CHANDRAASTROMETRY SETS A TIGHT UPPER LIMIT TO THE PROPER MOTION OF SGR 1900+14

Abstract

The soft gamma-ray repeater 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, suggests a test of the association with a proper motion measurement. We used a set of three Chandra/Advanced CCD Imaging Spectrometer observations of the field spanning approximately five 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 3σ upper limit of 70 mas yr^–1 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 of an origin of the SGR within a nearby compact cluster of massive stars.