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GCN Circular 28797

Subject
GRB 201026A: Fermi GBM detection
Date
2020-10-28T00:03:33Z (4 years ago)
From
Rachel Hamburg at UAH <rkh0007@uah.edu>
R. Hamburg (UAH) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 22:37:33.06 UT on 26 October 2020, the Fermi Gamma-Ray Burst Monitor
(GBM)
triggered and located GRB 201026A (trigger 625444658 / 201026943), which
was initially misclassified as a distant particle event by the GBM
flight software. GRB 201026A was also detected by the Swift/BAT and the
Swift/XRT (Cenko et al. 2020, GCN 28784). The GBM on-ground location
is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 58
degrees.

The GBM light curve shows a main pulse with a duration (T90) of about
35 s (50-300 keV). There is also later emission extending to
approximately T0+280 s. We cannot conclusively confirm it is
related to the main emission episode with GBM data alone;
however, similar late-time emission can be seen in the
Swift-XRT lightcurve (Evans et al. 2020, GCN 28796).

The time-averaged spectrum of the main pulse from T0-16 s to T0+23 s
is best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.83 +/- 0.10 and
the cutoff energy, parameterized as Epeak, is 68 +/- 3 keV.
A Band function fits the spectrum equally well with
Epeak = 63 +/- 5 keV, alpha = -0.73 +/- 0.14 and beta = -2.84 +/- 0.34.

The event fluence (10-1000 keV) in this time interval is
(3.96 +/- 0.14)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.47 s in the 10-1000 keV band
is 3.04 +/- 0.22 ph/s/cm^2.

For the later emission episode, the time-averaged spectrum
from T0+188 s to T0+237 s is best fit by
a simple power law function with index -1.84 +/- 0.04.
The event fluence (10-1000 keV) in this time interval is
(4.51 +/- 0.29)E-06 erg/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support
Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
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