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

[vsnet-grb-info 40103] LIGO/Virgo/KAGRA S250830bp: SOAR spectroscopy of two DESGW candidates
by GCN Circulars 30 Sep '25

30 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42033 SUBJECT: LIGO/Virgo/KAGRA S250830bp: SOAR spectroscopy of two DESGW candidates DATE: 25/09/30 21:11:30 GMT FROM: Hemanth kumar <hemanth.bommireddy195(a)gmail.com> Hemanth Bommireddy (U de Chile), Regis Cartier (UA), Felipe Olivares (U Hawaii), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) spectroscopy team: We report on AT2025wzx and AT2025wpo, which were observed by SOAR 2025-09-10T03:10:05 UTC (PI Bommireddy). We clearly see broad Halpha and Hbeta in AT2025wzx, securing its classification as an AGN at z~0.23, thus, we therefore conclude this candidate to be far too distant to be associated with S250830bp (GCN 41607). In contrast, AT2025wpo shows a noisy featureless spectrum, preventing a firm classification. We thank SOAR Staff for supporting these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/42033. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40102] LIGO/Virgo/KAGRA S250818k: further MeerKAT monitoring
by GCN Circulars 30 Sep '25

30 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42032 SUBJECT: LIGO/Virgo/KAGRA S250818k: further MeerKAT monitoring DATE: 25/09/30 17:24:39 GMT FROM: Gabriele Bruni at INAF <gabriele.bruni(a)inaf.it> G. Bruni [1], L. Piro [1], G. Gianfagna [1] and A. L. Thakur [1] report: We carried out a third epoch of MeerKAT observations on the field of AT2025ulz (Stein et al., GCN 41414), in the localization region of the subthreshold GW event S250818k (LVK Collaboration, GCNs 41437, 41440). Observations at 3 GHz (S4 band) started on 2025-09-13, 12:07 UT (26 days post-trigger) for a total of 4 hours. Given the previously reported discrepancies between the data reduction for this target carried out with the SARAO Science Data Processor (SDP) and other pipelines (GCN 41666), we reprocessed the three epochs using also oxkat (Heywood 2020, Astrophysics Source Code Library). While the results of the two pipelines agree for the first and third epochs, we find that the SDP pipeline image of the second epoch exhibited a flux density bias of up to 100% for field sources below ~200 μJy (S/N up to ~30-40), which led us to an incorrect conclusion about the variability of the target (GCN 41594). The reprocessed data for the three MeerKAT epochs at 3 GHz show emission at a position consistent with the host galaxy and compatible with a constant flux of ~80+/-10 uJy, thus constraining variability due to a transient. This suggests that the radio source is currently dominated by diffuse emission, likely star formation, by the host galaxy. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation. —------------------------ [1] INAF-IAPS View this GCN Circular online at https://gcn.nasa.gov/circulars/42032. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40101] GRB 250910A / EP250910a: VLT/X-shooter host galaxy redshift z = 0.592
by GCN Circulars 30 Sep '25

30 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42031 SUBJECT: GRB 250910A / EP250910a: VLT/X-shooter host galaxy redshift z = 0.592 DATE: 25/09/30 09:22:02 GMT FROM: Andrea Saccardi at CEA/Irfu <andrea.saccardi(a)cea.fr> A. Saccardi (CEA/Irfu), N. Habeeb (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud), B. Schneider (LAM), N. R. Tanvir (Leicester), report on behalf of the Stargate collaboration: We observed the object visible in the Legacy Survey underlying the position of the optical/NIR afterglow (Schneider et al., GCN 41794; Li et al., GCN41798) of GRB 250910A / EP250910a (Ma et al., GCN 41769; Liu et al., GCN 41776; Hubert et al., GCN 41842) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. A spectrum covering the wavelength range 3000-21000 AA was secured, with a total exposure time 2x1440 s in each of the UVB, VIS, and NIR arms. Our observation started at 03:01:23 UT on 2025 September 30, i.e. about 20 days after the SVOM trigger. Emission lines are detected in the visible and near-infrared arms, which we identify as H-alpha, the [O III] 4959, 5007 doublet, H-beta, and the [O II] 3726, 3729 doublet, all at a common redshift of z = 0.592. We suggest this to be the redshift of the host galaxy of GRB 250910A / EP250910a. We acknowledge excellent support from the ESO staff in Paranal, in particular Elisa Rita Garro, Rodrigo Romero and Jonathan Smoker. View this GCN Circular online at https://gcn.nasa.gov/circulars/42031. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40100] GRB 250925A: MAO/AZT-22 optical observations
by GCN Circulars 30 Sep '25

