SIMBAD references

Observations of the millisecond pulsar PSR 1937+21 at Nan cay Radio Observatory provide the densest series of times of arrival (TOA) and of flux densities on this pulsar. They were measured on 525 individual dates over 4.5years from 1988 December, 22. Comparison between the astrometric parameters fitted to the Nancay and Arecibo independent timing series shows that they are consistent at the level of 4 times the formal uncertainty (σ) for all parameters except the period (7σ) but that is likely caused by the different TAI time scales used in the 2 data sets. The post-fit TOA residuals of the two series are characterized by the same rms, 0.36µs at 1.4GHz, if the times of arrival with the highest flux densities (>345mJy) are selected at Nancay. We find also that there is a high correlation between the TOA residuals and the flux density of this pulsar as expected if refractive scintillation is important in the ionized interstellar medium. Finally, when the second period derivative is not solved for in the Nancay data, the post-fit TOA residuals are dominated by a low-frequency noise as already discovered in the Arecibo data on PSR 1937+21. In this context, we study the effects of the large minor planets recently discovered at the edge of the Solar System (Chiron, Phollus, 1992 QB1) and not included in the ephemerides used for the analysis. We conclude that they are negligible. However, the hypothetical more massive tenth Planet (Planet X) might already be partially responsible for the low-frequency noise in PSR 1937+21 residuals. We show that, if this planet exists, its signature will be large over 20years of high-precision timing of the millisecond pulsars PSR 1937+21, PSR 1855+09 and PSR 1821-24