TITLE:   GCN CIRCULAR
NUMBER:  41495
SUBJECT: GRB 250812A: SVOM/ECLAIRs refined analysis
DATE:    25/08/22 14:39:39 GMT
FROM:    SVOM_group <svomgroup@bao.ac.cn>

L. Bouchet, J.-L. Atteia , O. Godet, M. Brunet (IRAP), L. P. Xin(NAOC), Z.M. Wang(BNU)
report on behalf of the SVOM/ECLAIRs team:

Using the ECLAIRs event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250812A (SVOM burst-id sb25081201), triggered by ECLAIRs onboard SVOM (Xin et al., GCN 41322).

The burst is faint and the 4-120 keV lightcurve is featureless.   

The time-averaged spectrum from T0-51 s to T0+3 s (T0 =  2025-08-12T02:46:03  UTC) in the energy range 4-120 keV is relatively well fitted by a powerlaw model with index -1.19+/-0.27. With this model, the fluence in 4-120 keV is about 7.5 (-1.9,+0.6) e-7 erg/cm^2.

All quoted errors are at the 68% confidence level.

The spectral index suggests that the Epeak value is above 120 keV.

The source redshift is found to be z=2.571 (Van Dalen et al., GCN 41347; de Ugarte Postigo et al., GCN 41348). At this redshift, GRB 250812A lies in the region of type II GRBs in the Amati plot for values of Epeak ≤ 200 keV. 

We note that the calibration of SVOM/ECLAIRs is ongoing thus these results are preliminary. 

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC.

The SVOM/ECLAIRs point of contact for this GCN circular is: Laurent Bouchet (laurent.bouchet@irap.omp.eu).