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

[vsnet-grb-info 40153] GRB 251001B: AbAO optical upper limit
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42083 SUBJECT: GRB 251001B: AbAO optical upper limit DATE: 25/10/03 09:51:25 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of GRB 251001B detected by Fermi/GBM (The Fermi GBM team et. al, GCN 42038), and Swift/BAT (Beardmore et. al, GCN 42039) with the AS-32 0.7m telescope of the Abastumani Observatory (AbAO). The R-filter observations began on 2025-10-01 22:37 UT, i.e. ~0.35 days since trigger and consisted of 55x30 s exposures. The optical source at z = 2.162 (Sanchez-Ramirez et. al, GCN 42053) found by GOTO (Gompertz et. al, GCN 42040) and also observed by (An et. al, GCN 42041; Strausbaugh & Cucchiara, GCN 42043; O'Neill et. al, GCN 42046; de Ugarte Postigo et. al, GCN 42050; Ma et. al, GCN 42051; Sanchez-Ramirez et. al, GCN 42053; Schneider et. al, GCN 42054; Breeveld et. al, GCN 42055) is not detected in the co-add image of 51x30 s. Preliminary photometry and observation details are presented below: Date UT start t-T0 Exp. Filter OT Err. UL (mid, days) (s) (3sigma) 2025-10-01 22:37:48 0.35641 51x30 R n/d n/d 19.9 The photometry was calibrated using nearby stars from USNO-B1.0 (R2 magnitudes) and not corrected for the Galactic extinction. Ref. stars USNO-B1.0 RA Dec R2 42.63445 -23.02161 14.13 42.77496 -23.05166 13.47 View this GCN Circular online at https://gcn.nasa.gov/circulars/42083. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40152] GRB 251002A: Kilonova-Catcher optical afterglow detection
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42082 SUBJECT: GRB 251002A: Kilonova-Catcher optical afterglow detection DATE: 25/10/03 09:49:33 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> S. Leonini, M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN),S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 251002A detected by SVOM/ECLAIRs and GRM (Saccardi et al., GCN 42060) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC160FL and iT72 telescopes operated by M. Freeberg and with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88) operated by S. Leonini. Our observations started at TGRB+1.2hr. In our stacked frames, subtracted from the PanSTARRS DR2 template image, we detect the optical counterpart reported by SVOM/VT (Palmerio et al., GCN 42061), LCO-1m (Turpin et al., GCN 42062), FRAM-ORM (Jelinek et al., GCN 42063), LCO-40cm (Perez-Fournon et al., GCN 42064), SAO RAS (Moskvitin et al., GCN 42065), BOOTES-6 (Perez-Garcia et al., GCN 42066), MASTER (Lipunov et al., GCN 42067), VLT/Xshooter (Saccardi et al., GCN 42076), OHP/T193 (Mandrakas et al., GCN 42077), SYSU (Cao et al., GCN 42078), SVOM/COLIBRI (FM-GFT) (Schneider et al., GCN 42080) and AbAO (Pankov et al., GCN 42081). We report part of our follow-up results in the table below: +---------------+-----------+-----------+----------------------+-------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+===========+======================+=============+ | 2.28 | 60 x 40s | Rc (Vega) | 19.08 +/- 0.22 | Montarrenti | | 5.10 | 18 x 180s | Rc (Vega) | 19.86 +/- 0.09 | iT72 | | 8.54 | 20 x 180s | r (AB) | 20.42 (5 sigma U.L.) | TEC160FL | +---------------+-----------+-----------+----------------------+-------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. Images obtained with the Johnson-cousins filters were calibrated using the GAIA DR3 synphot catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42082. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40151] GRB 251002A: AbAO optical observations
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42081 SUBJECT: GRB 251002A: AbAO optical observations DATE: 25/10/03 08:39:52 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of GRB 251002A detected by SVOM (Saccardi et. al, GCN 42060) in the R-filter with the AS-32 0.7m telescope of the Abastumani Observatory (AbAO). The observations began on 2025-10-02 21:46 UT, i.e. ~0.09 days since trigger and consisted of 87x60 s exposures. The optical source found by SVOM (Palmerio et. al, GCN 42061) at z = 2.178 (Saccardi et. al, GCN 42076) and also observed by (Turpin et. al, GCN 42062; Jelinek et. al, GCN 42063; Juliá-Maroto et. al, GCN 42064; Moskvitin et. al, GCN 42065; Perez-Garcia et. al, GCN 42066; Saccardi et. al, GCN 42076; Mandarakas et. al, GCN 42077; Cao et. al, GCN 42078) is clearly visible in the co-add image of 87x60 s. Preliminary photometry and observation details are presented below: Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (s) (3sigma) 2025-10-02 21:46:03 0.09351 87*60 R 19.48 0.16 21.7 The photometry was calibrated using reference stars from (Moskvitin et. al, GCN 42065) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42081. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40150] GRB 251002A: SVOM/COLIBRÍ (FM-GFT) optical observations
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42080 SUBJECT: GRB 251002A: SVOM/COLIBRÍ (FM-GFT) optical observations DATE: 25/10/03 08:37:03 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Enrique Moreno Méndez (UNAM), Camila Angulo (UNAM), Ny Avo Rakotondrainibe (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (OCA), 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), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Antonio de Ugarte Postigo (LAM), Andrea Saccardi (CEA/Irfu), and Diego Gotz (CEA/Irfu): We imaged the field of the SVOM GRB 251002A (Saccardi et al., GCN Circ. 42060) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-10-03 03:33:53 to 05:48:35 UTC (from 7.32 to 9.56 hr after the trigger) and obtained 16 minutes of exposure in the g, r, i, z and y filters. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed 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 detected the optical counterpart reported by Palmerio et al., GCN Circ. 42061, Turpin et al., GCN Circ. 42062; Jelinek et al., GCN Circ. 42063; Juliá-Maroto et al. GCN Circ. 42064; Moskvitin et al. GCN Circ. 42065; Perez-Garcia et al. GCN Circ. 42066; Senik et al., GCN Circ. 42067; Saccardi et al., GCN Circ. 42076; Mandarakas et al., GCN Circ. 42077; Cao et al, GCN 42078 at preliminary magnitudes of: g = 20.96 +/- 0.09 (mid-time 8.41 hr) r = 20.82 +/- 0.07 (mid-time 8.44 hr) i = 20.64 +/- 0.07 (mid-time 8.46 hr) z = 20.76 +/- 0.15 (mid-time 8.42 hr) y = 20.30 +/- 0.22 (mid-time 7.84 hr) Further observations and analysis are ongoing in g, r, i, z and y filters. 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/42080. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40149] GRB 251001C: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42079 SUBJECT: GRB 251001C: CALET Gamma-Ray Burst Monitor detection DATE: 25/10/03 08:15:26 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> P. S. Marrocchesi (U of Siena), 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), S. Ricciarini (U of Florence), and the CALET collaboration: The GRB 251001C (Glowbug gamma-ray detection: Cheung et al., GCN Circ. 42049) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 15:07:25.84 UTC on 1 October 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1443366004/index.html) The burst signal was seen by only the SGM detector. The burst light curve shows a single pulse that starts at T+0.2 sec, peaks at T+1.0 sec, and ends at T+2.4 sec. The T90 and T50 durations measured by the SGM data are 2.0 +/- 0.1 sec and 0.7 +/- 0.2 sec (40-1000 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1443366004/ 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/42079. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40148] GRB 251002A: J band observations by SYSU 80cm infrared telescope
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42078 SUBJECT: GRB 251002A: J band observations by SYSU 80cm infrared telescope DATE: 25/10/03 07:45:53 GMT FROM: caodle(a)mail2.sysu.edu.cn Dou-Le Cao, Jia-Qi Lin, Chen Chun, Zhong-Nan Dong, Wei-Sen Huang, Jin-Ji Li, Pu Lin, Yan Yu, Hao-Nan Yang, Hao-Ran Zhang, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team: We observed the field of GRB251002A detected by SVOM/ECLAIRs (A. Saccardi et al., GCN 42060), using the Sun Yat-sen University 80cm infrared telescope with 20s exposures in J band. The calculated position is R.A. = 13.9082 deg, DEC = -5.5671 deg J2000, from SVOM/VT observation. Our observations began at 2025-10-2 20:55:00 UTC, 0.62 hours after the SVOM trigger. We detected an infrared counterpart at the position of the optical afterglow (J. T. Palmerio et al., GCN 42061; D. Turpin et al., GCN 42062; Martin Jelinek et al., GCN 42063; L. Juliá-Maroto et al., GCN 42064; A. S. Moskvitin et al., GCN 42065; I. Perez-Garcia et al., GCN 42066; V.Senik et al., GCN 42067) in the stacked images. The preliminary photometric magnitudes in J band are below: Start Time (UTC) |Band | Exp | Mag (Vega) ------------------------|-------|---------|------------------ 2025/10/2 20:55:00 | J | 300s | 17.03+/-0.24 2025/10/2 21:00:00 | J | 300s | 17.19+/-0.14 2025/10/2 21:05:00 | J | 300s | 17.64+/-0.20 2025/10/2 21:10:00 | J | 300s | 17.44+/-0.15 2025/10/2 21:15:00 | J | 300s | 17.74+/-0.19 2025/10/2 21:20:00 | J | 900s | 17.65+/-0.16 2025/10/2 21:35:00 | J | 2100s | 18.27+/-0.15 The photometric calibration was performed using nearby stars from the 2MASS catalog and the magnitudes are not corrected for Galactic extinction. The SYSU 80cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University. View this GCN Circular online at https://gcn.nasa.gov/circulars/42078. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40147] GRB 251002A: OHP/T193 MISTRAL optical afterglow detection
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42077 SUBJECT: GRB 251002A: OHP/T193 MISTRAL optical afterglow detection DATE: 25/10/03 07:34:37 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> N. Mandarakas (LAM), C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), B. Schneider (LAM), E. Le Floc'h (CEA/Irfu), S.D. Vergani (LUX-Paris Obs.) report on behalf of a larger collaboration: We observed the field of the SVOM/ECLARIs GRB 251002 (Saccardi et al., GCN 42060) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained three exposures of 240s (for a total of 12 min) in the r-band starting at 22:05:40 UT on 2025-10-02 (observations mid-time at T-To=2h20min), under modest weather conditions. In the stacked images, we detect the optical counterpart reported and followed by Palmerio et al. (GCN 42061), Turpin et al. (GCN 42062), Jelinek et al. (GCN 42063), Julia-Maroto et al. (GCN 42064), Moskvitin et al. (GCN 42065), Perez-Garcia et al. (GCN 42066), Senik et al. (GCN 42067), Sun et al. (GCN 42075), and Saccardi et al. (GCN 42076) The preliminary magnitude derived for that source is: r’ = 19.39 +/- 0.07 mag (AB) The detection limit (3 sigma) is r=21.10 +/- 0.15 The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025). We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Yoann Degot-Longhi. View this GCN Circular online at https://gcn.nasa.gov/circulars/42077. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40146] GRB 251002A: VLT/X-shooter spectroscopic redshift z = 2.178
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42076 SUBJECT: GRB 251002A: VLT/X-shooter spectroscopic redshift z = 2.178 DATE: 25/10/03 06:54:12 GMT FROM: Andrea Saccardi at CEA/Irfu <andrea.saccardi(a)cea.fr> A. Saccardi (CEA/Irfu), N. Habeeb (U. Leicester), A. de Ugarte Postigo (LAM), B. Schneider (LAM), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), S. D. Vergani (LUX-Paris Obs.), B. C. Rayson (Leicester), N. R. Tanvir (U. Leicester) report on behalf of the Stargate collaboration: We observed the optical counterpart (Palmerio et al., GCN 40061; Turpin et al., GCN 40062; Jelinek et al., GCN 40063; Juliá-Maroto et al. GCN 42064; Moskvitin et al. GCN 42065; Perez-Garcia et al. GCN 42066) of the SVOM/ECLAIRs GRB 251002A (Saccardi et al., GCN 42060) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. From the 3x30 s acquisition image at 2025-10-03 04:55:20 UT (8.67 hr post-trigger), the optical afterglow is well detected with a magnitude of r = 20.74 +/- 0.12 (AB) calibrated against PanSTARRS nearby stars and not corrected for Galactic extinction. Our spectra cover the wavelength range 3000-21000 AA and consist of 4 exposures of 600 s each. Observations started on 2025 October 3 at 05:04:11 UT (8.82 hr after the burst). In a preliminary reduction of the spectra, we clearly detect a continuum over the entire wavelength range. From the detection of multiple absorption features, including Lya, S II, Si II, Si II*, O I, O I*, C II, C II*, Si IV, C IV, Fe II, Al II, Zn II, Cr II, Ni II*, Fe II*, Mg II, and Mg I we infer a redshift of z = 2.178. We acknowledge the prompt response and excellent support of the ESO observing staff in Paranal, in particular Aaron Labdon, Jonathan Smoker and Rodrigo Palominos. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/42076. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40145] GRB 251002A: EP-FXT counterpart detection
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42075 SUBJECT: GRB 251002A: EP-FXT counterpart detection DATE: 25/10/03 06:02:41 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. X. Sun(NAO,CAS), Y.Q. Zhao(USTC,PRIC), Y. L. Wang (NAO, CAS; ICE, CSIC-IEEC)，and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 251002A (SVOM/sb25100211, Saccardi et al. GCN 42060) at 2025-10-02T20:52:13Z (UTC), 2239 seconds after the SVOM/ECLAIRs trigger, with an exposure time of 2918s. One uncatalogued source is detected within the ECLAIRs error circle, and the source is spatially consistent with the counterpart reported in optical bands (Palmerio et al. GCN 42061, Turpin et al. GCN 42062, Jelinek et al. GCN 42063, Juliá-Maroto et al. GCN 42064, Moskvitin et al. GCN 42065，Perez-Garcia et al. GCN 42066, Senik et al. GCN 42067). Preliminary analysis on this source are automatically conducted, and details are listed as follows. Source 1: EPF_J005537.9-053402 RA(J2000): 13.9078 Dec (J2000): -5.5669 Flux: 1.295e-11 erg/s/cm2 (observed, 0.5-10 kev) Flux_err: 7.6399e-13 erg/s/cm2 (1 sigma) The position uncertainty of the source is about 10 arcsec in radius (90% C.L. statistical and systematic). 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/42075. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40144] GRB 251003A: LCOGT Optical Detection
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42074 SUBJECT: GRB 251003A: LCOGT Optical Detection DATE: 25/10/03 04:04:06 GMT FROM: Robert Strausbaugh at Eastern Illinois University <rstrausbaugh(a)eiu.edu> R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the Swift GRB 251003A field (Beardmore et al., GCN 42070) with the LCOGT 1-meter Sinistro instrument at the McDonald Observatory, USA site, on October 3, from 03:07 to 03:39 UT (corresponding to 1.15 to 1.68 hours after the GRB trigger time) with the SDSS i and r filters. We performed a series of 3x300s exposures in i-band and r-band. We detect an uncatalogued source in the XRT enhanced error region (Evans et al. GCNC 42071) consistent with other optical counterpart observations (Aceituno et al., GCN 42072; Méndez et al., GCN 42073) in both bands. We note that the r-i color of this event may indicate a moderate redshift source (z>4). The following magnitudes are calculated using the PanSTARRS catalog as reference: r = 20.97 +/- 0.12 i = 19.25 +/- 0.04 These magnitudes are not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42074. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40143] GRB 251003A: COLIBRÍ optical detection of the fading afterglow
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42073 SUBJECT: GRB 251003A: COLIBRÍ optical detection of the fading afterglow DATE: 25/10/03 03:55:12 GMT FROM: enriquemm(a)astro.unam.mx Enrique Moreno Méndez (UNAM), Benjamin Schneider (LAM), Camila Angulo (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (OCA), 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), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM): We imaged the field of the Swift GRB 251003A (Beardmore et al., GCN Circ. 42070) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-03 02:19 to 02:22 UTC (from 0.3 to 0.7 hours after the trigger) and obtained 3 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and 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 detected the optical counterpart reported by Aceituno et al., GCN Circ. 42072, at a position of RA, Dec = 18.52939, 56.49110 (J2000), with preliminary magnitudes of: r = 20.34 +/- 0.11 z = 18.56 +/- 0.05 The object fades in subsequent observations, confirming that it is the optical afterglow. The very red color suggests that this might be either a moderate redshift GRB with a drop-out in r or a very heavily reddened GRB. Further observations in g/r/i/z/y 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/42073. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40142] GRB 251003A: 1.5m OSN afterglow candidate
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42072 SUBJECT: GRB 251003A: 1.5m OSN afterglow candidate DATE: 25/10/03 03:06:40 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct(a)iaa.es> F. J. Aceituno, R. Sanchez-Ramirez A. J. Castro-Tirado, S. Guziy, M.D. Caballero-Garcia, S.-Y. Wu and I. Perez-Garcia (IAA-CSIC), and Y.-D. Hu (GXI), on behalf of a larger collaboration, report: Following the detection of GRB 251003A by both Fermi (Fermi team, GCNC 42069) and Swift (Beardmore et al. GCNC 42070), we obtained a 300s exposure image (I-band) with the 1.5m OSN telescope in Sierra Nevada (Granada, Spain) starting on Oct 3 (02:34 UT, i.e. 36 min post burst). At the enhanced X-ray position (Evans et al. GCNC 42071) we identify an optical source with a preliminary magnitude of 21, which we propose to be the afterglow to GRB 251003A. Further observations are being gathered. View this GCN Circular online at https://gcn.nasa.gov/circulars/42072. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40141] GRB 251003A: Prompt enhanced Swift-XRT position
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42071 SUBJECT: GRB 251003A: Prompt enhanced Swift-XRT position DATE: 25/10/03 02:22:53 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Using 263 s of promptly downlinked XRT event data for GRB 251003A, we find an enhanced XRT position of the afterglow: RA, Dec: 18.52838, 56.49082 which is equivalent to: RA (J2000) = 01 14 06.81 Dec (J2000) = +56 29 26.9 with an uncertainty of 2.3 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/1400964. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42071. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40140] GRB 251003A: Swift detection of a burst
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42070 SUBJECT: GRB 251003A: Swift detection of a burst DATE: 25/10/03 02:10:50 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> A. P. Beardmore (U Leicester), R. Gupta (NASA GSFC), K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 01:58:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251003A (trigger=1400964). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 18.503, +56.507 which is RA(J2000) = 01h 14m 01s Dec(J2000) = +56d 30' 23" 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 ~1835 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 01:59:42.1 UT, 72.1 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source located at RA, Dec 18.52734, 56.49009 which is equivalent to: RA(J2000) = 01h 14m 06.56s Dec(J2000) = +56d 29' 24.3" with an uncertainty of 3.8 arcseconds (radius, 90% containment). This location is 77 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 consistent with the Galactic value of 4.39 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 1.66e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 78 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.408. Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). 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/42070. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40139] GRB 251003A: Fermi GBM Final Real-time Localization
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42069 SUBJECT: GRB 251003A: Fermi GBM Final Real-time Localization DATE: 25/10/03 02:09:08 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 01:58:31 UT on 3 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251003A (trigger 781149516.956282 / 251003082). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 31.9, Dec = 49.6 (J2000 degrees, equivalent to J2000 02h 07m, 49d 36'), with a statistical uncertainty of 18.2 degrees. The angle from the Fermi LAT boresight is 64.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251003082/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251003082/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251003082/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42069. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40138] Swift GRB251003.08: Global MASTER-Net observations report
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42068 SUBJECT: Swift GRB251003.08: Global MASTER-Net observations report DATE: 25/10/03 02:04:38 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB251003.08 (trigger No 1400964,01h 14m 00.72s , +56d 30m 25.2s, R=0.05) errorbox 10 sec after notice time and 34 sec after trigger time at 2025-10-03 01:59:04 UT, with upper limit up to 16.6 mag. Observations started at twilight. The observations began at zenith distance = 43 deg. The sun altitude is -13.7 deg. The galactic latitude b = -6 deg., longitude l = 126 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3005736 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 40 | MASTER-Kislovodsk | P- | 10 | 15.8 | 50 | MASTER-Kislovodsk | P- | 30 | 16.4 | Coadd 40 | MASTER-Kislovodsk | P| | 10 | 14.6 | 58 | MASTER-Kislovodsk | P- | 10 | 16.0 | 58 | MASTER-Kislovodsk | P| | 10 | 15.0 | 77 | MASTER-Kislovodsk | P- | 10 | 16.2 | 77 | MASTER-Kislovodsk | P| | 10 | 15.1 | 100 | MASTER-Kislovodsk | P- | 20 | 16.5 | 100 | MASTER-Kislovodsk | P| | 20 | 15.8 | 129 | MASTER-Kislovodsk | P- | 20 | 16.5 | 129 | MASTER-Kislovodsk | P| | 20 | 15.6 | 162 | MASTER-Kislovodsk | P- | 30 | 16.6 | 162 | MASTER-Kislovodsk | P| | 30 | 15.9 | The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42068. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40137] Fermi/SVOM GRB 251002A : MASTER OT earlier detection in 2 polarization filters
by GCN Circulars 03 Oct '25

