IceCube-Cascade 230109A

J. Sinapius (DESY-Zeuthen), S. Buson (Univ. of Wuerzburg), S. Garrappa 
(Ruhr-Universitaet Bochum) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the 
IceCube-Cascade-230109A high-energy neutrino event 
(https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/137527_43987982.amon) 
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 
2023-01-09 at 11:12:11.29 UT (T0) with J2000 position RA = (174.81 +/- 
7.07) deg, Decl. = (45.33 +/- 7.07) deg (90% PSF containment). Several 
cataloged gamma-ray (>100 MeV) sources are located within the 90% 
IceCube-Cascade-230109A localization region (4FGL-DR3; The Fermi-LAT 
collaboration 2022, ApJS, 260, 53). Based on a preliminary analysis of 
the LAT data over the timescales of 1-day and 1-month prior to T0, one 
of these objects is significantly detected (> 5 sigma). This source is 
the FSRQ 4FGL J1146.9+3958 at 5.45 deg from the IC-Cascade-230109A 
best-fit position.�� In a preliminary analysis of LAT data over 30 days 
before T0, the object is observed at a flux level of (9.38 +/- 1.70) e-8 
ph cm^-2 s^-1, consistent with the average value reported in 4FGL-DR3.

We searched for intermediate (days to months) timescale emission from a 
new gamma-ray transient source. Preliminary analysis indicates no 
significant (> 5 sigma) new excess emission (> 100 MeV) at the 
IceCube-Cascade-230109A best-fit position. Assuming a power-law spectrum 
(photon index = 2.0 fixed) for a point source at the 
IceCube-Cascade-230109A best-fit position, the >100 MeV flux upper limit 
(95% confidence) is < 2.6e-9 (< 5.2e-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 source will continue. For these observations the 
Fermi-LAT contact persons are J. Sinapius (jonas.sinapius at desy.de), 
S. Garrappa (simone.garrappa at ruhr-uni-bochum.de) and S. Buson 
(sara.buson at 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-Cascade 230109A (https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/137527_43987982.amon)
in a time range of 1000 seconds centered on the alert event time (2023-01-09 11:03:51.290 UTC to 2023-01-09 11:20:31.290 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-Cascade 230109A.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-Cascade 230109A ranges from 1.5e-01 to 1.6e-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 6e+04 GeV.

A subsequent search was performed including 2 days of data centered on the alert event time (2023-01-08 11:12:11.290 UTC to 2023-01-10 11:12:11.290 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-Cascade 230109A ranges from 1.7e-01 to 1.9e-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)