TITLE: GCN CIRCULAR NUMBER: 18711 SUBJECT: GRB 151221A: INTEGRAL detection of a short burst or possible SGR DATE: 15/12/21 10:18:14 GMT FROM: Sandro Mereghetti at IASF/CNR S.Mereghetti (IASF-Milano), D.Gotz (CEA, Saclay), C.Ferrigno, E.Bozzo (ISDC, Versoix), and J.Borkowski (CAMK, Torun) on behalf of the IBAS Localization Team report: a gamma ray burst lasting about 50 ms has been detected by IBAS in the IBIS/ISGRI data at 02:51:12.7 UT of December 21, 2015 with a significance below the threshold for automatic alert delivery (IBAS Weak Alert n.7313) The refined coordinates (J2000) are: R.A.= 293.7327 deg DEC.= 21.8843 deg with an uncertainty of 2 arcmin (90% c.l.). The burst had a fluence of about 4e-8 erg/cm2 (20-200 keV, 0.1-s integration time). The soft spectrum, short duration, low galactic latitude and position inside the supernova remnant G57.2+0.8 suggest taht this event could be due to a new Soft Gamma-ray Repeater. A plot of the light curve will be posted at http://ibas.iasf-milano.inaf.it/IBAS_Results.html