The Characteristics of Millisecond Pulsar Emission. III. From Low to High Frequencies

In this paper we present the first observations of a large sample ofmillisecond pulsars at frequencies of 2.7 GHz and 4.9 GHz. Our new fluxmeasurements extend the known spectra for millisecond pulsars to the highestfrequencies to date. The coverage of more than a decade of radio spectrumallows us for the first time to search for spectral breaks as so often observedfor normal pulsars around 1 GHz. We align the observed millisecond pulsarprofiles with data from lower frequencies. Deviations from a dipolar magneticfield structure are not evident and absolute timing across the wide frequencyrange with a single dispersion measure is possible. We seem to observe mainlyunfilled emission beams, which must originate from a very compact region. Acompact emission region is also suggested by a remarkably constant profilewidth or component separation over a very wide frequency range. For a fewsources, polarization data at 2.7 and 4.9 GHz could also be obtained whichindicate that millisecond pulsars are weakly polarized or even unpolarized atfrequencies above 3 GHz. The simultaneous decrease in degree of polarizationand the constant profile width thus question proposals which linkde-polarization and decreasing profile width for normal pulsars to the samepropagation effect (i.e. birefringence). Comparing the properties of core andconal like profile components to those of normal pulsars, we find lesssignificant patterns in their spectral evolution for the population ofmillisecond pulsars. Hence, we suggest that core and conal emission may becreated by the same emission process. In general, MSP emission properties tendto resemble those of normal pulsars only shifted towards higher frequencies.Comment: 49 pages, 18 figures, accepted for publication in Ap