The puzzling orbital residuals of XTE J1710–281: Is a Jovian planet orbiting the binary system?

¹ Dipartimento di Fisica e Chimica – Emilio Segrè, Università di Palermo, Via Archirafi 36, 90123 Palermo, Italy
e-mail: rosario.iaria@unipa.it
² INAF/IASF Palermo, Via Ugo La Malfa 153, 90146 Palermo, Italy
³ Department of Physics, University of Trento, Via Sommarive 14, 38122 Povo, TN, Italy
⁴ Dipartimento di Fisica, Università degli Studi di Cagliari, SP Monserrato-Sestu, KM 0.7, Monserrato 09042, Italy
⁵ INFN, Sezione di Cagliari, Cittadella Universitaria, 09042 Monserrato, CA, Italy

Received: 22 January 2024
Accepted: 12 April 2024

Abstract

Aims. XTE J1710−281 is a transient eclipsing binary system with a period close to 3.28 h that hosts a neutron star. The average eclipse duration is 420 s, 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 and allow for the identification of four distinct epochs, during which the orbital period derivative was estimated to be −1.8 × 10⁻¹² s s⁻¹, 0.07 × 10⁻¹² s s⁻¹, −1.8 × 10⁻¹² s s⁻¹, and 0.09 × 10⁻¹² s s⁻¹, respectively.

Methods. We reanalyzed the 78 eclipse arrival times spanning 18 years utilizing the eclipse timing technique to derive the corresponding delays as a function of time.

Results. We find that the observed delays align well with a fitting model that employs an eccentric sine function characterized by an amplitude of 6.1 ± 0.5 s, an eccentricity of 0.38 ± 0.17, and a period of 17.1 ± 1.5 years. Additionally, we identified the orbital period to be 3.28106345(13) h, with a reference epoch of T₀ = 54112.83200(2) MJD. We obtained an upper limit to the orbital period derivative of 3.6 × 10⁻¹³ s s⁻¹.

Conclusions. From the average value of the eclipse duration, we estimate that the companion star has a mass of 0.22 M_⊙ for a neutron star mass of 1.4 M_⊙ and that the inclination of the source is 78.1_−1.2^+1.5°. 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.