XMM-Newton view of Swift J1834.9-0846 and its Magnetar Wind Nebula

TL;DR

This paper analyzes XMM-Newton observations of the magnetar Swift J1834.9-0846, revealing a potential magnetar wind nebula with high X-ray efficiency likely powered by magnetar bursting activity, and characterizing its spectral and spatial properties.

Contribution

It presents the first evidence of a magnetar wind nebula around Swift J1834.9-0846 and analyzes its properties, suggesting a different energy source than rotation-powered pulsars.

Findings

Detection of a possible magnetar wind nebula with high X-ray efficiency.

Identification of a dust scattering halo around the source.

Decay of luminosity following a t^{-0.5} trend.

Abstract

We report on the analysis of two XMM-Newton observations of the recently discovered soft gamma repeater Swift J1834.9-0846, taken in September 2005 and one month after the source went into outburst on 2011 August 7. We performed timing and spectral analyses on the point source as well as on the extended emission. We find that the source period is consistent with an extrapolation of the Chandra ephemeris reported earlier and the spectral properties remained constant. The source luminosity decreased to a level of 1.6x10^34 erg s^-1 following a decay trend of $\propto t^{-0.5}$. Our spatial analysis of the source environment revealed the presence of two extended emission regions around the source. The first (Region A) is a symmetric ring around the point source, starting at 25arcsec and extending to ~50arcsec. We argue that Region A is a dust scattering halo. The second (Region B) has an asymmetrical shape extending between 50arcsec and 150arcsec, and is detected both in the pre- and post-outburst data. We argue that this region is a possible magnetar wind nebula (MWN). The X-ray efficiency of the MWN with respect to the rotation energy loss is substantially higher than those of rotation powered pulsars: $\eta_{\rm X}\equiv L_{\rm MWN,0.5-8 keV}/\dot{E}_{\rm rot}\approx0.7$. The higher efficiency points to a different energy source for the MWN of Swift J1834.9-0846, most likely bursting activity of the magnetar, powered by its high magnetic field, B=1.4x10^14 G.