Open Access
Table 3
List of all artefacts discussed in this paper along with their causes, manifestations, and solutions.
| Artefact | Cause and Manifestation | Solution |
|---|---|---|
| Dispersive Doppler variation (DDV) (see Section 4.1) | Neglecting the variation of pulsar spin frequency when computing the dispersive phase shift. It causes an apparent orbital DM variation, with maximum and minimum values at ψ = 180° and ψ = 0°, respectively. | The spin frequency variation has been implemented in PSRCHIVE and DSPSR and no longer results in apparent orbital DM variation, while for other software such as SIGPROC, the problem still persists. |
| Temporal dispersive Doppler smearing (TDDS) (see Section 4.2.1) | Neglecting the variation of spin frequency over the duration of the sub-integration when computing the dispersive phase shift. It causes profile smearing that increases with sub-integration duration and results in an apparent orbital DM variation with a maximum value at ψ = 0°. | De-dispersion before integrating the data in time while using DSPSR and PSRCHIVE. |
| Spectral dispersive Doppler smearing (SDDS) (see Section 4.2.2) | Neglecting the differential spin frequency over the observed bandwidth when computing the dispersive phase shift. It causes a similar profile smearing effect as TDDS; however, it does not depend on integration length. | De-dispersion before integrating the data in time while using DSPSR and PSRCHIVE, or implementing a two-dimensional phase predictor. |
| Topocentric dispersive Doppler variation (TopoDDV) (see Section 5.1) | Neglecting the barycentric correction of observed radio frequency when computing the dispersive delay. It causes an apparent annual DM variation. | This correction can be enabled in PSRCHIVE by setting Dispersion::barycentric_corr-ection = 1 in the psrchive.cfg file. |
| Topocentric temporal dispersive Doppler smearing (TopoTDDS) (see Section 5.2) | Neglecting the variation of the velocity of the observatory over the sub-integration time. It causes similar profile smearing effect as TDDS. | The effect is negligible and can be reduced by shortening the sub-integration time. |
| Folding issues with phase predictors (see Section 6) | Inaccurate polynomial phase predictions at superior conjunction. It causes biases in timing parameters, most notably in the Shapiro delay parameters. | Decreasing the time span and increasing the number of coefficients of each set of polynomials hit the limit for the SKA. Development of a more accurate phase predictor that describes the Shapiro delay is needed. |
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