[vsnet-grb-info 11694] GRB 120316A: Fermi-GBM and Fermi-LAT Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13085
SUBJECT: GRB 120316A: Fermi-GBM and Fermi-LAT Observations
DATE:    12/03/21 21:22:59 GMT
FROM:    Giacomo Vianello at SLAC  <giacomov at slac.stanford.edu>

Giacomo Vianello (CIFS/SLAC), Nicola Omodei (Stanford U.), J. L.
Racusin (NASA/GSFC), P. Jenke (MSFC/NPP) report on behalf of the Fermi
GBM and LAT Teams:

At 00:11:02.56 UT on 16 March 2012, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 120316A (trigger 353549464 / 120316008),
which was also detected by Konus-Wind (GCN 13074) and triangulated by
the IPN (GCN 13073). The GBM H.I.T.L. location is found to be RA, Dec
(J2000) = 48.5, -64.3 with a error radius (90% containment,
statistical) of 1.2 degrees.

The GBM light curve shows multiple peaks with a duration of T90 = 27.5
+/- 0.4 seconds, and a signal extending to 500 keV in the NaI's and
850 keV in the BGO's.

The GRB is barely detected by the LAT, with a Test Statistic slightly
below the TS=25 threshold usually adopted for issuing circulars. The
best LAT on-ground location is found to be RA,Dec (J2000) = 57.97,
-56.46 with an error radius of 0.65 deg (90% containment, statistical
error only). This was 9.7 deg from the LAT boresight at the time of
the trigger.

The LAT position is compatible with that found by Zheng et al. (GCN
13070) and by Hurley et al. (GCN 13073), and is ~9 deg away from the
best GBM localization. Modeling of the uncertainties in GBM
localizations, using known reference locations, suggests that whilst
the majority (>90%) are well-represented by a ~3 deg systematic error,
GRB120316A appears to belong to a small tail which has a much larger
systematic uncertainty, centered on ~10 deg (see Connaughton et al.,
in preparation).

The spectrum of this GRB from 10 keV to 300 GeV, integrated over the
time interval 0-32 s from the trigger time, is well described by a
Band function with Epeak = 552 -25 +22 keV, alpha = -0.77 +/- 0.02,
beta = -2.90 +/-0.15. The fluence in the 10 keV - 1 MeV energy range
is 2.57 ( +/- 0.03 (stat) +/- 0.2 (sys) ) x 10^-5 erg/cm2, compatible
with the value found by Golenetskii et al (GCN 13074).

The spectral analysis results presented above are preliminary;

The Fermi LAT point of contact for this burst is Giacomo Vianello
(giacomov at slac.stanford.edu). The GBM point of contact is Peter Jenke
(peter.a.jenke at nasa.gov).

The Fermi LAT is a pair conversion telescope designed to cover the
energy band from 20 MeV to greater than 300 GeV. It is the product of
an international
collaboration between NASA and DOE in the U.S. and many scientific
institutions across France, Italy, Japan and Sweden.

-- 
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Giacomo Vianello

"A few observation and much reasoning lead
to error; many observations and a little
reasoning to truth." (A.Carrell)

http://www.slac.stanford.edu/~giacomov/

SLAC, 2575 Sand Hill Rd
Menlo Park, CA 94025

ICQ: 566213964
phone: (001)-(650)-926-2866
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