TITLE:   GCN CIRCULAR
NUMBER:  31566
SUBJECT: GRB 210919A: SPI-ACS/INTEGRAL observation and evaluation of Ep
DATE:    22/02/10 18:14:13 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 investigated SPI-ACS/INTEGRAL data of GRB 210919A detected by Swift 
(Tohuvavohu et al. GCN 30846).  GRB 210919A was not triggered by IBAS at 
INTEGRAL observatory. We find the burst in SPI-ACS/INTEGRAL data with a 
significance of 5 sigma and duration of 0.15 s. The total count fluence 
of the burst is 900 ± 185 counts, which corresponds to the fluence of 
2.4e-7 erg/cm^2 in 10-1000 keV energy band (the 95% confidence region is 
7.2e-8 -- 8.4e-7 erg/cm^2, incl. systematics). We do not find both 
precursor and extended emission components for the burst. Light curve of 
GRB 210919A can be found in

http://grb.rssi.ru/GRB210919A/GRB210919A_SPI-ACS_light_curve.png

Using spectral data of BAT/Swift (Barthelmy et al. GCN 30863) and 
possible redshift of z = 0.2411 (Rossi et al. GCN 31453) we estimated 
Eiso = (1.3 ± 0.3)e49 erg in 15-150 keV energy band. Although spectral 
parameter Ep was not constrained yet, we can estimate Ep using T90,i - 
EH diagram [1] by constructing a trajectory depending on the Ep,i 
parameter, where Ep,i is Ep in a rest frame. The most probable value is 
found to be Ep,i = 90 keV with 95% confidence region of (14 – 640) keV 
which is converted into observable Ep = 73 (11 --  516) keV. Since GRB 
210919A was detected by SPI-ACS with a nominal lower threshold of >80 
keV, Ep can be further limited to the energy range of 80 - 516 keV.

The T90,i - EH diagram can be found in

http://grb.rssi.ru/GRB210919A/GRB210919A_EHD.png

[1] - Minaev et al., MNRAS, 492, 1919, 2020