IceCube-200926A

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

On 20/09/26 at 07:54:11.62 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 0.536 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/134533_53384881.amon), more 
sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 20/09/26
Time: 07:54:11.62  UT
RA: 96.46 (+ 0.73 - 0.55  deg 90% PSF containment) J2000
Dec: -4.33 (+ 0.61  - 0.76  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-LAT 4FGL or 3FHL sources inside the 90% localization region. The closest source is 4FGL J0613.7-0201 located at RA 93.44 deg and Dec -2.02 deg (J2000), at a distance of 3.8 degrees from the best-fit location.

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 
IC200926A neutrino event (GCN 28504
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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 2020-09-26 at 
07:54:11.62�UT (T0) with J2000 position RA = 96.46 (+0.73, -0.55) deg, 
Decl. = -4.33 (+0.61, -0.76) 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% IC200926A 
localization error.

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 
IC200926A�best-fit position. Assuming a power-law spectrum (photon index 
= 2.0 fixed) for a point source at the IC200926A�best-fit position, the 
 >100 MeV flux upper limit (95% confidence) is < 1.8e-10 ph cm^-2 s^-1 
for ~12-years (2008-08-04 / 2020-09-26 UTC), < 2.2e-8 (< 1.1e-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 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.

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 200926A (GCN Circ. 28504
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 ) between 11:44:33
2020 September 26 and 13:45:03 on 2020 September 26, collecting a total of 3.8 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 5 X-ray sources, as detailed below. All of these are either known X-ray
sources, consistent with catalogued fluxes, or are unknown but with count rate
consistent with the previous non-detections. We therefore do not claim any of
them as the likely counterpart to IceCube 200926A
A futher 4 sources were detected, but their detection flag of 4 indicates that
they were likely spurious.

The 3-sigma upper limit in the field was in the range 6-8 x 10^-3 ct/sec.

The detected sources were:

Source no:���� 1
RA (J2000):�� 96.44016 [degrees] = 06h 25m 45.64s
Dec (J2000): -4.3672 [degrees] = -04d 22' 02.0"
Error:������������ +5.5 [arcsec, 90% conf. radius]
Count rate (0.3-10 keV): 0.0104 (+0.0036, -0.0029) ct s-1
Flux (0.3-10 keV):������������ 4.5 (+1.5, -1.3) x 10-13 erg cm-2 s-1
Note: This is 3.0" from the SIMBAD object 2MASX J06254558-0422053


Source no:���� 2
RA (J2000):�� 96.44428 [degrees] = 06h 25m 46.63s
Dec (J2000): -4.28706 [degrees] = -04d 17' 13.4"
Error:������������ +6.1 [arcsec, 90% conf. radius]
Count rate (0.3-10 keV): 6.2 (+2.8, -2.2) x 10^-3 ct s-1
Flux (0.3-10 keV):������������ 2.68 (+1.19, -0.93) x 10^-13 erg cm-2 s-1


Source no:���� 3
RA (J2000):�� 96.71505 [degrees] = 06h 26m 51.61s
Dec (J2000): -4.3578 [degrees] = -04d 21' 27.9"
Error:������������ +4.7 [arcsec, 90% conf. radius]
Count rate (0.3-10 keV): 0.0114 (+0.0036, -0.0030) ct s-1
Flux (0.3-10 keV):������������ 4.9 (+1.5, -1.3) x 10-13 erg cm-2 s-1
Note: This is 3.3" from the SIMBAD object Cl* NGC 2232������ CPK���� 18627


Source no:���� 7
RA (J2000):�� 96.28302 [degrees] = 06h 25m 07.93s
Dec (J2000): -4.15135 [degrees] = -04d 09' 04.9"
Error:������������ +8.0 [arcsec, 90% conf. radius]
Count rate (0.3-10 keV): 9 (+5, -4) x 10-3 ct s-1
Flux (0.3-10 keV):������������ 3.8 (+2.1, -1.5) x 10-13 erg cm-2 s-1


Source no:���� 8
RA (J2000):�� 96.45055 [degrees] = 06h 25m 48.13s
Dec (J2000): -4.51977 [degrees] = -04d 31' 11.2"
Error:������������ +3.0 [arcsec, 90% conf. radius]
Count rate (0.3-10 keV): 0.049 (��0.011) ct s-1
Flux (0.3-10 keV):������������ 2.1 (��0.5) ��10-12 erg cm-2 s-1
Note: This is 0.4" from the SIMBAD object Gaia DR2 3104506437197663232

Simeon Reusch (DESY), Robert Stein (DESY), Sven Weimann (Ruhr University Bochum) 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-200926A (Lagunas et al. GCN 28504
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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 r-band beginning at 2020-09-26 11:58 UTC, approximately 4.1 hours after event time. We covered 1.3 sq deg, corresponding to 89.5% 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. 2020) 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.

No counterpart candidates were detected.

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).
Alert filtering is performed with the AMPEL Follow-up Pipeline (Stein et al. 2020).

[GCN OPS NOTE(28Sep20): Per author's request, the Subject line was changed from "200929A" to "200926A".]

