IceCube-230724A

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

On 2023-07-24 at 01:49:13.38 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 1.174 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/138181_66037171.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to:

Date: 2023-07-24
Time:  01:49:13.38 UT
RA: 32.52 (+0.58, -0.40 deg  90% PSF containment) J2000
Dec: -1.87 (+0.23, -0.33 deg 90% PSF containment) J2000

An error in the automatic processing pipeline that performs the offline reconstruction resulted in a delay in the circulation of the updated position. Therefore, an alternative reconstruction algorithm has been applied to this event. We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino.

 There are no Fermi 4FGL-DR3 or 3FHL catalog sources in the 90% uncertainty region. The nearest gamma-ray source in either catalog is 4FGL J0212.2-0219 at RA: 33.07 deg, Dec: -2.32 deg (0.71 deg away from the best-fit alert 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-230724A (https://gcn.nasa.gov/circulars/34265
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 ) in a time range of 1000 seconds centered on the alert event time (2023-07-24 01:40:53.380 UTC to 2023-07-24 01:57:33.380 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-230724A. 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-230724A is 1.5e-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 3e+02 GeV and 2e+05 GeV. 

A subsequent search was performed including 2 days of data centered on the alert event time (2023-07-23 01:49:13.380 UTC to 2023-07-25 01:49:13.380 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-230724A 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)

C. Bartolini (INFN Bari), S. Garrappa (Weizmann Institute of Science), 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 IC230724A  high-energy neutrino event (GCN 34265
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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 2023-07-24 at 01:49:13.38 UT (T0) with J2000 position RA =  32.52 (+0.58, -0.40) deg, Decl. = -1.87 (+0.23, -0.33) deg (90% PSF containment).  There are no Fermi 4FGL-DR3 cataloged  gamma-ray (>100 MeV; The Fermi-LAT collaboration 2022, ApJS, 260, 53) sources in the 90% IC230724A uncertainty localization region.

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 IC230724A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC230724A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 7.0e-10 ph cm^-2 s^-1 for ~15-years (2008-08-04 to 2023-07-24 UTC), and < 5.8e-9 (< 1.1e-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 C. Bartolini (chiara.bartolini at ba.infn.it), S. Garrappa (simone.garrappa at weizmann.ac.il), 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.

Sven Weimann (Ruhr University Bochum), Simeon Reusch (DESY), Jannis Necker (DESY), Robert Stein (Caltech) and Anna Franckowiak (DESY/Ruhr University Bochum) report:

On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations:

As part of the ZTF neutrino follow up program (Stein et al. 2022), we observed the localization region of the neutrino event IceCube-230724A (Santander et. al, GCN 34265
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 ) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2023-07-24 10:12 UTC, approximately 8.4 hours after event time. We covered 100.0% (0.5 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each exposure was 300s with a typical depth of 21.0 mag.

The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019).

No candidate counterparts were detected.

Additional observations are planned as part of our standard neutrino follow-up procedure, and any candidates will be reported.

ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA; WIS, Israel; OKC, Sweden; JSI/UMd, USA; DESY, Germany; TANGO, Taiwan; UW Milwaukee, USA; LANL, USA; TCD, Ireland; IN2P3, France.

GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949.
Alert distribution service provided by DIRAC@UW (Patterson et al. 2019).
Alert database searches are done by AMPEL (Nordin et al. 2019).
Alert filtering is performed with the nuztf package (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf).

Y. Urata, K.Y. Huang on behalf of a larger collaboration

We observed the field of IceCube-230724A (GCN Circ. 34265
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 ) using
SCUBA-2 attached to JCMT. The observations at 450 and 850 um were
conducted on 2023/07/28 and 2023/07/29. The individual observations
covered the 90% IceCube-230724A uncertainty localization region. The
rms of the stacked map in 850um is 7.7 mJy. There was no source
brighter than the 5-sigma limit.