03 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42067 SUBJECT: Fermi/SVOM GRB 251002A : MASTER OT earlier detection in 2 polarization filters DATE: 25/10/03 01:27:07 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Senik, V. Lipunov, E.Gorbovskoy, A.Kuznetsov, I.Panchenko, P.Balanutsa, N.Tiurina, A.Sankovich, G.Antipov, Yu. Tselik, A. Sosnovskiy, M.Shilova, A.Chasovnikov, V.Topolev, K.Zhirkov, Ya.Kechin, V.Senik, D.Vlasenko(Lomonosov MSU, SAI, Moscow), R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina); D.Buckley, (SAAO, South Africa) O.Gress, N.Budnev (ISU, Irkutsk), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) The MASTER-Kislovodsk robotic telescope of the MASTER Global Robotic Net [1], [2] started Fermi GRB 251002A (trigger 781128896, Ttrigger=2025-10-02 20:14:51UT) at 2025-10-02 20:19:42 (Lipunov et al. GCN 42059, cover map and OT https://master.sai.msu.ru/site/master2/event.php?id=3005541&action=12&SAT=S… ) in two mutually perpendicular polarization filters. There is MASTER OT J005537.81-053401.0 since the first image with unfiltered m_OT~17.2 at 2025-10-02 20:22:09.308(not first time) with preliminary detected polarization. This OT was first publishied (discovered) by SVOM (GCN 42061), and also by LCO (Turpin et al. GCN 42062), FREM-ORM (Jelinek et al. GCN 42063), SAO RAS (Moskvitin et al. GCN 42065) and BOOTES (Perez-Garcia et al. GCN 42066) Observations and reduction will be continued. [1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L [2] 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#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/42067. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40136] GRB 251002A: BOOTES-6 early optical detection
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42066 SUBJECT: GRB 251002A: BOOTES-6 early optical detection DATE: 25/10/02 23:27:43 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), P. J. Meintjes and H. J. van Heerden (UFS, South Africa), A. Martin-Carrillo and L. Hanlon (UCD, Ireland), M. Gritsevich (Univ. of Helsinki) and C. J. Perez del Pulgar (UMA, Malaga), on behalf of a larger collaboration, report: Following the detection of GRB 251002A by SVOM (Saccardi et al., GCN 42060), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) responded to this high-energy event starting on Oct 2, 20:17:55 UT (i.e., 186 sec after detection). Series of images in clear filter were gathered and we detect an optical source consistent with the one reported by Palmerio et al. (GCN 42061), Turpin et al. (GCN 42062), Jelinek et al. (GCN 42063), Juliá-Maroto et al. (GCN 42064) and Moskvitin et al. (GCN 42065). Using GaiaDR3 Gmag as reference we report our photometry analysis: | UT mid exposure | mag | error | filter | exposure time (sec) | | ------------------- | ----- | ----- | ------ | ------------------- | | 2025-10-02 20:18:25 | 15.47 | 0.03 | clear | 60 | | 2025-10-02 20:19:53 | 15.79 | 0.03 | clear | 60 | | 2025-10-02 20:21:21 | 16.16 | 0.05 | clear | 60 | Further analysis of the additional images is ongoing. We thank the staff at Boyden Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/42066. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40135] GRB 251002A: SAO RAS optical observations
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42065 SUBJECT: GRB 251002A: SAO RAS optical observations DATE: 25/10/02 23:10:11 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin (SAO RAS), V. P. Goranskij (SAI MSU), V. V. Vlasyuk, V. S. Shergin, V. A. Egorov, M. A. Pritychenko, I. V. Afanasieva (SAO RAS), report on behalf of GRB follow-up collaboration. We observed the field of the GRB 251002A (Saccardi et al., GCN 42060) with the 1-m SAO RAS telescope Zeiss-1000 equipped with the new CCD-photometer. The observations started at 20:31:30 UT, ~17 minutes after the trigger. The optical transient (Palmerio et al., GCN 42061; Turpin et al., GCN 42062; Jelinek et al., GCN 42063; Juliá-Maroto et al., GCN 42064) is clearly detected in the individual images with the brightness of R = 17.58 +/- 0.02 (t_mid - T0 = 0.41694 hours). Preliminary photometry is based on the nearby SDSS objects (magnitudes converted with Lupton 2005 equations) and has not corrected for the Galactic extinction. The observations with the 1-m telescope in BVRI filters and also with the 0.5-m telescope AS-500/2 are ongoing. We are grateful to the SAO RAS staff for their technical support. View this GCN Circular online at https://gcn.nasa.gov/circulars/42065. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40134] GRB 251002A: ULL-ASTRO-MASTER early detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42064 SUBJECT: GRB 251002A: ULL-ASTRO-MASTER early detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory DATE: 25/10/02 22:16:27 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> L. Juliá-Maroto, J. Basurto Merino, P.G. Berdayes, A. Caballero-Almagro, A. Cerón, M. Contreras, F. Díaz-Segado, T. Ferrer-Laviña, B. Gandolfi, V. Ghiraldo, J. Hernández Fung, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, A. Schenone-Zanuzzi, A. Selezneva, T. Tundidor Rodríguez, E. Urquijo-Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL). We report on a Las Cumbres Observatory (LCO) 40-cm telescope early observation of the Gamma-Ray Burst GRB 251002A, detected by SVOM/ECLAIRs(Saccardi et al., GCN circ. 42060). We observed the field of GRB 251002A with the LCO 40-cm telescope (a Planewave Delta Rho 350 telescope equipped with a CMOS QHY600 camera) located at the LCO node at Sutherland Observatory (South Africa). The observation, a single exposure of 300 sec in the SDSS g filter, started on 2025-10-02 at 20:39:46 UT, about 24.9 minutes after the SVOM trigger. The optical counterpart detected by SVOM/VT (Palmerio et al., GCN circ. 42061), LCO 1-m (Turpin et al., GCN circ. 42062), and FRAM-ORM (Jelinek et al., GCN circ. 42063) is clearly detected in our image with a magnitude of g = 18.13 +/- 0.09, calibrated against PanSTARRS-1 DR2 and not corrected for galactic extinction. Based on observations made with the Las Cumbres Observatory’s education network telescopes that were upgraded through generous support from the Gordon and Betty Moore Foundation (program IAC2025B-010). These observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (La Laguna, Tenerife, Canary Islands, Spain). View this GCN Circular online at https://gcn.nasa.gov/circulars/42064. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40133] GRB 251002A: FRAM-ORM afterglow detection
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42063 SUBJECT: GRB 251002A: FRAM-ORM afterglow detection DATE: 25/10/02 21:58:23 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek(a)asu.cas.cz> Martin Jelinek and Jan Strobl (ASU CAS Ondrejov, CZ), Sergey Karpov, Martin Masek, Petr Janecek, Jakub Jurysek, Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza (Institute of Physics, Prague, CZ) report: The 25cm robotic telescope FRAM-ORM at La Palma (Spain) reacted to the alert of GRB251002A (Saccardi et al. GCN 42060), obtaining a series of unfiltered images starting at 20:25:24 UT, i.e. ~10.5min post trigger. We clearly detect the optical transient reported by Palmerio et al. (GCN 42061) and Turpin et al. (GCN 42062). At the combination of 9 x 60 s images (Tmid=T0+23.5min) we measure the optical afterglow with the brightness r = 17.8 +/- 0.2 (AB) as calibrated against Atlas-REFCAT (Tonry et al. 2018, ApJ, 867, 105). View this GCN Circular online at https://gcn.nasa.gov/circulars/42063. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40132] GRB 251002A: LCO optical observation
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42062 SUBJECT: GRB 251002A: LCO optical observation DATE: 25/10/02 21:05:15 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), D. Gotz (CEA/Irfu), B. Cordier (CEA/Irfu), L. P. Xin (NAOC), C. Wu (NAOC), report on behalf of the SVOM mission team: We observed the field of GRB 251002A (Saccardi et al. GCN 42060) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started at 2025-10-02T20:34:02.740 about 19 min after the SVOM/ECLAIRs T0 time. We obtained 3x200 s exposures in the SDSS r filter. The optical counterpart reported by Palmerio et al. (GCN 42061) is clearly detected in our first image subtracted to the Pan-STARRS DR2 catalog image. We measure the following magnitude: r = 17.55 +/- 0.03 (AB), at a mid-time of 20.8 min after the trigger. Further observations are planned. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/42062. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40131] GRB 251002A: SVOM/VT optical observation
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42061 SUBJECT: GRB 251002A: SVOM/VT optical observation DATE: 25/10/02 20:58:44 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> J. T. Palmerio (CEA/Irfu), H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu report on behalf of the SVOM/VT team: After the trigger by SVOM/ECLAIRs at 2025-10-02T20:14:54 UTC (T0), SVOM performed an automatic slew on the burst location (Saccardi et al., GCN 42060). SVOM/VT began observing the field at 2025-10-02T20:19:44, 289.75 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below. VT_ID 36: This candidate was flagged as un uncatalogued source. The position of this candidate is R.A., Dec. 13.9082, -5.5671 degrees, corresponding to: R.A. (J2000) = 0h55m38.0s Dec. (J2000) = -5d34m01.5s with an uncertainty of 1 arcsec. This location is within the R90 uncertainty region of the SVOM/MXT onboard localization. The source was detected in both VT_R and VT_B. The candidate's magnitudes are: | date-obs (UTC) | mid-time | exposure | band | mag(AB) | | -------------------- | ----------- | --------- | ----- | ------------- | | 2025-10-02T20:19:44 | 6.50 min | 4*50 sec | VT_B | 16.81 ± 0.01 | | 2025-10-02T20:19:44 | 6.50 min | 4*50 sec | VT_R | 16.24 ± 0.01 | Magnitudes were not corrected for dust extinction. Given the VT color of the counterpart, it might be a low redshift gamma-ray burst. 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. SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. The SVOM/VT point of contact for this burst is Jesse Palmerio: jesse.palmerio(a)cea.fr. View this GCN Circular online at https://gcn.nasa.gov/circulars/42061. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40130] GRB 251002A: SVOM detection of a burst
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42060 SUBJECT: GRB 251002A: SVOM detection of a burst DATE: 25/10/02 20:43:05 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), D. Gotz (CEA/Irfu), S. Schanne (CEA/Irfu), M. G. Bernardini (INAF & LUPM), N. Dagoneau (CEA/Irfu), P. Maggi (ObAS), report on behalf of the SVOM mission team: At 2025-10-02T20:14:54 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251002A (SVOM burst-id sb25100211). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 15 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 22.39 in the [8-120] keV energy band over a time window of 10.20 seconds starting at 2025-10-02T20:14:49. The SVOM/ECLAIRs light curve showed a multiple peak structure with a T90 duration of 11.7 (+2.6/-1.5) s. The localization of the best alert is R.A., Dec. 13.9059, -5.5440 degrees (J2000) with a 90% confidence level (C.L.) radius of 3.98 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM at 2025-10-02T20:14:52 with an SNR of 10.40. SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-10-02T20:17:42 UTC, 168 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 13.9179, -5.5679 degrees: R.A. (J2000) = 0h55m40s Dec. (J2000) = -5d34m04s with a 90% C.L. radius of 81 arcseconds. This location is 1.60 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Andrea Saccardi: andrea.saccardi(a)cea.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42060. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40129] Fermi trigger No 781128896: Global MASTER-Net observations report
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42059 SUBJECT: Fermi trigger No 781128896: Global MASTER-Net observations report DATE: 25/10/02 20:30:48 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB251002.84 (trigger No 781128896,01h 12m 38.40s , -05d 24m 00.0s, R=5.51) errorbox 259 sec after notice time and 291 sec after trigger time at 2025-10-02 20:19:42 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 50 deg. The sun altitude is -49.8 deg. The galactic latitude b = -67 deg., longitude l = 138 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3005496 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 322 | 2025-10-02 20:19:42 | MASTER-Kislovodsk | (00h 53m 34.79s , -05d 12m 04.9s) | P- | 60 | 17.4 | 402 | 2025-10-02 20:19:42 | MASTER-Kislovodsk | (00h 53m 34.79s , -05d 12m 04.8s) | P- | 220 | 18.4 | Coadd 322 | 2025-10-02 20:19:42 | MASTER-Kislovodsk | (00h 53m 50.27s , -05d 35m 28.4s) | P| | 60 | 18.0 | 395 | 2025-10-02 20:20:50 | MASTER-Kislovodsk | (00h 53m 34.79s , -05d 12m 08.8s) | P- | 70 | 18.1 | 395 | 2025-10-02 20:20:50 | MASTER-Kislovodsk | (00h 53m 50.31s , -05d 35m 30.7s) | P| | 70 | 18.0 | 483 | 2025-10-02 20:22:09 | MASTER-Kislovodsk | (00h 53m 34.83s , -05d 12m 10.6s) | P- | 90 | 18.1 | 483 | 2025-10-02 20:22:09 | MASTER-Kislovodsk | (00h 53m 50.43s , -05d 35m 32.0s) | P| | 90 | 18.1 | 592 | 2025-10-02 20:23:47 | MASTER-Kislovodsk | (00h 53m 34.96s , -05d 12m 12.3s) | P- | 110 | 18.4 | 592 | 2025-10-02 20:23:47 | MASTER-Kislovodsk | (00h 53m 50.58s , -05d 35m 34.4s) | P| | 110 | 18.1 | The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42059. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40128] GRB 251001B: Swift-BAT refined analysis
