IceCube-160806A

D.F. Cowen reports on behalf of the IceCube Collaboration:

IceCube detected a candidate cosmic neutrino IceCube-160806A, "AMON 
ICECUBE EHE 128311 26552458" at 12:21:33.00 UT on 16/08/06 
(http://gcn.gsfc.nasa.gov/notices_amon/26552458_128311.amon) The event 
was an Extremely High Energy (EHE) event with track-like characteristics 
and it arrived when the IceCube detector was in a normal operating 
state.  EHE events satisfy a combination of high light level and zenith 
angle that enhances astrophysical signal relative to cosmic-ray-induced 
backgrounds.  In contrast to the other active IceCube high energy 
track-like neutrino alert stream, known as "HESE," EHE events are not 
required to start within the IceCube detector fiducial volume.

After the initial automated alert, more sophisticated reconstruction
algorithms have been applied offline, with the direction refined to
RA=122.81d and DEC=-0.8061d (J2000) in revision 1 of this alert.  The 
position uncertainty is estimated from the initial realtime 
reconstruction from revision 0 of this alert, at 0.1 degrees or 6.7 
arcminutes radius (stat. only, 50% containment).  Lacking inclusion of 
systematic effects, we expect this uncertainty underestimates the true 
uncertainty by roughly a factor of five.  We encourage followup by 
ground and space-based instruments to help identify a possible 
astrophysical source for the candidate neutrino.

The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector 
operating at the geographic South Pole, Antarctica.  The IceCube 
realtime alert point of contact can be reached at roc@icecube.wisc.edu

V. Savchenko (APC, Paris, France) , C. Ferrigno (ISDC, University of 
Geneva, CH), P. Ubertini,  A. Bazzano, L. Natalucci (IAPS-Roma, Italy), 
S. Mereghetti (IASF-Milano, Italy),  P. Laurent (CEA, Saclay, France),  
E. Kuulkers (ESAC/ESA, Madrid, Spain)

Using INTEGRAL/SPI-ACS and INTEGRAL/IBIS VETO we have performed a search 
for prompt gamma-ray counterpart of cosmic neutrino candidate 
IceCube-160806A (Cowen 2016, GCN 19787
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 ).

At the time of the event (2016-08-06T12:21:33 UTC, hereafter T0), 
INTEGRAL IBIS was operating in the nominal mode. INTEGRAL/SPI was 
finishing the annealing cycle: at this stage of the procedure it has no 
effect on SPI-ACS.
The spacecraft was pointing in the direction of Norma Arm Region, and 
the neutrino localization was at 110 deg angle with respect to the 
pointing axis.
This orientation enables high response of both SPI-ACS and IBIS_VETO.

The nearest confirmed GRB (GRB160806A), was triggered by 
INTEGRAL/SPI-ACS at 2016-08-06 14:00:57, 1h 40m after the event. This 
GRB is also detected in the IBIS_VETO light curve.

SPI-ACS and  IBIS_VETO (bottom) light-curves around the time of the 
neutrino candidate event can be found at:

http://isdc.unige.ch/~savchenk/IceCube-160806A/

The count rate data around the event reveals variability, including 
smooth background instabilities as well as burst-like events.

Several burst-like excesses can be seen, most prominent ones at T0+50s, 
T-150s, T0-2000s, and T0-10000s.
Ratio of SPI-ACS to IBIS_VETO rates for these events is compatible with 
a gamma-ray source from the direction of IceCube-160806A.
However, we note that these flares are coincident with GOES proton 
background flares.

Although we can not exclude cosmic origin of some of these bursts, 
judging from long-lasting background instability near the region of 
interest, as well as the activity observed by GOES, we are inclined to 
conclude that these bursts are associated with background variability 
introduced by solar activity.

We estimate a 3-sigma upper limit on fluence in 75-2000 keV energy range 
in the interval ��1000 s around the IceCube trigger of 3.3x10^-7 erg/cm^2 
for a burst with duration less than 1 s with a characteristic short GRB 
spectrum (an exponentially cut off power law with alpha=-0.5 and Ep=500 
keV).
For a typical long GRB spectrum (the Band function with alpha=-1, 
beta=-2.5, and Ep=250 keV), the corresponding limiting peak flux is 
~2.2x10^-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.

The IBIS_VETO light curves, binned at 8 s, are derived from 16 
independent detectors with lower energy thresholds near 80 keV and an 
upper threshold at about 50 MeV. Two groups of detector rates are 
recorded independently: bottom and lateral IBIS VETO. The response of 
the bottom IBIS VETO peaks in the direction opposite to satellite 
pointing axis, where the response of SPI-ACS is suppressed.

Due to solar angle constrains, INTEGRAL can not perform pointed 
observation of the location of IceCube-160806A until September 22, so no 
pointed follow-up will be scheduled.

M.I.Panasyuk, S.I.Svertilov, A.V.Bogomolov, V.V.Bogomolov, A.M.Amelushkin, 
V.O.Barinova, A.F.Iyudin, V.V.Kalegaev, D.Nguen,  V.L. Petrov, I.V.Yashin
Physics Department, Skobel`tsyn Institute of Nuclear Physics, Moscow State

V.Chazov, V. Lipunov, E.S. Gorbovskoy,
Lomonosov Moscow State University, Sternberg Astronomical Institute

I. Park, S. Jeong, M.B. Kim,  S. Jeong
Department of Physics, Sungkyunkwan University, Seobu-ro, Jangangu, Suwonsi, 
Korea

A.J. Castro-Tirado
Instituto de Astrofisica de Andalucia (IAA-CSIC), P.O.Box 03004, E-18080
Granada, Spain

V. Reglero
GACE, Edif. deCentros de Investigacion, Universidad de Valencia,
Burjassot, E-46100 Valencia, Spain



  IceCube-160806 (Cowen, GCN 19787
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 )  was in BDRG FOV of 47 deg from the 
axis of the most illuminated BDRG-1 detector (Direction of BDRG-1 axis
RA 05h05m08.96s DEC -25o24'44.54").

No significant GRB was detected by BDRG/Lomonosov in the 
interval +/-50 s from the moment of IC-160806 160806, 12:21:33. Upper 
limits (3 sigma) for 1 s exposition from BDRG-1 background counts:

<0.23 cm-2 s-1 for 20-60 keV,

<0.13  cm-2 s-1 for 60-300 keV

Fermi GBM event 160806 14:01:00.00 source was out of 
BDRG FOV and was shadowed by Earth at 160806 14:01:00.000UT (BDRG-1 axis 
RA 05h14m17.069s.DEC -11o30'33.16", BDRG-2 axis RA 05h30m09.243s.DEC 
-78o50'16.92",BDRG-3 axis RA 11h16m39.621s.DEC -01o02'44.44").

Moren detailes information are available at:
http://lomonosov.sinp.msu.ru/1081  .

The message csn be cited.

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.