IceCube-200107A

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

On 20/01/07 at 09:42:18.36 UT IceCube detected a high-energy starting event [1]. Though it did not pass the Gold or Bronze starting track classification, a new neural network classifier identified the event as a starting track. Visual inspection is consistent with this classification. High-energy starting events have a rate of ~12 per year, out of which ~2 per year are starting tracks. Because the event was not identified as either Gold or Bronze, we do not currently report a false alert rate or signalness. However, given the topology and light deposition of this event, we identify it as a potential astrophysical neutrino of interest to the community. The IceCube detector was in a normal operating state at the time of detection. 

Sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 20/01/07
Time: 09:42:18.36  UT
RA: 148.18 (+ 2.20 - 1.83 deg 90% PSF containment) J2000
Dec:  35.46 (+ 1.10 - 1.22 deg 90% PSF containment) J2000

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

There are two Fermi 4FGL sources located within the 90% localization region. The nearest gamma-ray source is 4FGL J0955.1+3551 at RA: 148.78 deg, Dec: 35.86 deg (0.63 deg away from the best-fit event position). Another source, 4FGL J0957.8+3423, is located at RA: 149.47 deg, Dec: 34.40 (1.50 deg away 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 <mailto:roc@icecube.wisc.edu>
[1] The IceCube Collaboration, Phys. Rev. Lett. 113, 101101 (2014)

P. Veres (UAH) reports on behalf of the Fermi-GBM team:

For the IceCube high-energy neutrino candidate event IceCube-200107A (GCN
26655
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 ), at the event time Fermi-GBM was observing the reported neutrino
location at:

RA: 148.18 (+ 2.20 - 1.83 deg 90% PSF containment) J2000
Dec:  35.46 (+ 1.10 - 1.22 deg 90% PSF containment) J2000

There was no Fermi-GBM onboard trigger around the event time of the
neutrino candidate. An automated, blind search for short gamma-ray bursts
below the onboard triggering threshold in Fermi-GBM also identified no
counterpart candidates. The GBM targeted search, the most sensitive,
coherent search for GRB-like signals, was run from +/-30 s around the
neutrino candidate time. From this search, no significant signal was found
related to IceCube-200107A.

We set upper limits on impulsive gamma-ray emission. Using the
representative soft, normal, and hard GRB-like templates described in
arXiv:1612.02395
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 , we set the following 3 sigma flux upper limits over
10-1000 keV (in units of 10^-7 erg/s/cm^2):

Timescale  Soft     Normal   Hard
-------------------------------------------
0.128 s:   6.7        15       25
1.024 s:   2.1        4.3      7.2
8.192 s:   0.79       1.2      1.8

Alexis Coleiro (APC, France), Carlo Ferrigno (ISDC/UniGE, Switzerland),
V. Savchenko (ISDC/UniGE, Switzerland),
J. Rodi (IAPS-Roma, Italy),
S. Mereghetti (INAF IASF-Milano, Italy)
on behalf of the INTEGRAL multi-messenger collaboration:
https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration

Using INTEGRAL/SPI-ACS realtime data (following [1]) we have performed
a search for a prompt gamma-ray counterpart of IceCube-200107A (GCN 26655
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 ).
At the time of the event (2020-01-07 09:42:18 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 78 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(24% of optimal) response of ISGRI, strongly suppressed (40% of
optimal) response of IBIS/Veto, and near-optimal (70% of optimal)
response of SPI-ACS.
The background within +/-300 seconds around the event was somewhat
unstable (excess variance 1.8).
We have performed a search for any impulsive events in INTEGRAL SPI-
ACS (as described in [2]) data (IBIS data are not considered since they are 
only partially available in the search region due to the instrument starting the 
observations after the perigee shortly before the IceCube trigger).
We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 2.8e-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 ~2.4e-07 (1.2e-07)
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 4 likely background
excesses:
T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP  
12.5 | 0.45 | 3.3 | 0.432 +/- 0.122 +/- 0.117 | 0.328 
-64.5 | 0.9 | 3.4 | 3.33 +/- 0.863 +/- 0.9 | 0.663 
-41.5 | 0.15 | 4.3 | 0.939 +/- 0.213 +/- 0.254 | 0.681 
-86.8 | 1.3 | 3.3 | 2.75 +/- 0.717 +/- 0.743 | 0.76  
Note that FAP estimates (especially at timescales above 2s) may be
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
GCN pipeline version: 88154a3


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Alexis Coleiro
Ma��tre de conf��rences - Universit�� Paris Diderot
Laboratoire Astroparticule et Cosmologie (APC)
10 rue Alice Domon et L��onie Duquet
75205 Paris Cedex 13 (France)
Tel.: +33 1 57 27 60 59 / coleiro@apc.univ-paris-diderot.fr

Robert Stein and Simeon Reusch (DESY) report,

On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: 

We observed the localization region of the neutrino event IceCube-200107A (Stein et al., GCN 26655
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 ) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We first started observations serendipitously in the g-band and r-band beginning at 2020-01-07T11:42:04.700 UTC, approximately 2.0 hours after event time. We covered 6.3 sq deg, corresponding to 84.2% of the reported localization region. This estimate accounts for chip gaps. Each exposure was 300s with a typical depth of 21.0 mag. 

The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019). We find no high-significance transient or variable candidates with our pipeline. 

We will continue to observe this field to search for new transients.

ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IITB, India; IIA, India; LJMU, UK; TTU, USA; SDSU, USA and USyd, Australia.