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42058 SUBJECT: GRB 251001B: Swift-BAT refined analysis DATE: 25/10/02 20:10:01 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> H. A. Krimm (NSF), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), R. Gupta (GSFC), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 251001B (trigger #1400467) (Beardmore, et al., GCN Circ. 42039). The BAT ground-calculated position is RA, Dec = 42.668, -22.990 deg which is RA(J2000) = 02h 50m 40.2s Dec(J2000) = -22d 59' 23.9" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 91%. The mask-weighted light curve shows a single FRED pulse from ~T0-5 s to ~T0+20 s. Statistically significant emission is found to occur out to ~T0+90 s. The T90 (15-350 keV) is 75.33 +- 46.90 sec (estimated error including systematics). The time-averaged spectrum from T-9.98 to T+91.72 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.49 +- 0.14. The fluence in the 15-150 keV band is 1.1 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+2.29 sec in the 15-150 keV band is 0.8 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1400467 View this GCN Circular online at https://gcn.nasa.gov/circulars/42058. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40127] GRB 251001A: SVOM/GRM observation
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42057 SUBJECT: GRB 251001A: SVOM/GRM observation DATE: 25/10/02 14:35:15 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang. Wen-Jun Tan, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Piron (LUPM), Olivier GODET (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 251001A (SVOM trigger reference: sb25100101) at 2025-10-01T02:40:58.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#42034) and Insight-HXMT (Wang et al., GCN#42056). 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 7.2 +1.8/-0.4 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251001A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 224.4, DEC= -56.2, GCN#42034), is located at about 101 degrees from the SVOM optical axis, which is outside the field of view of ECLAIRs. Nevertheless, ECLAIRs detected the GRB through the shield above 50 keV. With this localization, the time-averaged spectrum from T0-2 to T0+7 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.73 +0.41/-0.32 and the cutoff energy, parameterized as Epeak, is 51 +/-7 keV. The event fluence (10-1000 keV) in this time interval is (7.92 +0.94/-0.92)E-06 erg/cm^2. The localization of GRB 251001A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251001A_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/42057. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40126] GRB 251001A: Insight-HXMT detection
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42056 SUBJECT: GRB 251001A: Insight-HXMT detection DATE: 25/10/02 14:27:57 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Zheng-Hang Yu, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-10-01T02:40:57.600 (T0), Insight-HXMT/HE was trigger by the burst GRB 251001A, which is also detected by Fermi/GBM (Fermi GBM Team, GCN#42034). The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 8.2 +/-1.6 s. The 1s peak rate, measured from T0+5.300 s, is 759 cnts/sec. The total counts from this burst is 2439 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb251001A.png All measurements above are made with the CsI detectors operating in the regular 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://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/42056. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40125] GRB 251001B: Swift/UVOT Detection
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42055 SUBJECT: GRB 251001B: Swift/UVOT Detection DATE: 25/10/02 12:12:59 GMT FROM: Alice Breeveld at MSSL-UCL <a.breeveld(a)ucl.ac.uk> A.A. Breeveld (UCL-MSSL), S.P.R. Shilling (Lancaster U.) and A.P. Beardmore (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251001B 119 s after the BAT trigger (Beardmore et al., GCN Circ. 42039). A source consistent with the enhanced XRT position (Beardmore et al., GCN Circ. 42045) and also with the optical counterpart seen by Gompertz et al. (GCN Circ. 42040), An et al. (GCN Circ. 2041), Strausbaugh and Cucchiara (GCN Circ. 42043) and de Ugarte Postigo et al. (GCN Circ. 42050) is detected in the initial UVOT exposures. Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposures and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 119 269 147 18.76 +/- 0.06 u_FC 331 581 246 18.86 +/- 0.15 white 611 630 10 19.0 +/- 0.25 white 861 1010 147 19.6 +/- 0.2 b 587 779 39 > 19.0 v 661 681 20 > 17.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.023 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42055. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40124] GRB 251001B: COLIBRÍ optical observations
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42054 SUBJECT: GRB 251001B: COLIBRÍ optical observations DATE: 25/10/02 10:03:11 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Camila Angulo (UNAM), Rosa L. Becerra (U Roma), Antonio de Ugarte Postigo (LAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU) , Damien Dornic (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), and Fredd Sánchez Álvarez (UNAM): We imaged the field of the GRB 251001B (Fermi GBM team, GCN Circ. 42038; Beardmore et al. GCN Circ. 42039) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-02T06:13:31 to 08:49:34 UTC (from 15.94 to 18.54 hours after the trigger) and obtained 64 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and 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 detected the optical counterpart previously reported by Gompertz et al. GCN Circ. 42040; An et al. GCN Circ. 42041; Strausbaugh & Cucchiara GCN Circ. 42043; O'Neill et al. GCN Circ. 42046; A. de Ugarte Postigo et al., GCN Circ. 42050; Ma et al., GCN Circ. 42051 and Sanchez-Ramirez et al., GCN 42053 at preliminary magnitudes of: r = 21.56 +/- 0.06 z = 21.28 +/- 0.13 Our measured r-band magnitude is consistent with the magnitude reported by the NOT (Ugarte Postigo et al., GCN Circ. 42050), indicating a possible flattening in the optical afterglow. Further observations and analysis are ongoing in g, r, i, z and y filters. 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/42054. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40123] GRB 251001B: GTC/OSIRIS+ spectroscopic redshift z = 2.162
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42053 SUBJECT: GRB 251001B: GTC/OSIRIS+ spectroscopic redshift z = 2.162 DATE: 25/10/02 09:33:41 GMT FROM: Ruben Sanchez-Ramirez at IAA-CSIC <ruben(a)iaa.es> R. Sanchez-Ramirez (IAA-CSIC), Y.-D. Hu (GXI), A. J. Castro-Tirado, S. Guziy, M.D. Caballero-Garcia, S.-Y. Wu and I. Perez-Garcia (IAA-CSIC), R. Scarpa (GTC, IAC), D. Gonzalez (GTC), A. Cabrera-Lavers (GTC, IAC), S. B. Pandey (ARIES), M. Gritsevich (Univ. of Helsinki), J. Becerra-Gonzalez (IAC), L. Piro (INAF/IAPS) and B.-B. Zhang (NJU), on behalf of a larger collaboration, report: Following the detection of GRB 251001B by Fermi (Fermi Team, GCN 42038, Neights et al. GCN 42047) and Swift (Beardmore et al. GCN 42039), we observed the optical afterglow (Gompertz et al. GCN 42040, An et al. GCN 42041, Strausbaugh et al. GCN 42043, O'Neill et al. GCN 42046, de Ugarte Postigo et al., GCN 42050, Ma et al., GCN 42051) with the 10.4m GTC telescope, at the Spanish Roque de los Muchachos Observatory, on the island of La Palma, equipped with the OSIRIS+ instrument. The spectroscopic observations were performed at high airmass and consisted of 3x900s exposures using grism R1000B, with a spectral coverage between 3,600 and 7,700 A (R~600). The observations started on Oct 2, 02:39 UT (i.e. 12.35 h after the burst trigger). From a preliminary reduction, we find a strong DLA at ~4000A, as well as several metal absorption lines that we interpret as coming from NV, SiII, SiII*, OI, CII, SiIV, CIV, FeII, FeII*, AlII, AlIII, ZnII, CrII, all at z=2.162. The detection of SiII* and FeII* links this system to the GRB. We also note the presence of Lya in emission at the same redshift. View this GCN Circular online at https://gcn.nasa.gov/circulars/42053. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40122] GRB 251001B: Swift-XRT refined Analysis
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42052 SUBJECT: GRB 251001B: Swift-XRT refined Analysis DATE: 25/10/02 07:52:16 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 7.8 ks of XRT data for GRB 251001B, from 99 s to 40.1 ks after the trigger. The data comprise 540 s in Windowed Timing (WT) mode (the first 10 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=1.34 (+/-0.06). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.92 (+0.08, -0.07). The best-fitting absorption column is 8.8 (+2.0, -1.9) x 10^20 cm^-2, in excess of the Galactic value of 2.6 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.74 (+0.19, -0.18) and a best-fitting absorption column of 8.6 (+5.7, -4.8) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.9 x 10^-11 (4.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 8.6 (+5.7, -4.8) x 10^20 cm^-2 Galactic foreground: 2.6 x 10^20 cm^-2 Excess significance: 2.1 sigma Photon index: 1.74 (+0.19, -0.18) If the light curve continues to decay with a power-law decay index of 1.34, the count rate at T+24 hours will be 9.6 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.8 x 10^-14 (4.3 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01400467. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42052. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40121] GRB 251001B: SVOM/VT optical observation
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42051 SUBJECT: GRB 251001B: SVOM/VT optical observation DATE: 25/10/02 07:32:26 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, L. P. Xin, Z. H. Yao, Y. L. Qiu, C. Wu, H. L. Li, 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) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of GRB 251001B detected by Fermi/GBM and Swift/BAT (Fermi GBM team, GCN 42038; Beardmore et al., GCN 42039; Beardmore et al., GCN 42045; Neights & Meegan, GCN 42047). SVOM/VT began observing the field at 2025-10-01T15:03:04 UTC, 0.762 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Gompertz et al., GCN 42040; An et al., GCN 42041; Strausbaugh & Cucchiara, GCN 42043; O'Neill et al., GCN 42046; Lipunov et al., GCN 42048; de Ugarte Postigo et al., GCN 42050) was clearly detected in both VT_B and VT_R bands. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 3.790 | 38*70 | VT_B | 22.06 | 0.09 3.819 | 35*70 | VT_R | 21.31 | 0.07 Our photometry was 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 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/42051. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40120] GRB 251001B: NOT optical observations
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42050 SUBJECT: GRB 251001B: NOT optical observations DATE: 25/10/02 07:25:01 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> A. de Ugarte Postigo (LAM), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), B. Schneider (LAM), B. P. Gompertz (Birmingham), A. Martin-Carrillo (UCD) and J. Maiz Apellaniz (IAA-CSIC) report: We observed the field of GRB 251001B (Fermi GBM team, GCN 42038; Beardmore et al. GCN 42039) using the 2.5 m Nordic Optical Telescope (NOT) equipped with ALFOSC. Observations started on 2 October 2025 at 02:37:23 UT (12.33 hr after the trigger) and consisted of 3x300 s and 5x200 s in the SDSS r and z bands, respectively. The combined images reveal the presence of the afterglow identified by Gompertz et al. (GCN 42040; An et al. GCN 42041; Strausbaugh & Cucchiara GCN 42043; O'Neill et al. GCN 42046) at a magnitude of r = 21.54 +/- 0.06 (AB) calibrated against field stars of the Pan-STARRS catalogue and not corrected by Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42050. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40119] GRB 251001C: Glowbug gamma-ray detection
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42049 SUBJECT: GRB 251001C: Glowbug gamma-ray detection DATE: 25/10/02 01:49:29 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 251001C, which was also detected by CALET (Trigger 1443366004). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-01 15:07:24.688 with a duration of 11.0 s and a total significance of about 27.2 sigma. The light curve comprises a bright peak at ~T0+1s followed a faint peak at ~T0+7s. The best-fit localization is RA, Decl. (J2000, deg) = 82.7, 21.9 with a radius of 10.0 deg (95% confidence), with a highly uncertain systematic uncertainty. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was recently removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/42049. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40118] Swift GRB 251001B: Global MASTER-Net observations report
by GCN Circulars 02 Oct '25