30 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42030 SUBJECT: GRB 250925A: MAO/AZT-22 optical observations DATE: 25/09/30 08:51:39 GMT FROM: Yodgor Rajabov at UBAI <rajabov(a)astrin.uz> Y. Rajabov, O. Burkhonov, B.Abidkhanov, S. Ehgamberdiev, Y. Tillayev (UBAI), T. Boyqobilov, A. Shaymanov (Maidanak Observatory/UBAI) report on behalf of UBAI team. We observed the field of GRB 250925A detected by Swift (Dichiara et. al, GCN 41985), at z=3.899 (Castro-Tirado et. al, GCN 41997), with the AZT-22 1.5m telescope of the Maidanak Observatory (MAO) starting on 2025-09-25 at 19:13:36 UT, i.e. ~2.18 hours since trigger. In total we obtained 6x300 s exposures in the R-band using 4kx4k CCD SNUCAM camera (Im et al., 2010). The optical afterglow initially detected by NOT/ORM (Corcoran et. al, GCN 41990) and also observed (Saikia et. al, GCN 41986; Pavoni & Moretti et. al, GCN 41989; Bochenek & Perley, GCN 41991; Masi et. al, GCN 41992; Mendez et. al, GCN 41995; Castro-Tirado et. al, GCN 41997; Liu et. al, GCN 41998; Ochi et. al, GCN 41999; Xin et. al., GCN 42002; Rakotondrainibe et. al, GCN 42004; Pankov et. al, GCN 42005; Pankov et. al, GCN 42025 ) is detected in our stacked frames. Preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope (nxs) (mid, days) 2025-09-25 19:13:36 6x300 0.10011 R 21.74 0.17 21.82 MAO/AZT-22 All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousins filters were calibrated using the Gaia DR3 Synphot catalog. The data has not corrected for the Galactic extinction. Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/). View this GCN Circular online at https://gcn.nasa.gov/circulars/42030. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40099] Fermi GRB 250929A: Global MASTER-Net observations report
by GCN Circulars 29 Sep '25

29 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42029 SUBJECT: Fermi GRB 250929A: Global MASTER-Net observations report DATE: 25/09/29 20:31:09 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), C.Francile, 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250929A ( Fermi GBM team, GCN 42028) errorbox 364 sec after notice time and 395 sec after trigger time at 2025-09-29 20:12:42 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 53 deg. The sun altitude is -42.7 deg. The galactic latitude b = -45 deg., longitude l = 273 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3002549 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 425 | 2025-09-29 20:12:42 | MASTER-SAAO | (02h 49m 40.43s , -53d 58m 56.7s) | C | 60 | 18.9 | 425 | 2025-09-29 20:12:42 | MASTER-SAAO | (02h 52m 46.96s , -54d 14m 04.8s) | C | 60 | 18.9 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42029. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40098] GRB 250929A: Fermi GBM Final Real-time Localization
by GCN Circulars 29 Sep '25

29 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42028 SUBJECT: GRB 250929A: Fermi GBM Final Real-time Localization DATE: 25/09/29 20:16:36 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 20:06:07 UT on 29 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250929A (trigger 780869172.178268 / 250929838). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 58.2, Dec = -60.2 (J2000 degrees, equivalent to J2000 03h 52m, -60d 12'), with a statistical uncertainty of 11.5 degrees. The angle from the Fermi LAT boresight is 73.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250929838/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250929838/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250929838/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42028. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40097] GRB 250926A: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 29 Sep '25

