TITLE: GCN CIRCULAR NUMBER: 31544 SUBJECT: GRB 211227A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis DATE: 22/02/03 10:32:43 GMT FROM: Anastasia Tsvetkova at Ioffe Institute A. Tsvetkova, D. Frederiks, A.Lysenko, D. Svinkin, A. Ridnaia, M. Ulanov (all Ioffe), and A.Y. Lien (U Tampa), report: The long GRB 211227A (Swift-BAT detection: Beardmore et al., GCN 31316; Lien et al., GCN 31326; MAXI/GSC detection: Tominaga et al., GCN 31319; CALET-GRBM detection: Cherry et al., GCN 31333), T0 (BAT) = 23:32:06.867, was detected by Konus-Wind (KW) in the waiting mode. A Bayesian block analysis of the KW waiting mode data in 25-400 keV range reveals two episodes with count rate excess >10 sigma over background. The first one, lasting from ~T0-50 s to ~T0-10 s, is due to the solar activity and is not associated with the GRB. The second episode, from ~T0-1.5 s to ~T0+81 s, is consistent in time with the BAT detection. It has a double-peaked structure, with the first, narrow pulse peaking at ~T0, and the second, more broad pulse - at ~T0 + 11 s. To derive broad-band spectral parameters of this burst, we performed a joint spectral analysis of the Swift/BAT data (15-150 keV) and the KW 3-channel spectral data (25-1700 keV). A fit to the time-averaged spectrum, measured from T0-1.540 s  to T0+83.836 s, by the Band GRB function gives alpha = -1.34 (-0.08,+0.10), beta = -2.26 (-1.11,+0.24), and Ep = 192 (-42,+45) keV; chi^2 = 48.5/ 57 dof. A fit to the spectrum near the peak KW count rate, measured from T0+10.236 s to T0+19.068 s, by the Band function gives alpha = -1.09 (-0.07,+0.08), beta = -2.29 (-0.11,+0.28), and Ep = 374 (-70,+66) keV; chi^2 = 47.1/58 dof. The spectrum of the short initial pulse, measured from T0-1.540 s to T0+4.348 s, is well fit by a power law with an exponential cutoff (CPL), with alpha = -1.56 (-0.06,+0.15) and Ep = 366 (-179,+1201) keV; chi^2 = 49.3/59 dof. Although the Band model fit to this spectrum is not constrained, fixing beta to the value -2.26, obtained for the time-integrated spectrum, gives alpha = -1.49 (-0.18, +0.24) and Ep = 240 (-116, +759) keV; chi^2 = 49.0/59 dof. In the 15-1500 keV band, the total burst fluence is 2.60(-0.21,+0.21)x10^-5 erg/cm^2, and the 64 ms peak energy flux is 2.0(-0.4,+0.4)x10^-6 erg/cm^2/s. Assuming the redshift z=0.228 (Malesani et al., GCN 31324) of the host galaxy candidate (Fu et al., GCN 31320), and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the isotropic energy release E_iso to 4.9(-0.4,+0,4)x10^51 erg, the isotropic luminosity L_iso to 4.7(-1.0,+1,0)x10^50 erg/s, and the rest-frame peak energies of the time-integrated and peak spectra to 235(-51,+56) keV and 460 (-86, +81) keV, correspondingly. With these values, GRB 211227A is consistent with the 90% prediction bands for the 'Amati' relation and is an outlier in the 'Yonetoku' relation for the sample of  >300 long KW GRBs with known redshifts (Tsvetkova et al., 2021, ApJ, 908, 83). However, if we assume a higher burst redshift (z>0.5), GRB 211227A is consistent with both 'Amati' and 'Yonetoku' relations, see http://www.ioffe.ru/LEA/GRBs/GRB211227A/GRB211227A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB211227A/