Towards systematic searches for LISA white dwarf binaries with multiband photometry

Abstract

Ultra-compact double white dwarfs (DWDs) represent key targets for multi-messenger astrophysics, as they may be observed both through gravitational waves and the electromagnetic (EM) spectrum. The future Laser Interferometer Space Antenna (LISA) will detect thousands of these systems, and they are predicted to be the most numerous science targets of the mission. We develop a strategy to identify LISA source candidates in multiband photometric surveys. We constructed a synthetic EM catalogue of white dwarf (WD) detections based on a population synthesis code combined with a semi-analytical model of the Milky Way and a consistent cooling model for the evolution. We compared sources in the LISA band with other WD observations in magnitude-colour and colour-colour plots. From a full sky survey with $u\le$24.5, we find that 57$\%$ of the sources in the LISA band occupy a specific region in colour-colour diagrams. Inside this area, we find that $\sim 63\%$ (6.5 $\times 10^4$) of EM observations are LISA candidates, $\sim 31\%$ ($3.2\times 10^4$) are DWDs slightly outside the LISA frequency range, and only a small contamination comes from single WDs and wider binaries. We find that the colour distributions of close DWDs represent a powerful tool to distinguish potential LISA sources from the broader WD population. This is an avenue to select candidates for further follow-up and identification.

4 pages, 3 figures

References in corpus (7)

• The Zwicky Transient Facility: Science Objectives
• A million binaries from Gaia eDR3: sample selection and validation of Gaia parallax uncertainties
• A catalogue of white dwarfs in Gaia EDR3
• The ELM Survey. VIII. 98 Double White Dwarf Binaries
• White dwarf-main sequence binaries from Gaia EDR3: the unresolved 100pc volume-limited sample
• Measuring tides and binary parameters from gravitational wave data and eclipsing timings of detached white dwarf binaries
• Constraining parameters of white-dwarf binaries using gravitational-wave and electromagnetic observations