Galactic binary science with the new LISA design

Abstract: Building on the great success of the LISA Pathfinder mission, the outlines of a new LISA mission design were laid out at the $11^{\rm th}$ International LISA Symposium in Zurich. The revised design calls for three identical spacecraft forming an equilateral triangle with 2.5 million kilometer sides, and two laser links per side delivering full polarization sensitivity. With the demonstrated Pathfinder performance for the disturbance reduction system, and a well studied design for the laser metrology, it is anticipated that the new mission will have a sensitivity very close to the original LISA design. This implies that the mid-band performance, between 0.5 mHz and 3 mHz, will be limited by unresolved signals from compact binaries in our galaxy. Here we use the new LISA design to compute updated estimates for the galactic confusion noise, the number of resolvable galactic binaries, and the accuracy to which key parameters of these systems can be measured.

• The paper demonstrates that the updated LISA design enhances high-frequency sensitivity and maintains robust interferometric performance.
• The paper employs an updated binary population model and iterative subtraction to accurately estimate confusion noise and resolvable sources in the 0.5–3 mHz range.
• The paper finds that longer mission durations significantly improve parameter estimation, enabling precise orbital, chirp mass, and distance measurements for galactic binaries.

Summary of "Galactic Binary Science with the New LISA Design"

The paper "Galactic Binary Science with the New LISA Design" authored by Neil Cornish and Travis Robson, presents an analysis of the updated Laser Interferometer Space Antenna (LISA) mission design. This updated design reflects revisions discussed at the $11^{\rm th}$ International LISA Symposium, showcasing advancements from the LISA Pathfinder mission while considering both technical capabilities and budgetary factors.

Mission Design and Sensitivity

The new LISA design comprises three identical spacecraft in an equilateral triangle formation, with each arm measuring 2.5 million kilometers. This structure enables heterodyne laser interferometry with two laser links per side, ensuring polarimetric sensitivity. The Petit Prince interferometer's expected sensitivity closely aligns with earlier LISA designs, as it leverages performance achievements of the LISA Pathfinder in disturbance reduction and laser metrology systems. Though the spacecraft's reduced arm length decreases low-frequency sensitivity, it concurrently enhances high-frequency performance.

Galactic Confusion Noise and Sources

Building on established models of galactic binaries, the research in this paper employs an updated binary population model to estimate confusion noise, resolvable source numbers, and measurement accuracy of binary system parameters. Estimations indicate that unresolved galactic binary emissions will primarily contribute to mid-band noise within the 0.5 mHz to 3 mHz range.

Through iterative subtraction methodologies, the paper identifies the impact of mission duration on galactic confusion noise levels—longer missions resolve more sources, reducing confusion noise. Analytic fits for the evolving noise spectrum are detailed, incorporating factors to capture deviations from theoretical power-law spectra.

Resolvable Galactic Binaries

The paper predicts how many binary systems will be detectable and the precision of parameter estimations based on various observation durations. Detection and precise measurement of the orbital period are feasible for a substantial number of binaries, with the highest resolution between 2-3 mHz. A significant subset of detected binaries will have well-localized sky positions, and some will enable accurate chirp mass and distance measurements. These measurements enhance our understanding of stellar evolution and galactic structure.

Implications for Future Observations

The study emphasizes that the information obtained from resolvable galactic binaries can considerably enhance astrophysical models. The detailed predictions of resolved signals' frequency distribution assist in refining population synthesis models. Additionally, some high signal-to-noise ratio (SNR) galactic binaries are expected to be detected within the mission's early phases, making them prime candidates for multiband gravitational wave observations.

Conclusion

Cornish and Robson's study offers a comprehensive examination of the improved LISA mission's capabilities for detecting and characterizing galactic binaries. The paper highlights how LISA will manage the inherent galactic confusion noise over various mission durations, offering crucial insights into stellar population and gravitational wave science. Anticipated advances in parameter estimation could facilitate deeper integration between electromagnetic and gravitational wave astronomy, paving the way for novel astrophysical investigations.