New interpretation of the two hard X-ray sources IGR J17503-2636 and IGR J17507-2647

We report on the results of X-ray observations ( INTEGRAL and of two hard X-ray sources, IGR\,J17503-2636 and IGR\,J17507-2647, whose nature is not fully elucidated in the literature. Three observations covered the field of IGR\,J17503-2636, in 2020 and twice in 2023. The analysis of the two observations performed in September 2023, six days apart, did not detect allowing us to pose the most stringent 3sigma upper limit on the source flux to date (sim 9.5times 2-10 keV, flux corrected for absorption). This value implies that the amplitude of the X-ray flux variability exceeds a factor of sim 2100, compared with the discovery outburst in 2018. A candidate X-ray periodicity at 0.335397(3) seconds has been barely detected (significance of $ from with (pulsed fraction of (10 pm 1)). The new data, put into the context of previous literature, allow us to propose a new classification of IGR\,J17503-2636 as a symbiotic X-ray binary, rather than a candidate supergiant fast X-ray transient. IGR\,J17507-2647 was formerly reported below 10 keV only during Chandra observations performed in 2009. We report here on two observations that serendipitously covered the source field in 2020 and in 2023, finding a stable X-ray emission, both in X-ray flux and spectral shape. The long-term, persistent X-ray emission has also been probed by several short observations and by INTEGRAL data spanning several years. We have detected an iron line in the emission (with centroid energy in the range of 6.3-6.6 keV), never reported before in the IGR\,J17507-2647 spectrum. The source properties favor the identification with a cataclysmic variable. stars: neutron - X-rays: binaries - pulsars: individual: IGR\,J17503-2636, IGR\,J17507-2647, IGR\,J17505-2644