Gamma Probe is a generic UNSC term referring to one of the Slipstream Space probes used by Remote Scanning Outposts. It sends out radio pings and analyzes the spectrum from radio to X-ray. The Gamma Probe, like all probes used by the RSOs, is designed to be able to survive the transition from Slipspace to normal space in order to collect data.
The Gamma Probe of the Archimedes, directly before the Battle of Sigma Octanus IV reported the same findings as Alpha Probe and Beta Probe. It suggested the object's trajectory was parabolic, and would pass through Sigma Octanus IV.