IceCube-200911A

The IceCube Collaboration (http://icecube.wisc.edu/) reports:

On 20/09/11 at 14:19:46.23 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_Bronze alert stream.  The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 0.968 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. 

After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/134482_27754576.amon), more 
sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 20/09/11
Time: 14:19:46.23  UT
RA: 51.11 (+ 4.42 - 11.01  deg 90% PSF containment) J2000
Dec:  38.11 (+ 2.35  - 1.99  deg 90% PSF containment) J2000

We note that this updated direction has shifted from the initial alert.  The track from this neutrino event was just outside the instrumented volume, parallel to our detector string layout, which can introduce ambiguities in reconstructed directions.  The shape of the error region for this event���s reconstructed direction (https://roc.icecube.wisc.edu/public/alerts/run00134482.evt000027754576/) reflects this ambiguity.  

We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.

There is one Fermi 4FGL source located within the 90% localization region, 4FGL J0334.3+3920, located at RA: 53.58 deg, Dec: 39.34 deg (J2000), at a distance of 2.29 deg from the best-fit event position.

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

J. Wood (NASA/MSFC) reports on behalf of the Fermi-GBM team:

At the time of the neutrino candidate IceCube-200911A
(GCN 28411
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 ), Fermi was passing through the South Atlantic
Anomaly from 21.4 minutes prior until 3.0 minutes after the trigger
time; therefore the GBM detectors were disabled.

V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)
J. Rodi (IAPS-Roma, Italy)
A. Coleiro (APC, France)
S. Mereghetti (INAF IASF-Milano, Italy)

on behalf of the INTEGRAL multi-messenger collaboration:
https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration

Using combination of INTEGRAL all-sky detectors (following [1]):
SPI/ACS, IBIS/Veto, and IBIS  we have performed a search for a prompt
gamma-ray counterpart of unknown (GCN 28411
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 ).

At the time of the event (2020-09-11 14:19:46 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 84 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(15% of optimal) response of ISGRI, strongly suppressed (37% of
optimal) response of IBIS/Veto, and near-optimal (85% of optimal)
response of SPI-ACS.

The background within +/-300 seconds around the event was very stable
(excess variance 1.1).

We have performed a search for any impulsive events in INTEGRAL SPI-
ACS (as described in [2]), IBIS, and IBIS/Veto data.

We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 1.9e-07 erg/cm^2 (within the
50% probability containment region of the source localization) 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=600 keV)
occurring at any time in the interval within 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 ~1.6e-07 (5.6e-08)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.

We report for completeness and in order of FAP, all excesses
identified in the search region. We find: 1 tentatively associated
excess:

T-T0     | scale   | S/N | flux ( x 1e-06 erg/cm2/s)      | FAP    
0.211    | 0.7     | 3.5 |     2.67 +/- 0.751  +/- 0.739  | 0.00784 

4 likely background excesses:

T-T0     | scale   | S/N | flux ( x 1e-06 erg/cm2/s)      | FAP    
171      | 3.1     | 3.6 |     1.37 +/- 0.356  +/- 0.379  | 0.299 
20.4     | 0.05    | 4   |     1.17 +/- 0.287  +/- 0.324  | 0.705 
97.1     | 0.65    | 3.7 |     2.95 +/- 0.779  +/- 0.816  | 0.736 
-104     | 0.5     | 3.7 |     3.34 +/- 0.89   +/- 0.924  | 0.968 

Note that FAP estimates (especially at timescales above 2s) may be
possibly further affected by enhanced non-stationary local background
noise. This list excludes any excesses for which FAP is close to
unity.



All results quoted are preliminary.

This circular is an official product of the INTEGRAL Multi-Messenger
team.

