TITLE: GCN CIRCULAR NUMBER: 32661 SUBJECT: GRB221009A/Swift J1913.1+1946: Solar Orbiter STIX measurements DATE: 22/10/10 15:23:32 GMT FROM: Hualin Xiao at FHNW Hualin Xiao, Säm Krucker and Ryan Daniel on behalf of the STIX team report: At 2020-10-09T13:16:56 UT (Solar Orbiter onboard time), STIX detected GRB221009A, when STIX was 1.22 AU from the earth. The gamma-ray burst is clearly visible in the STIX quick-look light curves of five energy bands in the range between 4 -150 keV. The initial pulse lasted about 10 seconds, followed by two bright pulses, lasting about 80 seconds. The fourth pulse was detected at ~ 323 s after the initial pulse. STIX recorded 185000 triggers from the burst in total. STIX light curves can be found at: https://datacenter.stix.i4ds.net/pub/GRB/GRB221009A/stix_GRB221009A_light_curves.png and https://datacenter.stix.i4ds.net/view/ql/lightcurves Solar Orbiter location during the GRB: https://datacenter.stix.i4ds.net/pub/GRB/GRB221009A/GRB221009A_solar_orbiter_orbit.png The analysis results presented above are preliminary. The science data will only be down-linked from the instrument in a month or two. Detailed analysis of the event will be started after downloading the science data. The Solar Orbiter (SolO) is a Sun-observing satellite developed by the European Space Agency, it was launched on 10th Feb. 2020. It has a unique elliptical orbit around the sun, with distances varying from 0.3 - 1 AU. The Spectrometer Telescope for Imaging X-rays (STIX) is one of the ten instruments onboard the Solar Orbiter. It measures X-rays emitted during solar flares in the energy range of 4 – 150 keV and takes X-ray images by using an indirect imaging technique, based on the Moiré effect. Its detectors consist of thirty-two pixelated CdTe detectors with a total effective area of 6 cm^2. More information about STIX can be found on the STIX data center website: https://datacenter.stix.i4ds.net/