On the time lags of the LIGO signals (1706.04191v2)

Abstract: To date, the LIGO collaboration has detected three gravitational wave (GW) events appearing in both its Hanford and Livingston detectors. In this article we reexamine the LIGO data with regard to correlations between the two detectors. With special focus on GW150914, we report correlations in the detector noise which, at the time of the event, happen to be maximized for the same time lag as that found for the event itself. Specifically, we analyze correlations in the calibration lines in the vicinity of 35\,Hz as well as the residual noise in the data after subtraction of the best-fit theoretical templates. The residual noise for the other two events, GW151226 and GW170104, exhibits similar behavior. A clear distinction between signal and noise therefore remains to be established in order to determine the contribution of gravitational waves to the detected signals.

• The paper evaluates time lag correlations between LIGO detectors, revealing a significant noise peak at approximately 6.9 ms that questions signal integrity.
• The study employs detailed Fourier phase analysis to uncover unexpected frequency coupling and noise behavior that can mimic gravitational wave signatures.
• The paper advocates for improved data cleaning methods to better differentiate true gravitational wave events from systematic noise artifacts.

Analysis of Time Lag Correlations in LIGO Gravitational Wave Data

The paper "On the time lags of the LIGO signals" critically evaluates the data related to gravitational wave (GW) events detected by the LIGO collaboration, focusing specifically on the correlation of signals between the Hanford and Livingston detectors. Given the significant implications of gravitational wave astronomy for our understanding of the universe, the robustness of signal detections and interpretations is of utmost importance. The authors aim to investigate potential correlations in detector noise that could impact the reliability of previous detections.

Summary and Main Findings

The research presented in the paper primarily revolves around an in-depth analysis of the time lags observed in the GW150914 event, which was the first confirmed detection of gravitational waves. The authors revisit the LIGO raw data, paying particular attention to noise correlations with the aim to define the distinction between actual signal and residual noise components. The analysis shows that noise components exhibit a peak in correlation for the same time lag as the detected event itself, specifically 6.9 ms, raising concerns about the distinctness of detected signals from noise artifacts.

Key observations include:

1. Correlation of Noise Across Detectors: The paper identifies significant correlations in the calibration line noise near 35 Hz and residual noise that remains after subtracting theoretical GW templates. These correlations were noted for several other GW events (e.g., GW151226 and GW170104) as well, though with differing time lags of detection.
2. Potential Systematic Effects: The authors suggest that there might exist systematic effects inherent to the measurement process or noise characteristics, which could lead to observed correlations at specific time delays that coincide with expected GW signals, thereby complicating the discernment between real GW events and artifacts.
3. Phase Correlation Analysis: The paper places strong emphasis on Fourier phases, traditionally overlooked in favor of amplitude analysis. Substantial phase correlations were found, challenging the assumption of purely stochastic noise backgrounds and indicating that frequency coupling might be influencing signal morphology.
4. Calibration Line Influence: The interplay between calibration lines and potential cross-detector correlations was examined, pointing to the fact that artifact signals can mimic GW morphology under certain configurations, particularly when calibration lines interfere constructively or destructively within the observation window.

Numerical Results and Impact

The paper provides an extensive quantitative assessment demonstrating how certain noise features correlate for particular time delays, with detailed statistical analyses showing significant correlation coefficients for noise and GW signals. The evidence suggests that GW signal data can be heavily influenced by detector noise if proper cleaning methods are not implemented. These findings call for a re-evaluation of signal analysis techniques to ensure the integrity of gravitational wave detection.

From a practical perspective, this work suggests a need for refined data cleaning methodologies that can more accurately account for correlated noise in LIGO's detectors. The theoretical implications may also be profound as they necessitate more stringent criteria for the confirmation and analysis of gravitational wave events.

Speculative Implications and Future Directions

This paper raises important questions about the reliability of GW detection in complex noise environments. Upcoming observational runs would benefit from incorporating enhanced statistical noise models and more robust template-free validation techniques. Future developments could also explore deeper into time-frequency analysis methods that can simultaneously mitigate correlated noise effects while preserving real astrophysical signal features.

This paper adds a layer of scrutiny to GW astrophysics, emphasizing the need for continuous refinement in the methods used to distinguish true astrophysical phenomena from terrestrial noise signals. As gravitational wave astronomy matures, such critical evaluations will be key in reinforcing the scientific community's confidence in subsequent discoveries.