IceCube-230914A

S. Garrappa (Weizmann Institute of Science), C. Bartolini (INFN Bari),  S. Buson (Uni Wuerzburg) and J. Sinapius (DESY) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the IC230914A  high-energy neutrino event (GCN 34693
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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 2023-09-14 at 05:21:03.71 UT (T0) with J2000 position RA =  163.83 (+2.60, -2.02) deg, Decl. = +31.83 (+1.79, - 2.13) deg (90% PSF containment). There are two Fermi 4FGL-DR4 cataloged  gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53; Ballet et al. 2023, arXiv:2307.12546
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 ) sources in the 90% IC230914A uncertainty localization region. These are 4FGL J1051.6+3253 associated with the starburst galaxy NGC 3424 and 4FGL J1102.9+3014 associated with the FSRQ B2 1100+30B, at a distance of from the best-fit neutrino localization of 1.3 deg and 2.3 deg, respectively. Based on a preliminary analysis of the LAT data over a month and day timescale prior T0, these objects are not significantly detected at gamma rays.

We searched for intermediate (days to years) timescale emission from a new gamma-ray source. Preliminary analysis indicates no significant (> 5 sigma) new excess emission (> 100 MeV) at the IC230914A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC230914A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 3.9e-10 ph cm^-2 s^-1 for ~15-years (2008-08-04 to 2023-09-14 UTC), and < 3.6e-9 (< 4.2e-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 region will continue. For these observations the Fermi-LAT contact persons are S. Garrappa (simone.garrappa at weizmann.ac.il), C. Bartolini (chiara.bartolini at ba.infn.it), S. Buson (sara.buson at uni-wuerzburg.de) and J. Sinapius (jonas.sinapius at desy.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-230914A (https://gcn.nasa.gov/circulars/34693
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 ) in a time range of 1000 seconds centered on the alert event time (2023-09-14 05:12:43.710 UTC to 2023-09-14 05:29:23.710 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-230914A. 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-230914A is 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 2e+02 GeV and 7e+04 GeV. 

A subsequent search was performed including 2 days of data centered on the alert event time (2023-09-13 05:21:03.710 UTC to 2023-09-15 05:21:03.710 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-230914A is 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.

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

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

On 2023-09-14 at 05:21:03.71 UT IceCube detected a track-like event with a high 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 0.8823 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/138354_45413430.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2023-08-23
Time:  05:21:03.71 UT
RA: 163.83 (+2.60 / -2.02 deg  90% PSF containment) J2000
Dec: +31.83 (+1.79 / - 2.13 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.

Two Fermi 4FGL-DR4 sources are located in the 90% uncertainty region of the event. The sources are 4FGL J1051.6+3253 (NGC 3434) at RA 162.91, Dec +32.88 and 4FGL J1102.9+3014 at RA 165.74, Dec +30.24, located 1.31 and 2.28 deg away from the best fit position, respectively.

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