$\rm 4-8~GHz$ Spectro-temporal Emission from the Galactic Center Magnetar $\rm PSR~J1745-2900$

TL;DR

This study presents detailed spectro-temporal observations of the Galactic Center magnetar PSR J1745-2900 at 4-8 GHz, revealing its emission characteristics, spectral behavior, and pulse profile variations over time, with implications for understanding magnetar activity.

Contribution

First detailed 4-8 GHz spectro-temporal analysis of the GC magnetar PSR J1745-2900, highlighting its emission stability, spectral features, and pulse profile dynamics over several years.

Findings

Magnetar emitted a flat spectrum over 5-8 GHz.

Gradual weakening of activity from 2016-2019.

Detection of marginally resolved sub-pulses with opposing spectral indices.

Abstract

Radio magnetars are exotic sources noted for their diverse spectro-temporal phenomenology and pulse profile variations over weeks to months. Unusual for radio magnetars, the Galactic Center (GC) magnetar $\rm PSR~J1745-2900$ has been continually active since its discovery in 2013. We monitored the GC magnetar at $\rm 4-8~GHz$ for 6 hours in August$-$September 2019 using the Robert C. Byrd Green Bank Telescope. During our observations, the GC magnetar emitted a flat fluence spectrum over $\rm 5-8~GHz$ to within $2\sigma$ uncertainty. From our data, we estimate a $\rm 6.4~GHz$ period-averaged flux density, $\overline{S}_{6.4} \approx (240 \pm 5)~\mu$Jy. Tracking the temporal evolution of $\overline{S}_{6.4}$, we infer a gradual weakening of GC magnetar activity during $2016-2019$ relative to that between $2013-2015.5$. Typical single pulses detected in our study reveal marginally resolved sub-pulses with opposing spectral indices, a feature characteristic of radio magnetars but unseen in rotation-powered pulsars. However, unlike in fast radio bursts, these sub-pulses exhibit no perceptible radio frequency drifts. Throughout our observing span, $\rm \simeq 5~ms$ scattered pulses significantly jitter within two stable emission components of widths, $\rm 220~ms$ and $\rm 140~ms$, respectively, in the average pulse profile.