GCN Circular 20856

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 we have performed a search for a prompt gamma-ray
counterpart of the cosmic neutrino candidate IceCube HESE trigger
65274589 129281.

At the time of the event (2017-03-12 13:49:39.83 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The neutrino localization was
at an angle of 38 deg with respect to the spacecraft pointing axis.
For this orientation, the most sensitive INTEGRAL observation is
provided by SPI-ACS for transients of any duration and for typical GRB
spectra, although the response of SPI-ACS in this direction is lower
than optimal. This orientation also implies high response of IBIS
(PICsIT, and to lesser degree ISGRI).

The SPI-ACS background within +/- 300 seconds around the event was very
stable: we do not detect any significant counterparts and estimate a
3-sigma upper limit on the 75-2000 keV fluence of 4.6x10^-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
~1.3x10^-6 erg/cm^2/s at 8 s time scale in 75-2000 keV energy range.

We have also investigated serendipitous observation by IBIS/PICsIT and
IBIS/ISGRI. In ISGRI total count rate, we do not find any excesses
over constant background within +/- 300 seconds around the event. In
PICsIT spectral-timing data, we find a short (~0.4 s) excess at T0 +
86.5 s.  It is not clear at this point if this excess can be
classified as a cosmic GRB or a cosmic-ray induced background effect.
Further investigation is ongoing.

No pointed INTEGRAL observations of the location of IceCube HESE
trigger 65274589 129281 have been performed or planned due to
visibility constraints.