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Published January 1, 2012 | Version v1
Journal article Open

DETECTION OF SPECTRAL EVOLUTION IN THE BURSTS EMITTED DURING THE 2008-2009 ACTIVE EPISODE OF SGR J1550-5418

Creators

  • 1. Max Planck Inst Extraterr Phys, D-85748 Garching, Germany
  • 2. NASA, George C Marshall Space Flight Ctr, Space Sci Off, Huntsville, AL 35812 USA
  • 3. Open Univ Israel, IL-43537 Raanana, Israel
  • 4. Rice Univ, Dept Phys & Astron, Houston, TX 77251 USA
  • 5. Sabanci Univ, Fac Engn & Nat Sci, TR-34956 Istanbul, Turkey
  • 6. Univ Amsterdam, Astron Inst Anton Pannekoek, NL-1090 GE Amsterdam, Netherlands
  • 7. Univ Alabama, Ctr Space Plasma & Aeron Res, Huntsville, AL 35805 USA
  • 8. NSSTC, Univ Space Res Assoc, Huntsville, AL 35805 USA

Description

In early 2008 October, the soft gamma repeater SGR J1550-5418 (1E 1547.0-5408, AX J155052-5418, 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 for 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 similar to 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 less than or similar to 8 degrees. Our spectral analysis indicates significant spectral evolution between the first and last set of events. Although the 2008 October events are best fitted with a single blackbody function, for the 2009 bursts an optically thin thermal bremsstrahlung 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.

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