IceCube-200227A

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

On 20/02/27 at 05:36:31.50 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 2.34 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/133781_21701751.amon <https://gcn.gsfc.nasa.gov/notices_amon_g_b/133781_21701751.amon>), the detailed angular uncertainty is still being evaluated. At this time we propose to use the preliminary values reported in the GCN Notice:

Date: 20/02/27 
Time: 05:36:31.50 UT
RA:  348.26 deg J2000
Dec: +21.32 deg J2000
Error Radius: 30.80 arcmin (90% containment - statistical)

We stress that the reported error estimate only accounts for statistical errors, and that additional systematic uncertainties mean this containment radius is a lower limit.

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

The nearest 4FGL sources is 4FGL J2318.2+1915, located at RA 349.56 deg and Dec 19.26 deg a distance of  2.40 deg from the best-fit position. A second source, 4FGL J2323.1+2040, is located at RA 350.79 deg and Dec 20.68 deg, a distance of 2.45 deg from the best-fit 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

M. Doyle, (UCD, Ireland), A. Coleiro (APC, France),
V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)
J. Rodi (IAPS-Roma, Italy)
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-200227A (GCN 27235
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 ).

At the time of the event (2020-02-27 05:36:31 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 86 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(8.6% of optimal) response of ISGRI, strongly suppressed (31% of
optimal) response of IBIS/Veto, and somewhat suppressed (59% 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 2.9e-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 ~2.7e-07 (7.4e-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  
-2.83 | 0.4 | 3 | 0.512 +/- 0.186 +/- 0.242 | 0.168 
117 | 0.35 | 4.6 | 0.834 +/- 0.2 +/- 0.393 | 0.635 
-138 | 1.3 | 3.6 | 0.324 +/- 0.103 +/- 0.153 | 0.681 
87.8 | 1.5 | 3.3 | 2.74 +/- 0.956 +/- 1.29 | 0.688 
-25.4 | 0.35 | 3.4 | 0.597 +/- 0.199 +/- 0.281 | 0.71 

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

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

For the IceCube high-energy neutrino candidate event IceCube-200227A 
(GCN 27235
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 ), at the event time Fermi-GBM was observing the reported 
neutrino location at:

RA, Dec: 348.26, +21.32 (J2000)
Error Radius: 30.80 arcmin, 90% PSF containment

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-200227A.

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:  0.5   0.9   1.8
1.024 s:  0.2   0.3   0.7
8.192 s:  0.1   0.1   0.3

Q. Luo, Y. G. Zheng, C. Cai, Y. F. Du, W. C. Xue, 
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=2020-02-27T05:36:31.50 UTC) of this high-energy neutrino 
candidate event (GCN #27235
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 ), which was monitored without 
any occultation by the Earth. 

Within T0 +/- 100 s, no significant excess events (SNR > 4 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:  1.0e-07 erg cm^-2   
10s: 9.3e-07 erg cm^-2 

Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV):
1s:  1.6e-07 erg cm^-2   
10s: 1.5e-06 erg cm^-2

Band model 3 (alpha=-0.0, beta=-1.5, Ep=1000 keV):
1s:  3.3e-07 erg cm^-2  
10s: 2.6e-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 
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.

S. Buson (Univ. of Wuerzburg) and S. Garrappa (DESY-Zeuthen) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy IC200227A neutrino event (GCN 27235
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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 2020-02-27 05:36:31.50 UT (T0) with J2000 position RA = 348.26 deg, Decl. = 21.32 deg (30.80 arcmin 90% PSF containment - statistical). No cataloged >100 MeV gamma-ray sources are located within the 90% IC200227A 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 (> 100 MeV) within the IC200227A 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-9 ph cm^-2 s^-1 for ~11-years (2008-08-04 / 2020-02-27 UTC), < 7e-9 (< 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 this source 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.

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-200227A (https://gcn.gsfc.nasa.gov/gcn3/27235.gcn3
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 ) in a time
range of 2 days centered on the alert event time (2020-02-26 05:36:31.5 UTC to 2020-02-28 05:36:31.5 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-200227A. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/ dE = 4.49 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 (2020-01-28 05:36:31.5 UTC to 2020-02-28 05:36:31.5 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
6.92 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>.