[vsnet-grb-info 19152] GRB 170222A: Fermi GBM observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20728
SUBJECT: GRB 170222A: Fermi GBM observation
DATE:    17/02/22 22:52:42 GMT
FROM:    Rachel Hamburg at UAH  <rkh0007 at uah.edu>

R. Hamburg (UAH), E. Bissaldi (Politecnico & INFN Bari), and C. Meegan
(UAH)
report on behalf of the Fermi GBM Team:

"At 05:00:59.08 UT on 22 February 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170222A (trigger 509432464 / 170222209),
which was also reported by IPN (Hurley et al. 2017, GCN 20722).

The on-ground calculated location, using the GBM trigger
data, is RA = 312.10, DEC = +12.45 (J2000 degrees,
equivalent to 20h 48m, 12d 27'), with an uncertainty
of 3.6 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] ).

Although the GBM localization is not consistent within 3 sigma
of the IPN localization, the GBM localization places this event
in the same part of the sky and is the same event as that reported by IPN.
The angle from the Fermi LAT boresight at the GBM trigger time using
the IPN position is 120 degrees.

The GBM light curve shows a single multi-peaked emission episode
with a duration (T90) of about 1.7 s (50-300 keV).
The time-averaged spectrum from T0-0.64 s to T0+2.43 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.70 +/- 0.08 and
the cutoff energy, parameterized as Epeak, is 862 +/- 118 keV.

The event fluence (10-1000 keV) in this time interval is
(5.31 +/- 0.19)E-06 erg/cm^2. The 0.64-sec peak photon flux measured
starting from T0+1.15 s in the 10-1000 keV band
is 17.4 +/- 1.9 ph/s/cm^2.

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