GCN Circular 30452
Subject
GRB 210704A: classification as long GRB and redshift estimating
Date
2021-07-12T13:07:08Z (3 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@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
