Search

The International Gamma-Ray Astrophysics Laboratory (INTEGRAL), launched in 2002, continues its successful work in observing the sky at energies E > 20 keV. The legacy of the mission already includes a large number of discovered or previously poorly studied hard X-ray sources. The growing INTEGRAL archive allows one to conduct an all-sky survey including a number of deep extragalactic fields and the deepest ever hard X-ray survey of the Galaxy. Taking advantage of the data gathered over 17 yr with the IBIS coded-mask telescope of INTEGRAL , we conducted survey of hard X-ray sources, providing flux information from 17 to 290 keV. The catalogue includes 929 objects, 890 of which exceed a detection threshold of 4.5σ and the rest are detected at 4.0σ–4.5σ and belong to known catalogued hard X-ray sources. Among the identified sources of known or suspected nature, 376 are associated with the Galaxy and Magellanic clouds, including 145 low-mass and 115 high-mass X-ray binaries, 79 cataclysmic variables, and 37 of other types; and 440 are extragalactic, including 429 active galactic nuclei (AGNs), 2 ultra-luminous sources, 1 supernova (AT2018cow), and 8 galaxy clusters. 113 sources remain unclassified. 46 objects are detected in the hard X-ray band for the first time. The Log N -Log S distribution of 356 non-blazar AGNs is measured down to a flux of 2 × 10−12 erg s−1 cm−2 and can be described by a power law with a slope of 1.44 ± 0.09 and normalization 8 × 10−3 deg−2 at 10−11 erg s−1 cm−2. The Log N -Log S distribution of unclassified sources indicates that the majority of them are of extragalactic origin. [ABSTRACT FROM AUTHOR]

The molecular cloud Sgr B2 is a natural Compton mirror in the Central Molecular Zone. It is believed that the observed fading of the Sgr B2 X-ray emission in continuum and the Fe Kα 6.4 keV line indicates past X-ray flare activity of the supermassive black hole Sgr A⋆. Sgr B2 was investigated by the INTEGRAL observatory in the hard X-ray in 2003–2009, showing clear decay of its hard X-ray emission. In this work, we present a long-term time evolution of the Sgr B2 hard X-ray continuum after 2009, associated with the hard X-ray source IGR J17475−2822 as observed by INTEGRAL. The 30–80 keV sky maps, obtained in 2009–2019, demonstrate a significant excess spatially consistent with IGR J17475−2822. The observed 2003–2019 light curve of IGR J17475−2822 is characterized by a linear decrease by a factor of ∼2 until 2011, after which it reaches a constant level of ∼1 mCrab. The source spectrum above 17 keV is consistent with a power-law model with Γ = 1.4 and a high-energy cut-off at ∼43 keV. The Sgr B2 residual emission after ∼2011 shows a good correspondence with models of X-ray emission due to the irradiation of the molecular gas by hard X-rays and low-energy cosmic ray ions. We discuss the possible origin of the residual Sgr B2 emission after 2011 within these models, including theoretically predicted multiply scattered emission. [ABSTRACT FROM AUTHOR]

Recent NuSTAR and XMM–Newton observations of the molecular cloud around the Arches stellar cluster demonstrate a dramatic change both in morphology and intensity of its non-thermal X-ray emission, similar to that observed in many molecular clouds of the Central Molecular Zone at the Galactic Center. These variations trace the propagation of illuminating fronts, presumably induced by past flaring activities of Sgr A⋆. In this paper, we present results of a long NuSTAR observation of the Arches complex in 2016, taken a year after the previous XMM + NuSTAR observations which revealed a strong decline in the cloud emission. The 2016 NuSTAR observation shows that both the non-thermal continuum emission and the Fe K α 6.4 keV line flux are consistent with the level measured in 2015. No significant variation has been detected in both spectral shape and Fe K α equivalent width EW 6.4 keV, which may be interpreted as the intensity of the Arches non-thermal emission reaching its stationary level. At the same time, the measured 2016 non-thermal flux is not formally in disagreement with the declining trend observed in 2007–2015. Thus, we cannot assess whether the non-thermal emission has reached a stationary level in 2016, and new observations, separated by a longer time period, are needed to draw stringent conclusions. Detailed spectral analysis of three bright clumps of the Arches molecular cloud performed for the first time showed different EW 6.4 keV and absorption. This is a strong hint that the X-ray emission from the molecular cloud is a mix of two components with different origins. [ABSTRACT FROM AUTHOR]