GRB 231206A

Jia-Cong Liu , Shao-Lin Xiong report on behalf of the GECAM team:

GECAM-B was triggered in-flight by a short burst, GRB 231206A, at 2023-12-06T02:37:43.250 UTC (T0), which was also observed by INTEGRAL/SPI-ACS . 

According to the realtime alert data, the GECAM-B light curve shows a peak with a total duration of ~0.5 sec (15-1050 keV). 

The time-averaged spectrum of GECAM-B realtime data from about T0 to T0+0.1 s could be
adequately fit by a cut-off power-law with a fluence about 6.04E-6 erg/cm^2 in 20-1000 keV. 

Using the automatic in-flight localization pipeline with the realtime alert data, 
GECAM-B localized this burst to the following position (J2000): 
RA: 313.15 deg 
DEC: -23.54 deg
Err: 8.0 deg (1-sigma, statistical only)
The systematic error of this location is estimated to be several degrees.

The GECAM light curve could be found here: 
http://twiki.ihep.ac.cn/pub/GECAM/GRBList/GRB231206A_LC.png

We note that these results are based on realtime alert data and thus very preliminary. Refined analysis will be reported later.

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM) mission originally consists of two microsatellites (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).

Jia-Cong Liu , Shao-Lin Xiong report on behalf of the GECAM team:

There is a typo in our previous report (GCN 35283
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 ). Here we make the correction:
The time-averaged spectrum of GECAM-B realtime data from about T0-0.1 s to T0 could be
adequately fit by a cut-off power-law with an average flux of about 6.04E-6 erg/cm^2/s in 20-1000 keV. 

We are very sorry for any inconvenience.

Yanting Zhang, Shaolin Xiong, Yue Huang, Shuo Xiao, Xiaoyun Zhao, Ping Wang, 
report on behalf of the GECAM team:

The short burst, GRB 231206A, has been detected by GECAM-B (Liu et al., GCN 35283
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 ) and INTEGRAL/SPI-ACS. 
With the ETJASMIN pipeline (Energetic Transients joint analysis system for Multi-INstrument, Xiao et al.,
MNRAS, 514, 2397, 2022) and the data of GECAM-B and INTEGRAL/SPI-ACS, we did a joint location for this burst.

Firstly, we applied the Li-CCF method (Xiao et al., ApJ, 920, 43, 2021) to the high 
temporal resolution (~0.1 ms) light curve of GECAM-B and the low-latency public 50 ms 
light curve of INTEGRAL/SPI-ACS, and derived the triangulation location as the following annuli:

--------------------------------------------------------------------------------------------------
Annulus                 Ra (deg)      Dec (deg)     Radius (deg)      Radius-Error (deg, 3sigma)
GECAM-B + SPI-ACS       37.933        78.224        103.958           47.522
--------------------------------------------------------------------------------------------------

Then, we combined this triangulation location, the stand-alone location provided by GECAM-B 
(Liu et al., GCN 35283
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 ), as well as the Earth occultation of these instruments, 
and derived a refined location, which is much smaller than the stand-alone ones. 

The center (highest probability) of this refined location is:

--------------------------------------
            RA (deg)      Dec (deg)
Center      314.648	  -20.742   
--------------------------------------

The 1-simga region of this refined location is about 295 deg^2. 

The sky map and probability healpix data of this refined location could be found at:
Sky map: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/GRB231206-jointLoc-skymap-v01.png
Data file: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/GRB231206A-jointLoc-healpix-v01.fits

Note that a part of the location region is below the Earth limb of GECAM-B and thus excluded.

This location may be improved.

ETJASMIN is developed for joint observation of high energy transients by the GECAM team.
We acknowledge the public data of INTEGRAL/SPI-ACS.