Echoes from the companion star in Sco X-1

Abstract

We present simultaneous X-ray (RXTE) and optical (ULTRACAM) narrow band (Bowen blend/HeII and nearby continuum) observations of Sco X-1 at 2-10 Hz time resolution. We find that the Bowen/HeII emission lags the X-ray light-curves with a light travel time of ~11-16s which is consistent with reprocessing in the companion star. The echo from the donor is detected at orbital phase ~0.5 when Sco X-1 is at the top of the Flaring Branch. Evidence of echoes is also seen at the bottom of the Flaring Branch but with time-lags of 5-10s which are consistent with reprocessing in an accretion disc with a radial temperature profile. We discuss the implication of our results for the orbital parameters of Sco X-1.

arXiv commentAccepted for publication in MNRAS

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• Kepler K2 Observations of Sco X-1: Orbital Modulations and Correlations with Fermi GBM and MAXI
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• New Insights into X-ray Binaries
• FUSE Observations of a Full Orbit of Scorpius X-1
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