Period derivative of the M15 X-ray Binary AC211/X2127+119
arXiv:astro-ph/9808323 · doi:10.1016/S1384-1076(98)00026-8
Abstract
We have combined Rossi X-ray Timing Explorer observations of X2127+119, the low-mass X-ray binary in the globular cluster M15, with archival X-ray lightcurves to study the stability of the 17.1 hr orbital period. We find that the data cannot be fit by the Ilovaisky (1993) ephemeris, and requires either a 7sigma change to the period or a period derivative Pdot/P~9x10e-7 per year. Given its remarkably low L_X/L_opt such a Pdot lends support to models that require super-Eddington mass transfer in a q~1 binary.
11 pages, 3 figures, to be published in New Astronomy