Proper Motions and Origins of SGR 1806-20 and SGR 1900+14

TL;DR

This study uses high-resolution infrared observations over five years to measure the proper motions of magnetars SGR 1806-20 and SGR 1900+14, linking them to their progenitor clusters and estimating their ages and braking indices.

Contribution

It provides the first robust proper motion measurements of these magnetars, confirming their origins and offering insights into their spin-down mechanisms.

Findings

Proper motions confirm association with star clusters.

Measured transverse velocities are 350 km/s and 130 km/s.

Braking indices are lower than the canonical value, indicating alternative dissipation processes.

Abstract

We present results from high-resolution infrared observations of magnetars SGR1806-20 and SGR 1900+14 over 5 years using laser-supported adaptive optics at the 10-m Keck Observatory. Our measurements of the proper motions of these magnetars provide robust links between magnetars and their progenitors and provide age estimates for magnetars. At the measured distances of their putative associations, we measure the linear transverse velocity of SGR 1806-20 to be 350 +/- 100 km/s and of SGR 1900+14 to be 130 +/- 30 km/s. The transverse velocity vectors for both magnetars point away from the clusters of massive stars, solidifying their proposed associations. Assuming that the magnetars were born in the clusters, we can estimate the braking index to be ~1.8 for SGR 1806-20 and ~1.2 for SGR 1900+14. This is significantly lower than the canonical value of n = 3 predicted by the magnetic dipole spin-down suggesting an alternative source of dissipation such as twisted magnetospheres or particle winds.