The Square Kilometre Array (SKA)

Abstract:

We present radio coverage of the 2019 outburst of the accreting millisecond X-ray pulsar (AMXP) SAX J1808.4–3658, obtained with MeerKAT. We compare these data to contemporaneous X-ray and optical measurements in order to investigate the coupling between accretion and jet formation in this system, while the optical light curve provides greater detail of the outburst. The reflaring activity following the main outburst peak was associated with a radio re-brightening, indicating a strengthening of the jet in this phase of the outburst. We place quasi-simultaneous radio and X-ray measurements on the global radio:X-ray plane for X-ray binaries, and show they reside in the same region of luminosity space as previous outburst measurements, but significantly refine the correlation for this source. We also present upper limits on the radio emission from the AMXP MAXI J0911–655 and the transitional Z/Atoll-type transient XTE J1701–462. In the latter source, we also confirm that nearby large-scale structures reported in previous radio observations of the source are persistent over a period of ∼15 yr, and so are almost certainly background radio galaxies and not associated with the X-ray transient.

Abstract:

In spite of the rich phenomenology of the polarization properties of radio pulsars, the rotating vector model (RVM) created 50 years ago remains the best method to determine the beam geometry of a pulsar. We apply the RVM to a sample of 854 radio pulsars observed with the MeerKAT telescope in order to draw conclusions about the population of pulsars as a whole. The main results are that (i) the geometrical interpretation of the position angle traverse is valid in the majority of the population, (ii) the pulsars for which the RVM fails tend to have a high fraction of circular polarization compared to linear polarization, (iii) emission heights obtained through both geometrical and relativistic methods show that the majority of pulsars must have emission heights less than 1000 km independent of spin period, (iv) orthogonal mode jumps are seen in the position angle traverse in about one third of the population. All these results are weakly dependent on the pulsar spin-down energy.