4. Survey results
A total of seven pulsars were detected during the course of the survey, four of which were previously unknown. Follow-up observations carried out to confirm the existence of each of the new pulsars were used to check that the true period had been correctly identified by the search code. The basic properties and detection statistics of all seven pulsars are summarised in Table 1. Flux values for the previously known pulsars are taken from Lorimer et al. (1995). Flux values for the newly discovered pulsars are averages of a number of independent measurements based on the timing measurements described in Sect. 5 and have fractional uncertainties of about 30% in each case. The relative positions of all these pulsars are shown on our sensitivity curve in Fig. 2.
The astute reader will, by now, have noticed a striking similarity between the periods of PSRs J1842-0415 and J1844-0310 and, to a lesser extent, PSRs J1845-0316 and J1841-0345. This unexpected result initially gave us some cause for concern as to whether the signals we had detected were indeed pulsars! However, having thoroughly investigated each new pulsar, we are now confident that this is nothing more than a bizarre coincidence. A number of independent facts confirm this. Firstly, all the new pulsars are separated by a significant number of telescope pointings on the sky. Secondly, the periods are detected only at the nominal position of each pulsar, and therefore cannot be put down to terrestrial interference. Furthermore, all the dispersion measures are significantly different. Finally, our timing measurements show that each pulsar has a distinct set of spin-down parameters.
We note in passing that this survey places an upper limit to the pulsed radio emission from the 6.97-s anomalous X-ray pulsar J1845.0-0300 discovered by Torii et al. (1998) that lies in the search region. No radio pulsations were seen at the grid position closest to this pulsar, setting a 1400-MHz pulsed flux limit of mJy, where is the pulse duty cycle in percent. This limit assumes (possibly incorrectly) that the effects of interstellar scattering are negligible along this line of sight at this observing frequency. Deeper radio searches for this object, and also for the 11.8-s pulsar in Kes 73 (Vasisht & Gotthelf 1997), should be carried out in future at different observing frequencies.
© European Southern Observatory (ESO) 2000
Online publication: June 26, 2000