The Status and Future of the Third Interplanetary Network

The 3rd interplanetary network (IPN), which has been in operation since 1990, presently consists of 9 spacecraft: AGILE, 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. Ulysses and HETE have ceased operations, and the Fermi GBM is being incorporated into the network. 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^-2 s^-1. It detects about 275 cosmic gamma-ray bursts per year. These events are generally not the same ones detected by narrower field of view imaging instruments such as Swift, INTEGRAL IBIS, and SuperAGILE; the localization accuracy is in the several arcminute and above range.