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[vsnet-grb-info 40300] GRB 251013C: SAO RAS optical observations
by GCN Circulars 13 Oct '25

13 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42230 SUBJECT: GRB 251013C: SAO RAS optical observations DATE: 25/10/13 21:31:40 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin, O. I. Spiridonova, V. V. Vlasyuk (SAO RAS), N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Ghosh, S. Razzaque (CAPP, University of Johannesburg), Tao An and Yuanqi Liu (Shanghai Astronomical Observatory) report on behalf of GRB follow-up collaboration and IKI-GRB-FuN. We observed the field of the GRB 251013C (The Fermi GBM team, GCN 42221; Rakotondrainibe et al., GCN 42222) with the 1-m SAO RAS telescope Zeiss-1000 equipped with the CCD-photometer. The observations started on 2025.10.13T19:47:54 UT (t_mid - T0 = 2.1369 hours). The OT (Palmerio et al., GCN 42223; Perez-Garcia et al., GCN 42225; Konno et al., GCN 42226; Martin-Carrillo et al., GCN 42227; Masi, GCN 42228; Palmerio et al, GCN 42229) is clearly detected in the individual images with the following brightness. Date UT start t-T0 Exp. Filter OT Err. (mid, d) (s) 2025.10.13 19:47:54 0.03631 300 Rc 15.84 +/- 0.01 2025.10.13 20:04:02 0.04033 100 Rc 16.05 +/- 0.01 2025.10.13 20:15:34 0.04353 100 Rc 16.21 +/- 0.01 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42230. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40299] GRB 251013C: LCO optical afterglow detection
by GCN Circulars 13 Oct '25

13 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42229 SUBJECT: GRB 251013C: LCO optical afterglow detection DATE: 25/10/13 21:13:53 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> J. T. Palmerio, D. Turpin, A. Saccardi, 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 251013C (SVOM/ECLAIRs and GRM, Rakotondrainibe et al. GCN 42223; Fermi/GBM, Fermi GBM team, GCN 42221) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started at 2025-10-13T19:27:33.084 about 1.8 hours after the SVOM/ECLAIRs T0 time. We obtained 3 series of 3x200 s exposures in the SDSS gri filters. The bright optical counterpart detected by SVOM/VT (Palmerio et al. GCN 42223), BOOTES-6 (Perez-Garcia et al., GCN 42225), LAST (Konno et al., GCN 42226), NOT (Martin-Carrillo et al., GCN 42227 and the Visual Telescope Project (Masi et al., GCN 42228) is clearly detected in our first images subtracted to the Pan-STARRS DR2 catalog image. We measure the following magnitude: g = 16.30 +/- 0.01 (AB), at Tmid-T0 = 2.1 hours r = 15.99 +/- 0.01 (AB), at Tmid-T0 = 2.0 hours i = 15.70 +/- 0.01 (AB), at Tmid-T0 =1.8 hours Further observations are planned and spectroscopic observations are encouraged. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/42229. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40298] GRB 251013C: Optical Observations via Virtual Telescope Project, Italy
by GCN Circulars 13 Oct '25

13 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42228 SUBJECT: GRB 251013C: Optical Observations via Virtual Telescope Project, Italy DATE: 25/10/13 21:07:58 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 of GRB 251013C (Rakotondrainibe et al., GCN 42222) 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 three, 120-second unfiltered exposures, then we averaged them. The central time of the resulting stack was 13 Oct., 20:54:57 UTC, that is about 3.25 hours after the burst. We detected a bright object at the following position (J2000.0): R.A.: 23 03 20.56 Decl.: -00 13 37.1 mean residuals < 1” on both axes R= 15.9 (assuming R-mags from Gaia DR2 for the reference stars). This position is consistent with Palmerio et al. (GCN 42223)and Perez-Garcia et al., GCN 42225. View this GCN Circular online at https://gcn.nasa.gov/circulars/42228. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40297] GRB 251013C: NOT spectroscopic redshift z = 0.572
by GCN Circulars 13 Oct '25

