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[vsnet-grb-info 40454] EP251021b: BOOTES-7 optical upper limit
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42378 SUBJECT: EP251021b: BOOTES-7 optical upper limit DATE: 25/10/22 09:05:45 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, S.-Y. Wu, E. Fernandez-Garcia, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar, A. Castellon, A. Reina (Univ. de Malaga),Y.-D. Hu (GXU), L. Hernandez-Garcia (Univ. de Valparaiso), M. Gritsevich (Univ. of Helsinki), D. R. Xiong (Yunnan Observatories of CAS), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of the fast X-ray transient EP251021b by the Einstein Probe (Dai et al. GCN 42377), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) observed the fast X-ray transient location starting on Oct 22, 03:57 UT (~13.08 h after trigger) in different optical bands. No new optical source is detected on the first co-added clear-filter images (mid exposure time 2025-10-22 04:07:57) within the EP/FXT 20 arcsec radius error circle down to 20.0 mag. We thank the staff at San Pedro de Atacama Celestial Explorations observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/42378. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40453] EP251021b: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42377 SUBJECT: EP251021b: Einstein Probe detection of a fast X-ray transient DATE: 25/10/22 08:30:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Y. Dai (NJU), Q. J. Huang(PMO), W. F. Wen (SZTU), J. H. Wu (GZHU), H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251021b. The transient triggered EP-WXT (ID: 01709247263) at 2025-10-21T14:28:28 (UTC). The ground analysis of the WXT data shows that the event started at T0=2025-10-21T14:28:05 (UTC) and lasted for around 30 s. The WXT position of the source is R.A. = 306.742 deg, Dec. = -38.286 deg (J2000) with an uncertainty of 2.3 arcmin in radius (90% C.L. statistical and systematic). We performed a Target-of-Opportunity observation with the Follow-up X-ray Telescope on board EP. The observation began at 2025-10-22T04:41:25 (UTC), around 14 hours after the trigger. An uncatalogued X-ray source was detected within the WXT error circle at R.A. = 306.7451 deg, Dec. = –38.3048 deg (J2000), with a positional uncertainty of 20 arcsec in radius (90% confidence level, including both statistical and systematic uncertainties). Further information will be updated when the telemetry data is received. 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/42377. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40452] GRB 250911A: MAXI/GSC detection
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42376 SUBJECT: GRB 250911A: MAXI/GSC detection DATE: 25/10/22 05:22:50 GMT FROM: Hitoshi Negoro at Nihon University/MAXI team <negoro.hitoshi(a)nihon-u.ac.jp> H. Negoro (Nihon U.), T. Mihara (RIKEN), M. Serino (AGU), M. Nakajima, K. Takagi, H. Takahashi, H. Nishio (Nihon U.), T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, C. Kang, T. Nakamoto, M. Uenishi, T. Usuki, S. Yatsuzuka (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), and S. Yamada (Tohoku U), We report on the detection of GRB 250911A by MAXI (Swift-BAT: GCN 41781, 41812, COLIBRI: GCN 41782, Swift-XRT: GCN 41783, 41784, 41804, Swift-UVOT: 41800, MASTER: GCN 41806, GECAM-B: GCN 41813, Insight-HXMT: GCN 41827, Konus-Wind: GCN 41939). MAXI detected the burst for approximately 40 seconds, centered at around 01:29:46 on September 11, 2025. The period coincides with the main peak of the burst detected by Swift, HXMT, and Konus-Wind. The 4-10 keV X-ray flux averaged over the scan was 2041 ± 83 mCrab. The MAXI light curve is shown at https://maxi.riken.jp/grbs/250911a/ GRB 250911A was about 0.8 degrees away from the bright NS-LMXB GX 9+9. Due to the X-ray photon confusion from GX 9+9, we were unable to obtain firm upper limits or flux in the previous transit at 23:57 UT on September 10 and the next transit at 03:02 UT. Some software problem during the burst partly causes the late notice. View this GCN Circular online at https://gcn.nasa.gov/circulars/42376. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40451] LIGO/Virgo/KAGRA S251021u: Updated Sky localization
by GCN Circulars 21 Oct '25

21 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42375 SUBJECT: LIGO/Virgo/KAGRA S251021u: Updated Sky localization DATE: 25/10/21 16:18:24 GMT FROM: mattia.emma.2022(a)live.rhul.ac.uk The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S251021u (GCN Circular 42373). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S251021u For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 3859 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 5884 +/- 2089 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 View this GCN Circular online at https://gcn.nasa.gov/circulars/42375. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40450] GRB 251016A: SVOM/ECLAIRs refined analysis
by GCN Circulars 21 Oct '25

