Circumbinary Jovian planet around XTE J1710-281?

The puzzling orbital residuals of XTE J1710-281: is a Jovian planet orbiting around the binary system?

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XTE J1710-281 is a transient eclipsing binary system with a period close to 3.28 hours, hosting a neutron star. The average eclipse duration is 420 seconds, and eclipse arrival times reported in the literature span from 1999 to 2017. A previous analysis of the eclipse arrival times using the eclipse timing technique revealed a complex pattern of delays, indicating the presence of three orbital glitches. These glitches correspond to sudden variations in the orbital period, allowing for the identification of four distinct epochs. We have re-analyzed the 78 eclipse arrival times spanning 18 years utilizing the eclipse timing technique to derive the corresponding delays as a function of time. We find that the observed delays align well with a fitting model employing an eccentric sine function characterized by an amplitude of 6.1±0.5 s, eccentricity of 0.38±0.17, and a period of 17.1±1.5 years. Additionally, we identified the orbital period as 3.28106345(13) hours, with a reference epoch of T₀=54112.83200(2) Modified Julian Date (MJD). We obtained an upper limit of the orbital period derivative of 3.6×10^-13 s~s^-1. From the average value of the eclipse duration, we estimate that the companion star has a mass of 0.22 M_Sun for a neutron star mass of 1.4M_Sun, and the inclination of the source is 78.1^+1-5_-1.2 degrees. The companion star is in thermal equilibrium. The orbital period derivative is consistent with a conservative mass transfer scenario, where the angular momentum loss due to magnetic braking dominates over gravitational radiation angular momentum loss if the former is present. The eccentric modulation can be explained by a third body with a mass of 2.7 Jovian masses, orbiting with a revolution period close to 17 years and an eccentricity of 0.38.

Previous claim of a substellar third body by the same author but referring to a different neutron star binary system

Evidence of a non-conservative mass transfer in the ultra-compact X-ray source XB 1916-053

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The dipping source XB 1916-053 is a compact binary system with an orbital period of 50 min harboring a neutron star. Using ten new Chandra observations and one Swift/XRT observation, we are able to extend the baseline of the orbital ephemeris; this allows us to exclude some models that explain the dip arrival times. The Chandra observations provide a good plasma diagnostic of the ionized absorber and allow us to determine whether it is placed at the outer rim of the accretion disk or closer to the compact object. From the available observations we are able to obtain three new dip arrival times extending the baseline of the orbital ephemeris from 37 to 40 years. From the analysis of the dip arrival times we confirm an orbital period derivative of P˙=1.46(3)×10^-11 s s^-1. We show that the P value and the luminosity values are compatible with a mass accretion rate lower than 10\% of the mass transfer rate. We show that the mass ratio q=m₂/m₁ of 0.048 explains the apsidal precession period and the nodal precession period. The observed absorption lines are associated with the presence of Ne_X, Mg_XII, Si_XIV, S_XVI and  Fe_XXVI ions. We observe a redshift in the absorption lines between 1.1×10^-3 and 1.3×10^-3. By interpreting it as gravitational redshift, as recently discussed in the literature, we find that the ionized absorber is placed at a distance of 108 cm from the neutron star with a mass of 1.4 M⊙ and has a hydrogen atom density greater than 1015 cm^-3.