The Behavior of the Optical and X-Ray Emission from Scorpius X-1

Abstract

In 1970, Hiltner & Mook reported the results of the first multiyear study of the optical emission from Sco X-1. They found that the Sco X-1 B-magnitude histograms changed from year to year. Subsequent multiwavelength campaigns confirmed the variable nature of these optical histograms and also found that the X-ray and optical emissions were only correlated when Sco X-1 was brighter than about B = 12.6. Models had suggested that the optical emission from this source arose from X-rays reprocessed in an accretion disk surrounding the central neutron star. It was therefore difficult to explain why the optical and X-ray fluxes were not more closely correlated. In 1994 and 1995, two new simultaneous optical and X-ray campaigns on Sco X-1 were conducted with the Burst and Transient Source Experiment on the Compton Gamma Ray Observatory and the 1 m Yale telescope at Cerro Tololo Inter-American Observatory. Using these data and models by Psaltis, Lamb, & Miller, it is now possible to provide a qualitative picture of how the X-ray and optical emissions from Sco X-1 are related. Differences in the B-magnitude histograms are caused by variations in the mass accretion rate and the relatively short time period typically covered by optical investigations. The tilted-C pattern seen in plots of the simultaneous X-ray and optical emission from Sco X-1 arises from (1) the nearly linear relation between the optical B magnitude and the mass accretion rate in the range 13.3 ! B ! 12.3 and an asymptotic behavior in the B magnitude outside this range, and (2) a double-valued relation between the X-ray emission and mass accretion rate along the normal branch and lower flaring branch of this source.

Sco X-1 revisited withKepler, MAXI and HERMES: outflows, time-lags and echoes unveiled

“…This could be suggestive that an additional flux distribution exists at the highest fluxes, thus making the light curve non-stationary and breaking the rmsflux linearity. We note that this could be connected to the trimodal flux distribution previously reported in Sco X-1 (Mook et al 1975;McNamara et al 2003) and/or the extra variability component observed during the high optical luminosity state as seen in Fig. 9.…”

“…The optical depth then increases, causing more X-ray photons to be absorbed and re-emitted as optical photons. This phase is associated with an X-ray to optical anti-correlation (McNamara et al 2003). As the source transitions between the NB and the FB, the mass accretion rate exceeds the critical Eddington rate, causing the mass flow to become chaotic with material in the disk flowing both radially inwards and outwards.…”

High energy sources monitored with OMC

“…The histogram of measured magnitudes (see Fig. 3, on the left) shows three clear states of the Sco X-1 optical emission as previously reported (McNamara et al 2003(McNamara et al , 2005Wright et al 1975).…”

Polarized infrared emission from X-ray binary jets

“…Kemp et al 1983). In Sco X–1, this cannot be the case as the accretion disc dominates the optical and NIR and as such any polarized stellar light would be diluted by the light from the disc (McNamara et al 2003; Wachter et al 2006; Russell et al 2007). For GRO J1655−40, the star is large and bright and peaks in the optical (Migliari et al 2007) but the high level of NIR LP and the negative relation between LP and frequency allow us to rule out scattered stellar light as the origin of the NIR LP.Scattering also produces LP that is variable on time‐scales of the orbital period; this has been significantly detected from optical observations of both HMXBs and LMXBs (e.g.…”