GCN Circular 31230
Subject
GRB 211211A: redshift estimation and SPI-ACS/INTEGRAL detection
Date
2021-12-14T17:35:39Z (3 years ago)
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