First Very Low Frequency detection of short repeated bursts from magnetar SGR J1550-5418

TL;DR

This study demonstrates that Earth's ionosphere can detect magnetar gamma-ray bursts via VLF radio wave disturbances, offering a new method for monitoring high-energy astrophysical events.

Contribution

First detection of ionospheric disturbances caused by short gamma-ray bursts from a magnetar using VLF radio data.

Findings

VLF signals show amplitude and phase changes correlated with gamma-ray bursts.

Maximum VLF changes correlate with gamma-ray fluence.

VLF recovery timescales do not correlate with fluence.

Abstract

We report on the first detection of ionospheric disturbances caused by short repeated gamma-ray bursts from the magnetar SGR J1550-5418. Very low frequency (VLF) radio wave data obtained in South America clearly show sudden amplitude and phase changes at the corresponding times of eight SGR bursts. Maximum amplitude and phase changes of the VLF signals appear to be correlated with the gamma-ray fluence. On the other hand, VLF recovery timescales do not show any significant correlation with the fluence, possibly suggesting that the bursts' spectra are not similar to each other. In summary, the Earth's ionosphere can be used as a very large gamma-ray detector and the VLF observations provide us with a new method to monitor high energy astrophysical phenomena without interruption such as Earth Occultation.