L. Homer — Page 2 | Searcharxiv

arXiv1998

Period derivative of the M15 X-ray Binary AC211/X2127+119

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.

astro-ph↗

arXiv1998

Evidence for a 2 hr Optical Modulation in GS1826-24

We report the discovery of a 2.1hr optical modulation in the transient source GS1826-24, based on two independent high time-resolution photometric observing runs. There is additional irregular variability on shorter timescales. The source also exhibited an optical burst during each observation, with peak fluxes consistent with those of the three X-ray bursts so far detected by BeppoSAX. We compare the low-amplitude variation (0.06 mag) to that seen on the orbital periods of the short period X-ray bursters, X1636-536 and X1735-444, as well as the similarity in their non-periodic fluctuations. Other transient neutron star LMXBs possess short periods in the range 3.8-7.1 hrs. However, if confirmed as the orbital, a 2.1 hr modulation would make GS1826-24 unique and therefore of great interest within the context of their formation and evolution.

astro-ph↗