EXOSAT and Optical Observations of the X-Ray Burst Source 4U/MXB1636-53

During May 1984 we made a one-day EXOSAT observation of the X-ray burst source 4U/MXB1636-53, partly simultaneous with Tenma and with optical observations at ESO. In this paper we give a short description of the main results: (i) Discovery of a constant blackbody component in the persistent X-ray emission, with an apparent blackbody radius consistent with that derived from X-ray burst spectra. This persistent component is likely to originate from the neutron-star surface; (ii) Discovery of X-ray bursts which seem to proceed in two distinct steps; (iii) Evidence for a systematic deviation, at high temperatures, of X-ray burst spectra from Planckian curves; (iv) Some evidence for the preferential occurrence of a strong 4.1 keV feature in burst spectra during the initial stages of strong bursts; (v) Detection of a simultaneous optical burst, delayed by about 3 seconds, with a substantially smeared profile, indicative of reprocessing of X-rays in an accretion disk.