TITLE: GCN CIRCULAR NUMBER: 39011 SUBJECT: GRB 250121A: INTEGRAL/SPI-ACS detection DATE: 25/01/22 11:04:29 GMT FROM: Aishwarya L Thakur at INAF-IAPS, Rome Patrizia Barria(a,b), Giulia Gianfagna(a), James Craig Rodi(a), Aishwarya Linesh Thakur(a), Lorenzo Natalucci(a,b), Luigi Piro(a) report: GRB 250121A was discovered by Fermi/GBM (GCN 39006, Fermi/LAT GCN 39010) on 2025-01-21T23:36:05 (UTC). We searched for a corresponding counterpart in the INTEGRAL/SPI-ACS data. In an SPI-ACS light curve above 80 keV, we find a signal temporally coincident with the GBM detection, having an approximate duration of ~ 4 sec. The signal consists of a single pulse over this duration. The approximate peak count rate in SPI-ACS is 74,000 cts/s for E>80 keV, over a median background rate of 62,800 cts/s. This work is based on observations with INTEGRAL, an ESA project with instruments and a science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, and Spain), and with the participation of Russia and the USA. The SPI-ACS detector system has been provided by MPE Garching/Germany. ----- (a) INAF/IAPS-Rome (b) ICSC National Research Centre for High-Performance Computing