We do account for the expansion of the universe in fact. We estimated that this source was at about z ~ 0.2 (see https://en.wikipedia.org/wiki/Redshift). Roughly speaking this means there'll be only ~20% effect as the scale of the universe (a) has increased by (1+z) over the time it has traveled.
It's important to know that LISA and LIGO aren't really competing for sensitivity. Rather they complement each other by looking in different frequency ranges. The relationship between LISA and LIGO is analogous to a radio telescope and a gamma ray one. They observe different parts of the spectrum. At the frequencies that black holes merge for example, ground motion is not much of an issue, and other noise source dominate.
Hi Nonbel, I work within the LIGO Scientific Collaboration, and as another posted commented, manual intervention (in the case of GW170104 by me) was only necessary for the online analysis. The purpose of online analysis is for fast coordination with EM partners so that potentially interesting opportunities are not missed. In the case of binary black holes, the expectation is that there will be no electromagnetic counterpart, as the region is expected to be cleared of matter well before we observed the black holes merging. If one to were to be found however, that would be exciting.
By design, detection statements and significance estimates come solely from the offline analysis which is conducted separately (i.e. not triggered by) the online analysis. No human intervention is required here, as the issue with the online status information was known about at the time and was not an issue with the data itself. Even if there were no candidate events at the time, it would be been included in the offline analysis of the period containing the event.
In regards to GW150914 and iDQ, you should know that iDQ has never been approved as a veto for CBC (compact binaries such as neutron stars and black holes) searches. Again, no intervention was required to "remove" the veto as it was never used in the offline analysis nor would be in the first place. It's only use that I am aware of is as a veto against Burst triggers in online analysis. These searches look for generic signals, but may also detect some of the louder CBC sources, such as GW150914. In case you were wondering, there weren't dedicated online CBC searches at the time of GW150914, but there were offline analysis, and those produced the results reported in the original detection paper.
This is information that should be included in the papers because the current description is too terse. Basically you are saying that the filters used for online analysis have nothing to do with the background model, zero influence on what periods get included, etc. I'm still unclear on what exactly needed to be "restarted by hand" for the original GW150914 signal, but ok.
>"In the case of binary black holes, the expectation is that there will be no electromagnetic counterpart, as the region is expected to be cleared of matter well before we observed the black holes merging."
Is there any other type of event that is expected to be accompanied by some kind of corroborating evidence?
To get an electromagnetic counterpart, you need matter to be in the system. It may be possible for binary neutron star and some neutron-star black hole mergers. These types of mergers are one of the predicted sources of short gamma ray bursts, so if we get reasonably lucky it may be possible to find one in coincidence. Gamma ray burst are beamed, however, so to detect it, it would have to be point towards the earth, and many of the gamma bursts that we have accurate distance measurements for are currently outside our sensitivity range. We only have estimates for a fraction of GRBs though. Lower energy EM radiation may be possible to see as well with these mergers.
Before merging, yes, they do shed angular momentum before merging. In fact, if you calculated the angular momentum of two maximally spinning black holes, you'd realize that if you could combine them, it would larger than the maximal possible spin of a single black hole with the combined mass. They must and will radiate this away as gravitational waves before merging.
I think you might be confusing LVT151012 which was including in the announcement back in February and all the subsequent papers. That is a low significance trigger that may be another binary black hole merger. GW151226 is only being reported on now as it was still in the vetting process back in February.
For the most part, we concentrate on quantities far away from the sources as these are what we have a chance to measure and can more easily intuit. There are however, extremely precise simulations of GR that can numerically simulate the spacetime around close to mergers which of course includes all of these effects.
Funding for its construction was approved by India. We are hoping that it might coming online in ~ 5 years. It takes a long time to build everything from the ground up.
The answer is actually yes, at least in principle. In practice this would be extremely difficult (read impossible) due to the weakness of gravitational wave interactions.
