The Square Kilometre Array (SKA)

Abstract:

Stabilizing the gain of a radio astronomy receiver is of great importance for sensitive radio intensity mapping. In this paper we discuss a stabilization method using a continuous-wave reference signal injected into the signal chain and tracked in a single channel of the spectrometer to correct for the gain variations of the receiver. This method depends on the fact that gain fluctuations of the receiver are strongly correlated across the frequency band, which we can show is the case for our experimental set-up. This method is especially suited for receivers with a digital back-end with high spectral resolution and moderate dynamic range. The sensitivity of the receiver is unaltered except for one lost frequency channel. We present experimental results using a new 4–8.5 GHz receiver with a digital back-end that shows substantial reduction of the 1/f noise and the 1/f knee frequency.

Abstract:

The frequency widening of pulsar profiles is commonly attributed to lower frequencies being produced at greater heights above the surface of the pulsar; so-called radius-to-frequency mapping (RFM). The observer’s view of pulsar emission is a 1D cut through a 3D magnetosphere: we can only see that emission which points along our line of sight. However, by comparing the frequency evolution of many single pulses positioned at different phases, we can build up an understanding of the shape of the active emission region. We use single pulses observed with the Giant Metrewave Radio Telescope to investigate the emission region of PSR J1136+1551 and test RFM. Assuming that emission is produced tangential to the magnetic field lines and that each emission frequency corresponds to a single height, we simulate the single pulse profile evolution resulting from the canonical conal beam model and a fan beam model. Comparing the results of these simulations with the observations, we conclude that the emission region of PSR J1136+1551 is better described by the fan beam model. The diversity of profile widening behaviour observed for the single pulses can be explained by orthogonally polarized modes propagating along differing frequency-dependent paths in the magnetosphere.