TITLE:   GCN CIRCULAR
NUMBER:  31865
SUBJECT: GRB 220408A: redshift lower limit estimating
DATE:    22/04/09 15:51:10 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 analysed GRB 220408A detected by Fermi (Fermi GBM team, GCN 31847; 
Bissaldi et al., GCN 31856), by Swift (GCN Caputo et al., GCN 31848). 
Using publicly available data of GBM/Fermi we estimate the duration 
T_90 = 32.3 +/- 2.5 s in   (7 - 150) keV energy band. We performed 
spectral analysis in a time interval of (-1, 22) s since GBM trigger, 
the best fit is obtained for Band model with following parameters: E_p = 
36.5 +/- 5.0 keV, alpha = -0.50 +/- 0.35, beta = -2.5 +/- 0.2. The 
fluence of F = (2.0 +/- 0.2)E-6 erg/cm**2 is obtained in 10 - 1000 keV 
energy band. Using T_90,i - EH diagram [1,2] we can classify the burst 
as type II (long)  and find the minimal possible redshift value of z = 
0.03, which is excluding possible association with M51 galaxy and 
confirming larger distance of GRB 220408A  (Zhu et., GCN 31864).

The T_90,i - EH diagram can be found in 
http://grb.rssi.ru/GRB220408A/GRB220408A_EHD.png

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