[1] Savchenko et al. 2017, A&A 603, A46 
[2] Savchenko et al. 2012, A&A 541A, 122S

--

Alexis Coleiro (APC/Universite de Paris) and Damien Dornic (CPPM/CNRS) on behalf of the ANTARES Collaboration.   
Using data from the ANTARES detector, we have performed a follow-up analysis of the recently reported single track-like event IceCube-200911A (GCN 28411
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  <https://gcn.gsfc.nasa.gov/gcn3/28411.gcn3
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  <https://gcn.gsfc.nasa.gov/gcn3/28411.gcn3
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 >>). The reconstructed origin was 7.3 degrees below the horizon for ANTARES.  
 No up-going muon neutrino candidate events were recorded within the 90% error box of the IceCube event during a +/- 1h time-window centered on the IceCube event time, and over which the potential source remained visible all time. 
 This leads to a preliminary 90% confidence level upper limit on the muon-neutrino fluence from a point source of 14 GeV.cm^-2 over the energy range 10 TeV - 8 PeV (the range corresponding to 5-95% of the detectable flux) for an E^-2 power-law spectrum, and 34 GeV.cm^-2 (1.5 TeV - 740 TeV) for an E^-2.5 spectrum. A search over an extended time window of +/- 1 day has also yielded no detection (23.5% visibility).  
ANTARES <http://antares.in2p3.fr/ <http://antares.in2p3.fr/>> is the largest undersea neutrino detector (Mediterranean Sea) and it is primarily sensitive to astrophysical neutrinos in the TeV-PeV energy range. At 10 TeV, the median angular resolution for muon neutrinos is about 0.5 degrees. In the range 1-100 TeV ANTARES has a competitive sensitivity to this position in the sky.

The IceCube Collaboration (http://icecube.wisc.edu/) reports:

IceCube has performed a search for additional track-like muon neutrino events arriving
from the direction of IceCube-200911A (https://gcn.gsfc.nasa.gov/gcn3/28411.gcn3
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 ) in a time
range of 2 days centered on the alert event time (2020-09-10 14:19:46.23 UTC to 2020-09-12 14:19:46.23 UTC) during which IceCube was collecting good quality data. Excluding the
event that prompted the alert, two additional track-like events are found in spatial coincidence
with the 90% containment region of IceCube-200911A. We find that these data are consistent with atmospheric background expectations, with a p-value of 1.0. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/ dE = 5.2 x 10^-5 TeV cm^-2 at 90% CL, under the assumption of an E^-2 power law. 90% of events IceCube would detect from a source at this declination with an E^-2 spectrum are approximately between 700 GeV and 400 TeV.

A subsequent search was performed to include the month of data prior to the alert event (2020-08-12 14:19:46.23 UTC to 2020-09-12 14:19:46.23 UTC). In this case, we report a p-value of 1.0, consistent with no significant excess of track-like events, and a corresponding time-integrated muon-neutrino flux upper limit assuming an E^-2 spectrum (E^2 dN/dE) of
6.4  x 10^-5 TeV cm^-2 at the 90% CL.

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<mailto:roc@icecube.wisc.edu>.

S. Garrappa (DESY-Zeuthen) and S. Buson (Univ. of Wuerzburg) on behalf 
of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy 
neutrino event IC200911A (GCN 28411
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 ) with all-sky survey data from the 
Large Area Telescope (LAT), on board the Fermi Gamma-ray Space 
Telescope. The IceCube event was detected on 2020-09-11 at 14:19:46.23 
UT (T0) with J2000 position RA =51.11 (+4.42 -11.01) deg, Decl. =38.11 
(+2.35 -1.99) deg. The refined contour of the 90% PSF containment region 
is reported in GCN 28411
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 . One cataloged >100 MeV gamma-ray source is 
located within the 90% IC200911A localization region. This is 4FGL 
J0334.3+3920 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), 
associated with the radio galaxy 4C +39.12 at known redshift z = 0.02. 
Based on a preliminary analysis of the LAT data over the timescales of 
1-day and 1-month prior to T0, this object is not significantly detected 
(> 5 sigma).

We searched for intermediate (days to years) timescale emission from a 
new gamma-ray transient source. Preliminary analysis indicates no 
significant (> 5 sigma) new excess emission (> 100 MeV), at the 
IC200911A best-fit position. Assuming a power-law spectrum (photon index 
= 2.0 fixed) for a point source at the IceCube best-fit position, the 
 >100 MeV flux upper limit (95% confidence) is < 5.4e-10 ph cm^-2 s^-1 
for ~12-years (2008-08-04 / 2020-09-11 UTC), < 5.6e-9 (< 5.6e-8) ph 
cm^-2 s^-1 for a 1-month (1-day) integration time before T0.