29 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42027 SUBJECT: GRB 250926A: CALET Gamma-Ray Burst Monitor detection DATE: 25/09/29 15:19:54 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> S. Ricciarini (U of Florence), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The GRB 250926A (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 41993; AstroSat CZTI detection: Goyal et al., GCN Circ. 42008; Insight-HXMT detection: Wang et al., GCN Circ. 42013; triangulation location with Insight-HXMT/HE and Fermi/GBM: Zhang et al., GCN Circ. 42019) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 00:21:23.82 UTC on 26 September 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1442880852/index.html). The burst signal was seen by only the SGM detector. The burst light curve shows a single pulse that starts at T+0.75 sec, peaks at T+1.08 sec, and ends at T+1.35 sec. The T90 and T50 durations measured by the SGM data are 0.55 +/- 0.11 sec and 0.25 +/- 0.10 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1442880852/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/42027. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40096] LIGO/Virgo/KAGRA S250929c: Updated Sky localization
by GCN Circulars 29 Sep '25

29 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42026 SUBJECT: LIGO/Virgo/KAGRA S250929c: Updated Sky localization DATE: 25/09/29 14:29:17 GMT FROM: Aditya Vijaykumar <aditya.vijaykumar(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 S250929c (GCN Circular 42023). 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/S250929c For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 1828 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3796 +/- 1511 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/42026. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40095] GRB 250925A: Mondy I-band optical observations
by GCN Circulars 29 Sep '25

29 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42025 SUBJECT: GRB 250925A: Mondy I-band optical observations DATE: 25/09/29 13:09:19 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) report on behalf of GRB-IKI-FuN: We observed the field of GRB 250925A detected by Swift (Dichiara et. al, GCN 41985), at z=3.899 (Castro-Tirado et. al, GCN 41997), with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) starting on 2025-09-27 at 14:45 UT, i.e. ~1.93 days since trigger. In total we obtained 45x120 s exposures in the I-band using CMOS photometer. The optical afterglow initially detected by NOT/ORM (Corcoran et. al, GCN 41990) and also observed by (Saikia et. al, GCN 41986; Pavoni & Moretti et. al, GCN 41989; Bochenek & Perley, GCN 41991; Masi et. al, GCN 41992; Mendez et. al, GCN 41995; Castro-Tirado et. al, GCN 41997; Liu et. al, GCN 41998; Ochi et. al, GCN 41999; Xin et. al., GCN 42002; Rakotondrainibe et. al, GCN 42004; Pankov et. al, GCN 42005) is not visible in the stacked image. Preliminary photometry and observation properties are presented below: Date UTstart Exptime t-T0 Filter OT Err. UL FWHM (nxs) (mid, days) (3sigma) (") 2025-09-27 14:45:07 45x120 1.93451 I n/d n/d 22.3 1.6 The photometry was calibrated against nearby USNO-B1.0 stars (I-mags) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42025. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40094] GRB 250916A: SVOM/VT optical observation
by GCN Circulars 29 Sep '25

29 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42024 SUBJECT: GRB 250916A: SVOM/VT optical observation DATE: 25/09/29 01:39:36 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, H. L. Li, Y. N. Ma, Z. H. Yao, Y. L. Qiu, C. Wu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), W. K. Zheng (UCT), Z. Q. Wang (GXU) report on behalf of the SVOM/VT team: SVOM/VT performed a Target of Opportunity observation of GRB 250916A detected by Fermi GBM team (GCN 41839), starting at 2025-09-23T07:32:29 UTC, 6.66 days after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical counterpart (Belkin et al., GCN Circ. 41847; Mohan et al., GCN Circ. 41858; Moskvitin et al., GCN Circ. 41859; Burkhonov et al., GCN Circ. 41860; de Ugarte Postigo et al., GCN Circ. 41863; Moskvitin et al., GCN Circ. 41870; Zheng and Filippenko, GCN Circ. 41873; Pankov et al., GCN Circ. 41892; Hall et al., GCN Circ. 41921 and Moskvitin et al., GCN Circ. 41934, Breeveld et al., GCN 41938) was detected in both channels. The brightness was VT_R=23.0 +/-0.25 mag, VT_B=23.5+/-0.3 mag, with an effective exposure time of 97*70 seconds. Our photometry was in AB magnitude and not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre 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/42024. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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