TITLE: GCN CIRCULAR NUMBER: 30806 SUBJECT: Fermi GBM observation of a bright flare in the direction of SGR 1935+2154 DATE: 21/09/11 00:20:44 GMT FROM: Oliver J Roberts at USRA/NASA <oliver.roberts@nasa.gov> O.J. Roberts (USRA/NASA-MSFC), J. Wood (USRA/NASA-MSFC), report on behalf of the Fermi GBM Team: "At 00:45:46.94 UT on 10 September 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located a bright, SGR-like flare from the direction of the magnetar SGR 1935+2154 (trigger 652927551/210910032). The flare was also observed by Konus Wind (Ridnaia et al., GCN 30804) and triangulated to an annulus incorporating the SGR position by the IPN (Ridnaia et al., GCN 30803). The on-ground calculated location using the Fermi GBM trigger data, is consistent with the known position of the SGR and the IPN localization. The angle from the Fermi LAT boresight at the GBM trigger time is 102 degrees. The burst has a duration (T90) of about 1.4 s (10-1000 keV). It is best fit by a double-blackbody model with temperatures of kT1 = 8.51 +/- 0.08 keV and kT2 = 16.55 +/- 0.18 keV. The event fluence (10-1000 keV) from T0-0.064s to T0+1.328s is (3.858 +/- 0.011)E-05 erg/cm^2. The average photon flux in the 10-1000 keV band during this period is 522.7 +/- 1.5 ph/s/cm^2. Fermi GBM has also triggered on 14 other bursts from the direction of SGR 1935+2154 over the last 4 days, indicating it has entered a stage of heightened activity in this latest outburst: Date and Time in UTC Fermi MET (s) 2021-09-06T01:44:30.10 652585475 2021-09-09T18:57:14.86 652906639 2021-09-09T20:21:28.37 652911693 2021-09-10T00:45:46.94 652927551 2021-09-10T01:00:43.71 652928448 2021-09-10T01:13:17.40 652929202 2021-09-10T01:27:05.60 652930030 2021-09-10T02:21:06.44 652933271 2021-09-10T02:36:38.24 652934203 2021-09-10T02:55:10.17 652935315 2021-09-10T05:35:55.51 652944960 2021-09-10T09:12:48.91 652957973 2021-09-10T15:50:56.89 652981861 2021-09-10T23:40:34.46 653010039 The spectral analysis results presented above are preliminary. We encourage multi-wavelength observations to follow-up this most recent activation. For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"