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

[vsnet-grb-info 39853] GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41787 SUBJECT: GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 DATE: 25/09/11 09:25:59 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, H.-C. Feng and J.-M. Bai (YNAO, CAS) and D. B. Malesani (DAWN/NBI and Radboud) report: We carried out a full reduction of the spectrum of GRB 250404A / EP250404a observed with the GMG-2.4m telescope (Li et al., GCN 40084) using the most up-to-date calibrations and complete pipeline procedures. A Ly-alpha absorption feature at ~4400 AA was reported by the Xinglong-2.16 m telescope (Zhu et al., GCN 40061). In the GMG spectrum, the region around ~4400 AA exhibits a smooth continuum, and no typical Ly-alpha absorption feature is identified. However, we identified multiple metal absorption features, including Si IV at 1394 AA, Si IV at 1403 AA, Si II at 1527 AA, C IV at 1549 AA, Fe II at 1608 AA, Al II at 1671 AA, Al III at 1855 AA, Al III at 1863 AA, Zn II/Cr II at 2026 AA, Zn II/Cr II at 2062 AA, Fe II at 2344 AA, Fe II at 2374 AA, and Fe II at 2383 AA. These features consistently indicate a redshift of z = 1.88. In summary, we conclude that the redshift of the transient is z = 1.88 (see Figure B1 of Yin et al., 2025; doi:10.3847/2041-8213/adf552). We are grateful to D. B. Malesani for kindly pointing out the issue with the redshift determination. We apologize for any confusion that our preliminary report may have caused. View this GCN Circular online at https://gcn.nasa.gov/circulars/41787. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39852] LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41786 SUBJECT: LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate DATE: 25/09/11 08:46:44 GMT FROM: Iara Tosta e Melo at UniCT <iara.tosta.melo(a)dfa.unict.it> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250911ac during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-09-11 07:46:39.272 UTC (GPS time: 1441612017.272). The candidate was found by the Aframe [1], cWB BBH [2], GstLAL [3], MBTA [4], PyCBC Live [5], and SPIIR [6] analysis pipelines. S250911ac is an event of interest because its false alarm rate, as estimated by the online analysis, is 6e-09 Hz, or about one in 5 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250911ac The initial classification of the GW signal, in order of descending probability, based on chirp-mass information only [5], is BBH (84%), NSBH (13%), Terrestrial (4%), or BNS (<1%). Noise transients (glitches) were present in LIGO Hanford detector data within two seconds of the event time, which may affect the parameters or the significance of the candidate. 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%. [7] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [7] 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 7%. The source chirp mass falls with highest probability in the bin (5.5, 11.0) 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: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 27 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 1012 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1102 +/- 300 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] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018 [3] 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 [4] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [5] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [6] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [7] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [8] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41786. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39851] GRB 250903A: SVOM/ECLAIRs refined analysis
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41785 SUBJECT: GRB 250903A: SVOM/ECLAIRs refined analysis DATE: 25/09/11 08:37:06 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Nicolas Dagoneau (CEA), Jean-Luc Atteia (IRAP), Floriane Cangemi (APC), Tais Maiolino (LUPM), Claire Guépin-Detrigne (LUPM) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250903A (SVOM burst-id sb25090304). The burst that triggered ECLAIRs onboard (GCN 41677) was detected in the first trigger cycle that followed the SAA exit. Consequently, the precise duration of the event cannot be determined. The exposures in which the burst was detected onboard have durations spanning from 5.12 to 40.96 s starting from T0-13 s to T0+3 s (T0 = 2025-09-03T17:24:56 UTC). The time-averaged spectrum (from T0-8.7s to T0+7.5s) in the energy range 4-120 keV is best fit by a cutoff power-law with a photon index 1.28 +/- 0.22 and a peak energy Epeak 38 +/- 15 keV. With this model, the total fluence in the 4-120 keV band is (7.66 -5.78/+0.90)e-7 erg/cm^2. With a redshift of z = 1.59 (GCN 41691), the burst isotropic energy Eiso (from 1 keV to 10 MeV in its rest frame) is 6.4e51 erg. This is only a lower bound since we may have missed the beginning of the burst when SVOM was in the SAA. Still, this value makes this GRB consistent with type II GRBs in the 'Amati' relation diagram (Amati et al. 2002). The spectrum is also well fit by a simple power-law model with a photon index 1.62 +/- 0.08. With this model, the total fluence in the 4-120 keV band is (9.15 -1.74/+1.06) e-7 erg/cm^2. All the quoted errors are at the 90% 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. The SVOM/ECLAIRs point of contact for this burst is: Nicolas Dagoneau (CEA) (nicolas.dagoneau at cea.fr). View this GCN Circular online at https://gcn.nasa.gov/circulars/41785. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39850] GRB 250911A: Enhanced Swift-XRT position
