 0.41 Hz and 0.5 Hz.

We note that there has been no significant QPO signal detected during the main bursts of GRBs before, and the overall light curve of this burst looks atyptical for a GRB. We also note that this burst resembles the behavior of black holde X-ray binaries; the GECAM location coincides with the Galactic plane, thus the possiblity of a Galactic origin of this burst could be not excluded.

Since this burst seems not be a (typical) GRB, we tentatively name this source as GECAM 221124A. Follow-up observations are encouraged.

All analysis shown above is preliminary. Final results will be reported.

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission was funded by the Chinese Academy of Sciences (CAS). GECAM-A and GECAM-B microsatellites were launched on Dec 10, 2020, while GECAM-C was launched onboard SATech-01 satellite on July 27, 2022.