Rights:
© 1998 American Physical Society (APS). This is the accepted version of the following article: Hakonen, Pertti J. & Avenel, O. & Varoquaux, E. 1998. Evidence for Single-Vortex Pinning and Unpinning Events in Superfluid 4He. Physical Review Letters. Volume 81, Issue 16. 3451-3454. ISSN 0031-9007 (printed). DOI: 10.1103/physrevlett.81.3451, which has been published in final form at http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.81.3451.