On the symbiotic x-ray binary nature of the star CGCS 5926

We report on multiwavelength (from X-ray to optical) follow up observations of a carbon star CGCS 5926, motivated by the fact that it is positionally coincident with a faint X-ray source of the ROSAT catalog, thus suggesting its possible symbiotic X-ray binary (SyXB) nature. Our optical spectroscopy confirms that this is a carbon star of type C(6,2). This allows us to infer for CGCS 5926 a distance of ∼5 kpc. BVR_CI_C photometry of the star shows variability of ∼ 0.3 mag with a periodicity of 151 days, which we interpret as due to radial pulsations. The source is not detected with the Swift satellite in X-rays down to a 0.3-10 keV luminosity of ∼3 × 10³² ergs^-1. This nondetection is apparently in contrast with the ROSAT data; however, the present information does not rule out that CGCS 5926 can be a SyXB. This will be settled by more sensitive observations at high energies.