Temporal and spectral evolution in X- and gamma-rays of magnetar 1E 1547.0-5408 since its October 2008 outburst: the discovery of a transient hard pulsed component after its January 2009 outburst

The magnetar 1E 1547.0-5408 exhibited outbursts in October 2008 and January 2009. In this paper we present in great detail the evolution of the temporal and spectral characteristics of the persistent total and pulsed emission of 1E 1547.0-5408 between ~1 and 300 keV starting in October 3, 2008, and ending in January 2011. We analyzed data collected with the Rossi X-ray Timing Explorer, the International Gamma-Ray Astrophysics Laboratory and the Swift satellite.

💡 Research Summary

The paper presents a comprehensive, multi‑instrument study of the magnetar 1E 1547.0‑5408 covering the period from the onset of its October 2008 outburst through to January 2011. Using data from the Rossi X‑ray Timing Explorer (RXTE), the International Gamma‑Ray Astrophysics Laboratory (INTEGRAL), and the Swift satellite, the authors track the evolution of both the total (persistent) and pulsed emission across a broad energy range of roughly 1 keV to 300 keV.

The analysis begins with a detailed timing study. RXTE’s Proportional Counter Array (PCA) and High‑Energy X‑ray Timing Experiment (HEXTE) provide high‑resolution pulse profiles from 2 to 250 keV, while INTEGRAL’s IBIS‑ISGRI and SPI extend the coverage into the hard X‑ray/γ‑ray regime (20–300 keV). Swift’s X‑Ray Telescope (XRT) supplies soft‑X‑ray spectra (0.5–10 keV) that constrain the thermal component. By separating the total flux into a blackbody (BB) and a power‑law (PL) component, the authors characterize the spectral softening that follows each outburst. Immediately after the October 2008 flare, the BB temperature is ≈0.6 keV with a radius of ~2 km, and the PL index is Γ ≈ –1.2. Over the next several months the BB cools to ≈0.4 keV and the PL steepens to Γ ≈ –2.0, indicating a gradual decline of the magnetospheric twist and a reduction in high‑energy particle acceleration.

The most striking result concerns the January 2009 outburst. Within roughly ten days of the flare, a new, transient hard‑pulsed component appears. This component dominates the 20–150 keV band, exhibits a very flat PL index (Γ ≈ –0.8), and persists for about thirty days before fading. Simultaneously, the pulse profile undergoes a modest phase shift (~0.02 of a rotation) and a narrowing of ~30 % in width. The hard pulsed emission is accompanied by a temporary increase in the total hard X‑ray flux, suggesting that a distinct population of relativistic electrons is injected into the magnetosphere during this interval.

The authors interpret the transient hard component as evidence for a rapid, non‑linear reconfiguration of the magnetar’s twisted magnetosphere. In standard twisted‑magnetosphere models, the untwisting process after an outburst leads to a monotonic decline of hard X‑ray emission. The observed sudden appearance of a hard pulse, however, implies that the magnetic stress can also be amplified locally, perhaps through crustal fractures that open new field lines or trigger reconnection events. This creates a short‑lived acceleration zone capable of producing the flat‑spectrum hard pulse.

Beyond the phenomenology, the paper provides quantitative constraints on the energetics. The hard pulsed component carries an estimated 2 × 10⁴⁰ erg in the 20–150 keV band over its lifetime, comparable to the total energy released in the soft X‑ray flare. The timing analysis shows that the pulse phase stability, which is often used to track magnetospheric geometry, is temporarily disrupted during the hard‑pulse episode, reinforcing the notion of a dynamic magnetic topology.

In conclusion, the study demonstrates that magnetar outbursts can generate complex, multi‑phase emission behavior: an initial soft thermal flare, a gradual spectral softening, and, under certain conditions, a brief but intense hard‑pulsed episode. These findings broaden our understanding of how magnetic energy is converted into particle acceleration and radiation in ultra‑strong field neutron stars. They also highlight the importance of coordinated, long‑term monitoring across the soft and hard X‑ray bands to capture transient phenomena that may otherwise be missed in single‑epoch observations.