GCN Circular 15228

Andrew C. Collazzi (NASA/ORAU), Shaolin Xiong (UAH), and Chryssa 
Kouveliotou (NASA/MSFC), report on behalf of the GBM-Magnetar Team:

At 15:00:28.44 UT on 13 September 2013, the Fermi Gamma-Ray Burst
Monitor triggered and located a very bright, SGR-like burst (trigger 
400777231/130913625).  The on-ground calculated location, using the 
Fermi GBM trigger data, is RA = 278.88, Dec = -8.49 (J2000 degrees, 
equivalent to J2000 18h 35m, -8d 29'), with a statistical uncertainty 
of 1.0 degrees (radius, 1-sigma containment, statistical only; there 
is additionally a systematic error which is currently estimated to be
2 to 3 degrees).

This burst consists of a single pulse, with a duration of
T90 = 112 +/- 6 ms.  The burst is well-fit by a two blackbody model
with blackbody temperatures of kT1 = 5.3 +/- 0.2 keV and kT2 = 13.0
+/- 0.4 keV.  The corresponding peak flux integrated over 4ms
(8-200 keV) is (1.12 +/- 0.02)E-05 erg/s/cm^2. The fluence during
T0-0.016s to T0+0.132s is (1.66 +/- 0.02)E-6 erg/cm^2.  This
interval is also well fit by a Comptonized model with
Epeak = 32.4 +/- 0.6 and alpha = -0.40 +/- 0.09.

This burst was followed by another, fainter, SGR-like trigger at 
18:10:05.95 UT (trigger 400788608/130913757).  The on-ground 
calculated location, using the Fermi GBM trigger data, is RA = 281.25,
Dec = -8.35 (J2000 degrees, equivalent to J2000 18h 35m, -8d 29'),
with a statistical uncertainty of 7.6 degrees (see above on GBM 
location errors).

The second burst comprises a single pulse with a duration of T90 = 72
+/- 25 ms.  Its spectrum is best fit by a OTTB model with kT = 58.0
+/- 12.0 keV.  The corresponding peak flux, integrated over 4ms
(8-200 kev), is (6.2 +/- 0.7)E-07  erg/s/cm^2. The fluence during
T0-0.032s to T0+0.080s is (6.9 +/- 0.81)E-8 erg/cm^2.

Given the closeness of these bursts in location and in time, we
suggest that they come from the same source, most likely SGR J1833-0832; 
however, we note that the 3-sigma contour for both bursts contains 
several known magnetar sources.

The analysis results presented above are preliminary.