13 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42227 SUBJECT: GRB 251013C: NOT spectroscopic redshift z = 0.572 DATE: 25/10/13 21:02:05 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> A. Martin-Carrillo (UCD), L. Izzo (INAF/OACN and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), B. Schneider (LAM), A. de Ugarte Postigo (LAM), A. Saccardi (CEA/Irfu), B. P. Gompertz (Birmingham), K. Valeckas (NOT and NBI) report on behalf of a larger collaboration: We observed the optical afterglow (Palmerio et al., GCN 42223; Perez-Garcia et al., GCN 42225; Konno et al., GCN 42226) of GRB 251013C (Rakotondrainibe et al., GCN 42222; Fermi GBM team, GCN 42221) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A spectrum using grism #4 was secured starting on 2025-10-13 at 19:46:24 UT (2.11 hr after the GRB), under good conditions. The exposure time was 2x1200 s and the covered wavelength range is 3500-9600 AA. In a preliminary reduction of the spectra, we clearly detect a continuum over the whole covered wavelength range. From the detection of multiple absorption features, including Fe II 2600, the Mg II doublet, weak Mg I, and the Ca II doublet, we infer a redshift of z = 0.572. Photometry of the afterglow was carried out in the ugriz filters. In a 30-s r-band image, we measure r = 16.52 +/- 0.02 AB (at a time of 2.88 hr after the GRB), calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42227. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40296] GRB 251013C: LAST detection of optical counterpart
by GCN Circulars 13 Oct '25

13 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42226 SUBJECT: GRB 251013C: LAST detection of optical counterpart DATE: 25/10/13 20:58:35 GMT FROM: Ruslan Konno at Weizmann Institute of Science <ruslankonno(a)gmail.com> R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), and S. Spitzer (WIS) report on behalf of the LAST Collaboration. We report observations of GRB 251013C, detected by SVOM (Rakotondrainibe et al., GCN 42222) and Fermi (Fermi GBM Team, GCN 42221). Observations were conducted with the Large Array Survey Telescope (LAST; Ofek et al. 2023, PASP 135, 5001; Ben-Ami et al. 2023, PASP 135, 5002). We observed the field of GRB 251013C using four parallel telescopes (each with a 7.4 deg^2 FoV) in clear band (similar to the Gaia Bp band) over several epochs. Each coadd consists of 20x20 s exposures, yielding a limiting magnitude of about 20.5 AB mag. We clearly detect the optical counterpart reported by Palmerio et al. (GCN 42223) and Perez-Garcia et al. (GCN 42225). The earliest detection (20x20 s coadd) is confirmed at 2025-10-13 18:10:27 UTC (T − T0 = 0.51 h) with AB mag 16.14 +/- 0.02. Preliminary automated photometry shows a rise to 15.20 +/- 0.01 mag at 18:32:15 UTC (T − T0 = 0.87 h), followed by a power-law decay. The source remains detectable. We encourage continued multi-wavelength follow-up of this bright optical counterpart. LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/) View this GCN Circular online at https://gcn.nasa.gov/circulars/42226. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40295] GRB 251013C: BOOTES-6 early optical detection
by GCN Circulars 13 Oct '25

13 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42225 SUBJECT: GRB 251013C: BOOTES-6 early optical detection DATE: 25/10/13 19:07:16 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 251013C by SVOM (Rakotondrainibe et al., GCN 42222), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) responded to this high-energy event starting on Oct 13, 17:42:32 UT (i.e., 170 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 42223). Using GaiaDR3 Gmag as reference we report our photometry analysis: | UT mid exposure | mag | error | filter | exposure time (sec) | | ------------------- | ----- | ----- | ------ | ------------------- | | 2025-10-13 17:43:02 | 14.42 | 0.02 | clear | 60 | | 2025-10-13 17:44:31 | 14.82 | 0.02 | clear | 60 | | 2025-10-13 17:50:23 | 14.79 | 0.03 | clear | 60 | | 2025-10-13 17:51:52 | 15.03 | 0.02 | clear | 60 | | 2025-10-13 17:57:44 | 15.77 | 0.03 | clear | 60 | | 2025-10-13 17:59:13 | 15.79 | 0.03 | clear | 60 | | 2025-10-13 18:05:04 | 16.07 | 0.03 | 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/42225. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40294] GRB 251013D: Fermi GBM Final Real-time Localization
by GCN Circulars 13 Oct '25