02 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42048 SUBJECT: Swift GRB 251001B: Global MASTER-Net observations report DATE: 25/10/02 00:16:59 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB 251001B ( A. P. Beardmore et al., GCN 42039) errorbox 34585 sec after notice time and 35427 sec after trigger time at 2025-10-02 00:07:47 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 67 deg. The sun altitude is -32.7 deg. The galactic latitude b = -62 deg., longitude l = 211 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3004463 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 35517 | MASTER-Kislovodsk | C | 180 | 18.4 | 35517 | MASTER-Kislovodsk | C | 180 | 18.2 | 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/42048. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40117] GRB 251001B: Fermi GBM Observation
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42047 SUBJECT: GRB 251001B: Fermi GBM Observation DATE: 25/10/01 21:33:18 GMT FROM: eliza.neights(a)gmail.com Eliza Neights (GWU, NASA GSFC) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 14:17:19.05 UT on 01 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251001B (trigger 781021044/251001595) which was also detected by Swift BAT (A. P. Beardmore et al. 2025, GCN 42039). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 53 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 19 s (50-300 keV). The time-averaged spectrum from T0-3.7 to T0+16.7 s is best fit by a Comptonized function with index 0.22 +/- 0.03 and peak energy 107 +/- 5 keV. The event fluence (10-1000 keV) in this time interval is (1.3 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.7 s in the 10-1000 keV band is 1.4 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/42047. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40116] GRB 251001B: Further GOTO observations of optical counterpart.
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42046 SUBJECT: GRB 251001B: Further GOTO observations of optical counterpart. DATE: 25/10/01 20:34:36 GMT FROM: d.s.oneill(a)bham.ac.uk D. O'Neill, B. P. Gompertz, G. Ramsay, R. Starling, M. Kennedy, B. Godson, J. Lyman, K. Ackley, M. J. Dyer, K. Ulaczyk, A. Kumar,, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on new observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 251001B (Fermi GBM team, GCN 42038; Beardmore et al. GCN 42039). Following the detection of the optical counterpart of GRB 251001B (Gompertz et al. GCN 42040, An et al. GCN 42041, Strausbaugh & Cucchiara, GCN 42043) we detect the counterpart again in an additional epoch of GOTO L-band (400-700 nm) imaging taken at 2025-10-01 15:44:25 UT (1.45h post-trigger) consisting of 4x90s exposures. We find the counterpart has faded to L=20.6±0.3 AB mag, consistent with a power law decay with index: alpha = -0.75. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/42046. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40115] GRB 251001B: Enhanced Swift-XRT position
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42045 SUBJECT: GRB 251001B: Enhanced Swift-XRT position DATE: 25/10/01 18:10:10 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 700 s of XRT Photon Counting mode data and 2 UVOT images for GRB 251001B, 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 = 42.65089, -23.02048 which is equivalent to: RA (J2000): 02h 50m 36.21s Dec (J2000): -23d 01' 13.7" with an uncertainty of 2.1 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/42045. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40114] GRB 250930A: Fermi GBM Final Localization
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42044 SUBJECT: GRB 250930A: Fermi GBM Final Localization DATE: 25/10/01 17:22:07 GMT FROM: Eva MP <eva.palafox(a)gmail.com> The Fermi GBM team reports the detection of a likely LONG GRB "At 20:59:58.57 UT on 30 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250930A (trigger 780958803/250930875). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 336.97, Dec = -44.97 (J2000 degrees, equivalent to J2000 22h 27m, -44d 58'), with a statistical uncertainty of 3.27 degrees. The angle from the Fermi LAT boresight is 109 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250930875/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250930875/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250930875/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/42044. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40113] GRB 251001B: LCOGT Optical Observations
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42043 SUBJECT: GRB 251001B: LCOGT Optical Observations DATE: 25/10/01 15:44:16 GMT FROM: Robert Strausbaugh at Eastern Illinois University <rstrausbaugh(a)eiu.edu> R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the Swift GRB 251001B field (Beardmore et al., GCN 42039) with the LCOGT 1-meter Sinistro instrument at the Siding Spring Observatory, Australia site, on October 1, from 14:51 to 15:23 UT (corresponding to 0.57 to 1.10 hours after the GRB trigger time) with the SDSS i and r filters. We performed a series of 3x300s exposures in i-band and r-band. We detect an uncatalogued source consistent with other optical counterpart observations (Gompertz et al., GCN 42040; An et al., GCN 42041) in both bands. We note that our r-band measurement implies a rapidly fading source. The following magnitudes are calculated using the PanSTARRS catalog as reference: r = 20.26 +/- 0.04 i = 19.81 +/- 0.03 These magnitudes are not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42043. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40112] GRB 250930A: SVOM/GRM observation
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42042 SUBJECT: GRB 250930A: SVOM/GRM observation DATE: 25/10/01 15:31:52 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang. Wen-Jun Tan, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Daigne (IAP), Frédéric Piron (LUPM), Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 250930A (SVOM trigger reference: sb25093008) at 2025-09-30T21:00:23.000 UTC (T0), which is also detected by Fermi/GBM (TrigNum#780960200). 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 49 +8/-6 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250930A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 341.57, DEC= -47.95, TrigNum#780958803), is located at about 58 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, but this burst is still marginally detected by ECLAIRs above 50 keV. With this localization, the time-averaged spectrum from T0-37 to T0+24 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.13 +/-0.14 and the cutoff energy, parameterized as Epeak, is 107 +17/-12 keV. The event fluence (10-1000 keV) in this time interval is (8.58 +0.69/-0.57)E-06 erg/cm^2. The localization of GRB 250930A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb250930A_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/42042. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40111] GRB 251001B: TRT optical afterglow detection and potential host galaxy
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42041 SUBJECT: GRB 251001B: TRT optical afterglow detection and potential host galaxy DATE: 25/10/01 15:17:04 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> J. An, X. Liu (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Q. Jiang, L.B. He, Z.P. Zhu, D. Xu (NAOC), S.Y. Fu (HUST) report on behalf of a large collaboration: We observed the field of GRB 251001B detected by Swift/BAT (Beardmore et al., GCN 42039), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). A series of images were obtained in the R band. A varying optical transient (OT) is detected within the Swift/XRT error circle at coordinates R.A. (J2000) = 2:50:36.33 Dec.(J2000) = -23:01:11.96 with an uncertainty of ~ 0.6 arcsec. It has R ~ 18.9 mag at 21.1 min after the Swift/BAT trigger. We thus think the OT is the optical afterglow of the burst. We also note that there is a galaxy at the OT position from Legacy Survey DR10 with g ~ 25.16, r ~ 24.93, i ~25.06, z ~24.79, and a phot_z ~ 1.14 +/- 0.53, which is presumably the host galaxy of the burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/42041. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40110] GRB 251001B: GOTO optical counterpart detection
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42040 SUBJECT: GRB 251001B: GOTO optical counterpart detection DATE: 25/10/01 15:09:24 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> B. P. Gompertz, D. O'Neill, R. Starling, M. Kennedy, B. Godson, J. Lyman, K. Ackley, M. J. Dyer, K. Ulaczyk, A. Kumar, G. Ramsay, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 251001B (Fermi GBM team, GCN 42038; Beardmore et al. GCN 42039). Targeted observations were performed at 2025-10-01 14:33:37 (starting 16.3 minutes after trigger). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. At a position consistent with the Swift/XRT localisation, we detect a new optical source, GOTO25icy, with L = 19.33 ± 0.12 AB mag, at coordinates: RA,DEC (J2000) = 42.651328, -23.02001 | 02:50:36.32, -23:01:12.03 We find no evidence of this source prior to the GRB trigger time in the previous GOTO observation taken at 2025-10-01 14:01:01 UT (16.3 min pre-trigger) down to a 3-sigma depth of L > 20.1 AB mag. We note the source is coincident (~0.4”) with a faint g~25 AB mag source in Legacy Survey DR10, which may be the host galaxy of the GRB. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Observations are ongoing. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/42040. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40109] GRB 251001B: Swift detection of a burst
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42039 SUBJECT: GRB 251001B: Swift detection of a burst DATE: 25/10/01 14:44:42 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> A. P. Beardmore (U Leicester), J. A. Kennea (PSU), M. J. Moss (GSFC) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 14:17:20 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251001B (trigger=1400467). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 42.665, -23.020 which is RA(J2000) = 02h 50m 40s Dec(J2000) = -23d 01' 09" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of about 25 sec. The peak count rate was ~2,000 counts/sec (15-350 keV), at ~4 sec after the trigger. The XRT began observing the field at 14:19:17.0 UT, 116.5 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 42.65098, -23.02014 which is equivalent to: RA(J2000) = 02h 50m 36.24s Dec(J2000) = -23d 01' 12.5" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 46 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 consistent with the Galactic value of 2.65 x 10^20 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of nominal 150.000 seconds with the White filter starting 860 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. Data from the 2.7'x2.7' sub-image are not available at this time. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.023. Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). 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/42039. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40108] GRB 251001B: Fermi GBM Final Real-time Localization
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42038 SUBJECT: GRB 251001B: Fermi GBM Final Real-time Localization DATE: 25/10/01 14:28:02 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 14:17:19 UT on 1 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251001B (trigger 781021044.051374 / 251001595). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 52.0, Dec = -11.2 (J2000 degrees, equivalent to J2000 03h 28m, -11d 11'), with a statistical uncertainty of 5.6 degrees. The angle from the Fermi LAT boresight is 67.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251001595/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251001595/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251001595/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42038. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40107] GRB 251001A: Fermi GBM Detection
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42037 SUBJECT: GRB 251001A: Fermi GBM Detection DATE: 25/10/01 14:15:23 GMT FROM: Marianna Dafčíková at Masaryk University <500025(a)mail.muni.cz> M. Dafcikova (MUNI), S. Lesage (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 02:40:56.95 UT on 01 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251001A (trigger 780979261/251001112). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 224.44, Dec = -56.23 (J2000 degrees, equivalent to J2000 14h 57m, -56d 13'), with a statistical uncertainty of 1.79 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 116 degrees. The GBM light curve consists of two peaks with a duration (T90) of about 7 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+8.640 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.63 +/- 0.08 and the cutoff energy, parameterized as Epeak, is 138 +/- 7 keV. The event fluence (10-1000 keV) in this time interval is (4.4 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+6.0 s in the 10-1000 keV band is 24.8 +/- 0.6 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/42037. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40106] GRB 250910A / EP250910a: VLT limits on the possible associated supernova
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42036 SUBJECT: GRB 250910A / EP250910a: VLT limits on the possible associated supernova DATE: 25/10/01 12:16:53 GMT FROM: Ben Rayson at University of Leicester <br155(a)leicester.ac.uk> N. Habeeb (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), B. Rayson (U. Leicester), N. R. Tanvir (U. Leicester), report on behalf of the Stargate collaboration: We obtained late-time imaging of the GRB 250910A / EP250910a field (Schneider et al., GCN 41794; Li et al., GCN 41798; see also Ma et al., GCN 41769; Liu et al., GCN 41776; Hubert et al., GCN 41842) at z = 0.592 (Saccardi et al., GCN 42031) with the ESO VLT equipped with FORS2. Observations were carried out on 2025 Oct 1.16 UT, i.e. ~21 days after the trigger, in the z and R bands. At the position of the reported afterglow/NIR counterpart we detect a source in both filters. From photometry we measure z = 23.19 ± 0.11 (AB) and r = 23.97 ± 0.10 (AB) calibrated against nearby SkyMapper stars and not corrected for Galactic extinction (which is small, A_V = 0.05 mag). We note that a source is clearly visible at this location in the Legacy Survey images with magnitudes of z = 23.10 ± 0.20 and r = 23.73 ± 0.10 (both in AB). Within the present uncertainties and allowing for filter differences, the fluxes are consistent with the pre-existing host-galaxy brightness. Using SN1998bw as the canonical GRB-SN template, the expected associated SN would have a magnitude of z ~ 22.8 at this epoch, implying a total host+SN flux of z ~ 22.2, which is not observed in this case. We therefore find no evidence for an optically bright SN associated with GRB 250910A / EP250910a at ~21 days post-burst (~13 days in the rest frame). The lack of an additional component on top of the host galaxy suggests that the expected SN emission would need to have approximately z < 24.1, corresponding to a SN ~3x fainter than SN1998bw. Without additional epochs for accurate template subtraction, at this moment, we cannot confirm if GRB 250910A / EP250910a truly lacks an associated SN component or if it simply suffers from some extinction. We acknowledge excellent support from the ESO staff in Paranal, in particular Abel de Burgo Sierra and Cecilia Bustos. View this GCN Circular online at https://gcn.nasa.gov/circulars/42036. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40105] GRB 251001A: BALROG localization (Fermi Trigger 780979261 / GRB 251001112)
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42035 SUBJECT: GRB 251001A: BALROG localization (Fermi Trigger 780979261 / GRB 251001112) DATE: 25/10/01 04:34:51 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 780979261 at 02:40:56 on 01 Oct. 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) = 227.4 deg Decl.(2000.0) = -57.5 deg The 1 sigma statistical error radius is 2.5 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB251001112/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB251001112/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB251001112/json View this GCN Circular online at https://gcn.nasa.gov/circulars/42035. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40104] GRB 251001A: Fermi GBM Final Real-time Localization
by GCN Circulars 01 Oct '25

