The SGR 1806-20 magnetar signature on the Earth's magnetic field

TL;DR

This study detects a magnetar flare's signature in Earth's magnetic field using wavelet analysis on satellite data, revealing a 7.5-second modulation linked to the 2004 SGR 1806-20 event.

Contribution

First to identify the geomagnetic signature of a magnetar flare using satellite magnetic data and wavelet analysis.

Findings

Detected a 7.5 s modulated signal in Earth's magnetic field during the flare

Observed the event with both CHAMP magnetic data and DEMETER ion counters

Established a link between magnetar flares and geomagnetic disturbances

Abstract

SGRs denote ``soft $\gamma$-ray repeaters'', a small class of slowly spinning neutron stars with strong magnetic fields. On 27 December 2004, a giant flare was detected from magnetar SGR 1806-20. The initial spike was followed by a hard-X-ray tail persisting for 380 s with a modulation period of 7.56 s. This event has received considerable attention, particularly in the astrophysics area. Its relevance to the geophysics community lies in the importance of investigating the effects of such an event on the near-earth electromagnetic environment. However, the signature of a magnetar flare on the geomagnetic field has not previously been investigated. Here, by applying wavelet analysis to the high-resolution magnetic data provided by the CHAMP satellite, a modulated signal with a period of 7.5 s over the duration of the giant flare appears in the observed data. Moreover, this event was detected by the energetic ion counters onboard the DEMETER satellite.