Simultaneous U, B, V, and X-ray measurements of a burst from 4U/MXB 1636-53

Data are presented on the first simultaneous X-ray and optical burst to be measured in more than one optical color. Various analyses agree that, to a first approximation, the optical burst is produced through blackbody reprocessing of the X-ray burst, with a short delay. Depending on the technique used, the value of the delay is 2 or 3 s. The smearing of the optical signal is determined to be less than 3 s. The temperature of the optical reprocessor ranges from approximately 25,000 K at quiescence to approximately 50,000 K at burst maximum. An extinction toward the source is derived from the color-color diagram, suggesting a distance greater than or approximately equal to 2 kpc. The projected effective area of the blackbody reprocessor is approximately 5 x 10 to the 21st (D/5 kpc)-squared sq cm. The fraction of the total X-ray burst energy converted into optical energy at all wavelengths is, within an order of magnitude, approximately 3 percent. These parameters are discussed in relation to the 4 hr orbital periodicity in the system reported by Pedersen et al. (1981).