Investigation of the transient X-ray burster IGR J17380-3749 discovered by the INTEGRAL observatory

Abstract

Details of the discovery (in February 2004) and results of subsequent (in 2004-2009) INTEGRAL observations of the transient X-ray burster IGR J17380-3749 (IGR J17379-3747) are presented. Over the period of its observations, the INTEGRAL observatory recorded two hard X-ray flares and one type I X-ray burst from the source, which allowed the nature of IGR J17380-3749 to be determined. The burster radiation spectrum during the flares was hard—a power law with a photon index α = 1.8-2.0 or bremsstrahlung corresponding to a plasma with a temperature kT = 90-140 keV. The spectral shape at the flare peaks turned out to be the same, despite a more than twofold difference in flux (the peak flux recorded in the energy range 18-100 keV reached ∼20 mCrab). The upper limit on the flux from the source in its quiescent (off) state in the range of 18-40 keV was 0.15 mCrab (3 σ).