GCN Circular 17385

M. Axelsson (KTH Royal Institute of Technology, Stockholm) and G. Vianello (Stanford)
report on behalf of the Fermi-LAT team:

At 23:59:08.27 UT on February 2, 2015, Fermi-LAT detected
emission from GRB 150202B, which was also detected by Fermi-GBM
(trigger 444614351/150202999).

The GBM location was initially inside the LAT field of view at an angle of
~17 degrees to the LAT boresight and triggered an autonomous repoint
of the spacecraft. Using standard analysis procedures, we detect the GRB
with a significance barely above our 5-sigma threshold, when looking at
events >500 MeV in the interval 0s to 1300s relative to the trigger time. The
corresponding best location is

RA = 86.6 deg (J2000)
Dec = 59.1 deg (J2000)

with an estimated uncertainty of 0.4 degrees (90% containment). This is
0.5 deg from the GBM position.

Given the low significance, and the fact that there are only 4 photons compatible
with the position of the GBM trigger, we cannot firmly establish this excess as
the high-energy counterpart of GRB 150202B.

Using the LAT Low Energy (LLE) data selection, over 70 counts above
background were detected within a 20s interval coinciding with the time of
the GBM emission. This data selection has insufficient spatial resolution to
provide a reliable LAT localization. Since an excess of events was not firmly
seen using the standard analysis selection, this detection is likely due to low
energy gamma-rays (below 100 MeV).

The Fermi LAT point of contact for this burst is
Magnus Axelsson (magnus.axelsson@astro.su.se<mailto:magnus.axelsson@astro.su.se>).

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.

[GCN OPS NOTE(03feb15):  Per author's request, the "0127A" was changed to "202B"
in the phrase "counterpart of GRB 150202B".]