The Third Interplanetary Network

The 3rd interplanetary network (IPN), which has been in operation since 1990, presently consists of 9 spacecraft: AGILE, Fermi, RHESSI, Suzaku, and Swift, in low Earth orbit; INTEGRAL, in eccentric Earth orbit with apogee 0.5 light‐seconds; Wind, up to ∼7 light‐seconds from Earth; MESSENGER, en route to Mercury; and Mars Odyssey, in orbit around Mars. The IPN operates as a full‐time, all‐sky monitor for transients down to a threshold of about 6×10−7 erg cm−2 or 1 photon cm−2s−1. It detects ∼346 cosmic gamma‐ray bursts per year. These events are generally not the same ones detected by narrower field of view instruments such as Swift, INTEGRAL IBIS, and SuperAGILE; the localization accuracy is in the several arcminute and above range. The uses of the IPN data are described.