13 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42224 SUBJECT: GRB 251013D: Fermi GBM Final Real-time Localization DATE: 25/10/13 18:27:33 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 18:17:00 UT on 13 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251013D (trigger 782072225.388414 / 251013762). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 44.4, Dec = 10.2 (J2000 degrees, equivalent to J2000 02h 57m, 10d 11'), with a statistical uncertainty of 5.4 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/bn251013762/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251013762/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251013762/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42224. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40293] GRB 251013C: SVOM/VT optical observation
by GCN Circulars 13 Oct '25

13 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42223 SUBJECT: GRB 251013C: SVOM/VT optical observation DATE: 25/10/13 18:18:36 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> J. T. Palmerio (CEA/Irfu), Ny Avo Rakotondrainibe, C. Adami (LAM), H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu (NAOC) report on behalf of the SVOM/VT team: After the trigger by SVOM/ECLAIRs at 2025-10-13T17:39:42 UTC (T0), SVOM performed an automatic slew on the burst location (Rakotondrainibe et al., GCN 42222). SVOM/VT began observing the field at 2025-10-13T17:44:04, 261.08 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 117: This bright candidate was flagged as a catalogued source but significantly brighter than its catalogued magnitude. The position of this candidate is R.A., Dec. 345.8356, -0.2103 degrees, corresponding to: R.A. (J2000) = 23h03m20.6s Dec. (J2000) = -0d12m37.1s with an uncertainty of 0.5 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) | | -------------------- | ----------- | --------- | ----- | ------------- | | 2025-10-13T17:44:04 | 6.85 min | 6*50 sec | VT_B | 15.38 ± 0.01 | | 2025-10-13T17:44:04 | 6.85 min | 6*50 sec | VT_R | 14.76 ± 0.01 | Magnitudes were not corrected for dust extinction. The VT color of the counterpart suggests it is not very high redshift or highly extinguished. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42223. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40292] GRB 251013C: SVOM detection of a burst
by GCN Circulars 13 Oct '25

13 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42222 SUBJECT: GRB 251013C: SVOM detection of a burst DATE: 25/10/13 18:17:34 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> N. A. Rakotondrainibe, C. Adami (LAM), D. Turpin, D. Götz (CEA/Irfu), H. Yang (IRAP) At 2025-10-13T17:39:42 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251013C (SVOM burst-id sb25101311) also detected by Fermi/GBM (Fermi GBM team GCN 42221). 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 16 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 35.62 in the [8-120] keV energy band over a time window of 10.24 seconds starting at 2025-10-13T17:39:42. The SVOM/ECLAIRs light curve showed a single peak structure of a T90 duration of 17.1 (+6.9/-1.5) s. The localization of the best alert is R.A., Dec. 345.8809, -0.1698 degrees (J2000) with a 90% confidence level (C.L.) radius of 2.94 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM at 2025-10-13T17:39:43 on a timescale of 18 seconds with an SNR of 11. SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-10-13T17:43:05 UTC, 203 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 345.8301, -0.2207 degrees: R.A. (J2000) = 23h03m19s Dec. (J2000) = -0d13m14s with a 90% C.L. radius of 69 arcseconds. This location is 4.31 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 Ny Avo Rakotondrainibe: ny-avo.rakotondrainibe(a)lam.fr Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/42222. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40291] GRB 251013C: Fermi GBM Final Real-time Localization
by GCN Circulars 13 Oct '25

13 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42221 SUBJECT: GRB 251013C: Fermi GBM Final Real-time Localization DATE: 25/10/13 17:50:11 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 17:39:41 UT on 13 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251013C (trigger 782069986.941944 / 251013736). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 348.9, Dec = -6.3 (J2000 degrees, equivalent to J2000 23h 15m, -6d 17'), with a statistical uncertainty of 5.0 degrees. The angle from the Fermi LAT boresight is 65.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251013736/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251013736/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251013736/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42221. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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