GCN Circular 19817

E. Burns (UAH), A. Goldstein (USRA), P. Jenke (UAH) and
L. Blackburn (CfA) report on behalf of the Fermi GBM team:

We have searched the Fermi Gamma-ray Burst Monitor data for a
gamma-ray counterpart to the IceCube neutrino 160806A
(Cowen 2016, GCN 19787
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 ).

The location of the neutrino was observed by GBM with good
geometry. The closest on-board trigger was more than 90 minutes
after the neutrino time and came from a different position on the sky.

Measurements using the Earth Occultation technique (Wilson-Hodge et al.
2012,
ApJS, 201, 33) around this position place a three sigma flux upper limit of
about 160 mCrab between 12 and 100 keV between August 5th and 7th.

A seeded search for impulsive emission with duration between 0.256 s and
8.192 s around the time and sky location of the detected neutrino yielded no
candidates above the GBM background. The search method was developed
to look for electromagnetic counterparts in the GBM data of sub-threshold
gravitational wave signals found in the LIGO data
(Blackburn et al. 2015, ApJS, 217, 8), and implemented here searching from
30 s before to 30 s after and seeded with the position of the detected
neutrino.

A blind search for untriggered impulsive emission in the GBM data
centered on the neutrino detection looking for events between 0.1 s and 32
s
durations yielded no candidates consistent with the position of the
neutrino.
This search technique was developed for the detection of untriggered short
GRBs in the GBM data (Briggs et al., in prep.).

There is some flaring activity from Vela X-1 around the time of interest,
most
notably around T0+500 seconds. This is unrelated.

With no impulsive emission found we set model-dependent 1 second peak flux
3 sigma upper limits on prompt emission. Using a cutoff power law model with
index -0.42 and Epeak of 566 keV, representative of a typical short GRB,
the
limit in the 10-1000 keV range is 9.3x10^-7 erg/cm^2/s.

The INTEGRAL SPI-ACS found four intervals of burst-like excesses
(Savchenko 2016, GCN 19789
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 ). Both the Sun and the neutrino location were
occulted by the Earth for Fermi for the first interval. We found no
evidence
for the other three burst-like excesses in any detectors. Combining the
SPI-ACS detection with the GBM non-detection for these three times allows
us to infer that these SPI-ACS bursts are most likely due to a source
occulted by the Earth for Fermi rather than a solar or neutrino source
origin.