TITLE: GCN CIRCULAR NUMBER: 17552 SUBJECT: GRB 150305A: a long GRB detected by INTEGRAL DATE: 15/03/09 12:41:36 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 at least 100 s has been detected by IBAS in the IBIS/ISGRI data at 09:49:19 UT of March 5, 2015. The refined coordinates (J2000) are: R.A.= 269.7685 deg DEC.= -42.6481 deg with an uncertainty of 2.5 arcmin (90% c.l.). The burst had a peak flux of about 0.2 counts/cm2/s (20-200 keV, 1-s integration time) and a fluence in the same energy range of about 7e-7 erg/cmq (over 100 s). Due to the significance of the detection below the high confidence threshold, only an Alert Packet of WEAK type was distributed by IBAS in real time (Packet n. 6905). The X-ray afterglow has been detected with Swift/XRT (Starling 2015, GCN 17551). A plot of the light curve can be found at http://ibas.iasf-milano.inaf.it/IBAS_Results.html