Possible associated signal with GW150914 in the LIGO data

Abstract

We present a simple method for the identification of weak signals associated with gravitational wave events. Its application reveals a signal with the same time lag as the GW150914 event in the released LIGO strain data with a significance around 3.2σ. This signal starts about 10 minutes before GW150914 and lasts for about 45 minutes. Subsequent tests suggest that this signal is likely to be due to external sources.

On the time lags of the LIGO signals

“…10 These results, shown in the lower right panel of Fig. 8, resemble those of the lower left panel obtained with a far smaller time window and provide further support for the findings of our previous work [3]. We have also investigated the dependence of the cross-correlation function on the low frequency boundary of the band pass filter, which is summarized in Appendix F We have seen in several different ways that the 7 ms time lag is not a characteristic unique to the GW150914 event.…”

“…Bottom panels: Scatter plots of the Hanford (y-axis) and Livingston (x-axis) Fourier phases for the raw data (left), the clean data (center), and the phase differences of the cleaned data. a method, proposed in [2,3], for confirming this time lag using correlations and apply it to noise components of the data in the immediate vicinity of GW150914. This method can be used for all time sequences obtained and is independent of cleaning techniques.…”

“…The cross-correlation coefficient between the H and L strain data in a window of width w starting at time t is then given as (also shown in [3])…”

“…Following this announcement, considerable effort has been invested in discussing the consequences of this discovery in cosmology and astrophysics. However, substantially less attention has been paid to independent reexamination of the data and to the reliability of its physical interpretation [2,3]. There is little doubt that the signal is unique regarding both its amplitude and shape.…”

Looking for ancillary signals around GW150914

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We replicated the procedure in Liu and Jackson [1], who had found evidence for a low amplitude signal in the vicinity of GW150914. This was based upon the large correlation between the time integral of the Pearson cross-correlation coefficient in the off-source region of GW150914, and the Pearson cross-correlation in a narrow window around GW150914, for the same time lag between the two LIGO detectors as the gravitational wave signal.

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