GRB 210926A

C. Zheng, S. L. Xiong, X. Y. Zhao, Y. Huang, C. Cai, Z. W. Guo, C. Y. Li,
S. Xiao, S. L. Xie, W. C. Xue, Q. B. Yi, Y. Zhao, Y. Q. Zhang, J. C. Liu,
X. Y. Song, X. B. Li, P. Wang, J. Wang,  Q. Luo, W. Chen, J. J. He, H. Wu,
X. L. Zhang, C. W. Wang, P. Zhang, W. X. Peng, R. Qiao, D. Y. Guo, X. Ma, 
S. J. Zheng, G. Y. Zhao, Y. Q. Du, J. Liang, Z. Zhang, L. M. Song, 
F. J. Lu, S. N. Zhang (IHEP), report on behalf of GECAM team:

During the commissioning phase, GECAM-B was triggered in-flight by a long
burst, GRB 210926A, at 2021-09-26T20:52:28.250 UTC (denoted as T0). 
This burst consists of two episodes, with the first one triggered by
Fermi/GBM (trigger ID: 654382283). Both episodes were triggered by
GECAM-B with the on-ground pipeline.

Its alert data was promptly downlinked to the ground through the short
message service of BeiDou Navigation Satellite System (BDS). The time
latency of the first BeiDou message relative to the trigger time is about
1 minute.

According to the BDS alert data, this burst mainly consists of multiple
pulses with duration of about 90 s. 

The GECAM light curve could be found here:
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/GRB_210926A.png

GECAM-B localized this burst to the following position (J2000): 
Ra: 351.51 deg 
Dec: -18.21 deg
Err: 2.86 deg (1-sigma, statistical only)
The current systematic error of location is estimated to be several degrees 
which could be minimized by the ongoing calibration.

The GECAM preliminary location could be found here: 
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/210926Aloc.png

This location is consistent with Fermi/GBM position within the error.

Please note that all GECAM results here are preliminary. The final analysis
will be published in journal papers or GECAM online catalog.

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor
(GECAM) mission consists of two small satellites (GECAM-A and GECAM-B) in
Low Earth Orbit (600 km, 29 deg), launched on Dec 10, 2020 (Beijing Time),
which was funded by the Chinese Academy of Sciences (CAS).

P. Sawant (IUCAA), G. Waratkar (IITB), V. Prasad (IUCAA), A. Vibhute
(IUCAA), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A. R. Rao
(IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat
CZTI collaboration: 

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al.,
2021, JApA, 42, 73) showed detection of a long GRB 210926A, which was
also detected by GECAM (C. Zheng et al., GCN 30886
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 ).

The source was clearly detected in the 20-200 keV energy range. The
light curve showed multiple peaks of emission with the strongest peak at
2021-09-26 20:52:27.5 UT. The measured peak count rate associated with
the burst is 250 (+51, -16) cts/s above the background in the combined
data of four quadrants, with a total of 3971 (+446, -463) cts. The local
mean background count rate was 480 (+3, -3) cts/s. Using cumulative
rates, we measure a T90 of 26 (+6, -5) s. 

It was also clearly detected in the CsI anticoincidence (Veto) detector
in the 100-500 keV energy range. The light curve showed multiple peaks
of emission with the strongest peak at 2021-09-26 20:52:30.9 UT. The
measured peak count rate is 262 (+73, -38) cts/s above the background in
the combined Veto data of four quadrants, with a total of 3091 (+703,
-866 cts. The local mean background count rate was 1512 (+5, -4) cts/s.
We measure a T90 of 25 (+14, -10) s from the cumulative Veto light
curve. 

CZTI GRB detections are reported regularly on the payload site at
http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led
consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC,
and PRL. The Indian Space Research Organisation funded, managed and
facilitated the project.