TITLE: GCN CIRCULAR NUMBER: 32105 SUBJECT: GRB 220521A: classification and detection by SPI-ACS/INTEGRAL DATE: 22/05/24 14:55:52 GMT FROM: Alexei Pozanenko at IKI, Moscow P. Minaev (IKI), A. Pozanenko (IKI), G. Mozgunov (MIPT, IKI) report on behalf of GRB IKI FuN: We analyzed GRB 220521A till now detected by Swift and GBM/Fermi (Fermi GBM Team, GCN 32075; Dichiara et al., GCN 32076; Poolakkil and Meegan, GCN 32089) using publicly available data of GBM/Fermi and SPI-ACS/INTEGRAL. Using GBM/Fermi data we estimated the duration of T_90 = 12.0 +/- 0.5 s in 7 - 100 keV energy band and performed spectral analysis in the time interval of (-1, 12) s. The best fit is obtained for CPL model with following parameters: E_p = 62 (-15, +68) keV, alpha = -1.5 +/- 0.4. The fluence of F = (9.8 +/- 1.2)E-7 erg/cm**2 is obtained in 10 - 1000 keV energy band. The parameters are close to those reported in (Poolakkil and Meegan, GCN 32089). Using redshift of z = 5.6 (Fynbo et al., GCN 32079; Cucchiara et al., GCN 32099) we obtain E_iso = (6.2 ± 0.8)E52 erg in 1-10000 keV energy range. Using T_90,i - EH diagram [1,2] we classify the burst as type II (long burst) for any possible redshift greater than z = 0.07. T_90,i - EH diagram can be found in http://grb.rssi.ru/GRB220521A/GRB220521A_EHD.png The burst was also detected by SPI-ACS/INTEGRAL with total statistical significance of 5.8 sigma. The angle to the SPI-ACS axis is 47 degrees. Comparing fluences of long-duration GRBs registered by both SPI-ACS and GBM/Fermi (Chelovekov et al., in preparation) we estimated the GRB 220521A fluence to be 1.1E-6 erg/cm**2 in the 10-1000 keV energy band (the 95% confidence region 3.4E-7 – 4.1E-6 erg/cm**2, incl. systematics). Light curves based on GBM/Fermi and SPI-ACS/INTEGRAL data can be found in http://grb.rssi.ru/GRB220521A/GRB220521A_light_curves.png [1] - Minaev et al., MNRAS, 492, 1919, 2020 [2] - Minaev et al., Astronomy Letters, 46, 9, 573, 2020