The effect of Pulse profile evolution on Pulsar Dispersion Measure

Abstract

In an earlier paper (Ahuja, et al, 2005), based on simultaneous multi-frequency observations with the Giant Metrewave Radio Telescope (GMRT), we reported the variation of pulsar dispersion measures (DMs) with frequency. A few different explanations are possible for such frequency dependence, and a possible candidate is the effect of pulse shape evolution on the DM estimation technique. In this paper we describe extensive simulations we have done to investigate the effect of pulse profile evolution on pulsar DM estimates. We find that it is only for asymmetric pulse shapes that the DM estimate is significantly affected due to profile evolution with frequency. Using multi-frequency data sets from our earlier observations, we have carried out systematic analyses of PSR B0329+54 and PSR B1642-03. Both these pulsars have central core dominated emission which does not show significant asymmetric profile evolution with frequency. Even so, we find that the estimated DM shows significant variation with frequency for these pulsars. We also report results from new, simultaneous multi-frequency observations of PSR B1133+16 carried out using the GMRT in phased array mode. This pulsar has an asymmetric pulse profile with significant evolution with frequency. We show that in such a case, amplitude of the observed DM variations can be attributed to profile evolution with frequency. We suggest that genuine DM variations with frequency could arise due to propagation effects through the interstellar medium and/or the pulsar magnetosphere.

14 pages, 14 figures, 5 tables, to be published in MNRAS

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• A low frequency study of PSRs B1133+16, B1112+50, and B0031-07
• Dispersion by pulsars, magnetars, fast radio bursts and massive electromagnetism at very low radio frequencies
• LOFAR observations of PSR B0943+10: profile evolution and discovery of a systematically changing profile delay in Bright mode
• The low-frequency characteristics of PSR J0437-4715 observed with the Murchison Widefield Array
• High Precision Measurements of Interstellar Dispersion Measure with the upgraded GMRT
• Pulsar Observations at Low Frequencies: Applications to Pulsar Timing and Solar Wind Models
• A Multifrequency Census of 100 Pulsars below 100 MHz with LWA: A Systematic Study of Flux Density, Spectra, Timing, Dispersion, Polarization, and Its Variation from a Decade of Observations
• Testing the circularity of PSR B0818-41's carousel
• Tracking dispersion measure variations of timing array pulsars with the GMRT