IceCube-230217A

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

On 2023-02-17 at 20:49:43.4 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 1.877 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/137661_22129736.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2023-02-17
Time:  20:49:43.4 UT
RA: 124.54 (+1.67/-3.27  deg  90% PSF containment) J2000
Dec: 20.74 (+2.14/-2.46 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 gamma-ray sources listed in the 4FGL-DR3 Fermi-LAT catalog are located within the 90% error region of the candidate neutrino event. The sources are 4FGL J0816.9+2050 and 4FGL 4FGL J0817.1+1955, and are located 0.3 and 0.85 deg away from the best-fit position, respectively. The source 4FGL J0816.9+2050 is also listed in the Fermi 3FHL catalog as 3FHL J0816.9+2050.

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

We report an analysis of observations of the vicinity of the IC230217A high-energy neutrino event (GCN 33337
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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 2023-02-17 at 20:49:43.4 UT (T0) with J2000 position RA = 124.54 (+1.67, -3.27) deg, Decl. = +20.74 (+2.14, -2.46) deg (90% PSF containment). Three cataloged gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) sources are located within the 90% IC230217A localization region. These are the BL Lac object 4FGL J0816.9+2050 (a.k.a. 3FHL J0816.9+2050, 5BZB J0816+205), the blazar 4FGL J0817.1+1955 (a.k.a. CRATES J081705+1958) and the BL Lac object 4FGL J0823.3+2224 (a.k.a. OJ 233). Based on a preliminary analysis of the LAT data, these objects are not significantly detected (> 5 sigma) over the timescales of 1-day and 1-month prior to T0.

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 IC230217A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC230217A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 4.5e-10 ph cm^-2 s^-1 for ~14-years (2008-08-04 to 2023-02-17 UTC), and < 1.9e-8 (<7.8e-7) 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 ruhr-uni-bochum.de), J. Sinapius (jonas.sinapius at desy.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.

D. R. Xiong, J. M. Bai, Y. F. Fan, K. Ye, C. J. Wang, Y. X. Xin, B. L. Lun, J. R. Mao, X. H. Zhao, L. Xu, X. G. Yu, K. X. Lu, X. Ding, D. Q. Wang (Yunnan Observatories), A. J. Castro-Tirado, E. Fernandez-Garcia, Y. D. Hu (IAA-CSIC) and C. J. Perez del Pulgar (UMA) on behalf of the BOOTES team report:

On 2023-02-17 at 20:49:43.4 UT (T0) IceCube detected a track-like event with a moderate probability of being of astrophysical origin. Two gamma-ray sources (4FGL J0816.9+2050 and 4FGL J0817.1+1955) listed in the 4FGL-DR3 Fermi-LAT catalog are located within the 90% error region of the candidate neutrino event (GCN 33337
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 ).

We observed the two gamma-ray sources and the best-fit position of IceCube-230217A with BOOTES-4/MET robotic telescope.The magnitudes were calculated using bright stars in the same frame and the SDSS-DR16 catalogue as reference. We did not detect any optical source within the best-fit position and also not for the gamma-ray source 4FGL J0817.1+1955. The upper limits of magnitudes (without being corrected for Galactic extinction) are given as follows. 

Sources | Tmid-T0 (day) | UT (start) | Upper Limit (error) | Exposure Time | Filter 

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Best-fit position| 0.797 | 23-02-18 15:57:25.28 | 19.96 (0.11) | 2*350s (co-added) | Clear  

J0817.1+1955 | 0.725 | 23-02-18 14:14:38.47 | 19.44 (0.07) | 350s | Clear  

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0.674 days after T0, the magnitude value of 4FGL J0816.9+2050 in SDSS-r band is 18.055+/-0.17 (without being corrected for Galactic extinction). Compared with the magnitude value of SDSS-DR16, the target is not brightening during our observation period.

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The Burst Optical Observer and Transient Exploring System (BOOTES, bootes.iaa.es) is a completed world-wide network of robotic telescopes led at IAA-CSIC (Spain) which aims at following-up transients and other astrophysical sources in the sky for which the first station was installed in 1998 (Castro-Tirado et al. 1999). The fourth station of the BOOTES Network, BOOTES-4/MET, is located at the Lijiang Observatory of the Yunnan Observatories of China (Xiong et al. 2020). See also Hu et al. (2021). We acknowledge the support of BOOTES-4 technical staffs.

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-230217A (https://gcn.gsfc.nasa.gov/gcn3/33337.gcn3
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 ) in a time range of 1000 seconds centered on the alert event time (2023-02-17 20:41:23.370 UTC to 2023-02-17 20:58:03.370 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-230217A. 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-230217A 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 9e+04 GeV.


A subsequent search was performed including 2 days of data centered on the alert event time (2023-02-16 20:49:43.370 UTC to 2023-02-18 20:49:43.370 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-230217A ranges from 1.6e-01 to 1.7e-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)