GCN Circular 45999

B. Doty, H. Meyer and N. Solomey (Wichita State University) report on behalf of the SNAPPY CubeSat project

We observed the GRB 260903A in the gamma ray central detector of the SNAPPY CubeSat. This is the first Gamma Ray Burst seen by SNAPPY operating a GAGG:Ce ultra fast detector, with an active charged particle veto in polar orbit launched on May 4, 2026 UTC and began stable data taking August 4, 2026. 

The Cubesat detector energy spectrum (https://soar.wichita.edu/server/api/core/bitstreams/556ce006-a865-490c-bb15-90a62057e438/content?authentication-token=eyJhbGciOiJIUzI1NiJ9.eyJlaWQiOiJhOWVmMDM5OC02OTcxLTQyN2QtYTI3Mi01ZDU3YjliMWE0NTQiLCJzZyI6W10sImF1dGhlbnRpY2F0aW9uTWV0aG9kIjoicGFzc3dvcmQiLCJleHAiOjE3OTI1MTc1OTB9.YMDaDxRv7TOpt-DurQ8eeccaqLfmXCV69LTOrmpCt2s) shows 11,473 gamma rays that were only those events in the gamma ray detection without any associated charged particle signal in the veto array. It is an ultra quiet detector being highly shielding by 1 cm equivalent of steel resulting in a 50 keV lower edge cut off which results in low count rates during normal operations. 

The timing graph (https://soar.wichita.edu/server/api/core/bitstreams/a6567332-ee57-4125-acb2-54eadfd4a605/content?authentication-token=eyJhbGciOiJIUzI1NiJ9.eyJlaWQiOiJhOWVmMDM5OC02OTcxLTQyN2QtYTI3Mi01ZDU3YjliMWE0NTQiLCJzZyI6W10sImF1dGhlbnRpY2F0aW9uTWV0aG9kIjoicGFzc3dvcmQiLCJleHAiOjE3OTI1MTcxNjN9.8cYeYUFCF51IygC0cHEg6OeimY_giGXILXJpIYuJhdI) for the gamma ray burst was about 80 seconds long with 11,457 events in the main peak, but a small number of events, 16, before the burst can be seen distributed over 400 seconds, we believe these to be associated with the burst. The time was Sept. 3, 2026 at 12:26:25 UTC, but the CubeSat clock in UNIX time is set by ground station uploads via S-band and can be off from GPS time. The CubeSat has no directionality information but the spacecraft at the time of the burst was located at (latitude, longitude) in degrees: (-77.6595,10.3135) to (-72.1207, -2.6817).