ROTATIONAL PARAMETERS OF PSR-0540-69 AS MEASURED AT OPTICAL WAVELENGTHS

We have measured the rotation frequency of the 50 ms pulsar PSR 0540-69 utilizing data collected at the ESO 3.6 m telescope at La Silla. The observations were acquired in the interval 1989 January-1991 April. The average pulse shape displays a broad enhancement with a superposed double-peaked structure. We were able to phase-relate the data between 1990 March and 1991 April indicating the pulsar did not display any large spin discontinuities during that time span. Three solutions, incorporating a pulse number ambiguity of + 1, are presented. Our preferred solution yields a braking index of 2.04 +/- 0.02, comparable with GINGA measurements in 1987. Discrepancies between our results and extrapolation of the GINGA results are discussed.