[vsnet-grb-info 28349] GRB 210704A: classification as long GRB and redshift estimating

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30452
SUBJECT: GRB 210704A: classification as long GRB and redshift estimating
DATE:    21/07/12 13:07:08 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

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

We analyzed GRB 210704A (Ursi et al., GCN 30372; Berretta et al., GCN 
30375; Prasad et al., GCN 30378; D'Ai et al., GCN 30379; Malacaria 
etal., GCN 30380; Ridnaia et al., GCN 30388) using publicly available 
data of GBM/Fermi. The burst consists of several episodes of emission 
with duration of T_90 = 4.6 s, but the emission is visible up to 20 s 
after the trigger. Energy spectrum constructed in the time interval of 
(-0.2, 6.5) seconds relative to the GBM trigger time is best described 
by Bandmodel with relatively low E_peak = 294 keV corroborating with 
E_peak reported by GBM team (Malacaria et al., GCN 30380) and Konus-Wind 
(Ridnaia et al., GCN 30388).

Based on E_peak, Fluence in 1 keV — 10 MeV range (2.77e-5 erg cm^-2) and 
T_90 we draw a trajectory of the burst in EH - T_90 diagram varying the 
unknown source redshift 
(http://grb.rssi.ru/GRB210704A/GRB210704A_EH-T90_GBM.png , see [1-2] for 
details). The lower 2 sigma redshift limit of the source is z=0.11, 
which excludes the association of the GRB with the field galaxy at z = 
0.0817, but leaves a possibility of association with the field cluster 
at z = 0.203 (de Ugarte Postigo et al., GCN 30392). We also estimate 
E_iso = 8.2e50 erg at z = 0.11 and E_iso = 3.7e53 erg at z = 2.34 
(marginally suggested after GTC spectroscopy, de Ugarte Postigo et al., 
GCN 30392).
Based only on the trajectory at the EH - T_90 diagram we could suggest 
the collapsar origin (Type II) of GRB 210704A.

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