IceCube-200916A

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

On 20/09/16 at 20:40:30.95 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 threshold astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 2.48 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/134498_12605830.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 20/09/16
Time:  20:40:30.95 UT
RA: 109.78 +1.08  -1.44 (deg  90% PSF containment) J2000
Dec: 14.36 +0.88  -0.85  (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 J0725.2+1425, associated with the BL Lac object 4C +14.23, at RA: 111.32 deg, Dec: 14.42 deg (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

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 
IC200916A neutrino event (GCN 28433
Loading...
 
 ) 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 2020-09-16 20:40:30.95 UTC 
(T0) with J2000 position RA = 109.78 (-1.44,+1.08) deg, Decl. = 14.36 
(-0.85,+0.88) deg 90% PSF containment.�No cataloged >100 MeV gamma-ray 
sources (The Fourth Fermi-LAT catalog; The Fermi-LAT collaboration 2020, 
ApJS, 247, 33) are located within the 90% IC200916A localization error.

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 (0.1 - 
800 GeV) within the IC200916A 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 < 5.6e-10 ph cm^-2 s^-1 for ~12-years (2008-08-04 / 
2019-09-16 UTC), < 1e-8 (< 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 
<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.

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

For the IceCube high-energy neutrino candidate event IceCube-200916A
(GCN 28433
Loading...
 
 ), at the event time Fermi-GBM was observing the reported
neutrino location at:

RA: 109.78 +1.08  -1.44 (deg  90% PSF containment) J2000
Dec: 14.36 +0.88  -0.85  (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-200916A.

We set upper limits on impulsive gamma-ray emission. Using the
representative soft, normal, and hard GRB-like templates described in
arXiv:1612.02395
Loading...
 
 , 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:    4.8      8.1      18.
1.024 s:    1.7      2.8      4.6
8.192 s:    0.3      0.7      1.3

These results are preliminary.

Simeon Reusch, Robert Stein, Anna Franckowiak (DESY), Igor Andreoni (Caltech) and Michael Coughlin (UMN) 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-200916A (Blaufuss et. al, GCN 28433
Loading...
 
 ) 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 2020-09-17 11:23 UTC, approximately 14.7 hours after event time. We covered 3.6 sq deg, corresponding to >99% of the reported localization region. This estimate does not account 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 are left with the following high-significance transient candidates by our pipeline, all lying within the 90.0% localization of the skymap.

+----------------------------------------------------------------------------------------------------+
| ZTF Name     | IAU Name   | RA (deg)    | DEC (deg)   | Filter | Mag   | MagErr | MJD      | Notes |
+----------------------------------------------------------------------------------------------------+
| ZTF20acaapwk | AT2020tno
Loading...
 
   | 108.9968806 | +14.9039078 | r      | 19.24 | 0.06   | 59109.49 |  (a)  |
| ZTF20acaapwo | AT2020tnp
Loading...
 
   | 108.5820017 | +14.4452676 | r      | 20.41 | 0.14   | 59109.49 |  (a)  |
+---------------------------------------------------------------------------------+------------------+

(a) ZTF20acaapwk/AT2020tno
Loading...
 
  and ZTF20acaapwo/AT2020tnp
Loading...
 
  are both unclassified transients with a last upper limit from 20 days ago. Spectroscopic follow-up is recommended.
 
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.
ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341.
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).

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-200916A (GCN 28433
Loading...
 
 ).

At the time of the event (2020-09-16 20:40:30 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 21 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(19% of optimal) response of ISGRI, strongly suppressed (25% of
optimal) response of IBIS/Veto, and strongly suppressed (32% of
optimal) response of SPI-ACS.

The background within +/-300 seconds around the event was rather
stable (excess variance 1.3).

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 5.2e-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 ~4.7e-07 (8.2e-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
4.26 | 0.4 | 3.6 | 1.08 +/- 0.331 +/- 0.506 | 0.0658
-127 | 13.5 | 3.2 | 1.54 +/- 0.566 +/- 0.721 | 0.142
-149 | 14 | 3.2 | 1.36 +/- 0.556 +/- 0.638 | 0.168
38.7 | 0.25 | 3.7 | 1.45 +/- 0.42 +/- 0.68 | 0.704
93.7 | 0.65 | 3.7 | 0.869 +/- 0.259 +/- 0.408 | 0.722

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-200916A (GCN 28433
Loading...
 
  <https://gcn.gsfc.nasa.gov/gcn3/28433.gcn3
Loading...
 
