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[vsnet-grb-info 43642] Fermi-LAT Gamma-ray Observations of IceCube-260821A
by GCN Circulars 22 Aug '26

22 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45421 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-260821A DATE: 26/08/22 15:55:23 GMT FROM: Simone Garrappa at Weizmann Institute of Science <simone.garrappa(a)weizmann.ac.il> S. Garrappa (Weizmann Institute of Science), L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and C. Bartolini (INFN Bari) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC260821A neutrino event (GCN 45412) 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 2026-08-21 at 03:34:49.04 UTC (T0) with J2000 position RA = 116.67 (+0.49, -0.48) deg, Decl. = 10.05 (+0.44, -0.45) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC260821A localization error (FL16Y, The Fermi-LAT 16 Year Source List, The Fermi-LAT collaboration 2026, arXiv:2602.22148). 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 IC260821A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260821A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.9e-10 ph cm^-2 s^-1 for ~18-years (2008-08-04 / T0), <1.6e-08 (<1.0e-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 analysis, 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/45421. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43641] Fermi-LAT Gamma-ray Observations of IceCube-260807A
by GCN Circulars 22 Aug '26

22 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45420 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-260807A DATE: 26/08/22 15:52:10 GMT FROM: Simone Garrappa at Weizmann Institute of Science <simone.garrappa(a)weizmann.ac.il> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science) and C. Bartolini (INFN Bari) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC260807A neutrino event (GCN 45307) 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 2026-08-07 at 06:04:41.70 UTC (T0) with J2000 position RA = 325.37 (+4.26, -7.82) deg, Decl. = 0.07 (+0.98, -1.77) deg 90% PSF containment (J2000). Five cataloged gamma-ray sources are found within the 90% IC260807A localization error (FL16Y, The Fermi-LAT 16 Year Source List, The Fermi-LAT collaboration 2026, arXiv:2602.22148). Based on a preliminary analysis of the LAT data over the timescale of one month and one day prior T0, these objects are not significantly detected at gamma-rays. 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 IC260807A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260807A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.7e-10 ph cm^-2 s^-1 for ~18-years (2008-08-04 / T0), <1.2e-08 (<5.5e-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 analysis, the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/45420. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43640] IceCube-260821A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 22 Aug '26

22 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45419 SUBJECT: IceCube-260821A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/08/22 14:22:58 GMT FROM: Alicia Mand at IceCube/UW-Madison <aemand(a)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-260821A (https://gcn.nasa.gov/circulars/45412) in a time range of 1000 seconds centered on the alert event time (2026-08-21 03:26:29.044 UTC to 2026-08-21 03:43:09.044 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-260821A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.3e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260821A 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 (2026-08-20 03:34:49.044 UTC to 2026-08-22 03:34:49.044 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.5e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260821A 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(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/45419. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43639] GRB 260818B: VLA radio observations
by GCN Circulars 21 Aug '26

21 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45418 SUBJECT: GRB 260818B: VLA radio observations DATE: 26/08/21 22:41:23 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> G. Schroeder (U. Toronto), W. Fong (Northwestern), J. Rastinejad (UMD) report: We observed the location of the short-duration GRB 260818B (Cordier et al., GCN 45398; Wang et al., GCN 45408; Ren et al, GCN 45411) with the Karl G. Jansky Very Large Array (VLA) in D configuration under program 26A-062 (PI Schroeder) for two 0.75 hour epochs at a mean frequency of 6 GHz and mid times of 2026 Aug 20 at 07:58 UT (1.5 days post-burst) and 2026 Aug 21 at 11:23 UT (2.6 days post-burst). The images reached typical rms values of 7-10 uJy. In preliminary analysis, we detect 13 >= 5-sigma radio sources within the ECLAIRs error region across both epochs. Of them, 9 appear to vary on the 1 sigma level across the two epochs, only 1 of which appears to have faded by 3 sigma across the two epochs (S3). The details of the variable sources are as follows: | Source | R.A.| Dec. | Error (arcsec) | Fnu e1 (uJy) | Fnu e2 (uJy) | Notes | | ------------ | ------------ | ------------ | ------------ | ------------ | ------------ | ------------ | | S2 | 02:59:56.59 | +07:29:28.5 | 2.3 | 83 | 107 | Close to apparent galaxy | | S3 | 02:59:36.59 | +07:28:16.0 | 3.0 | 96 | 34 | Faded by >= 3sigma | | S4 | 02:59:51.45 | +07:27:41.8 | 5.2 | 63 | 90 | Close to apparent galaxy | | S5 | 03:00:00.19 | +07:27:23.4 | 0.4 | 1266 | 1200 | In VLASS/RACS | | S7 | 02:59:38.44 | +07:26:20.5 | 2.7 | 114 | 91 | | | S8 | 02:59:49.96 | +07:25:46.9 | 3.5 | 168 | 110 | | | S9 | 02:59:50.37 | +07:25:41.0 | 4.0 | 169 | 91 | | | S10 | 02:59:54.25 | +07:25:28.7 | 0.3 | 1232 | 1139 | Coincident with EPF_J025955.0+072535, in VLASS/RACS | | S11 | 02:59:44.77 | +07:25:25.0 | 1.1 | 200 | 178 | Close to apparent galaxy | Additionally, we note that EPF_J025955.0+072535 and EPF_J025936.6+072418 (Wu et al., GCN 45407) are coincident with long-lived radio sources present in VLASS and RACS (which are present in our observations as well). There is a faint radio source coincident with EPF_J025951.6+072917, however the flux density doesn’t vary significantly over the two epochs (~50 uJy). We thank the VLA staff for quickly approving and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/45418. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43638] GRB 260818B: SVOM/C-GFT optical upper limit
by GCN Circulars 21 Aug '26

