IceCube-240307A

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

On 2024-04-07 at 07:44:57.38 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 Gold alerts is 50%. This alert has an estimated false alarm rate of 0.233 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/139100_34742349.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2024-04-07
Time:  07:44:57.38 UT
RA: 239.63 (+13.20, -15.22 deg  90% PSF containment) J2000
Dec: 39.94 (+18.18, -14.92 deg 90% PSF containment) J2000

The large uncertainty on its directional reconstruction can be explained by the short track length observed, as the event was only partially contained in the detector volume. Nevertheless, this event remains interesting considering that it is an up-going track (indicative of a neutrino origin) with an estimated energy of around 190 TeV, making it potentially astrophysical. We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.

Given its large uncertainty, there is a large number (>40) of gamma-ray sources within the large 90% uncertainty region of the event, with the closest one listed in the 4FGL-DR4 Fermi-LAT catalog being 4FGL J1557.2+3822, located at RA: 239.31 deg, Dec: 38.38 deg J2000 (1.58 deg away from the best-fit event 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

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-240307A (https://gcn.nasa.gov/circulars/35898
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 ) in a time range of 1000 seconds centered on the alert event time (2024-03-07 07:36:37.380 UTC to 2024-03-07 07:53:17.380 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, one track-like event is found within the 90% containment region of IceCube-240307A. We find that this additional event is well described by atmospheric background expectations, with a p-value of 0.07. 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-240307A ranges from 1.4e-01 to 1.7e-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 (2024-03-06 07:44:57.380 UTC to 2024-03-08 07:44:57.380 UTC). In this case, we report a p-value of 0.75, 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-240307A ranges from 1.6e-01 to 2.0e-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)

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

We report an analysis of observations of the vicinity of the IC240229A high-energy neutrino event (GCN 35898
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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 2024-03-07 at 07:44:57.38 UT (T0) with J2000 position RA = 239.63 (+13.20, -15.22) deg, Decl. = +39.94 (+18.18, -14.92 ) deg (90% PSF containment). Several catalogued gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) sources are located within the 90% IC240307A localization region. Based on a preliminary analysis of the LAT data over the timescale of 1-day prior to T0, these objects are not significantly detected (> 5 sigma).

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 IC240307A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC240307A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 3.8e-8 ph cm^-2 s^-1 for a 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 is S. Garrappa (simone.garrappa at weizmann.ac.il).

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.