01 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42034 SUBJECT: GRB 251001A: Fermi GBM Final Real-time Localization DATE: 25/10/01 02:51:32 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 02:40:56 UT on 1 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251001A (trigger 780979261.951484 / 251001112). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 224.4, Dec = -56.2 (J2000 degrees, equivalent to J2000 14h 57m, -56d 12'), with a statistical uncertainty of 1.8 degrees. The angle from the Fermi LAT boresight is 116.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251001112/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251001112/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251001112/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42034. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[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…

1 0

[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…

1 0

[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…

1 0

[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…

1 0

[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…

1 0

[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…

1 0

[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…

1 0

[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…

1 0

[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…

1 0

[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…

1 0

[vsnet-grb-info 40093] LIGO/Virgo/KAGRA S250929c: Identification of a GW compact binary merger candidate
by GCN Circulars 29 Sep '25

29 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42023 SUBJECT: LIGO/Virgo/KAGRA S250929c: Identification of a GW compact binary merger candidate DATE: 25/09/29 00:53:38 GMT FROM: S. P. Stevenson at Swinburne University of Technology <simon.stevenson(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250929c during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-09-29 00:27:32.375 UTC (GPS time: 1443140870.375). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], and MBTA [5] analysis pipelines. S250929c is an event of interest because its false alarm rate, as estimated by the online analysis, is 2.5e-08 Hz, or about one in 1 year, 3 months. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250929c The classification of the GW signal, in order of descending probability, is BBH (98%), Terrestrial (2%), NSBH (<1%), or BNS (<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%. [6] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [6] 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 (22.0, 44.0) 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,1, an initial localization generated by BAYESTAR [7], distributed via GCN and SCiMMA notices about 26 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [7], 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,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 2197 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 4423 +/- 1342 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] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [7] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/42023. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40092] LIGO/Virgo/KAGRA S250927cy: Updated Sky localization
by GCN Circulars 28 Sep '25

28 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42022 SUBJECT: LIGO/Virgo/KAGRA S250927cy: Updated Sky localization DATE: 25/09/28 21:15:42 GMT FROM: John Veitch at U of Glasgow <john.veitch(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 S250927cy (GCN Circular 42016). 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/S250927cy For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 944 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 4089 +/- 1482 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/42022. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40091] LIGO/Virgo/KAGRA S250927ck: Updated Sky localization
by GCN Circulars 28 Sep '25

28 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42021 SUBJECT: LIGO/Virgo/KAGRA S250927ck: Updated Sky localization DATE: 25/09/28 21:09:53 GMT FROM: John Veitch at U of Glasgow <john.veitch(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 S250927ck (GCN Circular 42015). 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/S250927ck For the Bilby.multiorder.fits,0 sky map, the 90% credible region is well fit by an ellipse with an area of 67 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(05h14m, -49d19m, 6.23d, 3.44d, 38.55d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 3566 +/- 911 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/42021. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40090] Fermi-LAT Gamma-ray Observations of IceCube-250926A
by GCN Circulars 28 Sep '25

28 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42020 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250926A DATE: 25/09/28 17:52:33 GMT FROM: Sara Buson at DESY, Univ. of Wurzburg <sara.buson(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC250926A neutrino event (GCN 42003) 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 25-09-26 at 12:28:55.17 UTC (T0) with J2000 position RA = 131.0 (+0.56, -0.63) deg, Decl. = 9.97 (+0.55, -0.71) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC250926A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). 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 IC250926A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250926A best-fit position, the >100 MeV flux upper limit (95% confidence) is <1.8e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <4.4e-09 (<4.2e-08) 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/42020. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40089] GRB 250926A: triangulation location with Insight-HXMT/HE and Fermi/GBM
by GCN Circulars 28 Sep '25

28 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42019 SUBJECT: GRB 250926A: triangulation location with Insight-HXMT/HE and Fermi/GBM DATE: 25/09/28 11:53:08 GMT FROM: zhangjinpeng(a)ihep.ac.cn Jin-Peng Zhang, Cheng-Kui Li, Chen-Wei Wang and Shao-Lin Xiong report on behalf of the Insight-HXMT team: GRB 250926A was detected by Fermi/GBM (the Fermi GBM team, GCN 41993), Insight-HXMT (Chen-Wei Wang et al., GCN 42013) and AstroSat CZTI (A. Goyal et al., GCN 42008). A possible association with Orion Nebula was suggested according to the Fermi/GBM localization result of this burst (Rosa L. Becerra et al., GCN 42000). To evaluate this association, we triangulate GRB 250926A with Insight-HXMT/HE and Fermi/GBM event-by-event data using the Li-CCF method [1]. The resulted localization annulus with 3-sigma error (statistical only) is as follows: | Annulus Center RA (J2000, deg) | Annulus Center Dec (J2000, deg) | Annulus Radius (deg) | | ------------------------------ | ------------------------------- | -------------------- | | 356.91 | 27.35 | 113 +11/-10 | According to this result, the Orion Nebula falls well out of the 3-sigma region of the triangulation annulus of GRB 250926A, thus they are very likely unrelated. Further improvement in the localization of this GRB is possible with more data from other instruments. [1] Xiao, S. et al. ApJ 920, 43 (2021). https://doi.org/10.3847/1538-4357/ac1420 View this GCN Circular online at https://gcn.nasa.gov/circulars/42019. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40088] GRB 250924A: SVOM/GRM observation
by GCN Circulars 28 Sep '25

28 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42018 SUBJECT: GRB 250924A: SVOM/GRM observation DATE: 25/09/28 10:19:57 GMT FROM: tanwj(a)ihep.ac.cn SVOM/GRM team: Wen-Jun Tan, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered by GRB 250924A during the routine ground search at 2025-09-24T08:18:46.500 (T0), which is also detected by Swift (Swift team, GCN #41959, GCN #41973，GCN #41974 and GCN #41987) and AstroSat CZTI (M. Tembhurnikar, et al. GCN #41979) With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of two main pulses with a T90 of 20.11 +/-7.67 in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250924A.png In addition, the position of this burst, as determined by Swift/XRT (RA = 51.87237, Dec = 74.65846, GCN #41973), is located at about 96 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization given by Swift/XRT, the time-averaged spectrum from T0-20 to T0+2 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.52 +0.20/-0.46 and the cutoff energy, parameterized as Epeak, is 265 +165/-101 keV. The event fluence (10-1000 keV) in this time interval is (3.18 +0.47/-0.40)E-06 erg/cm^2. The localization of GRB 250922A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb250924A_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: Wen-Jun Tan (IHEP)(tanwj(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42018. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40087] GRB 250925A: Swift-XRT refined Analysis
by GCN Circulars 27 Sep '25

27 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42017 SUBJECT: GRB 250925A: Swift-XRT refined Analysis DATE: 25/09/27 18:53:06 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A. Melandri (INAF-OAR), S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 7.8 ks of XRT data for GRB 250925A, from 3.7 ks to 172.4 ks after the trigger. The data are entirely in Photon Counting (PC) mode. Using 4854 s of PC mode data and 10 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 341.21377, +46.55568 which is equivalent to: RA (J2000): 22h 44m 51.31s Dec(J2000): +46d 33' 20.5" with an uncertainty of 2.0 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=0.60 (+/-0.11). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.04 (+0.18, -0.17). The best-fitting absorption column is 3.1 (+0.7, -0.5) x 10^21 cm^-2, consistent with the Galactic value of 2.6 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.7 x 10^-11 (5.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.1 (+0.7, -0.5) x 10^21 cm^-2 Galactic foreground: 2.6 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 2.04 (+0.18, -0.17) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01352124. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42017. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40086] LIGO/Virgo/KAGRA S250927cy: Identification of a GW compact binary merger candidate
by GCN Circulars 27 Sep '25

27 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42016 SUBJECT: LIGO/Virgo/KAGRA S250927cy: Identification of a GW compact binary merger candidate DATE: 25/09/27 18:12:19 GMT FROM: avanivikrambhai.patel(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250927cy during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-09-27 17:30:41.678 UTC (GPS time: 1443029459.678). The candidate was found by the Aframe [1], GstLAL [2], and MBTA [3] analysis pipelines. S250927cy is an event of interest because its false alarm rate, as estimated by the online analysis, is 5.3e-08 Hz, or about one in 7 months. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250927cy The classification of the GW signal, in order of descending probability, is BBH (96%), Terrestrial (4%), NSBH (<1%), or BNS (<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%. [4] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [4] 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 (22.0, 44.0) 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,1, an initial localization generated by BAYESTAR [5], distributed via GCN and SCiMMA notices about 28 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [5], 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,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 1551 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 4064 +/- 1180 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] 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 [3] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [4] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [5] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/42016. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40085] LIGO/Virgo/KAGRA S250927ck: Identification of a GW compact binary merger candidate
by GCN Circulars 27 Sep '25

27 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42015 SUBJECT: LIGO/Virgo/KAGRA S250927ck: Identification of a GW compact binary merger candidate DATE: 25/09/27 16:38:19 GMT FROM: avanivikrambhai.patel(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250927ck during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-09-27 15:24:48.939 UTC (GPS time: 1443021906.939). The candidate was found by the Aframe [1], cWB BBH [2], and GstLAL [3] analysis pipelines. S250927ck is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.1e-08 Hz, or about one in 1 year, 3 days. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250927ck The classification of the GW signal, in order of descending probability, is BBH (98%), Terrestrial (2%), NSBH (<1%), or BNS (<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%. [4] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [4] 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: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [5], distributed via GCN and SCiMMA notices about 26 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [5], 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 177 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 4333 +/- 1544 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] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [5] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/42015. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40084] IceCube-250926A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 27 Sep '25

27 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42014 SUBJECT: IceCube-250926A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/09/27 16:01:16 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-250926A (https://gcn.nasa.gov/circulars/42003) in a time range of 1000 seconds centered on the alert event time (2025-09-26 12:20:35.170 UTC to 2025-09-26 12:37:15.170 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-250926A. 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-250926A 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 (2025-09-25 12:28:55.170 UTC to 2025-09-27 12:28:55.170 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-250926A 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/42014. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40083] GRB 250926A: Insight-HXMT detection
by GCN Circulars 27 Sep '25

