TITLE:   GCN CIRCULAR
NUMBER:  35268
SUBJECT: GRB 231205A: joint location of multiple instruments by ETJASMIN 
DATE:    23/12/05 16:33:30 GMT
FROM:    yqzhang_cl@163.com

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

The short burst, GRB 231205A, has been detected by GECAM-B (Tan et al., GCN 35266), Fermi/GBM (Fermi/GBM team, GCN 35263) 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 realtime data of GECAM-B, INTEGRAL/SPI-ACS and Fermi/GBM, we did a low-latency joint location for this burst.

Firstly, we applied the Li-CCF method (Xiao et al., ApJ, 920, 43, 2021) to the realtime high temporal resolution (~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       209.519       59.889        40.961            1.272
--------------------------------------------------------------------------------------------------

Then, we combined this annulus location, the stand-alone locations provided by GECAM-B (Tan et al., GCN 35266) and Fermi/GBM (Fermi/GBM team, GCN 35263), as well as the Earth occultation of these instruments, and derived a refined location, which is much smaller than stand-alone ones. 

This refined location (~3 sigma region) could be approximately described by a polygon region,
whose center and corners are:

--------------------------------------
            Ra (deg)      Dec (deg)
Center      205.313	  19.155   
Corner1     215.859       19.155
Corner2     209.883       18.724
Corner3     202.148       18.871
Corner4     194.766       20.427
Corner5     205.313       19.524
--------------------------------------

For this refined location, the sky map and probability data could be found at:
Sky map: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/GRB231205A-jointLoc-skymap-v01.png
Data file: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/GRB231205A-jointLoc-healpix-v01.fits


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