Volumetric Survey Speed: A Figure of Merit for Transient Surveys

TL;DR

This paper introduces the instantaneous volumetric survey speed as a new figure of merit to evaluate and compare the effectiveness of transient surveys, considering their cadence, volume, and follow-up capabilities.

Contribution

It proposes a novel metric for transient survey evaluation, extends control time algorithms for multiple detections, and analyzes how survey parameters influence transient detection rates.

Findings

Many surveys are limited by available sky coverage each night.

Spectroscopic accessibility is crucial for follow-up science.

Survey speed and cadence choice impact transient detection rates.

Abstract

Time-domain surveys can exchange sky coverage for revisit frequency, complicating the comparison of their relative capabilities. By using different revisit intervals, a specific camera may execute surveys optimized for discovery of different classes of transient objects. We propose a new figure of merit, the instantaneous volumetric survey speed, for evaluating transient surveys. This metric defines the trade between cadence interval and snapshot survey volume and so provides a natural means of comparing survey capability. The related metric of areal survey speed imposes a constraint on the range of possible revisit times: we show that many modern time-domain surveys are limited by the amount of fresh sky available each night. We introduce the concept of "spectroscopic accessibility" and discuss its importance for transient science goals requiring followup observing. We present an extension of the control time algorithm for cases where multiple consecutive detections are required. Finally, we explore how survey speed and choice of cadence interval determine the detection rate of transients in the peak absolute magnitude-decay timescale phase space.