September 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 39723] LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
by GCN Circulars 02 Sep '25

02 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41657 SUBJECT: LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search DATE: 25/09/02 13:11:05 GMT FROM: Erik Blaufuss at University of Maryland, College Park <blaufuss(a)umd.edu> IceCube Collaboration (http://icecube.wisc.edu/) reports: We have performed a search for track-like muon neutrino candidate events detected by IceCube consistent with the sky localization of the low-significance gravitational-wave candidate event S250902av in a time range of 1000 seconds centered on the alert event time (2025-09-02T07:01:18.83 UTC to 2025-09-02T07:17:58.83 UTC) [1,2]. During this time period, IceCube was collecting good quality data. A single hypothesis test was conducted using a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors, such as GW source distance, in the statistical significance estimation [3]. One track-like event was found in spatial and temporal coincidence with the gravitational-wave candidate S250902av calculated from the map circulated in the S250902av-2-Preliminary notice. This represents an overall p-value of 5.1e-03 for the Bayesian search. The p-value measures the consistency of the observed track-like events with the known atmospheric backgrounds for this single map (not accounting for statistical trials from multiple GW events). Further details are available at https://gcn.nasa.gov/missions/icecube and at https://roc.icecube.wisc.edu/public/LvkNuTrackSearch. Properties of the coincident event are shown below: dt(s) RA(deg) Dec(deg) Angular uncertainty(deg) p-value(Bayesian) ------------------------------------------------------------------------------------- 134.47 15.51 24.37 1.54 0.00533 where: dt = Time of track event minus time of GW trigger (sec) Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area. p-value = the p-value for this specific track event from this search. 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] M. G. Aartsen et al 2020 ApJL 898 L10 [2] Abbasi et al. Astrophys.J. 944 (2023) 1, 80 [3] I. Bartos et al. 2019 Phys. Rev. D 100, 083017 View this GCN Circular online at https://gcn.nasa.gov/circulars/41657. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39722] LIGO/Virgo/KAGRA S250901cb: Updated Sky localization
by GCN Circulars 02 Sep '25

02 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41656 SUBJECT: LIGO/Virgo/KAGRA S250901cb: Updated Sky localization DATE: 25/09/02 10:06:38 GMT FROM: Michael J. Williams at University of Portsmouth <michael.williams(a)ligo.org> 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 S250901cb (GCN Circular 41638). 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/S250901cb For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 581 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2018 +/- 482 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/41656. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39721] EP250827b: Liverpool Telescope observations
by GCN Circulars 02 Sep '25

02 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41655 SUBJECT: EP250827b: Liverpool Telescope observations DATE: 25/09/02 08:06:57 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris and R. L. C. Starling (U of Leicester) report on behalf of a larger collaboration: We observed the position of EP250827b/AT 2025wkm (Schroeder et al., GCN 41635) with the 2m Liverpool Telescope using the IO:O instrument. We obtained a series of exposures in the SDSS u’g’r’i’z’ filters starting at 2025-09-02 02:47:47 UT, approximately 139.5 hours after the X-ray detection. We performed image subtraction on the stacked g’r’i’z’ images using reference images from Pan-STARRS. We clearly detect a source consistent with AT 2025wkm in all our subtractions and measure r’ = 19.97 +/- 0.04. Our measured magnitude compared to Schroeder et al. (GCN 41635) and Hall et al. (GCN 41636) suggests AT 2025wkm may still be rising in the r band. The colour of the source (g’ - r’ ~ 0.0) is consistent with the blue spectrum observed by Sevilla and Ho (GCN 41639). Further observations are planned. View this GCN Circular online at https://gcn.nasa.gov/circulars/41655. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39720] GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
by GCN Circulars 02 Sep '25

02 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41654 SUBJECT: GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT DATE: 25/09/02 07:31:25 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, Z. H. Yao, Y. N. Ma, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM performed an automatic slew on the soft burst triggered by SVOM/ECLAIRs (Xie et al., GCN 41614). SVOM/VT began observing the field automatically on 2025-08-31T09:34:43, i.e., 335 sec with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X band downlinked data, we find that the position of the high proper motion star G 272-61 is consistent with XRT Source 1 (Evans et al., GCN 41617). With a refined analysis, it was decreasing in brightness from 7.6 mag to 10.0 mag in VT_B during the first 0.5 hour after the trigger time, confirming this event as due to a stellar flare. Our photometry was estimated in AB magnitude. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/41654. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39719] GRB 250902A: SVOM/GRM observation
by GCN Circulars 02 Sep '25

02 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41653 SUBJECT: GRB 250902A: SVOM/GRM observation DATE: 25/09/02 07:19:01 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Xiao-Yun Zhao, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Tais Maiolino (LUPM) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 250902A (SVOM trigger reference: sb25090201) at 2025-09-02T01:30:01.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #41648). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 6.9 +0.5/-0.3 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250902A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 159.3, Dec = 16.3, GCN #41648), is located at about 164 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. ECLAIRs was not collecting data at the time of this burst. With the localization from Fermi/GBM, the time-averaged spectrum from T0-1 to T0+15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.66 +0.06/-0.06 and the cutoff energy, parameterized as Epeak, is 431 +128/-76 keV. The event fluence (10-1000 keV) in this time interval is (4.47 +0.10/-0.10)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 250902A is shown at: https://www.bursthub.cn//admin/static/grb250902A_amati.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41653. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39718] EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
by GCN Circulars 02 Sep '25

