The relation between optical and X-ray flux variations of the black-hole candidate LMC X-3.
Maraschi, L.; Motch, C.; van Paradijs, J.; Pakull, M.; van der Klis, M.; Treves, A.; Ilovaisky, S.; Corbet, R. H. D.; Augusteijn, T.; Smale, A. P.; Charles, P.; van Amerongen, S.
Netherlands, United Kingdom
Abstract
The authors present the results of V-band photometry of the optical counterpart of the black-hole candidate LMC X-3. The observations were made during a three-week period in December 1984, using CCD cameras at the Danish 1.5 m, and MPI 2.2 m telescopes at ESO, and the 1.0 m telescope at SAAO. In addition to an orbital brightness modulation of 0.15 mag LMC X-3 showed a secular brightness increase of ≡0.3 mag. Evidence is found that either the non-orbital variations are not smooth on a time scale of days, or the shape of the orbital light curve is not constant (or both). During the period of the optical observations LMC X-3 was observed five times with EXOSAT. The long-term optical brightness variation is correlated with the X-ray flux. If the X-ray flux does not show orbital variations, the observed long-term correlated X-ray/optical brightness variations of LMC X-3 can be described by a model comprising a constant secondary star, with V ≡ 17.5 and B-V ≡ -0.20, and a rather cool (T < 15,000K) accretion disk of variable brightness, radiating through reprocessing of X rays.