[vsnet-grb-info 21381] GRB 181201A: Fermi-LAT detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23480
SUBJECT: GRB 181201A: Fermi-LAT detection
DATE:    18/12/02 02:41:40 GMT
FROM:    Magnus Axelsson at Stockholm U.  <magaxe at kth.se>

M. Arimoto (Kanazawa U.), M. Axelsson (KTH & Stockholm Univ.), and M. Ohno (Hiroshma U.) report on behalf of the Fermi-LAT team:

On December, 01, 2018, Fermi-LAT detected high-energy emission from GRB 181201A, which was also detected by INTEGRAL (Mereghetti et al., GCN 23469) and Swift/XRT (Pintore et al., GCN 23472).

The best LAT on-ground location is found to be

RA, Dec = 319.28, -12.60 (degrees, J2000)

with an error radius of 0.06 deg (90% containment, statistical error only).
This was 131 deg from the LAT boresight at the time of the INTEGRAL trigger:

T0 =  02:38:00 UT

and entered the LAT field of view ~2000 seconds later.

The data from the Fermi-LAT show a significant increase in the event rate that is spatially correlated with the INTEGRAL source (0.03 degrees from the INTEGRAL location) with high significance. The photon flux above 100 MeV in the time interval 2000-10000 s after the INTEGRAL trigger is (4.5 +/- 3.3) E-7 ph/cm2/s.

The estimated photon index above 100 MeV is -1.32+/-0.39.

The highest-energy photon is a 25.5 GeV event which is observed ~7600 seconds after the INTEGRAL trigger.

The Fermi-LAT point of contact for this burst is Masanori Ohno (ohno at astro.hiroshima-u.ac.jp<mailto:ohno at astro.hiroshima-u.ac.jp>).

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.