Swift X-Ray and UV Observations of six Gaia Binaries supposedly containing a Neutron Star

Abstract

Recent observations have led to the discovery of numerous optically selected binaries containing an undetected component with mass consistent with a compact object (neutron star or white dwarf). Using the the Neil Gehrels Swift Observatory we have carried out X-ray and UV observations of a small sample of these binaries. Four systems are wide (with orbital period P>300 d), and they were chosen because of their small distance (d<250 pc) and the mass of the collapsed component favoring a neutron star. Two other are compact systems (P<0.9 d), with convincing evidence of containing a neutron star. The source 2MASS J15274848$+$3536572 was detected in the X-ray band, with a flux of 5E-13 erg/cm2/s and a spectrum well fitted by a power law or a thermal plasma emission model. This source also showed an UV (2200 Angstrom) excess, which might indicate the presence of mass accretion. For the other targets we derived X-ray flux upper limits of the order of 1E-13}$ erg/cm2/s . These results are consistent with the hypothesis that the collapsed component in these six systems are neutron stars.