27 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42013 SUBJECT: GRB 250926A: Insight-HXMT detection DATE: 25/09/27 15:01:50 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-09-26T00:21:24.600 (T0), Insight-HXMT/HE was trigger by the burst GRB 250926A, which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41993) and AstroSat (A. Goyal et al., GCN#42008). The Insight-HXMT/HE light curve mainly consists of a precursor followed by a main pulse with a T90 of 2.1 +2.3/-0.7 s. The 1s peak rate, measured from T0-0.050 s, is 3838 cnts/sec. The total counts from this burst is 4746 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb250926A.png All measurements above are made with the CsI detectors operating in the regular 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://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/42013. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40082] GRB 250926B: Fermi GBM Final Localization
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42012 SUBJECT: GRB 250926B: Fermi GBM Final Localization DATE: 25/09/26 21:05:58 GMT FROM: Matt Godwin <msg0028(a)uah.edu> The Fermi GBM team reports the detection of a likely LONG GRB "At 19:50:31.07 UT on 26 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250926B (trigger 780609036/250926827). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 291.66, Dec = -80.93 (J2000 degrees, equivalent to J2000 19h 26m, -80d 55'), with a statistical uncertainty of 7.60 degrees. The angle from the Fermi LAT boresight is 23 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250926827/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250926827/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250926827/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/42012. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40081] GRB 250926B: Fermi GBM Final Localization
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42012 SUBJECT: GRB 250926B: Fermi GBM Final Localization DATE: 25/09/26 21:05:58 GMT FROM: Matt Godwin <msg0028(a)uah.edu> The Fermi GBM team reports the detection of a likely LONG GRB "At 19:50:31.07 UT on 26 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250926B (trigger 780609036/250926827). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 291.66, Dec = -80.93 (J2000 degrees, equivalent to J2000 19h 26m, -80d 55'), with a statistical uncertainty of 7.60 degrees. The angle from the Fermi LAT boresight is 23 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250926827/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250926827/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250926827/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/42012. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40080] Fermi trigger No 780609036: Global MASTER-Net observations report
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42011 SUBJECT: Fermi trigger No 780609036: Global MASTER-Net observations report DATE: 25/09/26 20:30:38 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 GRB250926.83 (trigger No 780609036,19h 26m 38.40s , -80d 55m 48.0s, R=7.6) errorbox 112 sec after notice time and 144 sec after trigger time at 2025-09-26 19:52:55 UT, with upper limit up to 18.2 mag. The observations began at zenith distance = 54 deg. The sun altitude is -40.0 deg. The galactic latitude b = -29 deg., longitude l = 313 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3000539 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 160 | 2025-09-26 19:52:55 | MASTER-SAAO | (00h 31m 12.67s , -84d 57m 34.6s) | C | 30 | 16.7 | 205 | 2025-09-26 19:52:55 | MASTER-SAAO | (00h 31m 12.74s , -84d 57m 34.5s) | C | 120 | 17.8 | Coadd 160 | 2025-09-26 19:52:55 | MASTER-SAAO | (00h 52m 18.08s , -85d 11m 39.8s) | C | 30 | 17.1 | 205 | 2025-09-26 19:52:55 | MASTER-SAAO | (00h 52m 18.11s , -85d 11m 39.9s) | C | 120 | 18.2 | Coadd 214 | 2025-09-26 19:53:44 | MASTER-SAAO | (00h 31m 11.30s , -84d 57m 37.0s) | C | 40 | 17.0 | 214 | 2025-09-26 19:53:44 | MASTER-SAAO | (00h 52m 17.26s , -85d 11m 41.8s) | C | 40 | 17.4 | 278 | 2025-09-26 19:54:43 | MASTER-SAAO | (00h 31m 10.47s , -84d 57m 38.0s) | C | 50 | 17.4 | 278 | 2025-09-26 19:54:43 | MASTER-SAAO | (00h 52m 16.41s , -85d 11m 42.8s) | C | 50 | 17.8 | 352 | 2025-09-26 19:55:52 | MASTER-SAAO | (00h 31m 09.08s , -84d 57m 36.9s) | C | 60 | 17.1 | 352 | 2025-09-26 19:55:53 | MASTER-SAAO | (00h 52m 14.97s , -85d 11m 43.7s) | C | 60 | 17.6 | 1541 | 2025-09-26 20:15:41 | MASTER-SAAO | (19h 47m 45.38s , -84d 30m 55.3s) | C | 60 | 14.1 | 1541 | 2025-09-26 20:15:41 | MASTER-SAAO | (19h 29m 45.92s , -84d 14m 40.6s) | C | 60 | 15.1 | 1796 | 2025-09-26 20:19:57 | MASTER-SAAO | (16h 56m 37.37s , -84d 03m 27.9s) | C | 60 | 17.4 | 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/42011. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40079] GRB 250920C: PRIME near-infrared detection
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41943 SUBJECT: GRB 250920C: PRIME near-infrared detection DATE: 25/09/22 20:28:38 GMT FROM: O. Guiffreda at UMD <oriogui(a)umd.edu> O. Guiffreda (UMD), J. Durbak (UMD), A. S. Kutyrev (NASA/GSFC), N. Passaleva (U Rome), M. El Kabir (U Rome), E. Troja (U Rome), S. B. Cenko (NASA/GSFC) The following correction is primarily the result of an error in Vega to AB magnitude conversion in J and H filters. Following the Fermi GBM (GCN 41903) and Swift BAT (GCN 41904), we observed the transient field in Z, Y, J and H filters with PRIME ~7 hours after the initial Fermi and Swift detection. At the position of the optical counterpart reported by GOTO (GCN 41907), we detect an uncatalogued source in all aforementioned bands. Using nearby 2MASS and PanSTARRS stars for preliminary calibration we derive the following magnitudes and limits, not corrected for Galactic extinction: |Filter | Mag(AB) | |-------|---------------| |Z | 19.8 +/- 0.10 | |Y | 19.7 +/- 0.07 | |J | 19.8 +/- 0.10 | |H | 19.4 +/- 0.07 | PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41943. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40078] GRB 250925A: Mondy and AbAO optical observations
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42005 SUBJECT: GRB 250925A: Mondy and AbAO optical observations DATE: 25/09/26 15:27:34 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO) 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) and the AS-32 0.7m telescope of the Abastumani Observatory (AbAO). The observations started at Mondy on 2025-09-25 at 20:00 UT, i.e. 0.118 days since trigger. In total we obtained 30x120 s exposures with AZT-33IK, and 85x60 s exposures with AS-32. 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) is clearly visible in the stacked images from Mondy. Preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope (nxs) (mid, days) (3sigma) 2025-09-25 20:00:15 6x120 0.12626 R 22.3 0.2 23.1 Mondy/AZT-33IK 2025-09-25 20:12:15 6x120 0.13460 R 22.1 0.2 23.0 Mondy/AZT-33IK 2025-09-25 20:24:16 6x120 0.14294 R 22.1 0.2 23.1 Mondy/AZT-33IK 2025-09-25 20:36:16 6x120 0.15128 R 22.1 0.1 23.1 Mondy/AZT-33IK 2025-09-25 20:48:16 6x120 0.15962 R 22.6 0.2 23.1 Mondy/AZT-33IK 2025-09-25 19:24:44 79x60 0.12486 R n/d n/d 21.7 AbAO/AS-32 The photometry was calibrated against nearby USNO-B1.0 stars (R2-mags) and not corrected for the Galactic extinction. Using all available r-data we estimate a temporal slope of alpha = -1.17 +/- 0.05. View this GCN Circular online at https://gcn.nasa.gov/circulars/42005. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40077] IceCube Alert 250926.52: Global MASTER-Net observations report
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42010 SUBJECT: IceCube Alert 250926.52: Global MASTER-Net observations report DATE: 25/09/26 20:00:38 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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the IceCube Alert 250926.52 (trigger No 64842455,08h 44m 07.68s , +10d 06m 07.2s, R=0.99) errorbox 26203 sec after notice time and 26266 sec after trigger time at 2025-09-26 19:46:41 UT, with upper limit up to 19.0 mag. The observations began at zenith distance = 79 deg. The sun altitude is -29.0 deg. The galactic latitude b = 30 deg., longitude l = 217 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3000303 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 26297 | 2025-09-26 19:46:41 | MASTER-Tunka | (08h 41m 52.46s , +09d 47m 01.3s) | C | 60 | 19.0 | 26297 | 2025-09-26 19:46:41 | MASTER- | (08h 42m 05.85s , +09d 40m 54.7s) | C | 60 | 18.5 | 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/42010. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40076] GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42009 SUBJECT: GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory DATE: 25/09/26 19:40:45 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> V. Ghiraldo, J. Basurto Merino, P.G. Berdayes, A. Caballero-Almagro, A. Cerón, M. Contreras, F. Díaz-Segado, T. Ferrer-Laviña, B. Gandolfi, J. Hernández Fung, L. Juliá-Maroto, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, A. Schenone-Zanuzzi, A. Selezneva, T. Tundidor Rodríguez, E. Urquijo-Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL). We report on a Las Cumbres Observatory (LCO) 40-cm telescope early observation of the long-duration Gamma-Ray Burst GRB 250920C, detected by Fermi (Fermi GBM team, GCN circ. 41903; and Mailyan et al., GCN circ. 41917), Swift (Gupta et al., GCN circ. 41904; Kuin et al., GCN circ. 41920; Goad et al., GCN circ. 41922; Gupta et al., GCN circ. 41924; and D'Ai et al. GCN circ. 41935), SVOM (Wang et al., GCN circ. 41929), and Konus-Wind (Panteleeva et al., GCN circ. 41957). We observed the field of GRB 250920C with one of the two LCO 40-cm telescopes (Planewave Delta Rho 350 telescopes equipped with CMOS QHY600 cameras) located at the LCO node at Siding Spring Observatory near Coonabarabran, New South Wales, Australia. The observation, a single exposure of 300 sec in the SDSS r filter, started on 2025-09-20 at 17:21:51 UT, about 1.94 hours after the Fermi and Swift trigger. The optical and near-infrared counterpart reported first by Wortley et al. using GOTO (GCN circ. 41907) and with observations by several other groups (GCN circ. 41911, GCN circ. 41913, GCN circ. 41916, GCN circ. 41920, GCN circ. 41925, GCN circ. 41928, GCN circ. 41943, GCN circ. 41947, GCN circ. 41951, GCN circ. 41952, GCN circ. 41955, GCN circ. 41956, GCN circ. 41965, and GCN circ. 41967) is clearly detected in our image, with a magnitude of r = 18.77 +/- 0.10, calibrated against PanSTARRS-1 DR2 and not corrected for galactic extinction, that is consistent with another reported r-band detection at a similar epoch. A redshift of z = 1.399 - 1.40 has been measured by Sánchez-Ramírez et al. (GCN circ. 41928), de Wet et al. (GCN circ. 41952), and Izzo et al. (GCN circ. 41955). Based on observations made with the Las Cumbres Observatory’s education network telescopes that were upgraded through generous support from the Gordon and Betty Moore Foundation (program IAC2025B-010). These observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (Tenerife, Canary Islands, Spain). View this GCN Circular online at https://gcn.nasa.gov/circulars/42009. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40075] GRB 250926A: AstroSat CZTI detection
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42008 SUBJECT: GRB 250926A: AstroSat CZTI detection DATE: 25/09/26 18:53:22 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> A. Goyal (IITB), A. Arya (IITB), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of GRB 250926A which was also detected by Fermi/GBM (GCN Circ. 41993). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-09-26 00:21:21.75 UTC. The measured peak count rate associated with the burst is 739 (+163, -167) counts/s above the background in the combined data of all four quadrants, with a total of 396 (+100, -119) counts. The local mean background count rate was 265 (+15, -17) counts/s. Using cumulative rates, we measure a T90 of 1.5 (+0.3, -0.7) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-09-26 00:21:21.04 UTC. The measured peak count rate associated with the burst is 763 (+72, -74) counts/s above the background in the combined data of all quadrants, with a total of 891 (+229, -239) counts. The local mean background count rate was 1162 (+8, -9) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 from it. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/42008. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40074] GRB 250925A: Swift/UVOT Upper Limits
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42007 SUBJECT: GRB 250925A: Swift/UVOT Upper Limits DATE: 25/09/26 16:33:59 GMT FROM: noelklin(a)umbc.edu N. J. Klingler (NASA-GSFC/UMBC/CRESST II) reports on behalf of the Swift-UVOT team: Swift-UVOT has performed follow-up observations of the Swift-BAT-detected burst GRB 250925A (Dichiara et al. GCN 41985), collecting 6.0 ks of observations between T0+3.74 ks and T0+16.74 ks. No source was detected in the UVOT data at the position of the optical source detected by the Nordic Optical Telescope (NOT) reported by Corcoran et al. (GCN 41990; RA, Dec = 22 44 51.31, +46 33 21.3), which is also consistent with the enhanced position of the X-ray source detected by Swift-XRT reported by Page et al. (GCN 41988; RA, Dec = 22 44 51.30, +46 33 20.6). 3-sigma upper limits (AB) using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are: Filter T_start(s) T_stop(s) Exp(s) Mag white 4150.3 4350.1 199.80 >21.55 white 9527.3 10434.5 907.20 >22.41 B 3945.3 5554.0 1608.70 >21.16 U 3739.8 3939.6 199.80 >20.48 U 5175.9 5375.7 199.80 >20.52 V 4560.9 4760.7 199.80 >19.94 V 15320.0 16227.1 907.10 >20.81 W1 4971.0 5170.7 199.70 >20.10 W2 4356.1 4555.9 199.80 >20.10 W2 10440.9 11158.4 717.50 >21.02 M2 4765.8 4965.6 199.80 >19.99 M2 16232.4 16737.3 504.90 >20.67 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.254 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42007. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40073] GRB 250925A: Swift-BAT refined analysis
