  The soft gamma-ray repeater (SGR) SGR 1900+14 lies a few arcminutes outside
the edge of the shell supernova remnant (SNR) G42.8+0.6. A physical association
between the two systems has been proposed - for this and other SGR-SNR pairs -
based on the expectation of high space velocities for SGRs in the framework of
the magnetar model. The large angular separation between the SGR and the SNR
center, coupled with the young age of the system, suggest a test of the
association with a proper motion measurement. We used a set of three
Chandra/ACIS observations of the field spanning 5 years to perform accurate
relative astrometry in order to measure the possible angular displacement of
the SGR as a function of time. Our investigation sets a 3-sigma upper limit of
70 mas/yr to the overall proper motion of the SGR. Such a value argues against
an association of SGR 1900+14 with G42.8+0.6 and adds further support to the
mounting evidence for an origin of the SGR within a nearby, compact cluster of
massive stars.
