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GCN Circular 8915

Subject
SGR J1550-5418
Date
2009-02-26T00:34:30Z (15 years ago)
From
Chryssa Kouveliotou at MSFC <chryssa.kouveliotou@nasa.gov>
SGR J1550-5418 (former AXP 1E 1547.0-5408): list of triggers from the Fermi Gamma-ray Burst Monitor (GBM)�� 

C. Kouveliotou (NASA-MSFC), A. von Kienlin (MPE), G. Fishman (NASA-MSFC), �V. Connaughton (UAH), A. van der Horst (NASA-MSFC/ORAU), and N. Bhat (UAH), report on behalf of the Fermi GBM Team:

During the current active period of SGR J1550-5418 which began on 22 January 2009 (GCNs 8833, 8835), the Fermi Gamma-ray Burst Monitor (GBM) has triggered on 117 discrete bursts through 24 February, of which 15 were extremely intense. Additionally, a multitude of untriggered events have also been recorded over the same period.� The source is still active, but with a decreased rate of triggers to ~twice per day, with exceptionally intense bursts occurring about once per week.� A list of all Fermi GBM triggers from SGR J1550-5418 in the time interval above, with the particularly intense events noted by an asterisk, is given at: http://gammaray.nsstc.nasa.gov/gbm/science/magnetars. NOTE: our trigger times are not necessarily the same as event peak times, depending on the event durations, which range from milliseconds to 1-2 sec. 

Many of the intense bursts from SGR J1550-5418 are expected to produce measurable ionospheric disturbances, as recorded by observations of VLF radio propagation (GCNs 8881, 8900).� Observations of these disturbances over different elevation angles could provide unique insight into the low energy (<2 keV) emission from this SGR during bursts, as well as the total ionizing X-ray fluence deposited in the upper atmosphere.� Correlations of these outbursts with data from detectors on other spacecraft are also encouraged.� Analyses of the duration, peak fluxes, fluences and spectral characteristics of these events from GBM data are in progress.

Finally, we would like to stress that the source bursting behavior clearly classifies it as a Soft Gamma Repeater, contrary to the initial classification as an Anomalous X-ray Pulsar (AXP) by Camilo et al. (2007, ApJL 666, 93), who only used the persistent source spectrum and pulsation period for a tentative classification. Similar to the Swift team (GCN 8901) therefore, we will call the source out as SGR J1550-5418 in the future.
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