 >). The reconstructed origin was -29.1 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 18 GeV.cm^-2 over the energy range 5 TeV - 4.5 PeV (the range corresponding to 5-95% of the detectable flux) for an E^-2 power-law spectrum, and 33 GeV.cm^-2 (1- 430 TeV) for an E^-2.5 spectrum. A search over an extended time window of +/- 1 day has also yielded no detection (42% visibility). 

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.

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

On 2020/09/16 20:40:30 UTC, the IceCube collaboration reported a
track-like very-high-energy event  that has a high probability of
being an astrophysical neutrino, IceCube-YYMMDDA. Location is at
RA: 109.78 (+1.08/-1.44 deg  90% PSF containment) J2000
Dec: 14.36 (+0.88/-0.85 deg 90% PSF containment) J2000
(GCN circular 28433
Loading...
 
 ).

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.
The most significant location, with p-value  6.64e-04 (1.46e-02
post-trials),
is at RA 108.78 deg, Dec +13.48 deg (��0.29 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 = 3.21e-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 2020/09/15 17:05:26 UTC and ended
2020/09/17 17:11:43 UTC.
The most significant location, with p-value 2.12e-02  (0.38e-01
post-trials),
is at RA 109.95 deg, Dec +15.06 deg (��0.23 deg 68% containment) J2000.
We set a time-integrated 95% CL upper limit at the position of
maximum significance of:

E^2 dN/dE = 6.22e-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.

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 200916A (GCN Circ. 28433
Loading...
 
 ) between 20:59:50 2020 September 16 and 01:26:43 on 2020 September 17, 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.

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

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-200916A (https://gcn.gsfc.nasa.gov/gcn3/28433.gcn3
Loading...
 
 ) in a time
range of 2 days centered on the alert event time (2020-09-15 20:40:30.95 UTC to 2020-09-17 20:40:30.95 UTC) during which IceCube was collecting good quality data. Excluding the
event that prompted the alert, one additional track-like event is found in spatial coincidence
with the 90% containment region of IceCube-200916A. 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 = 3.8 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 (2020-08-17 20:40:30.95 UTC to 2020-09-17 20:40:30.95 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
4.8  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>.

S. Belkin (IKI), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO), V. R. 
Ayvazian (AbAO),  G. V.  Kapanadze (AbAO),   A. Volnova (IKI), I. 
Molotov (KIAM)  report on behalf of IKI-GRB-FuN:

We observed the two candidate counterparts from ZTF (Reusch et al., GCN 
28441
Loading...
 
 ) of the neutrino event IceCube-200916A (Blaufuss et. al, GCN 
28433
Loading...
 
 ) with  AS-32 telescope of Abastumani observatory in R-filter.
In stacked images we cannot resolve point like sources of the 
candidates. Photometry of candidates include their (presumably) 
underlying host galaxies and presented below.


IAU Name, Date,      UT start, MJD,   Exp.,  Filter, OT, Err., UL, Ref.
                     (mid, days)

AT2020tno
Loading...
 
  2020-09-18 01:00:49 59110.04918 20*60 R  16.88 0.02 20.3 (1)
AT2020tnp
Loading...
 
  2020-09-18 01:39:12 59110.07306 12*60 R  19.62 0.22 20.0 (2)

The photometry is based on nearby USNO-B1.0 stars
Ref.(1)
USNO-B1.0_id R2
1049-0143702 14.84
1048-0142480 14.23
Ref.(2)
USNO-B1.0_id R2
1044-0132913 15.48
1044-0132991 15.73

In the case of AT2020tno
Loading...
 
  the brightness is not distinguished from 
magnitude of underlying object in catalogues.
The brightens of AT2020tnp
Loading...
 
   is might be somewhat brighter than reported 
by ZTF (r=20.41 +/- 0.14; Reusch et al., GCN 28441
Loading...
 
 ) and apparently 
brighter than reported in catalogues.

Simeon Reusch, Robert Stein, Anna Franckowiak (DESY), Steve Schulze (WIS) and Jesper Sollerman (Stockholm University) report:

We observed ZTF candidate ZTF20acaapwk/SN2020tno (Reusch et al., GCN 28441
Loading...
 
 ; see also Belkin et al., GCN 28453
Loading...
 
 ), a possible counterpart to high-energy neutrino IceCube-200916A (Blaufuss, GCN 28433
Loading...
 
 ), using the NOT+ALFOSC spectrograph on 21 September 2020.

We classify SN2020tno as a type Ia supernova, thereby excluding any connection to IC200916A.

ZTF20acaapwo/AT2020tnp
Loading...
 
  remains a candidate.

---
The data presented here were obtained with ALFOSC, which is provided by the Instituto de Astrofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOTSA.