Detection of the magnetar SGR J1745-2900 up to 291 GHz with evidence of polarized millimetre emission

TL;DR

This study reports the detection of the magnetar SGR J1745-2900 up to 291 GHz, providing evidence of polarized millimetre emission and revealing spectral variability that informs models of pulsar emission and Galactic Centre studies.

Contribution

First detection of SGR J1745-2900 up to 291 GHz with polarization evidence, extending previous frequency limits and highlighting spectral complexity.

Findings

Detection up to 291 GHz with polarization evidence

Spectral index slightly inverted with variability

Spectrum not well described by a single power law

Abstract

In Torne et al. (2015), we showed detections of SGR J1745-2900 up to 225 GHz (1.33 mm); at that time the highest radio frequency detection of pulsar emission. In this work, we present the results of new observations of the same magnetar with detections up to 291 GHz (1.03 mm), together with evidence of linear polarization in its millimetre emission. SGR J1745-2900 continues to show variability and is, on average, a factor $\sim$4 brighter in the millimetre band than in our observations of July 2014. The new measured spectrum is slightly inverted, with $\left<\alpha\right> = +0.4\pm0.2$ (for $S_{\nu} \propto \nu^{\alpha})$. However, the spectrum does not seem to be well described by a single power law, which might be due to the intrinsic variability of the source, or perhaps a turn-up somewhere between 8.35 and 87 GHz. These results may help us to improve our still incomplete model of pulsar emission and, in addition, they further support the search for and study of pulsars located at the Galactic Centre using millimetre wavelengths.