S5 update

Hi folks,

In LIGO land we've all been running full steam for a while, but it's time for an update.

S5 (the fifth science data run) has been going since early November and is scheduled to last about a year. It was certified (I think by the National Science Board?) as having reached the initial design goal, so we're officially in business.

Roughly speaking, S5 data is about twice as good as S4. That is, the strain noise is half what it was in S4. But there is room for improvement.

First, the duty cycle for triple coincidence (H1, H2, and L1 interferometers all running) wasn't so hot. The main culprit was L1. Before S4, Livingston was down every day due to logging next door. Improved seismic isolation fixed that, but for the first couple of months of S5 they started adding another building right next to the corner station. It's an education and outreach center, full of all sorts of goodies for the general public. That'll be great, but during the day it meant L1 was down even with the new isolation. The building is done, so we're seeing better duty cycle now.

Also, the noise below 100Hz was actually a bit worse than design. That's been slowly improving as some things were caught, but we still don't know what's causing it. Fair bet it's somehow up-conversion of 1-3Hz seismic noise from traffic, since it correlates pretty strongly with the working day and rush hour. Last time I did shifts in the control room was January, and during the day it was enough that we had to lower the laser power to avoid dropping out of lock constantly. One gravel truck wouldn't do it, but two in rapid succession would nail us. One figure of merit is the range to which we could see a signal from a binary neutron star signal. That was peaking at 12 megaparsecs for H1 back in January and dropping to 10 during the day. Now it's up to almost 14 on a good night.

Once the current Einstein@Home analysis finishes, we're probably going to do the same search on S5 data. That is, 30-hour chunks of data (which may span 40 hours of clock time due to dropouts) which require a search of a spindown parameter as well as sky position. But nothing is set in stone. We are still looking at the quality (duty cycle and stationarity) of the first few months of S5 data, and trying to decide if we want to do a longer search this time.

The reason we can contemplate doing that is that more of you have been joining and staying. And the ones running Windows have been a lot faster lately with help from Hungary.

Thanks from all of us,
Ben