21 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42374 SUBJECT: GRB 251016A: SVOM/ECLAIRs refined analysis DATE: 25/10/21 11:52:34 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet, S. Guillot (IRAP), B. Hubert (CEA), S.Basa, S.Boissier (LAM) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 251016A (SVOM burst-id sb2525101602, GCN 42308) detected at T0 = 2025-10-16T14:59:20, which was also detected by SVOM/GRM, Fermi/GBM (GCN 42309), CALET/GBM (GCN 42321), Glowbug (GCN 42313), AstroSat/CZTI (GCN 42327) and HXMT/HE (GCN 42359). The burst that triggered ECLAIRs consists of a single short peak, with a duration of T90 = 0.69 +0.09/-0.19 s in the 4-120 keV energy band. The time-averaged spectrum from the peak (T0-0.4 s to T0+0.4 s) in the 5-120 keV energy range is well fitted by a power-law model with a photon index of 1.00 +/-0.16, which is consistent with the results found by Smith at al. 2025 (GCN 42365). With this model, the total 4-120 keV fluence is (3.01 +0.27/-0.94) e-07 erg/cm^2 . All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical 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 CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at irap.omp.eu). View this GCN Circular online at https://gcn.nasa.gov/circulars/42374. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40449] LIGO/Virgo/KAGRA S251021u: Identification of a GW compact binary merger candidate
by GCN Circulars 21 Oct '25

21 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42373 SUBJECT: LIGO/Virgo/KAGRA S251021u: Identification of a GW compact binary merger candidate DATE: 25/10/21 03:49:52 GMT FROM: alvinli(a)g.ecc.u-tokyo.ac.jp The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S251021u during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-10-21 03:22:15.181 UTC (GPS time: 1445052153.181). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], PyCBC Live [6], and SPIIR [7] analysis pipelines. S251021u is an event of interest because its false alarm rate, as estimated by the online analysis, is 2.2e-09 Hz, or about one in 14 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S251021u The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%). Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [8] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [8] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. The source chirp mass falls with highest probability in the bin (44.0, 88.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * amplfi.multiorder.fits,0, an initial localization generated by AMPLFI [9], distributed via GCN and SCiMMA notices about 25 seconds after the candidate event time. * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [10], distributed via GCN and SCiMMA notices about 4 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,0. For the bayestar.multiorder.fits,0 sky map, the 90% credible region is 3742 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 7164 +/- 2185 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010 [2] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004 [3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [4] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008 [5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [6] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [7] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [8] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [9] Chatterjee et al. MLST 5, 045030 (2024) doi:10.1088/2632-2153/ad8982 [10] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/42373. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40448] LIGO/Virgo/KAGRA S251018bi: Updated Sky localization
by GCN Circulars 20 Oct '25

20 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42372 SUBJECT: LIGO/Virgo/KAGRA S251018bi: Updated Sky localization DATE: 25/10/20 19:58:14 GMT FROM: Nihar.Gupte(a)aei.mpg.de The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S251018bi (GCN Circular 42357). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S251018bi For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 883 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 4502 +/- 1313 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 View this GCN Circular online at https://gcn.nasa.gov/circulars/42372. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40447] Fermi-LAT gamma-ray observations of IceCube-251018A
by GCN Circulars 19 Oct '25

19 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42371 SUBJECT: Fermi-LAT gamma-ray observations of IceCube-251018A DATE: 25/10/19 23:49:18 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 (Univ. of Trento & INFN Bari) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the IC251018A high-energy neutrino event (GCN 42351) 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 25-10-18 at 05:05:42.97 UT (T0) with J2000 position RA = 321.11 (+3.09/-2.94) deg, Decl. = +41.31 (+2.46/-3.51) deg (90% PSF containment). There are three catalogued gamma-ray sources (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546) located within the 90% IC251018A localization region. These are: 4FGL J2118.3+4055: unassociated,at 1.2 deg distance from the best-fit neutrino position; 4FGL J2120.5+4331: unassociated, at 2.3 deg distance from the best-fit neutrino position; 4FGL J2136.5+4259: associated with the blazar of uncertain type TXS 2134+428, at 2.8 deg from the best-fit neutrino position; Based on a preliminary analysis of the LAT data over the timescale of one day and one month 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) at the IC251018A bestfit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC251018A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 8.4 e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), < 7.4e-09 (<5.9e-08) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. In the analysis of the ~17-years integrated LAT data (100 MeV - 1 TeV), a 5 sigma new excess of gamma rays, Fermi J2125.8+3940 was detected 1.65 deg offset from the best-fit IC251018A position and within the 90% confidence localization of the direction of the neutrino. Assuming a power-law spectrum, the best-fit localization is (J2000) RA = 321.46 deg, Dec = +39.69 deg (6 arcmin 99% containment, 3 arcmin 68% containment). The gamma-ray best-fit spectral parameters are flux = (8 +/- 3)e-10 ph cm^-2 s^-1 and index = 1.84+/-0.12. In a preliminary analysis of the LAT data over 1-day and 1-month prior T0, Fermi J2125.8+3940 is not significantly detected in the LAT data. All values include the statistical uncertainty only. The statistical significance is calculated following the prescription adopted in the 4FGL (Abdollahi et al. 2020, ApJS, 247, 33). Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this region will continue. For these observations 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/42371. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40446] GRB 251017A : RAPAS follow-up observations
by GCN Circulars 19 Oct '25

