Detection of spectral evolution in the bursts emitted during the 2008-2009 active episode of SGR J1550-5418
Von Kienlin, Andreas and Gruber, David and Kouveliotou, Chryssa and Granot, Jonathan and Baring, Matthew G. and Göğüş, Ersin and Huppenkothen, Daniela and Kaneko Göğüş, Yuki and Lin, Lin and Watts, Anna L. and Bhat, Narayana P. and Guiriec, Sylvain and Van der Horst, Alexander J. and Bissaldi, Elisabetta and Greiner, Jochen and Meegan, Charles A. and Paciesas, William S. and Preece, Robert D. and Rau, Arne (2012) Detection of spectral evolution in the bursts emitted during the 2008-2009 active episode of SGR J1550-5418. Astrophysical Journal, 755 (2). ISSN 0004-637X (Print) 1538-4357 (Online)
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Official URL: http://dx.doi.org/10.1088/0004-637X/755/2/150
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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