A 25.3 day periodicity in the timing of the pulsar PSR B1257+12: A planet or a heliospheric propagation effect?

Multifrequency observations of the planet pulsar PSR B1257 + 12 have been m ade to examine a possibility that the 25.3 day periodicity observed in its pulse timing residuals represents a variable delay generated by solar rotat ion-induced density fluctuations in the solar wind. New timing measurements of the pulsar show that the amplitude of these residuals is frequency inde pendent, implying that the periodicity cannot be caused by any arrival time delays related to the pulse propagation through an ionized medium. Therefo re, in agreement with the original assumption, the observed 25.3 day pulse timing periodicity is most plausibly explained in terms of the orbital moti on of a low-mass planet around the pulsar.