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-200926A (https://gcn.gsfc.nasa.gov/gcn3/28504.gcn3
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 ) in a time
range of 2 days centered on the alert event time (2020-09-25 07:54:11.62 UTC to 2020-09-27 07:54:11.62 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-200926A. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/ dE = 3.6 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 7 PeV.

A subsequent search was performed to include the month of data prior to the alert event (2020-08-27 07:54:11.62 UTC to 2020-09-27 07:54:11.62 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
4.3 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>.

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

On 2020-09-26 22:35:29 UTC, the IceCube collaboration reported a
track-like very-high-energy event  that has a high probability of
being an astrophysical neutrino, IceCube-200926A. Location is at
RA: 96.46 (+ 0.73 - 0.55 deg  90% PSF containment) J2000
Dec: -4.33 (+ 0.61  - 0.76 deg 90% PSF containment) J2000
(GCN circular 28504
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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  2.07e-02 (1.70e-01
post-trials),
is at RA 97.08 deg, Dec -3.73 deg (��0.26 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 = 2.64e-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 2020/09/24 15:08:36 UTC and ended
 2020/09/26 15:23:21 UTC.
The most significant location, with p-value 7.49e-02  (5e-1 post-trials),
is at RA 96.28 deg, Dec -4.18 deg (��2.37 deg 68% containment) J2000.
We set a time-integrated 95% CL upper limit at the position of
maximum significance of:

E^2 dN/dE = 1.25e-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.

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

For the IceCube high-energy neutrino candidate event IceCube-200926A
(GCN 28504
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 ), at the event time Fermi-GBM was observing the reported
neutrino location at:

RA: 96.46 (+ 0.73 - 0.55  deg 90% PSF containment) J2000
Dec: -4.33 (+ 0.61  - 0.76  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-200926A.

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:    7.1      9.7      17.
1.024 s:    2.3      3.4      5.9
8.192 s:    1.0      1.5      2.6

These results are preliminary.

Y. Urata (NCU) and K. Huang (CYCU)

We observed the field of IceCube-200926A (GCN 28532
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 ) using SCUAB-2 attached to JCMT.  
The observation was started at 2020/09/28 13:21 UTC and 
SCUBA2 imaged the field centered at RA 06:25:50 Dec -4:19:48 with 50 arcmin diameter.
We could not find any sources on the 850um image with the final map noise of 4.5 mJy.

We thanks staffs of East Asian Observatory.

Sven Weimann (Ruhr University Bochum), Robert Stein (DESY), 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-200929A (Lagunas et. al, GCN 28532
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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 2020-09-30T07:53:51.850 UTC, approximately 14.1 hours after event time. We covered 0.9 sq deg, corresponding to 88.72% 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. 2020) 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 looked for high-significance transient candidates with our pipeline, lying within the 90.0% localization of the skymap.

No counterpart candidates were detected.

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).
Alert filtering is performed with the AMPEL Follow-up Pipeline (Stein et al. 2020).

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

At the time of the event (2020-09-26 07:54:11 UTC, hereafter T0),
INTEGRAL was nearing the end of orbit, and although the data is available,
the excess variance due to local background environment was extreme
(excess variance 54), preventing search for any but the most intense 
counterparts, which would have been clearly detected by other instruments.

Yu-Ling Chang (TDLI), Jinyuan Liao (IHEP), Chen Wang (NAOC), Yi Nang (IHEP), Na Sai (IHEP), Youli Tuo (IHEP), Ju Guan (IHEP), Chengkui Li (IHEP), Yuan Liu (NAOC), Jianyin Nie (IHEP), Donglian Xu (TDLI), Marcos Santander (U. Alabama), Wenlian Li (TDLI), Lian Tao (IHEP), Shijie Zheng (IHEP), Shaolin Xiong (IHEP), Shuangnan Zhang (IHEP), report on behalf of the TDLI and Insight-HXMT teams

Insight-HXMT observed the field of IceCube-200926A (GCN Circ. 28504
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 ) from 01:34:59 UTC September 29, 2020 to 10:49:34 UTC October 1, 2020 collecting a total of 8-epoch of data spanning ~2.5 days. The observations were done with small-sky scan mode with a scanning radius ~7 degrees and a total observation time of 20 ks.

We searched for emission from a new X-ray transient source. Preliminary analysis indicates no significant (> 5 sigma) new excess emission in all three bands, LE, ME, and HE of Insight-HXMT, at the IceCube-200926A best-fit position. 

Assuming an absorbed power-law spectrum (photon power-law index = 1.9 and nH column density = 3.14e21 fixed) for a point source at the position of this neutrino event, the 5-sigma flux upper-limits are reported below:

LE Band (1-6 keV):
6.2e-11 erg cm^-2 s^-1 

ME Band (7-40 keV):
2.5e-10 erg cm^-2 s^-1   

HE Band (25-100 keV):
1.1e-10 erg cm^-2 s^-1  


All measurements above are made with the NaI detectors operating in the
regular mode with the energy range of about 1-250 keV (record energy).

Insight-HXMT is the first Chinese space X-ray telescope, which was 
fundedjointly by the China National Space Administration (CNSA) and 
the Chinese Academy of Sciences (CAS). 
More information could be found at: http://www.hxmt.org.