IceCube-190922A

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

On 19/09/22 at 09:42:45.62 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_Gold alert stream. Though the average astrophysical neutrino purity for Gold alerts is 50%, this particular event had a signalness of just 20%. This alert has an estimated false alarm rate of 0.23 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/133091_81419.amon <https://gcn.gsfc.nasa.gov/notices_amon_g_b/133091_81419.amon>), more  
sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 19/09/22
Time:  09:42:45.62 UT
RA: 167.43 (+ 3.40 - 2.63  deg  90% PSF containment) J2000
Dec: -22.39 (+ 2.88 - 2.89 deg 90% PSF containment) J2000

Though the initial reported event energy was in excess of 3PeV, the event had a topology with a short distance traversed through the detector. We caution that, in such cases, the energy of the event is highly uncertain. In this case, the true energy is likely significantly less than initially reported.

Due to the low signalness of the event and its large angular uncertainty, we do not believe this to be a strong candidate for dedicated follow up by ground and space-based instruments.

Two gamma-ray sources listed in the 4FGL Fermi-LAT catalog are located within the 90% uncertainty region of the event. The sources are 4FGL J1120.0-2204 and 4FGL J1103.6-2329, located respectively 2.6 deg and 1.9 deg away 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

Francesca Onori, Antonio Martin-Carrillo
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 INTEGRAL/SPI-ACS realtime data (following [1]) we have performed
a search for a prompt gamma-ray counterpart of the IceCube event
190922A (GCN 25802
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 ).

At the time of the event (2019-09-22 09:42:45 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 103 deg with respect to
the spacecraft pointing axis. This orientation implies strongly
suppressed (6.7% of optimal) response of ISGRI, strongly suppressed
(36% of optimal) response of IBIS/Veto, and somewhat suppresse d (48%
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 (as described in [2]) data.

We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 3.8e-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 ~3.4e-07 (9.6e-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: 4 likely background
excesses:

scale | T | S/N | flux ( x 1e-06 erg/cm2/s) | FAP
0.25 | 3.92 | 3.1 | 0.831 +/- 0.3 +/- 0.444 | 0.26
2.55 | -277 | 4.2 | 3.48 +/- 0.935 +/- 1.86 | 0.296
0.05 | 70.8 | 6.6 | 4.03 +/- 0.696 +/- 2.15 | 0.505
0.45 | 26.5 | 3.1 | 0.617 +/- 0.223 +/- 0.33 | 0.985

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

-- 
Dr. Francesca Onori
Postdoctoral Researcher
IAPS, via Fosso del Cavaliere, 100, 00133 - Rome, Italy
e-mail: francesca.onori@inaf.it
Tel: +39 06 45488128

Antonio Galvan (IA-UNAM) report on behalf of the HAWC collaboration
(http://www.hawc-observatory.org/collaboration/):

On 2019-09-22 at 09:42:45.62 UTC, the IceCube collaboration detected a
track-like event with a moderate probability of being of astrophysical
origin, IceCube-190922A, at RA= 167.43 deg and Dec= -22.39 deg, J2000 (GCN
circular 25802
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 ). In HAWC's sky, the neutrino was outside of our field of
view.
We have performed a search in our archival data for a steady source as
well as a transient source.

* Search for a steady source in archival data from November 2014 to May
2018. Assuming a  power law with a spectral index of -2.3 we searched in a
6.8 x 5.78 degree rectangle around IceCube's reported location.

The highest significance, 1.31 sigma, was at RA= 168.35 deg, Dec= -23.81 deg
(J2000). Note that there are at least 196.5 trials in this search, so
post-trials significance is consistent with 0. We set a
time-integrated upper limit 95% CL on the gamma-ray flux of E^2 dN/dE =
1.2e-12 (E/TeV)^-0.3 TeV cm^-2 s^-1.

* Search for a transient source: Since the events was not in our field of
view at the time reported on the GCN we did a search for the day before and
after as well. The results are the following:

Data acquisition on 2019-09-21 16:27:31 and ends 2019-09-22 18:45:53 (UTC),
1.32 sigma pre-trials (0 post trials), was at RA= 166.14 deg, Dec= -23.01
deg
(J2000). We set a time-integrated upper limit 95% CL on the gamma-ray flux
of: E^2 dN/dE = 6.1e-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.

E. Burns (NASA/GSFC) reports on behalf of the Fermi-GBM Team:

For the IceCube high-energy neutrino candidate event 190922A (GCN 25802
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 ),
at the event time Fermi-GBM was observing about half the reported neutrino
probability map of:

RA: 167.43 (+ 3.40 - 2.63  deg  90% PSF containment) J2000
Dec: -22.39 (+ 2.88 - 2.89 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-190922A. Over the 1 minute search interval the
Earth-occulted region for Fermi shifted by about 4 degrees, resulting in
time-varying exposure to the neutrino localization.

We set upper limits on impulsive gamma-ray emission for the fraction of
localization region observed as a function of time. 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     norm     hard
--------------------------------------
0.128 s:   3.8      6.3      13.
1.024 s:   1.0      1.8      3.7
8.192 s:   0.3      3.9      1.0

S. Garrappa (DESY-Zeuthen) and S. Buson (Univ. of Wuerzburg; UMBC) on behalf of the Fermi-LAT collaboration:
We report an analysis of observations of the vicinity of the high-energy IC190922A neutrino event (GCN 25802
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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  2019-09-22 at 09:42:45.62 UT (T0) with J2000 position RA = 167.43 (+3.40, -2.63) deg, Decl. = -22.39 (+2.88, -2.89) deg 90% PSF containment. 
Three cataloged >100 MeV gamma-ray sources are located within the 90% IC190922A localization error. These are the BL Lac object 4FGL J1103.6-2329 (a.k.a. 1ES 1101-232), and the unassociated sources 4FGL J1120.0-2204 and 4FGL J1100.0-2044 (The Fermi-LAT collaboration, 2019, arXiv:1902.10045
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 ) at a distance of roughly 1.8 deg, 2.4 deg and 2.8 deg, respectively. Based on a preliminary analysis of the LAT data over the timescale of 1-day and 1-month before T0, these objects are not significantly detected at gamma rays.
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 IC190922A 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 < 8.1e-10 ph cm^-2 s^-1 for ~11-years (2008-08-04 / 2019-09-22 UTC), < 4.6e-8 (< 1.4e-8) ph cm^-2 s^-1 for a 1-day (1-month) 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 person are Simone Garrappa (simone.garrappa at desy.de <http://desy.de/>) and Sara Buson (sara.buson at gmail.com <http://gmail.com/>). 
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-190922A (https://gcn.gsfc.nasa.gov/gcn3/25802.gcn3
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 ) in a time
range of 2 days centered on the alert event time (2019-09-21 09:42:45.62 UTC to 2019-09-23 09:42:45.62 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-190922A. We find that these data are well described by atmospheric background expectations, with a p-value of 1.0. Accordingly, these data would represent a time-integrated muon-neutrino flux upper limit at the alert position assuming an E^-2 spectrum (E^2 dN/dE) at the 90% CL of 3.3 x 10^-4 TeV cm^-2 for this observation period. 90% of events IceCube would detect from a source at this declination with an E^-2 spectrum are approximately between 100 TeV and 30 PeV.

A subsequent search was performed to include the previous month of data (2019-08-22 09:42:45.62 UTC to 2019-09-23 09:42:45.62 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
 6.6 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>.