Near IR Astrometry of Magnetars

TL;DR

This study reports high-precision near-infrared astrometry of magnetars, measuring their proper motions to understand their origins and kinematic properties, linking some to star clusters and comparing their velocities to pulsars.

Contribution

First precise proper motion measurements of magnetars using laser guide star adaptive optics, linking some to star clusters and comparing their velocities to pulsars.

Findings

Proper motions of SGR 1806-20 and SGR 1900+14 link them to young star clusters.

Measured transverse velocities of 350±100 km/s and 130±30 km/s for two magnetars.

Magnetar kinematics are similar to those of pulsars.

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.