IceCube-210629A

Simeon Reusch, Jannis Necker, Robert Stein (DESY), Anna Franckowiak (DESY/Ruhr-University Bochum), Sven Weimann (Ruhr-University Bochum), Sjoert van Velzen (Leiden University), Marek Kowalski (DESY), Mansi Kasliwal and Matthew Graham (Caltech) report:

We observed ZTF candidate AT2021osi
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  (Necker et al, GCN 30349
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 ), a possible counterpart to high-energy neutrino IceCube-210629A (Santander et. al, GCN 30342
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 ), with the Gemini GMOS-N spectrograph on 2 July 2021. Using the R400 grating (1 arcsec slit), we obtained 2 x 750s observations under our ToO program GN-2021A-Q-116 (PI: Kasliwal). These were reduced and flux-calibrated with PypeIt (Prochaska et al. 2020).

The spectrum of AT2021osi
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  shows AGN-like features, namely prominent and broad Balmer lines (alpha, beta and gamma). Based on these lines, we also infer a redshift z=0.194.

We thank the GMOS-N observing staff for quickly scheduling and executing our observations, in particular Atsuko Nitta.

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-210629A (https://gcn.gsfc.nasa.gov/gcn3/30342.gcn3
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 ) in a time
range of 2 days centered on the alert event time (2021-06-28 18:09:44.22 UTC to 2021-06-30 18:09:44.22 UTC) during which IceCube was collecting good quality data. Excluding the
event that prompted the alert, 0 additional track-like event is found in spatial coincidence
with the 90% containment region of IceCube-210629A. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/dE = 3.9 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 1 PeV.

A subsequent search was performed to include the month of data prior to the alert event (2021-05-30 18:09:44.22 UTC to 2021-06-30 18:09:44.22 UTC). In this case, we report a p-value of 0.09, 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
6.2 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>.

Jannis Necker (DESY), Robert Stein (DESY), Sven Weimann (Ruhr University Bochum), Simeon Reusch (DESY) and Anna Franckowiak (DESY/Ruhr University Bochum) 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-210629A (Santander et. al, GCN 30342
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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-band and r-band beginning at 2021-06-30 at 09:35 UT, approximately 15.4 hours after event time. We covered 4.6 sq deg, corresponding to 79.6% 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). We are left with the following high-significance transient candidate, lying within the 90.0% localization of the skymap:

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| ZTF Name     | IAU Name  | RA (deg)    | DEC (deg)   | Filter | Mag   | MagErr |
+--------------------------------------------------------------------------------+
| ZTF21abecljv | AT2021osi
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  | 341.4907741 | +12.1537928 | g      | 20.42 | 0.14   |
+--------------------------------------------------------------------------------+

AT2021osi
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  (ZTF21abecljv) is an unclassified transient first reported on 2021-06-04 by ALeRCE (F��rster et al. 2020). The position of this transient appears to be consistent with the nucleus of its host galaxy. Forced photometry shows no optical detections prior to 2021-05-06.

We encourage spectroscopic observations of this object to establish its nature.
 
Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW.
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).

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-210629A (GCN 30342
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 ).

At the time of the event (2021-06-29 18:09:44 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 42 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(20% of optimal) response of ISGRI, strongly suppressed (37% of
optimal) response of IBIS/Veto, and near-optimal (84% 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 2.2e-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 ~1.9e-07 (5.8e-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: 5 likely background
excesses:

T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
-11.3 | 0.8 | 3.4 | 2.69 +/- 0.792 +/- 0.849 | 0.127
50.3 | 1.6 | 3.7 | 2.08 +/- 0.559 +/- 0.657 | 0.165
-33.3 | 1.5 | 3.1 | 1.83 +/- 0.577 +/- 0.579 | 0.363
-15.5 | 0.05 | 3.9 | 1.26 +/- 0.323 +/- 0.397 | 0.711
16.7 | 0.05 | 3.8 | 1.24 +/- 0.323 +/- 0.39 | 0.863

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) 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 
IC210629A neutrino event (GCN 30342
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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 2021-06-29 at 18:09:44 UT 
(T0) with J2000 position RA = 340.75 (+ 1.11, - 2.23) deg, Decl. = 
+12.94 (+ 0.91, - 0.93) deg (90% PSF containment). No cataloged >100 MeV 
gamma-ray source is located within the 90% IC210629A localization region.

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 IC210629A 
best-fit position. Assuming a power-law spectrum (photon index = 2.0 
fixed) for a point source at the IC210629A best-fit position, the >100 
MeV flux upper limit (95% confidence) is < 3.8e-10 ph cm^-2 s^-1 for 
~12-years (2008-08-04 to 2021-06-29 UTC), and < 3.4e-9 (< 6.5e-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 the IceCube event region 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.

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

For the IceCube high-energy neutrino candidate event IceCube-210629A (GCN 30342
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 ),
at the event time Fermi-GBM was observing the reported neutrino location at:

RA: 340.75 (+1.11 -2.23 deg  90% PSF containment) J2000
Dec: +12.94 (+0.91 -0.93 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-210629A.

We set upper limits on impulsive gamma-ray emission. Using the
representative soft, normal, and hard GRB-like templates
(arXiv:1612.02395
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 ), we report 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:   5.2      8.3        18.
1.024 s:   1.3      2.4        5.0
8.192 s:   0.5      0.9        1.8

These results are preliminary.

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

On 2021-06-29 at 18:09:44 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 2.085 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/135440_3139778.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2021-06-29
Time:  18:09:44 UT

RA: 340.75 (+ 1.11 - 2.23 deg  90% PSF containment) J2000
Dec: +12.94 (+ 0.91 - 0.93 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 J2252.6+1245 at RA: 343.17 deg, Dec: 12.75 deg J2000 (2.36 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