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42006 SUBJECT: GRB 250925A: Swift-BAT refined analysis DATE: 25/09/26 15:51:01 GMT FROM: Hans Krimm at NSF/NASA-GSFC <hkrimm(a)nsf.gov> S. D. Barthelmy (GSFC), S. Dichiara (PSU), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250925A (trigger #1352124) (Dichiara, et al., GCN Circ. 41985). The BAT ground-calculated position is RA, Dec = 341.207, 46.549 deg which is RA(J2000) = 22h 44m 49.7s Dec(J2000) = +46d 32' 57.0" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 76%. The mask-weighted light curve shows a broad, multi-peaked structure starting at ~T-25 sec and decaying to background by T+50 sec. T90 (15-350 keV) is 64.51 +- 6.59 sec (estimated error including systematics). The time-averaged spectrum from T-23.52 to T+64.42 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.87 +- 0.09. The fluence in the 15-150 keV band is 2.7 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+0.19 sec in the 15-150 keV band is 1.2 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1352124 View this GCN Circular online at https://gcn.nasa.gov/circulars/42006. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40072] GRB 250529A: Mondy and AbAO optical observations
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42005 SUBJECT: GRB 250529A: Mondy and AbAO optical observations DATE: 25/09/26 15:27:34 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO) 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) and the AS-32 0.7m telescope of the Abastumani Observatory (AbAO). The observations started at Mondy on 2025-09-25 at 20:00 UT, i.e. 0.118 days since trigger. In total we obtained 30x120 s exposures with AZT-33IK, and 85x60 s exposures with AS-32. 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) is clearly visible in the stacked images from Mondy. Preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope (nxs) (mid, days) (3sigma) 2025-09-25 20:00:15 6x120 0.12626 R 22.3 0.2 23.1 Mondy/AZT-33IK 2025-09-25 20:12:15 6x120 0.13460 R 22.1 0.2 23.0 Mondy/AZT-33IK 2025-09-25 20:24:16 6x120 0.14294 R 22.1 0.2 23.1 Mondy/AZT-33IK 2025-09-25 20:36:16 6x120 0.15128 R 22.1 0.1 23.1 Mondy/AZT-33IK 2025-09-25 20:48:16 6x120 0.15962 R 22.6 0.2 23.1 Mondy/AZT-33IK 2025-09-25 19:24:44 79x60 0.12486 R n/d n/d 21.7 AbAO/AS-32 The photometry was calibrated against nearby USNO-B1.0 stars (R2-mags) and not corrected for the Galactic extinction. Using all available r-data we estimate a temporal slope of alpha = -1.17 +/- 0.05. View this GCN Circular online at https://gcn.nasa.gov/circulars/42005. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40071] GRB 250925A: COLIBRÍ photometric redshift
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42004 SUBJECT: GRB 250925A: COLIBRÍ photometric redshift DATE: 25/09/26 15:11:23 GMT FROM: Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe(a)gmail.com> N. A. Rakotondrainibe (LAM), Enrique Moreno Méndez (UNAM), Alan M. Watson (UNAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), 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), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM): COLIBRÍ performed follow-up observations of the Swift GRB 250925A (Dichiara et al., GCN Circ. 41985, Moreno Méndez et al., GCN Circ. 41995) from 2025-09-26 04:47 to 06:46 UTC (from 11.7 to 13.7 hours after the trigger) and obtained 16/16 minutes of exposure in the g/y filters. We report a detection in the y-filter, with a magnitude of y = 20.64 +/- 0.13 mag and a non-detection of the burst in the g-filter with a 3-sigma upper limit of g > 23.75 mag. The photometry was performed using STDWeb/STDPipe (Karpov 2025), was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. After correcting for the Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.212 mag (Schlafly & Finkbeiner 2011) and fitting a power-law model to the grizy-bands using the LMC extinction curve, we derive a photometric redshift of z = 4.20+0.34-0.52 (1-sigma c.l.), according to the g- and r-band dropouts with g-r > 0.68 mag and r-i ~ 1.45 mag. Our result is consistent with the GTC/OSIRIS+ redshift of z=3.899 (Castro-Tirado et al., GCN Circular 41997). 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/42004. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40070] IceCube-250926A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42003 SUBJECT: IceCube-250926A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/09/26 13:38:42 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-09-26 at 12:28:55.17 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. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 3.2659 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/141390_64842455.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-09-26 Time: 12:28:55.17 UT RA: 131.0 (+0.56/-0.63 deg 90% PSF containment) J2000 Dec: 9.97 (+0.55/-0.71 deg 90% PSF containment) J2000 We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the 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/42003. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40069] GRB 250925A: SVOM/GWAC-F60A upper limit
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42002 SUBJECT: GRB 250925A: SVOM/GWAC-F60A upper limit DATE: 25/09/26 13:10:46 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, X. H. Han, J. Wang, P. P. Zhang, W. L. Dong, H. L. Li, C. WU, Y. L. Qiu, X .M. Lu, R. S. Zhang, Y. Xu, L. Huang, H. B. Cai, Y. J. Xiao, L. Lan, W. J. Xie, Z. H. Yao, J. Y. Wei(NAOC), X. G. Wang, E. W. Liang(GXU) report on behalf of the SVOM follow-up team: We observed the field of GRB 250925A (Dichiara et al., GCN 41985) with the GWAC-F60A at Xinglong Observatory, China. F60A started observing at 2025-09-25T17:05:15 UTC, about 49 sec after the burst. After the image stacking with the exposure time 9*20sec, we do not detected the optical counterpart at the location (Corcoran et al., GCN 41990, Bochenek et al., GCN 41991, Masi et al., GCN 41992,Méndez et al., GCN 41995, Castro-Tirado et al., GCN 41997, Liu et al., GCN 41998) within the XRT error box (Page et al., GCN 41988). The upper limit of R~17.0 mag for GWAC-F60A at mid time of 132 seconds after burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/42002. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40068] GRB 250925A/EP250925a: EP-WXT detection
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42001 SUBJECT: GRB 250925A/EP250925a: EP-WXT detection DATE: 25/09/26 13:07:12 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Zhou, D. F. Hu (PMO, CAS), Z. H. Yang, Q. C. Zhao (IHEP, CAS), Y. L. Wang (NAO, CAS; ICE, CSIC-IEEC) and C. C. Jin (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 EP250925a. This transient was found in the ground-processed data, and consistent with GRB250925A in terms of time and space (Dichiara et al., GCN 41985). The start time of EP250925a is around 2025-09-25T17:03:22 UTC. The ground-porcessed WXT location of GRB 250925A is R.A. = 341.205 deg, DEC = 46.564 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic), which is consistent with the localization reported by other groups (Dichiara et al., GCN 41985; Page et al., GCN 41988; Corcoran et al., GCN 41990; Bochenek et al., GCN 41991; Masi et al., GCN 41992; Méndez et al., GCN 41995; Castro-Tirado et al., GCN 41997; Liu et al., GCN 41998). The analysis of the WXT data shows that the event lasted for about 200 seconds with a peak flux of 1.5 x 10^-8 erg/s/cm^2. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.58 x 10^21 cm^-2 and a photon index of 1.18 +/- 0.18. The derived average unabsorbed 0.5-4 keV flux is (5.1 +/- 0.5) x 10^-9 erg/s/cm^2. 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/42001. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40067] GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42000 SUBJECT: GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula DATE: 25/09/26 12:19:19 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Sahil Atri (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of GRB 250926A detected by Fermi/GBM (Fermi GBM Team GCN Circ. 41993) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-09-26 UTC. DDOTI imaged the GBM error region (Fermi GBM Team, GCN Circ. 41993) from 09:06 to 11:53 UTC (T+8.6 to T+11.5 hours after the trigger), covering the entire region and obtaining a total exposure of 64 minutes. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect no uncatalogued fading sources within the observed field down to a 10-sigma limiting AB magnitude of: w > 20.3 This value is not corrected for Galactic extinction. We note that the Orion Nebula (d ~400 pc) lies within the error region reported by the Fermi/GBM Team. Given the possible association with this nearby star-forming region and the moderate duration of the signal (T90 ~ 5 s), we strongly encourage follow-up observations of this event. Further analysis is ongoing. We thank the staff of the Observatorio Astronómico Nacional at the Sierra de San Pedro Mártir, especially María H. Riesgo Tirado, for their invaluable assistance during the night. View this GCN Circular online at https://gcn.nasa.gov/circulars/42000. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40066] GRB 250925A : MITSuME Akeno optical upper limits
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41999 SUBJECT: GRB 250925A : MITSuME Akeno optical upper limits DATE: 25/09/26 11:39:31 GMT FROM: ochi.a.21f9(a)m.isct.ac.jp A. Ochi, Y. Kubo, I. Takahashi, R. Kato, H. Hagio, M. Sasada, H. Seki, S. Joshima, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration: We observed the field of GRB 250925A detected by Swift/BAT (Dichiara et al. GCN 41985) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. The observation started at 2025-09-25 17:05:14 UT (48 seconds after the Swift/BAT trigger). We stacked the images with good conditions. We did not detect any obvious point sources at the position reported by Saikia et al., GCN 41986, Pavoni et al., GCN 41989, Corcoran et al., GCN41990, Bochenek et al., GCN41991, Gianluca et al., GCN41992, Enrique et al., GCN41995, Castro-Tirado et al., GCN41997. We obtained the 5-sigma limits of the stacked images as follows: T0+[s] | MID-UT | T-EXP[sec] | 5-sigma limits ------------------------------------------------------------------------------------------------ 633 | 2025-09-25 17:15:00 | 600 | g'>18.2, Rc>18.1, Ic>17.6 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the trigger T-EXP: Total Exposure time We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire) View this GCN Circular online at https://gcn.nasa.gov/circulars/41999. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40065] GRB 250925A: JinShan optical observations
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41998 SUBJECT: GRB 250925A: JinShan optical observations DATE: 25/09/26 09:44:45 GMT FROM: liuxing(a)nao.cas.cn GRB 250925A: JinShan optical observations X. Liu (NAOC), S.Y. Fu (HUST) S.Q. Jiang, J. An, Z.P. Zhu, D. Xu (NAOC), A.D. Zhu, L. Lei (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of GRB 250925A detected by Swift/BAT (Dichiara, GCN 41985), using the 100cm-A (100A) and 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. The 100A observation automatically started at 17:05:21.07 UT on 2025-09-25, i.e., 54.57 seconds after the BAT trigger, and the 100C observation started one hour later. A series of frames were obtained in the Sloan r- and z- bands. The reported optical afterglow (Corcoran et al., GCN41990; Bochenek et al., GCN 41991; Masi et al., GCN 41992; Méndez et al., GCN 41995; Méndez et al., GCN 41995) was detected in our stacked 100C images in both r- and z- bands. Preliminary photometric results are as follows: T-mid (hr) | Filter | Exposure | Mag 2.05 | z | 24x180s | 20.26 +/- 0.15 3.02 | r | 8x200s | 22.10 +/- 0.20 calibrated with nearby Pan-STARRS1 DR2 stars without the Galactic extinction correction. We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41998. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40064] GRB 250925A: 1.5m OSN optical detection and redshift with the 10.4m GTC/OSIRIS+
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41997 SUBJECT: GRB 250925A: 1.5m OSN optical detection and redshift with the 10.4m GTC/OSIRIS+ DATE: 25/09/26 09:41:57 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct(a)iaa.es> A. J. Castro-Tirado, A. Sota, R. Sanchez-Ramirez, S. Guziy, M.D. Caballero-Garcia, S.-Y. Wu and I. Perez-Garcia (IAA-CSIC), D. Garcia-Alvarez (GTC, IAC), A. Perez-Romero (GTC), A. Cabrera-Lavers (IAC, GTC), S. B. Pandey (ARIES), M. Gritsevich (Univ. of Helsinki), Y.-D. Hu (GXI), A. Nicuesa Guelbenzu (Tautenburg Obs.), L. Piro (INAF/IAPS) and B.-B. Zhang (NJU), on behalf of a larger collaboration, report: Following the detection of GRB 250925A by Swift (Dichiara et al. GCNC 41985) we conducted optical follow-up observations with the 1.5m OSN at Observatorio de Sierra Nevada (Granada), starting on Sep 25 at 21:47 UT. At the position of the X-ray afterglow (Page et al. GCNC 41988), we detect the optical afterglow (with I = 19.7 +/- 0.1) previously discovered at the NOT (Corcoran et al. (GCNC 41990) and also reported by means of other ground-based telescopes (Bochenek et al. GCNC 41991, Masi et al. GCNC 41992, Moreno Mendez et al. GCNC 41995). Additional observations were conducted with the 10.4m GTC telescope, at the Spanish Roque de los Muchachos Observatory, on the island of La Palma, equipped with the OSIRIS+ instrument. The spectroscopic observations consisted of 900s exposures using grisms R1000B and R2500I, with a joint spectral coverage between 3,600 and 10,000 A. The observations started on Sep 25, 21:57 UT (i.e. 4.9 h after the burst trigger). We detect a strong DLA at ~6000 A, among a plethora of metal absorption lines, that we interpret as coming from NV, SiII, SiII*, OI, CII, SiIV, CIV, FeII, FeII*, AlII, AlII, NiII, MgII, MgI at z=3.899, consistent with the COLIBRI photometry as suggested (Moreno Mendez et al. GCNC 41995). The detection of fine structure features confirms the association of this absorption system to GRB 250925A. View this GCN Circular online at https://gcn.nasa.gov/circulars/41997. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40063] GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41996 SUBJECT: GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations DATE: 25/09/26 06:58:48 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni., Argentina); N.Tiurina, E.Gorbovskoy, V.Lipunov, A.Kuznetsov, A.Sankovich, G.Antipov, P.Balanutsa, Yu. Tselik, A. Sosnovskiy, M.Shilova, A.Chasovnikov, V.Topolev, K.Zhirkov, Ya.Kechin, V.Senik, D.Vlasenko(Lomonosov MSU, SAI, Moscow), D.Buckley, (SAAO, South Africa) O.Gress, N.Budnev (ISU, Irkutsk), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) The MASTER-OAFA robotic wide-field camera, located in Argentina (OAFA observatory of San Juan National University [1], during a regular survey, obtained an image of the region of the sky containing the point with coordinates MASTER OT J195412.89-485016.4 (GCN 41893) and source (Li et al., GCN 41877) before, during and after the Fermi trigger moment (GBM GCN 41874, GCN 41876, GCN 41890; LAT GCN 41884, Ttrigger=00:28:52) of GRB 250919A . Very bright optical counterpart MASTER OT J195412.89-485016.4 promptly detected at the agnitude ~ 9 m. This transient was first publishied as EP250919a optical counterpart by Las Cumbres observatory (GCN 41877, t_detection=03:02:52.800 UTC) and as Fermi GRB 250919A/EP250919a optical counterpart by Gemini-South (LEvan et al. GCN 41883) with reshift detection z = 1.145 X-ray counterpart was also detected by Swift (Osborne et al. GCN 41885) with OT afterglow detection by UVOT (Oates et al. GCN 41886), NuSTAR (GCN 41888) and Svom (41882). The full 4 nights light curve is currently being processed. [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#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/41996. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40062] GRB 250925A: COLIBRÍ optical photometry of the afterglow
