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GCN Circular 20505

Subject
GRB 170121B: Fermi GBM detection
Date
2017-01-23T01:04:55Z (7 years ago)
From
Rachel Hamburg at UAH <rkh0007@uah.edu>
R. Hamburg (UAH), C. Meegan (UAH), and P. Veres (UAH)
report on behalf of the Fermi GBM Team:

"At 14:44:22.41 UT on 21 January 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170121B (trigger
506702667 / 170121614).

It may be noted that this burst is distinct from GRB 170121A
(trigger 506655418 / 170121067), which was also detected by POLAR
(H.L. Xiao et al. 2017, GCN 20501).

A potential optical counterpart to GRB 170121B was detected
by MASTER, although it was referenced as GRB 170121A
(V. Lipunov et al. 2017, GCN 20502).

The on-ground calculated location, using the GBM trigger
data, is RA = 72.84, DEC = -12.65, with an uncertainty
of 1.78 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which we have characterized as a core-plus-tail model, with 90% of
GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg
systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ).

The angle from the Fermi LAT boresight at the GBM trigger time is 74
degrees.

The GBM light curve shows two main peaks
with a duration (T90) of about 46 s (50-300 keV).
The time-averaged spectrum from T0-2.05 s to T0+43.01 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.00 +/- 0.02 and
the cutoff energy, parameterized as Epeak, is 455.90 +/- 27.70 keV.

The event fluence (10-1000 keV) in this time interval is
(2.97 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+24.6 s in the 10-1000 keV band
is 9.4 +/- 0.3 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

[GCN OPS NOTE(23jan17), Per author's request, the Subject and first sentence
were changed from "160121B" to "170121B".]
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