IceCube-250416A

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

On 25-04-16 at 18:32:14.97 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 2.3036 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/140799_37236133.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 25-04-16
Time: 18:32:14.97 UT
RA: 83.1 (+0.57/-0.58 deg 90% PSF containment) J2000
Dec: 15.64 (+0.49/-0.5 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.

No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event.

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

Rosa L. Becerra (U Roma), Sahil Atri (U Roma), Alan M. Watson (UNAM), Eleonora Troja (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM) and Margarita Pereyra (UNAM) report:

We observe the field of the IceCube-250416A (bronze) (IceCube Collaboration, GCN Circ. 40153
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 ) event with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on the Sierra of San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2025-04-17 UTC.

DDOTI observed from 03:20 UTC to 04:31 UTC (from T+8.8 h to T+10.0 h after the trigger) with a total exposure of 24 min, alternating with other scientific programs.

Comparing our observations to the USNO-B1 and PanSTARRS PS1 DR2 catalogues and after performed image subtraction against PanSTARRS PS1 DR2, we detect no uncatalogued sources within the observed field to an average 5-sigma limiting AB magnitude of:

w > 20.5.

This value has not been corrected for Galactic extinction (A_r​∼1.7 mag; Schlafly et al. 2011).

We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir.

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

We report an analysis of observations of the vicinity of the high-energy IC250416A neutrino event (GCN 40153
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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 2025-04-16 at 18:32:14.97 (T0) with J2000 position RA = 83.1 (+0.57, -0.58) deg, Decl. = 15.64 (+0.49, -0.5) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC250416A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546
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 ).

We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC250416A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250416A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 3.1 e-10 ph cm^-2 s^-1 for ~16-years (2008-08-04 / T0), < 7.2e-09 (<1.2e-07) 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 person 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.

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-250416A (https://gcn.nasa.gov/circulars/40153
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 ) in a time range of 1000 seconds centered on the alert event time (2025-04-16 18:23:54.970 UTC to 2025-04-16 18:40:34.970 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-250416A. 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-250416A 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 1e+05 GeV. 

A subsequent search was performed including 2 days of data centered on the alert event time (2025-04-15 18:32:14.970 UTC to 2025-04-17 18:32:14.970 UTC). In this case, we report a p-value of 0.39, 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-250416A 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)