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41995 SUBJECT: GRB 250925A: COLIBRÍ optical photometry of the afterglow DATE: 25/09/26 05:52:29 GMT FROM: enriquemm(a)astro.unam.mx Enrique Moreno Méndez (UNAM), N. A. Rakotondrainibe (LAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), 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), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM): We imaged the field of the Swift GRB 250925A (Dichiara et al., GCN Circ. 41985) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-09-26 02:45 to 04:30 UTC (from 9.7 to 11.4 hours after the trigger) and obtained 32/32/64 minutes of exposure in the r/i/z filters. The data were reduced and coadded with the COLIBRÍ pipeline and 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 detected the optical source reported by Corcoran et al. (GCN Circ. 41990) at preliminary magnitudes of: r = 23.07 +/- 0.18 i = 21.62 +/- 0.07 z = 21.02 +/- 0.06 The source has faded, confirming that it is the afterglow. Compared to the early observations reported by Corcoran et al., we derive a temporal index of about -0.9 in z. The very red r-i color is suggestive of a GRB at a moderately high redshift with a break in r. 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/41995. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40061] Fermi GRB 250926A: Global MASTER-Net observations report
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41994 SUBJECT: Fermi GRB 250926A: Global MASTER-Net observations report DATE: 25/09/26 01:31:05 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 250926A ( Fermi GBM team, GCN 41993) errorbox 71 sec after notice time and 114 sec after trigger time at 2025-09-26 00:23:18 UT, with upper limit up to 19.5 mag. The observations began at zenith distance = 53 deg. The sun altitude is -47.4 deg. The galactic latitude b = -20 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=3000001 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 124 | 2025-09-26 00:23:18 | MASTER-SAAO | (05h 28m 42.38s , -08d 02m 54.5s) | C | 20 | 18.4 | 159 | 2025-09-26 00:23:18 | MASTER-SAAO | (05h 28m 42.37s , -08d 02m 54.4s) | C | 90 | 19.4 | Coadd 124 | 2025-09-26 00:23:18 | MASTER-SAAO | (05h 30m 34.49s , -08d 18m 14.3s) | C | 20 | 18.4 | 159 | 2025-09-26 00:23:18 | MASTER-SAAO | (05h 30m 34.49s , -08d 18m 14.2s) | C | 90 | 19.5 | Coadd 168 | 2025-09-26 00:23:57 | MASTER-SAAO | (05h 28m 42.29s , -08d 02m 53.3s) | C | 30 | 18.6 | 168 | 2025-09-26 00:23:57 | MASTER-SAAO | (05h 30m 34.43s , -08d 18m 12.4s) | C | 30 | 18.7 | 222 | 2025-09-26 00:24:46 | MASTER-SAAO | (05h 28m 42.23s , -08d 02m 51.9s) | C | 40 | 18.8 | 222 | 2025-09-26 00:24:46 | MASTER-SAAO | (05h 30m 34.40s , -08d 18m 10.2s) | C | 40 | 18.8 | 286 | 2025-09-26 00:25:45 | MASTER-SAAO | (05h 28m 42.20s , -08d 02m 50.5s) | C | 50 | 18.9 | 286 | 2025-09-26 00:25:45 | MASTER-SAAO | (05h 30m 34.36s , -08d 18m 08.0s) | C | 50 | 19.0 | 360 | 2025-09-26 00:26:54 | MASTER-SAAO | (05h 28m 42.14s , -08d 02m 49.6s) | C | 60 | 19.1 | 360 | 2025-09-26 00:26:54 | MASTER-SAAO | (05h 30m 34.29s , -08d 18m 06.4s) | C | 60 | 19.2 | 651 | 2025-09-26 00:31:44 | MASTER-SAAO | (05h 28m 05.28s , -07d 01m 44.0s) | C | 60 | 18.7 | 711 | 2025-09-26 00:31:44 | MASTER-SAAO | (05h 28m 05.28s , -07d 01m 44.0s) | C | 180 | 19.4 | Coadd 651 | 2025-09-26 00:31:44 | MASTER-SAAO | (05h 29m 57.17s , -07d 16m 59.6s) | C | 60 | 18.8 | 711 | 2025-09-26 00:31:44 | MASTER-SAAO | (05h 29m 57.17s , -07d 16m 59.6s) | C | 180 | 19.5 | Coadd 731 | 2025-09-26 00:33:04 | MASTER-SAAO | (05h 28m 05.23s , -07d 01m 43.2s) | C | 60 | 18.7 | 731 | 2025-09-26 00:33:04 | MASTER-SAAO | (05h 29m 57.12s , -07d 16m 58.5s) | C | 60 | 18.8 | 810 | 2025-09-26 00:34:23 | MASTER-SAAO | (05h 28m 05.16s , -07d 01m 43.1s) | C | 60 | 18.7 | 810 | 2025-09-26 00:34:23 | MASTER-SAAO | (05h 29m 57.08s , -07d 16m 58.0s) | C | 60 | 18.8 | 890 | 2025-09-26 00:35:43 | MASTER-SAAO | (05h 28m 05.10s , -07d 01m 42.8s) | C | 60 | 18.6 | 890 | 2025-09-26 00:35:43 | MASTER-SAAO | (05h 29m 57.06s , -07d 16m 57.6s) | C | 60 | 18.8 | 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/41994. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40060] GRB 250926A: Fermi GBM Final Real-time Localization
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41993 SUBJECT: GRB 250926A: Fermi GBM Final Real-time Localization DATE: 25/09/26 00:31:52 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 00:21:23 UT on 26 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250926A (trigger 780538888.96614 / 250926015). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 83.0, Dec = -7.0 (J2000 degrees, equivalent to J2000 05h 31m, -7d 00'), with a statistical uncertainty of 1.8 degrees. The angle from the Fermi LAT boresight is 79.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250926015/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250926015/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250926015/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41993. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40059] GRB 250925A: Optical Observations via Virtual Telescope Project, Italy
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41992 SUBJECT: GRB 250925A: Optical Observations via Virtual Telescope Project, Italy DATE: 25/09/26 00:08:38 GMT FROM: Gianluca Masi at Virtual Telescope Project <gianluca(a)bellatrixobservatory.org> Gianluca Masi, Virtual Telescope Project (Italy), reports: We attempted to observe the optical counterpart (Dichiara et al., GCN 41985) of GRB 250925A with the 14” robotic unit available at the Virtual Telescope Project facility in Manciano, Italy, equipped with a KAF-3200E based CCD camera, its QE peaking (90%) in the red part of the spectrum. We collected 9, 300-second unfiltered exposures, then we averaged them. The central time of the resulting stack was 25 Sept., 23:27 UTC, that is about 6.38 hours after the burst. We detected a faint object at the following position (J2000.0): RA: 22 44 51.32 Decl.: +46 33 20.7 R= 21.5 (assuming R-mags from Gaia DR2 for the reference stars). This position is consistent with Corcoran et al., GCN 41990 and Bochenek et al., GCN 41991 View this GCN Circular online at https://gcn.nasa.gov/circulars/41992. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40058] GRB250925A: Liverpool Telescope optical observations
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41991 SUBJECT: GRB250925A: Liverpool Telescope optical observations DATE: 25/09/25 21:46:51 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We observed the field of GRB250925a detected by Swift (Dichiara et al., GCN 41915) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x100s exposures in the SDSS i’ filter starting at 2025-09-25 20:59:51 UT, approximately 3.92 hours after the trigger. We report a detection in the stacked image at the position of the candidate optical counterpart (Corcoran et al., GCN 41990), inside the XRT error field (Page et al., GCN 41988). The magnitude of the candidate afterglow is i = 20.78 ± 0.03. The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41991. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40057] GRB 250925A: NOT optical afterglow candidate
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41990 SUBJECT: GRB 250925A: NOT optical afterglow candidate DATE: 25/09/25 21:19:47 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> G. Corcoran (UCD), L. Cotter (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. de Ugarte Postigo (LAM), B. Schneider (LAM), K. Valeckas (NOT and NBI), report on behalf of a larger collaboration: We observed the field of GRB 250925A (Dichiara et al., GCN 41985) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. Observations started on 2025 Sep 25.847 UT (3.254 hr after trigger) and consisted of 3x300 s and 5x200 s in each of the SDSS r and z bands. Within the UVOT-enhanced XRT position (Page et al., GCN 41988), we detect an object which is not seen in Pan-STARRS archival imaging of this field. Its coordinates are: RA(J2000) = 22:44:51.31 Dec(J2000) = +46:33:21.3 with an estimated error of 0.3”. Calibrated against nearby objects from Pan-STARRS, we measure AB magnitudes (not corrected for Galactic extinction): r = 21.99 +- 0.10 (3.30 hr after the trigger) z = 19.96 +- 0.05 (3.69 hr after the trigger) We note that this is a rather red r-z color, even considering the non-negligible but still modest Galactic extinction A_V ~ 0.75 mag along this line of sight (Schlafly & Finkbeiner 2011; doi:10.1088/0004-637X/737/2/103). This might indicate either an intrinsic spectral slope, or unaccounted extinction in our Galaxy or in the GRB host. View this GCN Circular online at https://gcn.nasa.gov/circulars/41990. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40056] GRB 250925A: Leavitt Observatory optical upper limit
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41989 SUBJECT: GRB 250925A: Leavitt Observatory optical upper limit DATE: 25/09/25 21:19:01 GMT FROM: leavittob(a)gmail.com E. Pavoni, L. Moretti (Leavitt Observatory, Italy) Members of: GRB/UAI - Gamma Ray Burst Section of Unione Astrofili Italiani ATA - Associazione Tuscolana di Astronomia In a large collaboration with: M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy), K. Kalinowski (Aarhus University, Department of Physics and Astronomy), report: We observed the field of GRB 250925A detected by Swift (Dichiara et al., GCN 41985), using our Ritchey-Chrétien telescope (D=250 mm, F/D=8). The observations began approximately 128 minutes after the trigger, stacking a set of CCD images of 180 seconds each, with good weather conditions. All images were processed by a single data processing pipeline based on astropy package (Astropy Collaboration et al., 2022ApJ...935..167A). No credible candidate was detected in our stacked frame within the Swift error circle. We derived the following upper limit: | Mid-Time (UTC) | Filter | Exp. Time | Upper limit (3-sigma) | | ------------------- | ------ | ----------- | ----------------------| | 2025-09-25T19:42:51 | CR | 20x180 sec | 20.49 | CR magnitude is unfiltered with R zero point. The photometry was calibrated with the Pan-STARRS cat. (R-mags obtained via Lupton 2005 transformations). Not corrected for the Galactic extinction. This upper limit is consistent with the report by GROWTH-India Telescope (Saikia et al., GCN 41986). This message may be cited. Reference: https://leavittobservatory.altervista.org View this GCN Circular online at https://gcn.nasa.gov/circulars/41989. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40055] GRB 250925A: Enhanced Swift-XRT position
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41988 SUBJECT: GRB 250925A: Enhanced Swift-XRT position DATE: 25/09/25 20:39:16 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L Page, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team: Using 1810 s of XRT Photon Counting mode data and 4 UVOT images, 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 = 341.21375, 46.55573 which is equivalent to: RA (J2000): 22 44 51.30 Dec (J2000): +46 33 20.6 with an uncertainty of 2.3 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 is an official product of the Swift-XRT team View this GCN Circular online at https://gcn.nasa.gov/circulars/41988. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 40054] GRB 250924A: Swift-BAT refined analysis
by GCN Circulars 25 Sep '25

25 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41987 SUBJECT: GRB 250924A: Swift-BAT refined analysis DATE: 25/09/25 19:39:17 GMT FROM: Hans Krimm at NSF/NASA-GSFC <hkrimm(a)nsf.gov> D. Sadaula (GSFC/UMBC), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), T. Sakamoto (AGU), M. H. Siegel (PSU), (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250924A(trigger #1351790) (Siegel, et al., GCN Circ. 41959). The BAT ground-calculated position is RA, Dec = 51.908, 74.665 deg, which is RA(J2000) = 03h 27m 37.8s Dec(J2000) = +74d 39' 55.1" with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment). The partial coding was 12%. The mask-weighted light curve shows a single broad pulse, extending from approximately T-10 to T+20 seconds. T90 (15-350 keV) is 26.53 +- 3.72 sec (estimated error including systematics). The time-averaged spectrum from T-9.92 to T+20.00 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.47 +- 0.17. The fluence in the 15-150 keV band is 2.5 +- 0.3 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+15.78 sec in the 15-150 keV band is 2.1 +- 0.7 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1351790 View this GCN Circular online at https://gcn.nasa.gov/circulars/41987. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0