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41784 SUBJECT: GRB 250911A: Enhanced Swift-XRT position DATE: 25/09/11 06:48:39 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 2239 s of XRT Photon Counting mode data and 6 UVOT images for GRB 250911A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 263.75012, -16.85418 which is equivalent to: RA (J2000): 17h 35m 00.03s Dec (J2000): -16d 51' 15.0" with an uncertainty of 2.0 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41784. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39849] GRB 250911A: Swift-XRT observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41783 SUBJECT: GRB 250911A: Swift-XRT observations DATE: 25/09/11 05:16:58 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M. Perri (SSDC & INAF-OAR), P.A. Evans (U. Leicester) and J.A. Kennea (PSU) report on behalf of the Swift-XRT team: The XRT began observing the field of GRB 250911A at 02:25:07.6 UT, 3441.5 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source located at RA, Dec 263.75102, -16.85448 which is equivalent to: RA(J2000) = 17h 35m 00.24s Dec(J2000) = -16d 51' 16.1" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 53 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (3.44 x 10^21 cm^-2, Willingale et al. 2013), with an excess column of 4.3 (+3.44/-2.88) x 10^21 cm^-2 (90% confidence). View this GCN Circular online at https://gcn.nasa.gov/circulars/41783. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39848] GRB 250911A: COLIBRÍ optical counterpart candidate
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41782 SUBJECT: GRB 250911A: COLIBRÍ optical counterpart candidate DATE: 25/09/11 03:50:26 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo(a)astro.unam.mx> Camila Angulo (UNAM), Sarah Antier (OCA), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM): We imaged the field of the Swift GRB 250911A (Palmer et al., GCN Circ. 41781) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed at 2025-09-11 02:41 UTC (1.2 hours after the trigger) and obtained 60 second exposures in the r and z filters. The data were analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect an uncatalogued source consistent with the BAT 3.0 arcmin error circle (Palmer et al., GCN Circ. 41781) at: RA(J2000) = 17:35:00.05 = 263.75021 degrees Dec(J2000) = -16:51:14.40 = -16.8540 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitudes derived for that source are: r = 19.19 +/- 0.08 z = 18.46 +/- 0.10 We suggest that this source is the optical counterpart of the GRB. Further observations are ongoing. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41782. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39847] GRB 250911A: Swift detection of a burst
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41781 SUBJECT: GRB 250911A: Swift detection of a burst DATE: 25/09/11 01:43:39 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> N. J. Klingler (GSFC/UMBC/CRESSTII), S. Dichiara (PSU), R. Gupta (NASA GSFC), A. Y. Lien (U Tampa) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 01:27:46 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250911A (trigger=1348587). Due to an observing constraint Swift did not immediately slew to the burst. The BAT on-board calculated location is RA, Dec 263.762, -16.844 which is RA(J2000) = 17h 35m 03s Dec(J2000) = -16d 50' 36" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 20 sec. The peak count rate was ~1200 counts/sec (15-350 keV), at ~3 sec after the trigger. Due to an observing constraint, Swift will not slew until T0+50 minutes. There will be no XRT or UVOT data until this time. Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.edu) Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41781. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39846] LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41780 SUBJECT: LIGO/Virgo/KAGRA S250906ca: Updated Sky localization DATE: 25/09/10 19:56:00 GMT FROM: natalie.williams(a)uni-potsdam.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 S250906ca (GCN Circular 41745). 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/S250906ca For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 516 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1121 +/- 266 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/41780. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39845] GRB 250910B: BALROG localization (Fermi Trigger 779223130 / GRB 250910786)
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41779 SUBJECT: GRB 250910B: BALROG localization (Fermi Trigger 779223130 / GRB 250910786) DATE: 25/09/10 19:25:58 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 779223130 at 18:52:05 on 10 Sept. 2025 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 74.2 deg Decl.(2000.0) = -47.5 deg The 1 sigma statistical error radius is 3.6 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB250910786/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB250910786/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB250910786/json View this GCN Circular online at https://gcn.nasa.gov/circulars/41779. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 39844] GRB 250910B: Fermi GBM Final Real-time Localization
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41778 SUBJECT: GRB 250910B: Fermi GBM Final Real-time Localization DATE: 25/09/10 19:02:42 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 18:52:05 UT on 10 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250910B (trigger 779223130.045678 / 250910786). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 80.2, Dec = -46.4 (J2000 degrees, equivalent to J2000 05h 20m, -46d 23'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 35.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910786/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910786/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910786/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41778. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0