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GCN Circular 30806

Fermi GBM observation of a bright flare in the direction of SGR 1935+2154
2021-09-11T00:20:44Z (3 years ago)
Oliver J Roberts at USRA/NASA <>
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:"
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