Object orbiting Jupiter

During stargazing, I aimed my 1.5 inch refractor at Jupiter, and while viewing, I saw a light slowly fade in over (north pole of Jupiter?) the disk of jupiter 2 disk diameters to the right.  It remained in sight for ~20 seconds then faded out at the same distance as it had appeared. 
I remained watching and found that this ball of light, approximately the same brightness as Jupiter's closest moon, had a period of approximately 5 minutes.  The site I viewed from was very dark and isolated, near the edge of a forest.  
This phenomenon lasted for about 2 weeks where I viewed it from several different spot.  
The only other person to have witnessed this event passed away 15 years ago.  I was 15 yrs old when we saw this object and I did not report it to anyone. 
My naieve thinking was that Jupiter had captured an asteroid. 
Whatever it was it had to be moon-sized in order for me to see its reflection.
Witness indicates that the date of the sighting is approximate.  PD