Detection of spectral evolution in the bursts emitted during the 2008-2009 active episode of SGR J1550 - 5418

Abstract

In early October 2008, the Soft Gamma Repeater SGRJ1550 - 5418 (1E 1547.0 - 5408, AXJ155052 - 5418, PSR J1550 - 5418) became active, emitting a series of bursts which triggered the Fermi Gamma-ray Burst Monitor (GBM) after which a second especially intense activity period commenced in 2009 January and a third, less active period was detected in 2009 March-April. Here we analyze the GBM data all the bursts from the first and last active episodes. We performed temporal and spectral analysis for all events and found that their temporal characteristics are very similar to the ones of other SGR bursts, as well the ones reported for the bursts of the main episode (average burst durations \sim 170 ms). In addition, we used our sample of bursts to quantify the systematic uncertainties of the GBM location algorithm for soft gamma-ray transients to < 8 deg. Our spectral analysis indicates significant spectral evolution between the first and last set of events. Although the 2008 October events are best fit with a single blackbody function, for the 2009 bursts an Optically Thin Thermal Bremsstrahlung (OTTB) is clearly preferred. We attribute this evolution to changes in the magnetic field topology of the source, possibly due to effects following the very energetic main bursting episode.

17 pages, 7 figures, 2 tables

References in corpus (6)

• The strongest cosmic magnets: Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars
• 1E 1547.0-5408: a radio-emitting magnetar with a rotation period of 2 seconds
• A Swift gaze into the 2006 March 29th burst forest of SGR 1900+14
• The Compact X-ray Source 1E 1547.0-5408 and the Radio Shell G327.24-0.13: A New Proposed Association between a Candidate Magnetar and a Candidate Supernova Remnant
• Ground-based calibration and characterization of the Fermi Gamma-Ray Burst Monitor Detectors
• The 2008 May burst activation of SGR 1627-41

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• Quasi-Periodic Oscillations in Short Recurring Bursts of the Soft-Gamma Repeater J1550-5418
• High Frequency Radio Observations of Two Magnetars, PSR J1622$-$4950 and 1E 1547.0$-$5408
• Burst and Outburst Characteristics of Magnetar 4U 0142+61
• Prospects for Time-Domain and Multi-Messenger Science with eXTP
• Spectral Evidence of Heavy Nuclei from the Neutron Star Crust in Magnetar Bursts