21 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45417 SUBJECT: GRB 260818B: SVOM/C-GFT optical upper limit DATE: 26/08/21 16:21:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y.X Guan(GXU), Z. Kang (CHO), C. Wu , L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC), Bertrand Cordier (CEA), Hatsune Goto (RIKEN, CEA) , report on behalf of the SVOM/C-GFT team: We observed the field of GRB 260818B detected by SVOM/ECLAIRs (Bertrand Cordier et al., GCN 45398)， HXMT (Wang et al., GCN 45408), and SVOM/GRM (Ren et al., GCN 45411) with LATIOS on SVOM/C-GFT. Observations started at 2026-08-20T17:09:40.28 UTC, ~1.87 days after the trigger. We obtained i-band follow-up imaging. After preliminary analysis, no credible candidate was detected within the error box provided by EP-FXT (Wu et al., GCN 45407) in our images. We measure the following upper limit calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: i > 19.9 AB (3-sigma, mid-time 1.88 days after the trigger). This is consistent with the non-detection reported by Shi et al.(GCN 45399) and Neill et al.(GCN 45403) We thank the observation assistants Y.-H. Hao and C.-L. Guo at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcmin x 21 arcmin FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/45417. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43637] EP260731a: SVOM/ECLAIRs detection through offline targeted search
by GCN Circulars 21 Aug '26

21 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45416 SUBJECT: EP260731a: SVOM/ECLAIRs detection through offline targeted search DATE: 26/08/21 13:10:00 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> H. Yang, S. Guillot, O. Godet (IRAP) report on behalf of the SVOM team: The SVOM/ECLAIRs telescope detected EP260731a (EP team, GCN 45261), starting at 2026-07-31T00:53:19 UTC (T0), through an offline targeted search with the event-by-event data downloaded via the X-band ground station. The ECLAIRs detection, at T0, occurred 31 s before the EP-WXT detection that began at 2026-07-31T00:53:50 UTC (EP team, GCN 45301). The burst was detected within several timescales and energy ranges. The best detection is obtained by the image trigger with a signal-to-noise ratio of 6.4 within 8-120 keV over a time window of 82 s starting at T0. This event was not detected onboard because it was too faint. The localization of the source is RA, Dec = 344.500, -11.872 degrees: RA (J2000) = 22h58m00s Dec (J2000) = -11d52m19s with a 90% C.L. radius of 12.14 arcmin (including systematic error of 2 arcmin added in quadrature). This position is consistent with that measured by EP/FXT, with an angular separation of 7.8 arcmin. The ECLAIRs lightcurve shows a multi-peaked structure lasting around 82 s in the 4 - 120 keV band. The time-averaged spectrum from T0 to T0+82 s in the 5-120 keV is well fitted by a power law with a photon index of -1.4 +/- 0.2, a 4-120 keV photon flux of 0.22 +0.02/-0.06 photons/cm^2/s, and a corresponding 4-120 keV fluence of (7 +/- 1)e-7 erg/cm^2. Using the same extraction time window from T0+31 s to T0+66 s as EP/WXT, the time-averaged spectrum in the 5-120 keV is also well fitted by a power law with a photon index of -1.4 +/- 0.2, a 4-120 keV photon flux of 0.28 +0.02/-0.08 photons/cm^2/s, and a corresponding 4-120 keV fluence of (3.7 +/- 0.8)e-7 erg/cm^2. The spectral properties measured with SVOM/ECLAIRs are broadly consistent with those reported by EP/WXT (EP team, GCN 45301). All quoted errors are at the 68% confidence level. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by APC, CEA, CNES, and IRAP. The SVOM/ECLAIRs point of contact for this event is : Hui Yang (hui.yang(a)cnrs.fr) Please contact him by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/45416. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43636] IceCube Alert 260821A: Global MASTER-Net observations report
by GCN Circulars 21 Aug '26

