IceCube-210922A

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

On 2021-09-22 at 18:17:20.948 UT IceCube detected a track-like event with a high probability of being of astrophysical origin. 
The event was selected by the ICECUBE_Astrotrack_GOLD alert stream.  The average astrophysical neutrino purity for Gold alerts is 50%. This alert has an estimated false alarm rate of 0.1472 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/135736_30987826.amon), more  
sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2021-09-22
Time: 18:17:20.948
RA: 60.73 (+0.96/-0.66 deg 90% PSF containment) J2000
Dec: -4.18 (+0.42/-0.55 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 no Fermi 4FGL or 3FHL catalog sources in the 90% uncertainty region. The nearest gamma-ray source in either catalog is 4FGL J0357.2-0319 / 3FHL J0357.3-0316 at RA: 59.32 deg, Dec: -3.32 deg (1.64 deg away from the best-fit event position). The source is classified as having a possible blazar origin. 

This neutrino candidate event has an estimated neutrino energy of ~750 TeV and an estimated signalness of >90%, making it one of the most interesting neutrino alerts issued in the last year.  

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

S. Garrappa (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg) and R. de 
Menezes (Univ. of Sao Paulo, Univ. of Wuerzburg) on behalf of the 
Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy 
IC210922A neutrino event (GCN 30862
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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 2021-09-22 at 18:17:20.948 
UT (T0) with J2000 position RA = 60.73 (+0.96, -0.66) deg, Decl. = -4.18 
(+0.42, -0.55) deg (90% PSF containment). No cataloged gamma-ray (>100 
MeV) source is located within the 90% IC210922A localization region 
(4FGL-DR2, The Fermi-LAT collaboration 2020, ApJS, 247, 33).

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 IC210922A 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC210922A best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 1.4e-10 ph cm^-2 s^-1 for 
~13-years (2008-08-04 to 2021-09-22 UTC), and < 7.5e-9 (< 5.5e-8) 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 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.

Sven Weimann (Ruhr University Bochum), Simeon Reusch, Jannis Necker, Robert Stein (DESY) and Anna Franckowiak (DESY/Ruhr University Bochum),

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-210922A (Lincetto et. al, GCN 30862
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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 started observations in the g- and r-band beginning at 2021-09-23 10:25 UTC, approximately 16.1 hours after event time. We covered 79% (1.2 sq deg) 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, Stein et al. 2021) 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).

No candidate counterparts were detected.

ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA; WIS, Israel; OKC, Sweden; JSI/UMd, USA; DESY, Germany; TANGO, Taiwan; UW Milwaukee, USA; LANL, USA; TCD, Ireland; IN2P3, France.

GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949.
Alert distribution service provided by DIRAC@UW (Patterson et al. 2019).
Alert database searches are done by AMPEL (Nordin et al. 2019).
Alert filtering is performed with the AMPEL Follow-up Pipeline (Stein et al. 2021).

C. Malacaria (USRA) reports on behalf of the Fermi-GBM team:

For the IceCube high-energy neutrino candidate event IceCube-210811A
(GCN 30862
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 ), at the event time Fermi-GBM was observing the reported
neutrino location at:

RA: 60.73 (+0.96, -0.66 deg  90% PSF containment) J2000
Dec: -4.18 (+0.42, -0.55 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-210922A.

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    norm    hard
--------------------------------------
0.128 s:       6.4      11.        14.
1.024 s:       2.1      3.4        4.6
8.192 s:       0.6      0.9        1.4

These results are preliminary.

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-210922A (https://gcn.gsfc.nasa.gov/gcn3/30862.gcn3
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 ) in a time
range of 2 days centered on the alert event time (2021-09-21 18:17:20.95 UTC to 2021-09-23 18:17:20.95 UTC) during which IceCube was collecting good quality data. Excluding the
event that prompted the alert, zero additional track-like events are found in spatial coincidence
with the 90% containment region of IceCube-210922A. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/dE = 3.5 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 2 TeV and 5 PeV.

A subsequent search was performed to include the month of data prior to the alert event (2021-08-23 18:17:20.95 UTC to 2021-09-23 18:17:20.95 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
4.1 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>.

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-210922A (GCN #30862
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 ). The reconstructed origin was -37 degrees below the horizon for ANTARES. 
No up-going muon neutrino candidate events were recorded within 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 16 GeV.cm^-2 over the energy range 3 TeV ��� 3.3 PeV (the range corresponding to 5-95% of the detectable flux) for an E^-2 power-law spectrum, and 30 GeV.cm^-2 (580 GeV - 300 TeV) for an E^-2.5 spectrum. 

A search over an extended time window of +/- 1 day has also yielded no detection (52% 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.

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

On 2021/09/22 18:17:20 UTC, the IceCube collaboration reported a
track-like very-high-energy event that has a high probability of
being an astrophysical neutrino, IceCube-210922A. Location is at
RA: 60.73 (+0.96/-0.66 deg 90% PSF containment) J2000
Dec: -4.18 (+0.42/-0.55 deg 90% PSF containment) J2000
(GCN circular 30862
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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 3.72e-2 (0.26 post-trials),
is at RA 60.03 deg, Dec -3.84 deg (��0.30 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 = 3.42e-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 2021/09/21 12:58:23 UTC and ended
2021/09/23 13:05:05 UTC.
The most significant location, with p-value 0.12  (0.64 post-trials),
is at RA 60.12 deg, Dec -4.74 deg (��0.30 deg 68% containment) J2000.
We set a time-integrated 95% CL upper limit at the position of
maximum significance of:

E^2 dN/dE = 8.8e-12 (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.

