In order to investigate the coupling mechanism of the 401 Hz peak to hrec, we injected a line at 405 Hz:

• Magnetic injection: using the small coil, varying its orientation, (Figure 3, 4, 5)

• Seismic injection: using the shaker at the same frequency.

Preliminary observations:
The injected line at 405 Hz is slightly visible in hrec for both magnetic and seismic injections, Figure 1 and Figure 2.
Looking at the coherence between hrec and the magnetometer (*DT_MAG*) on the DET tower base (inside lab), as well as the accelerometer (*DT_ACC*) on the flange, the magnetic coherence appears slightly higher than the seismic coherence.

The injection times are reported in the attached file.