TITLE:   GCN CIRCULAR
NUMBER:  31230
SUBJECT: GRB 211211A: redshift estimation and SPI-ACS/INTEGRAL detection
DATE:    21/12/14 17:35:39 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

P. Minaev (IKI), A. Pozanenko (IKI) report on behalf of GRB IKI FuN:

We analyzed GRB 211211A (D'Ai et al. GCN 31202; Mangan et al. GCN 31210; 
Tamura et al. GCN 31226) using publicly available data of GBM/Fermi and 
SPI-ACS/INTEGRAL. Using GBM/Fermi we estimate a duration in 7 - 850 keV 
energy band T_90 = 50.6 +/- 0.1 s, while the emission is seen at least 
up to 130 s after the trigger. We performed spectral analysis in time 
interval of (-0.5, 60) s, covering the main part of GRB activity. The 
best fit is obtained for (Band model + thermal component) with following 
parameters: E_p = 758 +/- 13 keV, alpha = -1.21 +/- 0.01, beta = -2.54 
+/- 0.03 and thermal spectral component with kT = 13.9 +/- 0.3 keV. The 
fluence of F = (5.47 +/- 0.01)E-4 erg/cm**2 is obtained in 10 - 1000 keV 
energy band. The  parameter E_p = 758 +/- 13 keV is higher than 
preliminary value presented by GBM team (Mangan et al., GCN 31210) due 
to inclusion of the thermal component in the fit.

Assuming a redshift of z = 0.076 (Malesani et al., GCN 31221) we 
estimated E_iso = (1.161 +/- 0.006)E52 erg in the 1 keV - 10 MeV energy 
band. The burst is placed very close but outside the 2 sigma correlation 
region at E_p,i - E_iso and T_90,i - EH diagrams [1,2], see the Figures in

http://grb.rssi.ru/GRB211211A/GRB211211A_Ep-Eiso-2.png
http://grb.rssi.ru/GRB211211A/GRB211211A_EHD.png

Using T_90,i - EH diagram we found minimal possible redshift value of z 
= 0.080, very close to the redshift of z = 0.076 (Malesani et al., GCN 
31221). Therefore, we consider GRB 211211A as not a significant outlier.

The burst was also detected by SPI-ACS/INTEGRAL. Its duration in the 
SPI-ACS energy band (> 80 keV) is T_90 = 30.0 +/- 0.2 s, while the 
emission is seen up to 70 s. Comparing fluences of long-duration GRBs 
simultaneously recorded by SPI-ACS and Fermi/GBM (Chelovekov et al., in 
preparation) we estimated the GRB 211211A fluence to be 5.5E-4 erg/cm**2 
in the 10-1000 keV energy band (the 95% confidence region 1.6-4 – 1.9E-3 
erg/cm**2, incl. systematics). GRB 211211A is one of the brightest GRBs 
of SPI-ACS/INTEGRAL sample in terms of peak flux (about 40000 cnts/50 
ms). The SPI-ACS light curve of GRB 211211A can be found in

http://grb.rssi.ru/GRB211211A/GRB211211A_SPI-ACS_lc-2.png

[1] - Minaev et al., MNRAS, 492, 1919, 2020
[2] - Minaev et al., Astronomy Letters, 46, 9, 573, 2020