02 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41652 SUBJECT: EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope DATE: 25/09/02 04:39:41 GMT FROM: kde1(a)mit.edu K. De (Columbia/CCA), S. Ibrahim (Columbia), T. Suen (Columbia), M. Sitaram (Columbia), D. Schiminovich (Columbia), G. Mo (Caltech/Carnegie), K. Shin (Caltech) We observed the field of the X-ray transient EP250828a (Liu et al., GCN 41574; Aryan et al., GCN 41579; Taguchi et al., GCN 41582; Yao et al., GCN 41583; Fu et al., GCN 41584; Zheng et al., GCN 41586; Lipunov et al., GCN 41588; Bochenek et al., GCN 41590; Aryan et al., GCN 41591; Ni et al., GCN 41592) during commissioning operations of the MDM InfraRed Astronomy inGaas Explorer (MIRAGE) instrument on the MDM 1.3m telescope. Observations were carried out starting at UTC 2025-08-28 10:59:08, starting ~ 3.4 hours after the time of the X-ray detection. We obtained a series of dithered exposures in Y-band amounting to a total exposure time of 850 s. Images were aligned, stacked and calibrated to the PS1 catalog. Performing forced photometry at the position of the X-ray and optical counterpart reported in GCN 41582, 41583, 41591, 41592, we do not detect a point source to a 5 sigma limiting magnitude of > 19.1 AB mag. Analysis will be improved as further commissioning data is processed. MIRAGE is a new YJH-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the commissioning observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41652. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39717] EP250901a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 02 Sep '25

02 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41651 SUBJECT: EP250901a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/09/02 04:26:12 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. J. Song, T. Zhao, J. W. Hu, C. L. Guo, Z. X. Ling (NAO, CAS), on behalf of the Einstein Probe (EP) team: The X-ray transient EP250901a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Song et al., GCN 41627), with several multi-wavelength follow-up observations (Lipunov et al., GCN 41629; Liu et al., GCN 41631; Evans et al., GCN 41644). The refined WXT data shows that the event started at T0=2025-09-01T12:02:50 (UTC) and lasted for about 150 s before the interruption of the autonomous follow-up. It has a peak flux of ~1 x 10^-9 erg/s/cm^2 in the 0.5-4 keV band. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.1 x 10^21 cm^-2 and a photon index of 1.02 (-0.79/+0.84). The derived average unabsorbed 0.5-4 keV flux is around 5.05 (-1.54/+2.40) x 10^(-10) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 250s after T0. On-ground analysis of the FXT data found an fading source at R.A. = 273.0416, DEC = 18.7052 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), within the WXT error circle. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 3.0(-0.06/+0.07) x 10^21 cm^-2 and a photon index of 2.01(-0.15/+0.17). The derived average unabsorbed 0.5-10 keV flux is around 6.03 (-0.27/+0.43) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. A historical ROSAT detection (1RXS J181210.7+184228) lies 10.1 arcsec away from the FXT position, with a flux of 3 x 10^(-13) erg/s/cm^2 at 0.5-4 keV by assumimg a power-law spectrum with NH=3x10^20 cm^-2 and photon index =1.7. 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/41651. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39716] GRB 250901A: EP-FXT follow-up observation
by GCN Circulars 02 Sep '25

02 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41650 SUBJECT: GRB 250901A: EP-FXT follow-up observation DATE: 25/09/02 04:04:05 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. N. Yang (NAO, CAS), Z. Y. Liu (USTC), Y. J. Zhang (THU), C. C. Jin (NAO, CAS) report on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of GRB 250901A (GCN 41634) at 2025-09-01T20:03:51 (UTC), about 2 hours after the SVOM/ECLAIRs detection, with an exposure time of 5 ks. The source was also followed by Swift-XRT (GCN 41645). The optical afterglow was also detected by SVOM/VT (GCN 41646). FXT detected an uncatalogued source at R.A. = 356.1845, DEC = -15.7418 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), consistent with the position of the source reported by Swift/XRT (offset is 4.0 arcsec). The FXT spectrum of this source can be fitted with an absorbed powerlaw with the absorption fixed at the Galactic value of 1.7x10^20 cm^-2, and a photon index of 1.97(+/-0.16). The derived unabsorbed 0.5-10 keV flux is approximately 2.4(+/-0.3)x10^-12 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. 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/41650. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39715] GRB 250901A: NOT optical observations
by GCN Circulars 02 Sep '25

02 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41649 SUBJECT: GRB 250901A: NOT optical observations DATE: 25/09/02 01:45:56 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), B. Schneider (LAM), G. Corcoran (UCD), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), V. Vuolteenaho (NOT and Oulu Univ.), report on behalf of a larger collaboration: We observed the optical counterpart (Xin et al., GCN 41646; Osborne et al., GCN 41645) of GRB 250901A (Piron et al., GCN 41634) using the Nordic Optical Telescope (NOT), located in the Canary Islands, equipped with the ALFOSC camera. Observations were carried out in the r (3x300 s) and z (5x200 s) bands. In a preliminary stack of the images, the afterglow is faintly detected in both filters. At a mean epoch of 2025 September 2.00 UT (5.73 hr after the trigger), we measure an AB magnitude r = 23.1 +- 0.2, calibrated against nearby stars from the Pan-STARRS catalog, and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41649. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39714] GRB 250902A: Fermi GBM Final Real-time Localization
by GCN Circulars 02 Sep '25

02 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41648 SUBJECT: GRB 250902A: Fermi GBM Final Real-time Localization DATE: 25/09/02 01:40:30 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 01:30:00 UT on 2 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250902A (trigger 778469405.491528 / 250902062). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 159.3, Dec = 16.3 (J2000 degrees, equivalent to J2000 10h 37m, 16d 18'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 78.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250902062/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250902062/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250902062/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41648. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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