A refined dynamical mass for the black hole in the X-ray transient XTE J1859+226

I. V. Yanes Rizo; M. A. P. Torres; J. Casares; S. E. Motta; T. MuÃ±oz-Darias; P. RodrÃ­guez-Gil; M. Armas Padilla; F. JimÃ©nez-Ibarra; P. G. Jonker; J. Corral-Santana; R. Fender

doi:10.1093/mnras/stac2719

paper

A refined dynamical mass for the black hole in the X-ray transient XTE J1859+226

arXiv:2209.10395 · doi:10.1093/mnras/stac2719

Abstract

We present two contiguous nights of simultaneous time-resolved GTC spectroscopy and WHT photometry of the black hole X-ray transient XTE J1859+226, obtained in 2017 July during quiescence. Cross-correlation of the individual spectra against a late K-type spectral template enabled us to constrain the orbital period to $0.276 \pm 0.003$ d and the radial velocity semi-amplitude of the donor star to $K_{2} = 550 \pm 59$ km s $^{- 1}$ . An ellipsoidal modulation is detected in the photometric $r$ - and $i$ -band light curves, although it is strongly contaminated by flickering activity. By exploiting correlations between the properties of the double-peaked H $I^\pm$ emission-line profile and the binary parameters, we derived an orbital inclination of $66.6 \pm 4.3$ deg, a refined $K_{2} = 562 \pm 40$ km s $^{- 1}$ and mass ratio $q = M_{2} / M_{1} = 0.07 \pm 0.01$ . From these values we obtained an updated black hole mass of $M_{1} = 7.8 \pm 1.9$ M $_{⊙}$ . An independent mass estimate based on X-ray timing agrees well with our value, which gives further support for the outburst QPO triplet being explained by the relativistic precession model. We also obtained a companion star mass $M_{2} = 0.55 \pm 0.16$ M $_{⊙}$ , which is consistent with its K5-K7 V spectral type.

7 pages, 5 figures