21 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45415 SUBJECT: IceCube Alert 260821A: Global MASTER-Net observations report DATE: 26/08/21 10:27:04 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), M. Segura, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the IceCube Alert 260821A (trigger No 51776820,07h 44m 40.80s , +10d 03m 00.0s, R=0.46) errorbox 22610 sec after notice time and 22930 sec after trigger time at 2026-08-21 09:56:59 UT, with upper limit up to 16.5 mag. Observations started at twilight. The observations began at zenith distance = 76 deg. The sun altitude is -15.2 deg. The galactic latitude b = 17 deg., longitude l = 210 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3484669 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 22961 | 2026-08-21 09:56:59 | MASTER-OAFA | (07h 45m 46.70s , +10d 07m 14.0s) | C | 60 | 15.9 | 23036 | 2026-08-21 09:58:15 | MASTER-OAFA | (07h 45m 48.09s , +10d 08m 19.8s) | C | 60 | 16.0 | 23115 | 2026-08-21 09:59:34 | MASTER-OAFA | (07h 45m 53.62s , +10d 07m 28.0s) | C | 60 | 15.9 | 23189 | 2026-08-21 10:00:48 | MASTER-OAFA | (07h 45m 47.68s , +10d 06m 34.3s) | C | 60 | 16.1 | 23266 | 2026-08-21 10:02:05 | MASTER-OAFA | (07h 45m 54.73s , +10d 06m 52.0s) | C | 60 | 16.1 | 23419 | 2026-08-21 10:04:37 | MASTER-OAFA | (07h 45m 51.54s , +10d 07m 21.1s) | C | 60 | 16.3 | 23496 | 2026-08-21 10:05:54 | MASTER-OAFA | (07h 45m 55.51s , +10d 08m 42.3s) | C | 60 | 16.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/45415. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43635] The EP-WXT trigger 01709286204 is likely a flaring star
by GCN Circulars 21 Aug '26

21 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45414 SUBJECT: The EP-WXT trigger 01709286204 is likely a flaring star DATE: 26/08/21 10:00:40 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T. Y. Liu (NAO, CAS), D. F. Hu (PMO, CAS)，Z. M. Wang (BNU), Q. Y. Wu, Z. X. Ling (NAO, CAS). on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709286204 at the time of 2026-08-21T09:06:36, is likely a stellar flare associated with CD-55 8799. The estimated flux of the flare is around 1.0 x 10^-10 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 4.8 x 10^32 erg/s. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/45414. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43634] GRB 260820A: Insight-HXMT/HE detection
by GCN Circulars 21 Aug '26

21 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45413 SUBJECT: GRB 260820A: Insight-HXMT/HE detection DATE: 26/08/21 09:35:34 GMT FROM: yzh807926(a)163.com Zheng-Hang Yu, Chao Zheng, and Shao-Lin Xiong (IHEP) report on behalf of the Insight-HXMT team: At 2026-08-20T04:24:39.950 (T0), Insight-HXMT/HE detected GRB 260820A, which is also detected by Fermi/GBM (Fermi GBM team, GCN #45409). The Insight-HXMT/HE light curve mainly consists of a pulse with a T90 of 0.22 +0.19/-0.13 s. The 1 s peak rate, measured from T0-0.15 s, is 707 cnts/sec. Insight-HXMT/HE detected a total of 690 counts from this burst. The Insight-HXMT/HE light curve can be found here: https://www.bursthub.cn/gcn/2026/hxmtgrb260820A.png All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the Normal mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn View this GCN Circular online at https://gcn.nasa.gov/circulars/45413. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43633] IceCube-260821A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 21 Aug '26

21 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45412 SUBJECT: IceCube-260821A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 26/08/21 07:23:37 GMT FROM: Cristobal Zilleruelo Cañas at DESY <cristobal.zilleruelo.canas(a)desy.de> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 26-08-21 at 03:34:49.04 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. Documentation regarding the alert streams and their astrophysical purity can be found here: https://gcn.nasa.gov/missions/icecube. This alert has an estimated false alarm rate of 2.3966 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/143020_51776820.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 26-08-21 Time: 03:34:49.04 UT RA: 116.67 (+0.49/-0.48 deg 90% PSF containment) J2000 Dec: 10.05 (+0.44/-0.45 deg 90% PSF containment) J2000 As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419) IceCube alert notices for high-energy track alerts are now also streamed via Kafka. IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'. The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts. The corresponding sky map is distributed as a FITS file and follows the explicit naming convention IceCube-YYMMDDX, where YYMMDD indicates the date of the event and X is a letter distinguishing multiple alerts on the same day. The download link is provided through the GCN schema distributed via Kafka. Detailed documentation describing the alert distribution, schemas, and probability maps is available at: https://gcn.nasa.gov/missions/icecube. No known gamma-ray sources listed in the Fermi LAT 16-year Source List (FL16Y) are located within the 90% uncertainty region of this 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(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/45412. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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