GCN Circular 19828

V. Savchenko (APC, Paris, France) , 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 (ESAC/ESA, Madrid, Spain)

Using INTEGRAL/SPI-ACS we have performed a search for a prompt gamma-ray 
counterpart of the cosmic neutrino candidate IceCube HESE 128340 58537957.

At the time of the event (2016-08-14 21:45:54 UTC, hereafter T0), 
INTEGRAL/SPI-ACS was operating in the nominal mode. The spacecraft was 
pointing in the direction of Norma Arm Region, and the neutrino 
localization was at an angle of 47.3 deg with respect to the pointing 
axis. This orientation enables high response of SPI-ACS.

The background within +/-7000 seconds around the event was very stable, 
with only low-significance variations at 100 second time scale.

We estimate a 3-sigma upper limit on the 75-2000 keV fluence of 
3.1x10^-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 
+/-1000 s around T0.

For a typical long GRB spectrum (Band function with alpha=-1, beta=-2.5, 
and Ep=250 keV), the derived peak flux upper limit is ~1.9x10^-7 
erg/cm^2/s at 1 s time scale in 75-2000 keV energy range.

The SPI-ACS light curves, binned at 50 ms, are derived from 91 
independent detectors with different lower energy thresholds (mainly 
between 50 keV and 150 keV) and an upper threshold at about 100 MeV.

INTEGRAL has performed a pointed observation of the location of IceCube 
HESE 128340 58537957, starting 36 hours after the event. The results of 
this observation will be reported separately.