What is the SKA-Low sensitivity for your favourite radio source?

Abstract

The Square Kilometre Array (SKA) will be the largest radio astronomy observatory ever built, providing unprecedented sensitivity over a very broad frequency band from 50 MHz to 15.3 GHz. The SKA’s low frequency component (SKA-Low), which will observe in the 50–350 MHz band, will be built at the Murchison Radio-astronomy Observatory (MRO) in Western Australia. It will consist of 512 stations each composed of 256 dual-polarised antennas, and the sensitivity of an individual station is pivotal to the performance of the entire SKA-Low telescope. The answer to the question in the title is, it depends. The sensitivity of a low frequency array, such as an SKA-Low station, depends strongly on the pointing direction of the digitally formed station beam and the local sidereal time (LST), and is different for the two orthogonal polarisations of the antennas. The accurate prediction of the SKA-Low sensitivity in an arbitrary direction in the sky is crucial for future observation planning. Here, we present a sensitivity calculator for the SKA-Low radio telescope, using a database of pre-computed sensitivity values for two realisations of an SKA-Low station architecture. One realisation uses the log-periodic antennas selected for SKA-Low. The second uses a known benchmark, in the form of the bowtie dipoles of the Murchison Widefield Array. Prototype stations of both types were deployed at the MRO in 2019, and since then have been collecting commissioning and verification data. These data were used to measure the sensitivity of the stations at several frequencies and over at least 24 h intervals, and were compared to the predictions described in this paper. The sensitivity values stored in the SQLite database were pre-computed for the X, Y, and Stokes I polarisations in 10 MHz frequency steps, $\scriptsize{1/2}$ hour LST intervals, and $5^\circ$ resolution in pointing directions. The database allows users to quickly and easily estimate the sensitivity of SKA-Low for arbitrary observing parameters (your favourite object) using interactive web-based or command line interfaces. The sensitivity can be calculated using publicly available web interface (http://sensitivity.skalow.link) or a command line python package (https://github.com/marcinsokolowski/station_beam), which can also be used to calculate the sensitivity for arbitrary pointing directions, frequencies, and times without interpolations.

An Empirical Study On Imaging Sensitivity Of SKA1-LOW Based on Point Source Sensitivity

“…We compared the predicted values of the rascil_sensitivity with the output of the imaging sensitivity calculator of Sokolowski et al (2022) under the same observing conditions. 4 The parameters are expressed as follows: phase center (0°, − 27°), hour angle range 1 hr, integration time 60 s, number of stations 512, efficiency factor 1, polarization number 2, and total bandwidth 30 MHz.…”

“…We suspect that this is most likely due to T sys . In Braun et al (2019) the sky is isotropic, and in the calculator by Sokolowski et al (2022) they used a Haslam map scaled in frequency with ν −2.5 (Mozdzen et al 2018). According to Experiment 1, the results of rascil_sensitivity are in general agreement with those given by the calculator when using natural weighting.…”

“…The system temperature is influenced by the sky temperature, which is affected by the galactic foreground (Braun et al 2019). As the foreground is unevenly distributed across the sky, sky temperatures vary in different directions (Sokolowski et al 2022). In the rascil_sensitivity, the system temperature is a fixed value manually entered.…”

“…Then, a series of studies Braun et al (2015bBraun et al ( , 2019, analyzed the station, array sensitivity, and expected performance of SKA1-LOW and provided a comprehensive assessment of the sensitivity of SKA1-LOW. Sokolowski et al (2022) presented a new software tool that enables astronomers and engineers to rapidly predict the anticipated sensitivity of SKA1-LOW prototype stations for arbitrary frequencies, times, and pointings.…”

Spectral analysis of 22 radio pulsars using SKA-Low precursor stations

“…The gain is also a function of frequency due to its dependence on the effective collecting area of the array elements. To calculate the SEFD, the beam response was simulated using PYTHON code f detailed in Sokolowski et al (2022). The simulation code finds T sky and G, calculates the SEFD in the X and Y polarisations, and combines them in quadrature according to…”