Echoes in X-ray binaries

K O'Brien, Keith Douglas Horne, RI Hynes, W Chen, CA Haswell, MD Still

Research output: Contribution to journalArticlepeer-review

62 Citations (Scopus)


We present a method of analysing the correlated X-ray and optical/UV variability in X-ray binaries, using the observed time delays between the X-ray driving light curves and their reprocessed optical echoes. This allows us to determine the distribution of reprocessing sites within the binary. We model the time-delay transfer functions by simulating the distribution of reprocessing regions, using geometrical and binary parameters. We construct best-fitting time-delay transfer functions, showing the regions in the binary responsible for the reprocessing of X-rays. We have applied this model to observations of the soft X-ray transient GRO J1655-40. We find that the optical variability lags the X-ray variability with a mean time delay of 19.3+/-2.2 s. This means that the outer regions of the accretion disc are the dominant reprocessing site in this system. On fitting the data to a simple geometric model, we derive a best-fitting disc half-opening angle of 13.5(-2.8)(+2.1degrees), which is similar to that observed after the previous outburst by Orosz & Bailyn. This disc thickening has the effect of almost entirely shielding the companion star from irradiation at this stage of the outburst.

Original languageEnglish
Pages (from-to)pp.426-434.
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - Aug 2002


  • accretion, accretion discs
  • binaries : close
  • stars : individual
  • Nova Sco 1994 (GRO J1655-40)
  • ultraviolet : stars
  • X-rays : binaries
  • X-rays : stars
  • GRO J1655-40
  • NGC-5548
  • MASS


Dive into the research topics of 'Echoes in X-ray binaries'. Together they form a unique fingerprint.

Cite this