Phase Drifts of Sub-pulses during the 2004 Giant Flare of SGR 1806-20 and Settling of the Magnetic Fields

TL;DR

This study analyzes the phase evolution of sub-pulses during the 2004 giant flare of SGR 1806-20, revealing how the magnetic field and emission regions stabilize over time after a major magnetic reconfiguration.

Contribution

It provides the first measurement of the timescale for magnetic field stabilization following a giant flare in a magnetar.

Findings

Sub-pulses' phases drift and then settle over time.

Characteristic timescale for magnetic field settling is between 37 and 84 seconds.

Insights into magnetic field reconfiguration dynamics in magnetars.

Abstract

We analyzed the observations of SGR 1806-20 performed with the \textit{Rossi X-ray Timing Explorer} (RXTE) during its 2004 giant flare. We studied the phase evolution of the sub-pulses identified in the X-ray waveform and found that the sub-pulses varied in phase with time and then gradually settled, which might indicate drifts of the emission regions in relative to the neutron star surface, or changes in the local emission geometry before the magnetic field became stable. The characteristic e-folding timescale of the phase drifts measured starting about 15 s following the initial flux spike are in the range between 37 s and 84 s. This leads to the first measurements of the characteristic timescale for the magnetic field of the neutron star to settle after a field reconfiguration during the giant flare.