Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006apj...637.1148v&link_type=abstract
The Astrophysical Journal, Volume 637, Issue 2, pp. 1148-1148.
Astronomy and Astrophysics
Astronomy
Errata, Addenda
Scientific paper
In the published version of our original paper, two sentences were truncated and spliced in the abstract. The abstract (with the missing segment underlined) should read:
``We present ultraviolet results from a multiwavelength campaign on the low-mass X-ray binary Sco X-1. The ultraviolet observations were obtained with the International Ultraviolet Explorer (IUE) and coincided with X-ray observations taken with the Japanese satellite Ginga and other observations from numerous ground-based observatories. Our observations strongly support a direct relationship between the strengths of the UV continuum and line fluxes and the X-ray spectral states. Models predicting UV continuum emission from the X-ray-heated surface of the companion star and from an X-ray-illuminated accretion disk were adjusted for parameters intrinsic to Sco X-1 and fitted to the data. It is found that for Sco X-1, as for Cyg X-2: (1) X-ray heating of the accretion disk is the dominant source of UV emission; (2) the mass accretion rate increases monotonically along the Z-shaped curve in an X-ray color-color diagram; and (3) the disk structure does not change as a function of X-ray spectral state. The accretion disk model gives a best-fit outer disk radius of (6.3+/-0.3)×1010 cm. Mass accretion rates range from 0.6×10-8 Msolar yr-1 in the normal branch (NB) to 1.1×10-8 Msolar yr-1 in the flaring branch (FB). The horizontal branch (HB) was not observed simultaneously in the UV and X-rays, but if the weakest state seen from earlier UV observations corresponds to the HB state, the mass accretion rate there is 0.4×10-8 Msolar yr-1. UV emission lines from He, C, N, O, and Si are detected; all increase in intensity from the HB to the FB state. A model in which emission lines are due to photoionization of the outer-disk by the X-ray source is developed and gives good agreement with the line fluxes observed in each state. The X-ray:UV:radio flux ratios of Sco X-1 measured at the lower vertex of the Z in the X-ray color-color diagram agree with those previously observed in five other X-ray binaries. We suggest that the flux at this vertex, which several theories identify with an accretion rate at the Eddington limit, may be used as a distance indicator; the distance to Sco X-1 would then be 2.0+/-0.5 kpc.
Hertz Paul
Lewin Walter H. G.
Mitsuda Kazu
Penninx Wim
Raymond John C.
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