SFT data preparation using GEO E7 data m.alessandra papa max planck institut f. gravitationasphysik

What time baseline ? in principle the longer the better and the constraint comes from highest intrinsic search frequency that you want to search for in practice, if you want consecutive stretches of data during which the detector was in-lock as input to your FFT routines and if the detector is not always in-lock, longer time baseline means reducing the amount of data that you consider

What time baseline ? 60 seconds in order to get 72% of data

Why did we decide not to pad if you pad with zeros you exploit the data best but you waste computational power in the Demod if you pad with the average value of the noise you waste computational power and you add noise in the filtering. if you require continuous stretches of data, the SFTs are simpler objects, you may throw away some data but you can minimize this by going to shorter time baselines. In turn this enhances the computational load in Demod.

The E7 GEO SFTs A complete copy of all GEO data from E7 run was stored in Hannover and at the AEI. Frame servers were running at both locations and data could be easily downloaded on-line (channel x from time t1 to time t2) using M. Hewtson’s software GEOTOOLS from remote locations. During E7 we have lost some data: total of 1 minute. Based on quality-channel 1s average trend-data, the 60s stretches where selected. A timestamp list was created: entries – roughly 10 days, starting on Jan 1 at 00:00

The timestamps Maximum out-of-lock: 3.8 hours

The SFT format Simple binary format first set up for driver of Hough hierarchical code: FFT Data Re Im Re Im. header 32 bytes: REAL8 endian INT4 gps_sec INT4 gps_nsec REAL8 tbase INT4 firstfreqindex INT4 nsamples 1 2 nsamples There’s only few relevant standard commands: fopen, fclose,fread,fwrite,fseek

A Power Spectral Density figure derived from one of the SFT files sampling: Hz, calibrated hoft channel, samples

100 SFTs, sqrt(power spectr. density) 1e-19 1e-18 1e-17 1e Hz Hz1283.4

Six power spectral density plot from consecutive SFTs

It’s the system settling back after loss of lock. Mean sqrt PSD in band ΔT / Tsft between 2 consecutive SFTs