GCN Circular 20928

V. Savchenko, C. Ferrigno (ISDC, University of Geneva, CH),
P. Ubertini, A. Bazzano, L. Natalucci (INAF IAPS-Roma, Italy),
S. Mereghetti (INAF IASF-Milano, Italy),
P. Laurent (CEA, Saclay, France),
E. Kuulkers (ESTEC/ESA, The Netherlands)

Using INTEGRAL SPI-ACS we have performed a search for a prompt
gamma-ray counterpart of the cosmic neutrino candidate AMON IceCube
EHE 80305071 129307.

At the time of the event (2017-03-21 07:32:20.69 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The neutrino localization was
at an angle of 101 deg with respect to the spacecraft pointing axis.
This orientation implies near-optimal response of SPI-ACS, and this
instrument provides best sensitivity to both short and long GRBs.

The background within +/-300 seconds around the event was very stable.
However, 136.5 seconds after T0 INTEGRAL/SPI-ACS detected a short
excess (about 50 ms), consistent with the properties of the excesses
produced in SPI-ACS by cosmic ray interactions.

We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 1.9x10^-7 erg/cm^2 for a
burst lasting less than 1 s with a characteristic short GRB spectrum
(an exponentially cut off power law with alpha=-0.5 and Ep=500 keV)
occurring at any time in the interval +-300 s around T0.

For a typical long GRB spectrum (Band function with alpha=-1,
beta=-2.5, and Ep=300 keV), the derived peak flux upper limit is
~1.7x10^-7 (4.3x10^-7) erg/cm^2/s at 1 s (8 s) time scale in 75-2000
keV energy range.