19 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42370 SUBJECT: GRB 251017A : RAPAS follow-up observations DATE: 25/10/19 21:33:07 GMT FROM: Thierry Midavaine at SAF - RAPAS <thierrymidavaine(a)sfr.fr> Thierry Midavaine on behalf of the RAPAS network reports (#5) : Pascal André, David Fardin, Patrick Martinez [1], Christian Pantacchini [2], Jean-Marie Lopez, Cyril Cavadore [3], Lisa Maris [4] observed the field of Gamma-Ray Burst GRB 251017A (R. Gupta et al. GCN 42322, I. Perez-Garcia GCN 42323) using : [1] ADAGIO N 820mm telescope f=3.1m at Belesta Observatory (IAU A05) equipped with a Moravian C3 CMOS camera, [2] N308 mm telescope f=1.1m equipped with a Moravian g3 KAI11000 CCD camera, [3] Société Astronomique de Montpellier N 500mm telescope f=2.2m at Observatoire des Pises (IAU 122) equipped with an ASI6200MMPro CMOS camera, [4] SC 280mm f=1.8m equipped with an ATIK4000 CCD camera. [1][2][3][4] are equipped with RAPAS filters meeting the Gaia G, Gbp, Grp photometric bands. The FITS files are reduced with the Gaia photometric catalog in respective G, Gbp and Grp bands. The afterglow is detected at RA(J2000) = 22h 21m 36.22s ; Dec(J2000) = +07° 02’ 23.6” ; ± 0.5’’ in G and Grp bands [1] RA(J2000) = 22h 21m 36.956s; Dec(J2000) = +07° 02’ 21.90” in G band [3] At this RA Dec location the GRB is above the respective upper limit magnitude Gbp for [1], G for [2] and [4], Gbp and Grp for [3] MJD (mid) Gaia band exp(s) mag.(Gaia) upperlim RAPAS station 60965.81618 G 1200 22.5 ± 0.3 [3] 60965.82986 G 4500 20.24 [4] 60965.83819 G 3600 22.0 ± 0.3 [1] 60965.83819 Gbp 600 21 [1] 60965.83819 Grp 600 >20.00 [1] 60965.89722 G [2] Acknowledgements : RAPAS ( https://gemini.obspm.fr/20220101-rapas/ ) is a ProAm collaboration created by T. Midavaine (SAF), W. Thuillot (LTE, Obs. de Paris-PSL) and M. Dennefeld (IAP/CNRS and Sorbonne Univ.) and funded by the Paris Observatory under API ProAm of the Scientific Council. It aims at homogenizing observing procedures and filters, and is delivering to a network of french amateur observatories a set of 3 filters which have been chosen to meet the Gaia G, Gbp and Grp spectral bands. This network produces data on astrophysical alerts delivered by various Alert systems (Gaia Alerts, Atlas, ZTF, etc…) and collected by Astro-COLIBRI ( https://astro-colibri.science ). This network is similarly progressing towards an homogeneous spectroscopic equipment to deliver SED. View this GCN Circular online at https://gcn.nasa.gov/circulars/42370. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40445] IceCube-251018A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 19 Oct '25

19 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42369 SUBJECT: IceCube-251018A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/10/19 18:45:31 GMT FROM: Yuhua Yao at IceCube/UW-Madison <yyao255(a)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-251018A (https://gcn.nasa.gov/circulars/42352) in a time range of 1000 seconds centered on the alert event time (2025-10-18 04:57:22.970 UTC to 2025-10-18 05:14:02.970 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-251018A. 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 1.5e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-251018A 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 (2025-10-17 05:05:42.970 UTC to 2025-10-19 05:05:42.970 UTC). In this case, we report a p-value of 0.02, 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, ranges from 1.7e-01 to 1.8e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-251018A 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/42369. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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