It is assumed that the radioactive decay of Ti-44 powers the infrared, optical and UV emission of supernova remnants after the complete decay of Co-56 and Co-57 (the isotopes that dominated the energy balance during the first three to four years afte
r the explosion) until the beginning of active interaction of the ejecta with the surrounding matter. Simulations show that the initial mass of Ti-44 synthesized in core-collapse supernovae is (0.02-2.5) x 10^{-4} solar masses (M_sun). Hard X-rays and gamma-rays from the decay of this Ti-44 have been unambiguously observed from Cassiopeia A only, leading to the suggestion that the values of the initial mass of Ti-44 near the upper bound of the predictions occur only in exceptional cases. For the remnant of supernova 1987A, an upper limit to the initial mass of Ti-44 of < 10^{-3} M_sun has been obtained from direct X-ray observations, and an estimate of (1-2) x 10^{-4} M_sun has been made from infrared light curves and ultraviolet spectra by complex model-dependent computations. Here we report observations of hard X-rays from the remnant of supernova 1987A in the narrow band containing two direct-escape lines of Ti-44 at 67.9 and 78.4 keV. The measured line fluxes imply that this decay provided sufficient energy to power the remnant at late times. We estimate that the initial mass of Ti-44 was (3.1+/-0.8) x 10^{-4} M_sun, which is near the upper bound of theoretical predictions.
In 2003-2012, the INTEGRAL observatory has performed long-term observations of the Large Magellanic Cloud (LMC). At present, this is one of the deepest hard X-ray (20-60 keV) surveys of extragalactic fields in which more than 20 sources of different
natures have been detected. We present the results of a statistical analysis of the population of high-mass X-ray binaries in the LMC and active galactic nuclei (AGNs) observed in its direction. The hard X-ray luminosity function of high-mass X-ray binaries is shown to be described by a power law with a slope alpha~1.8, that in agreement with the luminosity function measurements both in the LMC itself, but made in the soft X-ray energy band, and in other galaxies. At the same time, the number of detected AGNs toward the LMC turns out to be considerably smaller than the number of AGNs registered in other directions, in particular, toward the source 3C 273. The latter confirms the previously made assumption that the distribution of matter in the local Universe is nonuniform.
All the observations performed with the IBIS telescope aboard the INTEGRAL observatory during the first 2.5 years of its in-orbit operation have been analyzed to find X-ray bursts. There were 1788 statistically confident events with a duration from 5
to 500 s revealed in time records of the 15-25 keV count rate of the IBIS/ISGRI detector, 319 of them were localized and, with one exception, identified with persistent X-ray sources. The known bursters were responsible for 215 of the localized events. One burst was detected from AXJ1754.2-2754, the source previously unknown as a burster, and another burst - from a new source. There was duality in determining its position - its name could be either IGR J17364-2711 or IGR J17380-3749. Curiously enough, the 138 bursts were detected from one X-ray burster - GX 354-0.
We report the discovery with INTEGRAL on March 24, 2005, and follow-up observations of the distant Galactic X-ray nova IGR J17098-3628.
