Measurements on the Period of the Pulsating Radio Source at 1919 + 21
Observations at several frequencies were recently made at Parkes of the pulsating radio source reported by Hewish et al.1. Four receivers centred at 85, 150, 630 and 1,410 MHz were operated simultaneously on the 210-ft telescope during the period March 22–25, 1968. This short communication reports only the measurements made on the arrival time of pulses. Other characteristics of the radiation are dealt with in a seRefste communication. The highest signal to noise ratio was at 150 MHz and 630 MHz, and it was possible, on the basis of measurements at either of these two frequencies, to establish the period of the pulsations to better than 1 part in 107. The combined results for observations during the 4 day period give a value of 1•33730109 ±0•00000007s.