Starting from April 2007 , a search for solar daily variation of the muon intensity ( E _ { \mu } > 0.2 GeV ) at sea level and using two directional muon telescopes is in progress .
In this survey , several ground level enhancements ( GLEs ) on the muon counting rate background have been found .
Here , we highlight one of them , observed in the vertical telescope on 07 August 2007 for the following reasons : The GLE consists of a single narrow peak , with a statistical significance of 4.4 \sigma .
The GLE is in temporal coincidence with a SWIFT trigger N ^ { 0 } 287222 , at 21:16:05 UT according to the Burst Alert Telescope ( BAT ) on board of the SWIFT spacecraft .
However , the Swift StarTracker had lost stellar lock minutes before that and the resulting improper s/c attitude information caused BAT to ” trigger ” on a known source .
Even so , the SWIFT trigger coordinates are inside the effective field of view of the vertical Tupi muon telescope .
The temporal and directional coincidences between this GLE and the SWIFT satellite unknown event strongly suggest that they may be physically associated .
Details and implications of this possible association are reported in this work .