One ipothesized sorce for the site-wide correlated glitches are railway tracks. the closest train stations to Virgo NEB are S.Frediano a Settimo (2.5km from NEB) and Cascina (2.9 km fron NEB). We took a 2hours magnetic (fluxgate probe) recording at about 50m from the S.Frediano train station. Data are from Sunday January 29 between 20:17 UTC and 22:18 UTC. Figure 1 shows the spectrogram of the recording (top), on the bottom is the correspondig specrogram of the NEB N magnetometer.

Several correlated transients are evident. Figures 2 and 3 show some. These are generally significanlty more intense in the magnetometer near the station than at NEB. Figure 4 compares the spectra during a bunch of these transients: they are ~ ten times more intense at the station, and the coherence is very good.

During the two hours four trains stopped and reparted from the station, at (LT): 21:12, 21:42, 22:41, 23:05. Only the first one produced a very intense magnetic signal at the station consisting of non stationary frequency lines (Figure 5). Noticeably there is no counterpart of it in the NEB magnetometer.

These data support the hypothesis that the observed correlated magnetic glitches at Virgo originate from railways. The specific location or track section which produce the disturbance is not identified.

We noticed, first in VIM spectrograms, that the infamous low frequency magnetic glitches seen by all magnetometers site-wide suddenly disappeared during last week-end.

Searching information we found out that railway traffic was suspended during those two days between Pisa and Empoli stations because of works along the line (also in the attached pdf):

https://www.rfi.it/it/news-e-media/comunicati-stampa-e-news/2026/1/16/rfi---linea-firenze---empoli---pisa--lavori-di-manutenzione-e-po.html?utm_source=chatgpt.com

Few observations:

We altready knew that these glitches are related to trains but...

• This finally proves that they are generated within the Pisa - Empoli railway section
• These glitches disappeared completely from CEB and NEB magnetometers, instead some are still seen in WEB magnetometers (Figure 4). This probably tell us that the WEB sees also glitches from a different railway line, the freight line that runs approx. North-South: see the map in Figure 5.

Spectrograms in Figures 6 to 9 show an insight of the time of the disappearing/reappearing:

• Figure 6, 7 and 8 show the NEB magnetometer (the closest to the Pisa-Empoli railway): the interpretation (Federico) is that first the train transit stops, than approx one hour later (/ one hour before) the electric line is de-electrified (/ re-electrified). A large glitch can be seen at these times: in Figures 7 and 8, respectively.
• Figure 9 is the WEB magnetometer, on the same color scale and time window as Figure 6: note that in this case the glitch density reduces just a bit.