Fermi/GBM View of the 2019 and 2020 Burst Active Episodes of SGR J1935+2154

TL;DR

This study analyzes 148 bursts from SGR J1935+2154 observed with Fermi/GBM, revealing longer, softer bursts during recent activation, spectral evolution linked to magnetospheric plasma, and no direct radio-X-ray burst association except for the FRB 200428 event.

Contribution

It provides detailed spectral and temporal analysis of recent SGR J1935+2154 bursts, highlighting their evolution and contrasting radio associations, including the unique FRB event.

Findings

Bursts are longer and softer than previous activations.

Spectral evolution suggests increased plasma loading in the magnetosphere.

No typical radio bursts are associated with X-ray bursts, except for FRB 200428.

Abstract

We present temporal and time-integrated spectral analyses of 148 bursts from the latest activation of SGR J1935+2154, observed with Fermi/GBM from October 4th 2019 through May 20th 2020, excluding a ~130 s segment with a very high burst density on April 27th 2020. The 148 bursts presented here, are slightly longer and softer than bursts from earlier activations of SGR J1935+2154, as well as from other magnetars. The long-term spectral evolution trend is interpreted as being associated with an increase in the average plasma loading of the magnetosphere during bursts. We also find a trend of increased burst activity from SGR J1935+2154 since its discovery in 2014. Finally, we find no association of typical radio bursts with X-ray bursts from the source; this contrasts the association of FRB 200428 with an SGR J1935+2154 X-ray burst, to date unique among the magnetar population.