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GCN Circular 19581

GRB 160625B: Fermi GBM initial observations
2016-06-26T00:53:38Z (8 years ago)
Eric Burns at U of Alabama <>
E. Burns (UAH) reports on behalf of the Fermi GBM Team:

"At 22:40:16.28 UT on 25 June 2016, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 160625B for the first time
(trigger 488587220 / 160625945).

The trigger resulted in an Autonomous Repoint Request (ARR)
by the GBM Flight Software owing to the high peak flux of the GRB.
This ARR was accepted and the spacecraft slewed to the GBM in-flight
location. The initial angle from the Fermi LAT boresight to
the GBM ground location is 40 degrees.

At 22:43:24.82 the Fermi LAT triggered on a bright
pulse from the same GRB (Dirirsa et al. 2016, GCN 19580). Owing to
the ARR the initial angle from the Fermi LAT boresight to the
LAT position at LAT trigger time was 12 degrees.

At 22:51:16.03 GBM triggered again on GRB 160625B
(trigger 488587880 / 160625952).

GRB 160625B is distinct from the Swift BAT GRB 160625A
(Maselli et al. 2016, GCN 19577).

The GBM light curve consists of multiple peaks over
approximately 700 seconds. The first peak is soft with a
duration of about 1 second. The main peak, corresponding
to the LAT trigger, is about 25 seconds long and is very
hard. The peak that triggered GBM for the second time is
about 30 seconds long and soft.

Standard GBM temporal and spectral analysis is awaiting
downlink of the full dataset and will be reported when
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