NuSTAR Observations of the Magnetar 1E 2259+586

TL;DR

This paper presents simultaneous NuSTAR and Swift observations of the magnetar 1E 2259+586, revealing pulsations above 20 keV, energy-dependent pulse shifts, and spectral features that support a coronal outflow model.

Contribution

It provides the first detection of pulsations above 20 keV in this magnetar and tests a coronal outflow model to explain its hard X-ray emission.

Findings

Pulsations detected above 20 keV for the first time.

Pulse profile shifts with energy observed.

Spectral data favor a coronal outflow from a ring over a polar cap.

Abstract

We report on new broad band spectral and temporal observations of the magnetar 1E 2259+586, which is located in the supernova remnant CTB 109. Our data were obtained simultaneously with the Nuclear Spectroscopic Telescope Array (NuSTAR) and Swift, and cover the energy range from 0.5-79 keV. We present pulse profiles in various energy bands and compare them to previous RXTE results. The NuSTAR data show pulsations above 20 keV for the first time and we report evidence that one of the pulses in the double-peaked pulse profile shifts position with energy. The pulsed fraction of the magnetar is shown to increase strongly with energy. Our spectral analysis reveals that the soft X-ray spectrum is well characterized by an absorbed double-blackbody or blackbody plus power-law model in agreement with previous reports. Our new hard X-ray data, however, suggests that an additional component, such as a power-law, is needed to describe the NuSTAR and Swift spectrum. We also fit the data with the recently developed coronal outflow model by Beloborodov for hard X-ray emission from magnetars. The outflow from a ring on the magnetar surface is statistically preferred over outflow from a polar cap.