IceCube-200410A

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

On 20/04/10 at 23:19:55.49 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 2.55 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/133945_24635982.amon <https://gcn.gsfc.nasa.gov/notices_amon_g_b/133945_24635982.amon>), more 
sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 20/04/10
Time: 23:19:55.49 UT
RA: 242.58 (+14.05 -13.35  deg 90% PSF containment) J2000
Dec: 11.61 (+7.87 -6.21 deg 90% PSF containment) J2000

This event had a topology with a short distance traversed through the detector, which makes it challenging to reconstruct. The 90% containment region reported by the reconstruction algorithms is thus significantly larger than average error contours.

Due to the large localization uncertainty for this event, there are many Fermi 4FGL catalog sources in the 90% containment region, including 8 sources lying 5 degrees or less from the best-fit position. The closest is 4FGL J1608.7+1029, at RA: 242.18 deg, Dec: 10.49 deg (1.18 deg away from the best-fit event position). 

We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.

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. Mereghetti (INAF IASF-Milano, Italy), E. Bozzo, V. Savchenko, C.
Ferrigno (ISDC/UniGE, Switzerland), A. Martin-Carrillo (UCD, Ireland), J.
Rodi, F.Onori (IAPS-Roma, Italy), A. Coleiro (APC, France)

on behalf of the INTEGRAL multi-messenger collaboration:
https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration

Using INTEGRAL/SPI-ACS realtime data (following [1]) we have performed
a search for a prompt gamma-ray counterpart of IceCube-200410A (GCN 27534
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 ).

At the time of the event (2020-04-10 23:19:55 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 139 deg with respect to
the spacecraft pointing axis. This orientation implies strongly
suppressed (3.7% of optimal) response of ISGRI, near-optimal (72% of
optimal) response of IBIS/Veto, and strongly suppressed (33% of
optimal) response of SPI-ACS.

The background within +/-300 seconds around the event was rather
stable (excess variance 1.2).

We have performed a search for any impulsive events in INTEGRAL SPI-
ACS data (as described in [2].

On a timescale of 1s we found an event with S/N=4 and a false alarm
probability of 0.0124, about 4 s before T0.
Its properties are the following

T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
-4.09 | 1 | 4 | 0.728 +/- 0.209 +/- 0.393 | 0.0124

Besides this possible associated excess, 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 ~5e-07 (1.4e-07)
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.

3 likely background excesses:

T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
96.6 | 1.6 | 3.3 | 0.479 +/- 0.164 +/- 0.259 | 0.613
240 | 1.25 | 3.9 | 0.614 +/- 0.186 +/- 0.332 | 0.74
204 | 0.85 | 3.9 | 0.753 +/- 0.226 +/- 0.407 | 0.899

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

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

For the IceCube high-energy neutrino candidate event IceCube-200410A
(GCN 27534
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 ), at the event time Fermi-GBM was observing the reported
neutrino location at:

RA: 242.58 (+14.05 -13.35  deg 90% PSF containment) J2000
Dec: 11.61 (+7.87 -6.21 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-200410A.

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:    5.7      8.0      18.
1.024 s:    2.3      3.7      6.4
8.192 s:    0.7      1.1      1.9

These results are preliminary.

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 
IC200410A neutrino event (GCN 27534
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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 2020-04-10 at 23:19:55.49 
UT (T0) with J2000 position RA = 242.58 (+14.05, -13.35) deg, Decl. = 
11.61 (+7.87, -6.21) deg 90% PSF containment. Several cataloged >100 MeV 
gamma-ray sources (The Fermi-LAT Collaboration 2019, 
arXiv:1902.10045
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 )�are located within the 90% IC200410A localization 
error. Based on a preliminary analysis of the LAT data over the 
timescales of 1-day prior to T0, these objects are not significantly 
detected at gamma-rays. Two of these objects are significantly detected 
over the timescale of 1-month prior to T0, these are 4FGL J1548.3+1456 
(associated with the BL Lac�object�NVSS J154824+145702) and 4FGL 
J1555.7+1111 (associated with the BL Lac object�PG 1553+113). Based on a 
preliminary analysis at this timescale, both objects show a gamma-ray 
flux comparable to the catalog value.

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 (> 100 
MeV) within the IC200410A 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 < 1e-8 (< 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 this source 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.

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-200410A (https://gcn.gsfc.nasa.gov/gcn3/27534.gcn3
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 ) in a time
range of 2 days centered on the alert event time (2020-04-09 23:19:55.489 UTC to 2020-04-11 23:19:55.489 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-200410A. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/ dE = 7.7 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 (2020-03-11 23:19:55.489 UTC to 2020-04-11 23:19:55.489 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
1.8 x 10^-4 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>.

Y. G. Zheng, C. Cai, Y. F. Du, W. C. Xue, 
Q. Luo, S. Xiao, Q. B. Yi, Y. Huang, C. K. Li, G. Li, 
X. B. Li, J. Y. Liao, S. L. Xiong,C. Z. Liu, 
X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang, Y. F. Zhang, 
X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), 
T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, 
M. Wu, Y. P. Xu, S. N. Zhang (IHEP), 
report on behalf of the Insight-HXMT team:

Insight-HXMT was taking data normally around the trigger time
(T0=2020-04-10T23:19:55.49 UTC) of this high-energy neutrino event 
(GCN #27534
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 ), which was monitored without any occultation by 
the Earth. 

Within T0 +/- 100 s, no significant excess events (SNR > 3 sigma) 
are found in a search of the Insight-HXMT/HE raw light curves.

Assuming the counterpart GRB with three typical GRB Band spectral 
models, two typical duration timescales(1 s, 10 s) coming from the position
of this neutrino event, the 5-sigma upper-limits fluence 
(0.2 - 5 MeV, incident energy) are reported below:

Band model 1 (alpha=-1.9, beta=-3.7, Ep=70 keV):
1s:  1.3e-07 erg cm^-2   
10s: 6.1e-07 erg cm^-2 

Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV):
1s:  2.1e-07 erg cm^-2   
10s: 9.6e-07 erg cm^-2

Band model 3 (alpha=-0.0, beta=-1.5, Ep=1000 keV):
1s:  5.4e-07 erg cm^-2  
10s: 2.1e-06 erg cm^-2 

Further analysis will be reported in the following circulars.

All measurements above are made with the CsI detectors operating in the
regular mode with the energy range of about 80-800 keV (record energy).
Only gamma-rays with energy greater than about 200 keV can penetrate
the spacecraft and leave signals in the CsI detectors installed inside
of the telescope.

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

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

On 2020/04/10 23:19:55 UTC, the IceCube collaboration reported a
track-like very-high-energy event  that has a high probability of
being an astrophysical neutrino, IceCube-200410A. Location is at
RA: 242.58 (+14.05/-13.35 deg  90% PSF containment) J2000
Dec: 11.61 (+7.87/-6.21 deg 90% PSF containment) J2000
(GCN circular 27534
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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 May 2018. We searched
inside the reported IceCube error region.
The highest significance, 4.06 sigma (1.66 post-trials),
is at RA 247.42 deg, Dec +8.08 deg  (+-0.11 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 = 1.94e-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 2020/04/09 12:22:11 UTC and ended
2020/04/DD 12:28:48 UTC.
The most significant location, with 3.22 sigma (-0.57 post-trials),
is at RA 241.44 deg, Dec +12.14 deg (+-0.12 deg 68% containment) J2000.
We set a time-integrated 95% CL upper limit at the position of
maximum significance of:

E^2 dN/dE = 1.01e-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.