Felicia Krauss, Timoth��e Gregoire, Derek Fox, Doug Cowen, Hugo Ayala
(PSU) and Alexis Coleiro (APC) report for AMON (https://amon.psu.edu/):

The Neil Gehrels Swift Observatory X-ray Telescope (XRT) observed the
uncertainty region of the IceCube neutrino event IceCube-210922A (GCN
Circ. 30862
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 ) on 2021-09-23, between 02:00 and 21:52 UTC .
A 6-point tiling observation centered on the neutrino position was taken
for a total of 3.5 ksec.
Of the 90% confidence 1.23 sq. degrees uncertainty region, the XRT
observations cover roughly 75% of the central area.

No X-ray candidate counterparts were detected above a level of 3 sigma.

The 3 sigma upper limit for the flux is  1.2x10^(-13) ergs/s/cm^2.

Y. Urata and K. Huang on behalf of a larger collaboration

We observed the field of IceCube-210922A (GCN Circ. 30862
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 ) using
Scuba-2 attached to JCMT. The observation was started at 2021/09/24
13:15 UTC and SCUBA-2 imaged the field centered at RA 04:02:55.200,
Dec -04:10:48.00 with 50 arcmin diameter.

There is one bright submm source with ~70 mJy/beam at 850um not listed
in the Planck catalog of compact sources.

The position is
RA  04:02:05.362
Dec -04:24:28.80

Within the JCMT beam (14 arcsec), there are two catalog sources,
WISEA J040205.29-042428.5 and NVSS J040205-042434.
Based on the Pan-STARRS1 images, there are no optical sources.

Additional monitoring observation with Scuba-2 is scheduled.
Further detailed multi-wavelength investigation of the source is encouraged.

We would like to thank Harriet Parsons and JCMT staff.

Y. Urata, G. Petitpas on behalf of a larger collaboration

We observed the JCMT source (GCN 30882
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 ) using SMA.
The SMA 230GHz observation was started at 2021 Sep 27, 15:21 (UT).
The JCMT source was clearly identified at
04h02m05.304s -04d24m28.14s (0.5���) with ~17 mJy/beam.

The position is consistent with the cataloged IR source (WISEA
J040205.29-042428.5).  The radio source, NVSS J040205-042434 is also
counterpart when we consider the margin of position error.

Further detailed multi-wavelength investigations are encouraged.

We would like to thank SMA staff.

Antonella Palmese (UC Berkeley), Segev BenZvi (U of Rochester), Stephen Bailey (LBNL), Tamara Davis (U of Queensland), Alex Kim (LBNL), Martin Landriau (LBNL), David Moutard (Wayne State University), Adam Myers (U of Wyoming), Peter Nugent (LBNL), Anand Raichoor (LBNL), Edward Schlafly (LLNL), David Schlegel (LBNL), Umut Demirbozan (IFAE), John Della Costa (SDSU), on behalf of the DESI Transients and Low-z Cosmology Working Group report:

We observed the location of IceCube 210922A (GCN 30862
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 ) using the Dark Energy Spectroscopic Instrument (DESI), a multi-object spectrograph with 5000 fibers installed on the Mayall 4m telescope at Kitt Peak National Observatory.

On the night of September 23 2021, we recorded spectra of 249 galaxies in the 90% CL of the IceCube event, which represent ~20% of all DESI Bright Galaxy Sample (BGS) galaxies in the region, a sample of galaxies complete down to r-band apparent magnitude of 19.5. Each fiber covers a circular region of 1.5��� in diameter centered on the core of the galaxy. Observations started at 02:48 MST and lasted a total of 2200s. We searched for core-collapse SNe using a Convolutional Neural Network algorithm (DESITRIP - DESI Transients Identification Pipeline) optimized to identify transients on top of galaxy emission in DESI spectra. We also searched for Tidal Disruption Events based on spectral lines. Observations were deeply affected by the vicinity to the Moon, so that our searches are mostly based upon the r and z arm observations, where the mean SNR per 0.8 Ang reached in the spectra was 8 and 10 after calibration, respectively. The mean SNR was 3 in the b arm. We did not find significant evidence for the presence of an interesting optical counterpart in the DESI spectra.

A list of the positions of the observed galaxies is available at https://data.desi.lbl.gov/public/transients/icecube/IC210922A_DESI210923.txt<https://data.desi.lbl.gov/desi/public/transients/icecube/IC210922A_DESI210923.txt>

Felicia Krauss, Timoth��e Gregoire, Derek Fox, Doug Cowen, Hugo Ayala 
(PSU) and Alexis Coleiro (APC) report for AMON (https://amon.psu.edu/):

The Nuclear Spectroscopic Telescope Array (NuSTAR) has observed the 
JCMT/SCUBA2 source NVSS J040205-042434, proposed as a possible 
counterpart to the IceCube-210922A high-energy neutrino (GCN Circ. 
30862
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 , 30882
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 ).
NuSTAR observed the position October 10 (13:55:13 UTC) -�� October 11�� 
(17:20:00 UTC) for a total of 49.2 ksec.

No X-ray source is visible in the field of view. The 3 sigma upper limit 
for the 3-70 keV flux is 1.6x10^-11 ergs/cm^2/s assuming a photon index 
of 2.