Near IR Astrometry of Magnetars

Abstract

We report on the progress of our five-year program for astrometric monitoring of magnetars using high-resolution NIR observations using the laser guide star adaptive optics (LGS-AO) supported NIRC2 camera on the 10-meter Keck telescope. We have measured the proper motion of two of the youngest magnetars, SGR\,1806$-$20 and SGR\,1900+14, which have counterparts with K $\sim$21\,mag, and have placed a preliminary upper limit on the motion of the young AXP\,1E\,1841$-$045. The precision of the proper motion measurement is at the milliarcsecond per year level. Our proper motion measurements now provide evidence to link SGR\,1806$-$20 and SGR\,1900+14 with neighboring young star clusters. At the distances of these magnetars, their proper motion corresponds to transverse space velocities of $350\pm100\,\mathrm{km\,s^{-1}}$ and $130\pm30\,\mathrm{km\,s^{-1}}$ respectively. The upper limit on the proper motion of AXP\,1E\,1841$-$045 is $160\,\mathrm{km\,s^{-1}}$. With the sample of proper motions available, we conclude that the kinematics of the magnetar family are not distinct from that of pulsars.