I've been following the news about the detection of gravitational waves with interest and had a question for those with a physics background. I've gathered that the preferred explanation for GW150914 (Fig 1) is a binary black hole inspiral because it is characterized by an increasing frequency and amplitude over time (Fig 2). However, the other types of signal expected (termed "bursts") have the opposite properties, ie a decreasing amplitude and frequency with time (Fig 3), something like what you get out of a bass drum.
As I understand it, the speed at which this signal propagated is constrained to between the speed of light (c) and 1.7*c. [ref 1] Consistent with a superluminal velocity, the only other observation that has been proposed to have some relation was by the Fermi Gamma-ray Burst Monitor. That team reported a gamma ray burst 0.4 s after GW150914. [ref 2]
I searched the literature a bit and found that apparently what we would expect from a superluminal signal is that it appears in chronologically reversed order from a subluminal signal. Here is a quote [ref 3]:
Therefore, if a macroscopic phenomenon is known to produce a radioemission obeying a certain chronological law, and one happens to detect the reversed radioemission, the observed source should be considered as a Superluminal, approaching object.
My questions are:
- Has anyone been searching the LIGO data for such "reverse" signals?
- Would this be considered a useful line of inquiry? If not, why not?
Figure 1. GW150914 Signal https://losc.ligo.org/events/GW150914/
Figure 2. A typical expected inspiral signal http://www.ligo.org/science/GW-Inspiral.php
Figure 3. A typical expected burst signal http://www.ligo.org/science/GW-Burst.php
- Blas et al. On constraining the speed of gravitational waves following GW150914. 12 Feb 2016. http://arxiv.org/abs/1602.04188
- Connaughton et al. Fermi GBM Observations of LIGO Gravitational Wave event GW150914. 16 Feb 2016. http://arxiv.org/abs/1602.03920
- R. Mignani, E. Recami. Astrophysics and tachyons. Il Nuovo Cimento B (1971-1996) May 1974, Volume 21, Issue 1, pp 210-226. http://link.springer.com/article/10.1007%2FBF02737452