Variation of Spectral and Timing Properties in the Extended Burst Tails from the Magnetar 4U 0142+61

TL;DR

This study analyzes spectral and timing variations in extended burst tails from magnetar 4U 0142+61, revealing distinct behaviors and proposing a trapped fireball model to explain the observed properties and spectral features.

Contribution

It provides detailed analysis of spectral and temporal evolution in magnetar burst tails and introduces a model involving a trapped fireball to explain the energetics and features.

Findings

Enhanced pulsation amplitude during bursts

Cooling trend in X-ray emission during tails

Detection of spectral lines possibly due to cyclotron resonance

Abstract

Extended emission episodes with intensity above the pre-burst level are observed following magnetar bursts from a number of soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs). Such extended tail emission were observed subsequent to two events detected from AXP 4U 0142+61. We investigated in detail the evolution of spectral and temporal properties during these two tail segments using RXTE/PCA observations, and report distinct variations both in the spectral and temporal behavior throughout the tails. In particular, sudden enhancement of pulsation amplitude in conjunction with bursts, and smooth decline of X-ray emission (cooling) during the tail were observed in both cases. We suggest that an inefficiently radiating trapped fireball formed during the burst, which can heat up the stellar surface, is able to explain the tail properties and its energetics. We also present the episodic detection of absorption and emission features during tails. One possible mechanism that has been proposed to give rise to such spectral lines is the proton/ion cyclotron resonance process which has been suggested to offer a valuable tool in probing the complex magnetic field of magnetars.