[vsnet-grb-info 20271] GRB 180120A: Fermi GBM Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22367
SUBJECT: GRB 180120A: Fermi GBM Detection
DATE:    18/01/23 22:32:28 GMT
FROM:    Matthew Stanbro at UAH/Fermi  <mcs0001 at uah.edu>

M. Stanbro and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 04:58:13.00 UT on 20 January 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180120A (trigger 538117098 / 180120207)
which was also detected by the CALET Gamma-ray Burst Monitor
(Y. Shimizu et al. 2018, GCN 22366).

The on-ground calculated location, using the GBM trigger
data, is RA = 151.77, DEC = 27.79, with an uncertainty
of 1 degree (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 85
degrees.

The GBM light curve consists of several episodes
with a duration (T90) of about 29 s (50-300 keV).
The time-averaged spectrum from T0+0.90 s to T0+30.59 s is
best fit by a Band function with Epeak = 130 +/- 2 keV,
alpha = -1.05 +/- 0.01, and beta = -2.58 +/- 0.05.

The event fluence (10-1000 keV) in this time interval is
(6.27 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+17.66 s in the 10-1000 keV band
is 36.70 +/- 0.50 ph/s/cm^2.

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