Within the 90% confidence localization of the neutrino, ~1.2 deg offset 
from the best-fit IC200911A position, a >5 sigma excess of gamma rays, 
Fermi J0330.1+3743 was detected in an analysis of the integrated LAT 
data (> 100 MeV) between 2008-08-04 and 2020-09-11. Assuming a power-law 
spectrum, the best-fit localization is (J2000) RA: 52.51, Dec: 37.73 
(0.12 deg 99% containment, 0.06 deg 68% containment), with best-fit 
spectral parameters flux = (3 +/- 1)e-9 ph cm^-2 s^-1 and index = 2.2 
+/- 0.1. In a preliminary analysis of the LAT data over one day and one 
month prior T0, Fermi J0330.1+3743 is not significantly detected in the 
LAT data. All values include the statistical uncertainty only.

Since Fermi normally operates in an all-sky scanning mode, regular 
monitoring of this source will continue. For these observations the 
Fermi-LAT contact persons are S. Garrappa (simone.garrappa at desy.de) 
and S. Buson (sara.buson at uni-wuerzburg.de).
The Fermi LAT is a pair conversion telescope designed to cover the 
energy band from 20 MeV to greater than 300 GeV. It is the product of an 
international collaboration between NASA and DOE in the U.S. and many 
scientific institutions across France, Italy, Japan and Sweden.

Hugo Ayala (PSU) reports on behalf of the HAWC
collaboration (http://www.hawc-observatory.org/collaboration):

On 2020/09/11 14:19:46 UTC, the IceCube collaboration reported a
track-like very-high-energy event  that has a high probability of
being an astrophysical neutrino, IceCube-200911A. Location is at
RA: 51.11 (+4.42/-11.01 deg  90% PSF containment) J2000
Dec: 38.11 (+2.35/-1.99 deg 90% PSF containment) J2000
(GCN circular 28411
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 ).

We performed two types of analyses for the follow-up. The first is for
a steady source in archival data and the second is a search for a
transient source. We assume a power-law spectrum with an index of -2.3
for both analyses. The positions found in the analysis are not coincident
with the new source detection from Fermi-LAT (see GCN  28421
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 ).

Search for a steady source in archival data:
The archival data spans from November 2014 to May 2018. We searched
inside the reported IceCube error region.
The most significant location, with p-value 4.61e-5 (1.56e-2 post-trials),
is at RA 48.56 deg, Dec +36.98 deg (��0.13 deg 68% containment) J2000.
We set a time-integrated 95% CL  upper limit on gamma rays at the
maximum position of:

E^2 dN/dE = 3.86e-13 (E/TeV)^-0.3 TeV.cm^-2.s^-1

Search for a transient source.
Since the event was not in our field of view at the time reported,
we report the combined result for the transits before and after the
IceCube event.

Data acquisition started on 2020/09/09 13:29:22 UTC and ended
2020/09/11 13:48:10 UTC.
The most significant location, with p-value 4.15e-03  (7.57e-1 post-trials),
is at RA 50.32 deg, Dec +39.84 deg (��0.19 deg 68% containment) J2000.
We set a time-integrated 95% CL upper limit at the position of
maximum significance of:

E^2 dN/dE = 1.18e-11 (E/TeV)^-0.3 TeV.cm^-2.s^-1

HAWC is a very-high-energy gamma-ray observatory operating in Central
Mexico at latitude 19 deg. north. Operating day and night with over
95% duty cycle, HAWC has an instantaneous field of view of 2 sr and
surveys 2/3 of the sky every day. It is sensitive to gamma rays from
300 GeV to 100 TeV.

T. Gregoire (PSU), P.A. Evans (U. Leicester), J.A. Kennea (PSU),
H. A. Ayala Solares (PSU), D.F. Cowen (PSU), J. DeLaunay (PSU) , D. B. 
Fox (PSU),
A. Keivani (Columbia U.), J.P. Osborne (U. Leicester) report:

Swift observed the field of IceCube 200911A (GCN Circ. 28411
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 ) between 
16:38:01
2020 September 9 and 19:38:41 on 2020 September 9, collecting a total of 
3.7 ks of
cleaned photon counting (PC) mode data. The observations used a 4-point 
tiling
pattern with a radius of ~0.3 degrees.

We found no X-ray sources beyond artifacts caused by bright Earth limb 
contamination.

The 3-sigma upper limit in the field was in the range 5-8 x10^-3 ct/sec.