IceCube-211208A

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

On 2021-12-08 at 20:02:51.1 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 1.197 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/136015_21306805.amon, more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2021-12-08  
Time: 20:02:51.1 UT
RA: 114.52 (+2.82 -2.50 deg  90% PSF containment) J2000
Dec: 15.56 (+1.81 -1.39 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.

Two gamma-ray sources listed in the 4FGL-DR2 Fermi-LAT catalog, 4FGL J0738.4+1539 and 4FGL J0743.1+1713, are located within the 90% error region for the event, located 0.1 and 2.1 deg away from the best-fit position, respectively. 

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, 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 IceCube-211208A (GCN 31191
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 ).

At the time of the event (2021-12-08 20:02:51 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 75 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(24% of optimal) response of ISGRI, somewhat suppressed (40% of
optimal) response of IBIS/Veto, and near-optimal (69% 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 2.4e-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 ~2e-07 (6.7e-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: 3 likely background
excesses:

T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
231 | 9.35 | 3.9 | 0.922 +/- 0.254 +/- 0.247 | 0.0958
55.3 | 0.5 | 3.5 | 0.404 +/- 0.11 +/- 0.108 | 0.805
34.9 | 0.35 | 3.4 | 0.46 +/- 0.132 +/- 0.123 | 0.955

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

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

We report an analysis of observations of the vicinity of the high-energy 
IC211208A neutrino event (GCN 31191
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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 2021-12-08 at 20:02:51.1 UT 
(T0) with J2000 position RA = 114.52 (+2.82, -2.50) deg, Decl. = 15.56 
(+1.81, -1.39) deg (90% PSF containment). Two cataloged gamma-ray (>100 
MeV) sources are located within the 90% IC211208A localization region 
(4FGL-DR2, The Fermi-LAT collaboration 2020, ApJS, 247, 33). These are 
4FGL J0738.4+1539, associated with the radio source of unknown type NVSS 
J073824+153839 at 0.13 deg and 4FGL J0743.1+1713, associated with the BL 
Lac object TXS 0740+173 at 2.05 deg. Based on a preliminary analysis of 
LAT data at timescales of 1-month and 1-day prior to T0, these objects 
are not significantly detected (>5sigma).

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 IC211208A 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC211208A best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 3.0e-10 ph cm^-2 s^-1 for 
~13-years (2008-08-04 to 2021-12-08 UTC), and < 4.5e-9 (< 7.0e-8) ph 
cm^-2 s^-1 for a 1-month (1-day) integration time before T0.

In the vicinity of the IC211208A best-fit position, outside the 90% 
localization region at 2.1 deg from the best-fit IC211208A localization, 
the cataloged >100 MeV gamma-ray source 4FGL J0738.1+1742 is 
significantly detected (> 5 sigma) integrating 1-day LAT data before T0. 
This source is associated with the BL Lac object PKS 0735+17 at z = 0.45 
(Gattano et al, 2018 A&A, 618, A80). Preliminary analysis indicates that 
on 2021-12-08 the gamma-ray source was observed with a daily averaged 
flux (E>100 MeV) of (3+/-1) x 10^-7 photons cm^-2 s^-1 (statistical 
uncertainty only), about 5 times greater than the average flux reported 
in the fourth Fermi LAT source catalog (4FGL-DR2). The source was 
significantly detected at 1-day timescale on 2021-12-01 and was observed 
on 2021-12-04 with peak daily flux value of (5+/-2) x 10^-7 photons 
cm^-2 s^-1 (statistical uncertainty only), about 10 times greater than 
the average 4FGL-DR2 flux. The source was reported to be in optical 
brightening on 2021-11-08 and is currently at its brightest state in R 
band https://vo.astro.spbu.ru/sites/default/files/optic/pks0735R.png 
(see also ATel #15021).

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 gmail.com).

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.

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

IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-211208A (https://gcn.gsfc.nasa.gov/gcn3/31191.gcn3
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 ) in a time range of 1000 seconds centered on the alert event time (2021-12-08 19:54:31.100 UTC to 2021-12-08 20:11:11.100 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-211208A. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-211208A is 1.4e-01 GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 1e+05 GeV. 

A subsequent search was performed including 2 days of data centered on the alert event time (2021-12-07 20:02:51.100 UTC to 2021-12-09 20:02:51.100 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-211208A is 1.6e-01 GeV cm^-2 in a 2 day time window. 

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.

[1] IceCube Collaboration, R. Abbasi  et al., ApJ 910 4 (2021)

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

On 2021/12/08 20:02:51 UTC, the IceCube collaboration reported a
track-like very-high-energy event  that has a high probability of
being an astrophysical neutrino, IceCube-211208A. Location is at
RA: 114.52 (+2.82/-2.50 deg  90% PSF containment) J2000
Dec: 15.56 (+1.81/-1.39 deg 90% PSF containment) J2000
(GCN circular 31191
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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 June 2019. We searched
inside the reported IceCube error region.
The most significant location, with p-value 7.8e-3 (0.02 post-trials),
is at RA 115.31 deg, Dec +14.52 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 = 2.27e-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 2021/12/07 11:57:44 UTC and ended
2021/12/09 12:17:24 UTC.
The most significant location, with p-value 2.12e-3  (0.96 post-trials),
is at RA 113.55 deg, Dec +17.23 deg (��0.18 deg 68% containment) J2000.
We set a time-integrated 95% CL upper limit at the position of
maximum significance of:

E^2 dN/dE = 1.16e-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.

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 bronze track event IceCube-211208A (GCN#31191
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  <https://gcn.gsfc.nasa.gov/gcn3/31191.gcn3
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 >). The reconstructed origin was about 10 degrees above the horizon for ANTARES at the time of the alert.

Extending slightly the analysis to include the events just above the horizon, no 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.

A search over an extended time window of +/- 1 day also yielded no detection (41% visibility). Over this time period, and restricting the search to the periods when the source remained below the horizon, this leads to a preliminary 90% confidence level upper limit on the muon-neutrino radiant fluence from a point source of about 17 GeV.cm^-2 over the energy range 5 TeV ��� 5 PeV (the range corresponding to 5-95% of the detectable flux) for an E^-2 power-law spectrum, and 43 GeV.cm^-2 (1 - 500 TeV) for an E^-2.5 spectrum. 

ANTARES <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.

D. R. Xiong, J. Mao, Y. Xin���D. H. Yan, J.-M. Bai (YNAO), and Y. L. Chang, W. Li, D. L. Xu (TDLI) report: 




We follow the IceCube-211208A alert (GCN circ. 31191
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 ), and we observe the BL Lac object PKS0735+178,

which might be the source candidate of IceCube-211208A. We have performed the optical monitor in each

night since 11, Dec. 2021. The 2.4-meter telescope and the BOOTES-4 telescope located at Gao-Mei-Gu (GMG)

station of Yunnan Observatories are utilized for the multi-band photometry. We have obtained the very

preliminary results. As an example, the magnitude of r=14.69 was measured from the observation

in 11, Dec. 2021, and the the magnitude of r=15.60 was measured from the observation in 14, Jan. 2022.

We note that the magnitude of r=15.50 is provided for this source by the Sloan Digital Sky Survey.

The multi-band photometric monitor is ongoing. We are working on the careful data reduction.

The long-term multi-wavelength observation for this target is encouraged.




We acknowledge the support of the staff from the Lijiang GMG 2.4-m telescope and the BOOTES

telescopes (A. J. Castro-Tirado and E. Fernandez- Garcia et al.).