The High Frequency Radio Emission of the Galactic Center Magnetar SGR J1745-29 During a Transitional Period

TL;DR

This study reports the detection and analysis of high-frequency radio emission from the Galactic Center magnetar SGR J1745-29, revealing pulsed emission, bright short pulses, and flux variability, advancing understanding of magnetar radio emission mechanisms.

Contribution

First detection of pulsed radio emission at frequencies above 20 GHz from SGR J1745-29, showing flux variability and short-duration pulses, indicating magnetospheric origin.

Findings

Detected pulsed emission at >20 GHz with ~75 ms pulse width.

Observed bright, short (<10 ms) pulses in ~70% of rotations.

Flux density varied by a factor of two over ~20 minutes.

Abstract

The origin of the high-frequency radio emission detected from several magnetars is poorly understood. In this paper, we report the ~40 GHz properties of SGR J1745-29 as measured using Jansky Very Large Array (JVLA) and Robert C. Byrd Green Bank Telescope (GBT) observations between 2013 October 26 and 2014 May 31. Our analysis of a Q-band (45 GHz) GBT observation on 2014 April 10 resulted in the earliest detection of pulsed radio emission at high frequencies (>20 GHz); we found that the average pulse has a singly peaked profile with width ~75 ms (~2% of the 3.764 s pulse period) and an average pulsed flux density of ~100 mJy. We also detected very bright, short (<10 ms) single pulses during ~70% of this neutron star's rotations, and the peak flux densities of these bright pulses follow the same log-normal distribution as measured at 8.5 GHz. Additionally, our analysis of contemporaneous JVLA observations suggest that its 41/44 GHz flux density varied between ~1-4 mJy during this period, with a ~2x change observed on ~20 minute timescales during a JVLA observation on 2014 May 10. Such a drastic change over short time-scales is inconsistent with the radio emission resulting from a shock powered by the magnetar's supersonic motion through the surrounding medium, and instead is dominated by pulsed emission generated in its magnetosphere.