GCN Circular 25726

The Fermi GBM Team reports an improvement to its automated final
localizations for onboard triggered GRBs.  These are the localizations
reported in the "Fermi GBM Final Real-time Localization" GCN Circulars and
the "GCN/FERMI_GBM_FINAL_POSITION" GCN Notices.

The RoboBA, in operation since early 2016, has been improved to provide
more accurate localizations, and the systematic uncertainty has been
reduced.  Specifically, the overall estimated systematic uncertainty for
localizations is a mixture of two Gaussians, one with a radius of 1.8
degrees (52% contribution) and one with a radius of 4.1 degrees (47%
contribution).

The RoboBA provides an estimate on the classification of the GRB: long or
short, with an accuracy of 92-95% relative to the T90 = 2 s split. Based on
the RoboBA classification, a long GRB will have a systematic uncertainty of
1.9 degrees (58% contribution) and 4.1 degrees (42% contribution).  A short
GRB will have a systematic uncertainty of 2.6 degrees (39% contribution)
and 4.4 degrees (61% contribution).  The HEALPix FITS files provided for
each localization will already incorporate the systematic.

The median 50% localization area has been reduced from 81 square degrees to
46 square degrees, and the median 90% localization area has been reduced
from 400 square degrees to 200 square degrees.  The 5%-95% range of the 90%
localization area has been reduced from (~400-6000) square degrees to
(~170-1100) square degrees.

We anticipate an automated localization for ~95% of triggered GRBs within
10 minutes of trigger time, and we will continue providing
Human-in-the-Loop localizations for the rest of the triggered GRBs with a
latency of up to a couple of hours.

For more details on the RoboBA, systematics estimation, and localization
improvement, please see https://arxiv.org/abs/1909.03006
Loading...