IceCube-220509A

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

On 2022-05-09 at 18:19:04.12 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 Bronze alerts is 50%. This alert has an estimated false alarm rate of 1.53 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/136615_14688828.amon), more  
sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2022-05-09
Time:  18:19:04.12 UT
RA: 334.25 (+2.01, -1.44 deg  90% PSF containment) J2000
Dec: 5.38 (+1.63, -1.65 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 2 known gamma-ray sources in the 90% containment region for the event.  The sources are 4FGL J2215.4+0544 and 4FGL J2212.8+0647.   The closest source in the  4FGL-DR3 Fermi-LAT catalog is 4FGL J2215.4+0544 (333.86 deg, 5.75 deg J2000, 0.54 deg away from the best-fit neutrino candidate 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. 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 IC220509A neutrino event (GCN 32013
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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 2022-05-09 at 18:19:04.12 UT (T0) with J2000 position RA = 334.25 (+2.01, -1.44) deg, Decl. = 5.38 (+1.63, -1.65) deg (90% PSF containment). Three cataloged gamma-ray (>100 MeV) sources are located within the 90% IC220509A localization region (4FGL-DR3; arXiv:2201.11184
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 ; The Fermi-LAT collaboration 2020, ApJS, 247, 33). These are :
4FGL J2215.4+0544, associated with the blazar of uncertain type NVSS J221513+054454 (Condon et al. 1998, AJ, 115, 1693);
4FGL J2212.8+0647, associated with the flat-spectrum radio source TXS 2210+065 (Healey et al. 2007, ApJS, 171, 61);
4FGL J2224.5+0353, associated with the high-synchrotron peaked object 1RXS J222426.5+035445 (Jackson et al. 2007, MNRAS, 376, 371).
Based on a preliminary analysis of the LAT data over the timescales of 1-day and 1-month prior to T0, these objects are not significantly detected (> 5 sigma). 4FGL J2212.8+0647 displays gamma-ray activity at the ~3 sigma level during the 1-month time interval prior to T0. This is consistent with the detection of sporadic gamma-ray activity on monthly timescales from this object, as observed in a preliminary 1-month binned LAT light curve.
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 IC220509A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC220509A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.4e-10 ph cm^-2 s^-1 for ~13-years (2008-08-04 to 2022-05-09 UTC), and < 5.3e-9 (< 3.5e-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.

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

IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-220509A (https://gcn.gsfc.nasa.gov/gcn3/32013.gcn3
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 ) in a time range of 1000 seconds centered on the alert event time (2022-05-09 18:10:44.110 UTC to 2022-05-09 18:27:24.110 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-220509A. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-220509A ranges from 1.3e-01 to 1.4e-01 GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 3e+02 GeV and 1e+05 GeV.

A subsequent search was performed including 2 days of data centered on the alert event time (2022-05-08 18:19:04.110 UTC to 2022-05-10 18:19:04.110 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-220509A ranges from 1.5e-01 to 1.6e-01 GeV cm^-2 in a 2 day time window.

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>.

[1] IceCube Collaboration, R. Abbasi  et al., ApJ 910 4 (2021)

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

On 2022/05/09 18:19:04 UTC, the IceCube collaboration reported a
track-like very-high-energy event  that has a high probability of
being an astrophysical neutrino, IceCube-220509A. Location is at
RA: 334.25 (+2.01/-1.44 deg  90% PSF containment) J2000
Dec: 5.38 (+1.63/-1.65 deg 90% PSF containment) J2000
(GCN circular 32013
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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 5.74e-4 (3.27e-2 post-trials),
is at RA 336.05 deg, Dec +4.93 deg (��0.12 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 = 2.9e-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 2022/05/08 16:29:11 UTC and ended
2022/05/10 16:34:36 UTC.
The most significant location, with p-value 9.14e-3  (4.11e-1 post-trials),
is at RA 333.02 deg, Dec +3.70 deg (��0.21 deg 68% containment) J2000.
We set a time-integrated 95% CL upper limit at the position of
maximum significance of:

E^2 dN/dE = 8.24e-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.