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GCN Circular 30831

Subject
Fermi GBM observation of another bright burst in the direction of SGR 1935+2154
Date
2021-09-13T03:33:14Z (3 years ago)
From
Oliver J Roberts at USRA/NASA <oliver.roberts@nasa.gov>
O.J. Roberts (USRA/NASA-MSFC) reports on behalf of the Fermi GBM Team:

"At 20:16:10.44 UT on 12 September 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located a bright, SGR-like burst from the direction of
the magnetar SGR 1935+2154 (trigger 653170575/210912845).

The GBM on-ground location is consistent with the known position of the SGR.

The angle from the Fermi LAT boresight at the GBM trigger time is 96 degrees.

The event episode has a duration (T90) of about 1 s (10-1000 keV). During this
time interval, there are several very short bursts. The first burst has a
rapid risetime.

The whole event is best fit with a power law function
with an exponential high-energy cutoff. The power law index is 0.08 +/- 0.08 and
the cutoff energy, parameterized as Epeak, is 32.1 +/- 0.3 keV.

The time-integrated event fluence (10-1000 keV) from T0-0.064 to T0+0.944s is
(3.545 +/- 0.038)E-6 erg/cm^2. The average photon flux in the
10-1000 keV band during this period is 84 +/- 1 ph/s/cm^2.

Fermi GBM has also triggered on a further 24 bursts from the direction of SGR 1935+2154
since yesterday's GCN (Roberts and Wood, GCN 30806Not found
 
 
):

Date and Time in UTC     Fermi MET (s)
2021-09-12T23:19:32.08  653181577
2021-09-12T20:16:10.44  653170575
2021-09-12T15:03:50.60  653151835
2021-09-12T13:55:16.45  653147721
2021-09-12T12:19:20.44  653141965
2021-09-12T10:10:11.73  653134216
2021-09-12T07:28:07.46  653124492
2021-09-12T06:51:13.22  653122278
2021-09-12T05:14:07.84  653116452
2021-09-11T02:36:38.24  653093506
2021-09-11T20:22:59.04  653084584
2021-09-11T20:05:46.22  653083551
2021-09-11T18:54:36.05  653079281
2021-09-11T17:01:09.77  653072474
2021-09-11T16:50:03.83  653071808
2021-09-11T16:36:57.91  653071022
2021-09-11T15:26:11.55  653066776
2021-09-11T15:15:25.44  653066130
2021-09-11T15:03:00.55  653065385
2021-09-11T13:27:33.85  653059658
2021-09-11T11:53:57.29  653054042
2021-09-11T10:42:51.85  653049776
2021-09-11T05:32:38.65  653031163
2021-09-11T03:02:28.36  653022153

Fermi GBM will not report on future triggers from this event.

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/"