TITLE:   GCN CIRCULAR
NUMBER:  17806
SUBJECT: GRB 150510A: Fermi-LAT Refined Analysis
DATE:    15/05/10 13:13:28 GMT
FROM:    Judith Racusin at GSFC  <judith.racusin@nasa.gov>

J. L. Racusin (NASA/GSFC), M. Axelsson (KTH), M. Yassine (LUPM), D. Kocevski (NASA/GSFC) 
report on behalf of the Fermi-LAT team:

Additional data on GRB 150510A has been downlinked from Fermi and processed, and we report 
an improved LAT localization of 

R.A., Dec = 16.16,  4.79 (J2000)

with an error radius of 0.36 deg (90% containment, statistical error only).  This was 55 deg from the 
LAT boresight at the time of the trigger.  The GRB position was within the LAT FoV from ~500 s prior 
to the trigger to ~T0+600 s, when an autonomous repoint request to the initial GBM flight position 
caused the spacecraft to slew away.

There are 13 photons with energies >100 MeV within a 12 degree radius around the GRB position. 
The highest energy photon is detected at T0+170 s with an energy of 1.5 GeV.  The burst is also 
detected in the LAT Low Energy (LLE) data with energies >30 MeV with a significance of 9 sigma 
above background with a duration of ~20 s, coinciding with the time of the GBM emission.

The GRB localization is within the Swift Sun avoidance constraint, and will not emerge until May 25, 
therefore a Swift TOO is not being requested.

The Fermi-LAT point of contact for this burst is Judith Racusin (judith.racusin@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.