Optimization of Survey Strategies for Detecting Slow Radio Transients

TL;DR

This paper analyzes how to optimize survey strategies for detecting slow radio transients by balancing sensitivity and field of view, providing formulas for maximizing detection rates under various distribution scenarios.

Contribution

It introduces a framework for optimizing survey parameters for slow radio transients, considering different source distributions and telescope characteristics.

Findings

Optimal number of pointings depends on survey duration and slew time.

Detection rate can improve by several orders of magnitude through parameter optimization.

Scaling laws for detection rates vary with source distribution and telescope sensitivity.

Abstract

We investigate the optimal tradeoff between sensitivity and field of view in surveys for slow radio transients using the event detection rate as the survey metric. We investigate (i) a survey in which the events are distributed homogeneously throughout a volume centred on the Earth, (ii) a survey in which the events are homogeneously distributed, but are only detectable beyond a certain minimum distance, and (iii) a survey in which all the events occur at an identical distance, as is appropriate for a targetted survey of a particular field which subtends N_point telescope pointings. For a survey of fixed duration, T_obs, we determine the optimal tradeoff between number of telescope pointings, N, and integration time per field. We consider a population in which the event luminosity distribution follows a power law with index -\alpha, and t_slew is the slewing time between fields or, for a drift scan, the time taken for the telescope drift by one beamwidth. Several orders of magnitude improvement in detection rate is possible by optimization of the survey parameters. The optimal value of N for case (i) is N_max ~ T_obs/4 t_slew, while for case (iii) we find N_max = (L_max/L_0)^2 [ (3 -\alpha)/2 ]^{2/(\alpha-1)}, where L_max is the maximum luminosity of a transient event and L_0 is the minimum luminosity event detectable in an integration of duration T_obs. For a telescope field of view, \Omega, and a minimum detectable flux density, S_0, the detection rate scales as N \Omega S_0^{-3/2} for homogeneously distributed events, while for targetted events (iii) it scales as N \Omega S_0^{1-\alpha}. The quantity \Omega S_0^{-2} is often used as the metric of telescope performance in the SKA transients literature, but only under special circumstances is it the metric that optimizes the event detection rate. [abstract abbreviated]