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We report on the 2003-2005 INTEGRALobservations of the Neutron Star Low Mass X-ray Binary 4U 1722–30 (also known as GRS 1724–30) located in the Globula r Cluster Terzan 2. The JEM-X and IBIS light curves show the source with a persistent yet va riable flux. The Hardness-Intensity diagrams highlight the behaviour of a typical Atoll source: 4U 1722–30 repeatedly moves in the diagrams from the Banana (Soft state) to the Island (Hard sta te). We report on the detailed spectral analysis of Soft and Hard states and, for the first time, also o f an Intermediate state. The Hard spectra reveal a Comptonised corona emission up to 200 keV ch ara terized by a high temperature of 40 keV and optical depth of 0.5. In the Soft state the main em ission is from the accretion disk (with kTin ∼ 0.5 keV) whereas the Comptonised emission decreases showin g an optically thick and cold corona ( τ ∼ 9, kTe ∼ 2 keV). During the hardening there is an increase of the inner radius of the accretion disk suggesting a system expansion d uri g the spectral transition. This behaviour is reminescent of the Soft X-ray transient source s though 4U 1722–30 never reaches a real "quiescent" state.

INTEGRAL long term monitoring of 4U 1722-30: evidence for spectral state variations