Hugo Ayala (PSU) reports on behalf of the HAWC

collaboration (http://www.hawc-observatory.org/collaboration):

On 2020/01/07 09:42:18.36 UTC, the IceCube collaboration reported a

track-like very-high-energy event  that has a high probability of

being an astrophysical neutrino, IceCube-200107A. Location is at

RA: 148.18 (+2.20/-1.83  90% PSF containment) J2000

Dec: 35.46 (+1.10/-1.22 deg 90% PSF containment) J2000

https://gcn.gsfc.nasa.gov/gcn3/26655.gcn3
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(GCN circular 26655
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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.

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 from the circular.

The highest significance, 3.37 sigma (2.10 post-trials),

is at RA 147.79 deg, Dec 34.68 deg (+-1.71 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 = 3.01439e-13 (E/TeV)^-0.3 TeV cm^-2 s^-1

Search for a transient source.

Since the IceCube event fall inside the HAWC field of view,

we report on the result for the current transit of the IceCube

position.

Data acquisition started on Data Start: 2020/01/07 06:02:39 UTC and ended

2020/01/07 12:24:01 UTC.

The most significant location, with 2.16 sigma (-0.62 post-trials),

is at RA 149.55 deg, Dec 34.68 deg (+-1.8 deg 68% containment) J2000.

We set a time-integrated 95% CL upper limit at the position of

maximum significance of:

E^2 dN/dE = 4.10782e-12 (E/1TeV)^-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.

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 
IC200107A neutrino event (GCN 26655
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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 2020-01-07 at 09:42:18.36 
UT (T0) with J2000 position RA =148.18 (+ 2.20, - 1.83) deg, Decl. = 
35.46 (+ 1.10, - 1.22) deg 90% PSF containment. Two cataloged >100 MeV 
gamma-ray sources (The Fermi-LAT Collaboration 2019, 
arXiv:1902.10045
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 )�are located within the 90% IC200107A localization 
error. These are the objects 4FGL J0955.1+3551 associated with the BL 
Lac object 1RXS J095508.2+355054 and 4FGL J0957.8+3423 associated with 
the blazar candidate object of uncertain type B2 0954+34. Based on a 
preliminary analysis of the LAT data over the timescales of 1-day and 
1-month prior to T0, these objects are not significantly detected at 
gamma-rays.

We searched for the existence of intermediate (months to years) 
timescale emission from a new gamma-ray transient source. Preliminary 
analysis indicates no significant (>5sigma) new excess emission (> 100 
MeV) within the IC200107A 90% confidence localization. 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 < 1e-10 ph cm^-2 s^-1 for ~11-years (2008-08-04 / 
2020-01-07 UTC), < 1e-8 (< 1e-7) ph cm^-2 s^-1 for a 1-month (1-day) 
integration time before T0.

Since Fermi normally operates in an all-sky scanning mode, regular 
monitoring of this source will continue. For this source the Fermi-LAT 
contact persons are S. Garrappa (simone.garrappa at desy.de 
<http://desy.de/>) and S. Buson (sara.buson at uni-wuerzburg.de 
<http://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.

F. Krauss, T. Gregoire, D.B. Fox, J. Kennea (PSU) and P. Evans
(U. Leicester) report for AMON (https://amon.psu.edu/):

"We have observed the positions of the two Fermi/LAT sources (Garrappa
et al., GCN Circ. 26669
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 ), positionally coincident with the IceCube
neutrino event IceCube-200107A (GCN Circ. 26655
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 ) with the Neil Gehrels
Swift Observatory X-ray Telescope (XRT). We detect the blazar 4FGL
J0955.1+3551 with an observed 2-10 keV flux of 4.7 (+/- 0.8) x 10^-12
erg cm-2 s-1 (2-10 keV). A spectrum constructed from these data can be 
well described by an absorbed power law with N_H = 5.3 x 10^20 cm-2
(wilm abundances, vern cross-sections), and a photon index of 1.8
(+0.23, -0.13). These data have also been reported in ATel #13394. 

This object has been previously observed by Swift/XRT, and its
historical behavior can be seen in the 2SXPS catalogue (Evans et al.,
2019):  https://www.swift.ac.uk/2SXPS/2SXPS%20J095507.8%2B355100
Our recent observations are significantly brighter than the average
flux in archival data: 1.78 (+0.14, -0.13) x 10-12 erg cm-2 s-1
(observed 2-10 keV flux), although the historical light curve does
show that the source flux was gradually increasing in 2012 to
2013. The catalogued ROSAT flux of this source (as 1RXS
J095508.2+355054) is 0.11 ct/sec which, assuming the above spectrum,
corresponds to a 2-10 keV observed flux of ~1.9 x 10-12 erg cm-2 s-1;
therefore we suggest that this source is currently in a high
state. Further observations of this source are strongly recommended. 

The other source reported in GCN Circ. 26669
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  (4FGL J0957.8+3423) was
not detected in our observations, with a 3-sigma upper limit of 0.010
ct/sec (0.3-10 keV). Assuming a standard spectrum (N_H = 3 x 10^20
cm-2, Gamma=1.7) this corresponds to a observed 2-10 keV flux upper
limit of 2.7 x 10-13 erg cm-2 s-1. This source has not been previously
covered by Swift/XRT observations."

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-200107A (https://gcn.gsfc.nasa.gov/gcn3/26655.gcn3
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 ) in a time
range of 2 days centered on the alert event time (2020-01-06 09:42:18.36 UTC to 2020-01-08 09:42:18.36 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-200107A. We find that these data are consistent with atmospheric background expectations, with a p-value of 0.040. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/ dE = 6.7 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 1 TeV and 500 TeV.

A subsequent search was performed to include the month of data prior to the alert event (2019-12-08 09:42:18.36 UTC to 2020-01-08 09:42:18.36 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
 9.8 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>.