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[vsnet-grb-info 40570] EP251027.145: COLIBRÍ optical upper limits
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42485 SUBJECT: EP251027.145: COLIBRÍ optical upper limits DATE: 25/10/27 15:48:00 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> William H. Lee (UNAM), Damien Dornic (CPPM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU),Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Kin Ramandeep Gill (UNAM), Noémie Globus (UNAM), Ocelotl López (UNAM), Diego López-Cámara (UNAM), Nikos Mandarakas (LAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP251027.145 (ID=01709247525) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-27 07:47 to 09:09 UTC (from 4.3 to 5.7 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. In the stacked image, we do not detect any uncatalogued source at the EP/WXT position down to the following 5-sigma limit: r > 23.6 z > 22.3 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/42485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40569] GRB 251022A: SVOM/GRM observation
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42484 SUBJECT: GRB 251022A: SVOM/GRM observation DATE: 25/10/27 15:46:15 GMT FROM: renyz16607(a)163.com GRB 251022A: SVOM/GRM observation SVOM/GRM team: Yang-Zhao Ren, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Nicolas Dagoneau (CEA), Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 251022A at 2025-10-22T22:34:19.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #42380), Swift/BAT (James DeLaunay et al., GCN#42409) and Fermi/LAT ( N. Di Lalla et al., GCN #42384), With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 106 +6/-2 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb251022A.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 74.5, Dec = -22.7, GCN #42380), is located at about 102 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-20 to T0+101 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.49 +0.12/-0.11 and the cutoff energy, parameterized as Epeak, is 330 +162/-80 keV. The event fluence (10-1000 keV) in this time interval is (4.07 +0.27/-0.27)E-05 erg/cm^2. The localization of GRB 251022A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb251022A_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: Yang-Zhao Ren (IHEP)(renyz(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/42484. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40568] GRB 251026B: Swift ToO observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42483 SUBJECT: GRB 251026B: Swift ToO observations DATE: 25/10/27 15:40:49 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 team: Swift has initiated a ToO observation of the Fermi/GBM-detected event GRB 251026B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021872 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Fermi/GBM event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42483. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40567] GRB 251026A/EP251026a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42482 SUBJECT: GRB 251026A/EP251026a: Einstein Probe detection of a fast X-ray transient DATE: 25/10/27 15:36:49 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A. Li (BNU), J. H. Wu (GZHU), H. Q. Cheng and H. Sun (NAOC) 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 EP251026a. The ground analysis of the WXT data shows that the event started at T0=2025-10-26T08:26:33 (UTC). The WXT position of the source is R.A. = 72.663 deg, DEC = 51.775 deg (J2000) with an uncertainty of 2.1 arcmin in radius (90% C.L. statistical and systematic). This transient is temporally and spatially coincident with GRB 251026A (GCN 42454). The analysis of the WXT data shows that the event lasted for about 500 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.77 x 10^21 cm^-2 and a photon index of 1.00 (-0.37/+0.38). The derived average unabsorbed 0.5-4 keV flux is 1.35 (-0.6/+0.7) x 10^-9 erg/s/cm^2. The peak flux is around 2.1 x 10^-9 erg/s/cm^2 with a fixed Galactic hydrogen column density of 3.77 x 10^21 cm^-2 and a photon index of 1.07 (-0.53/+0.55). We note that the late release of this transient is mostly due to the delay in the data transmission. Follow-up observations with EP-FXT has been scheduled and more information will be reported when the telemetry data arrives. 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/42482. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40566] GRB 251027A: LCO optical upper limit
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42481 SUBJECT: GRB 251027A: LCO optical upper limit DATE: 25/10/27 15:13:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), L. P. Xin (NAOC), D. Turpin (CEA/Irfu), B. Cordier (CEA/Irfu), Y. H. Cheng (YNU), Y. F. Liang (PMO), report on behalf of the SVOM mission team: We observed the field of the GRB 251027A detected by SVOM/ECLAIRs (Cheng et al., GCN 42471) with the LCO 1m telescope at McDonald Observatory equipped with the Sinistro instrument. Our observation started on 2025-10-27 at 10:22:43 UT (~45 min after the trigger) and we obtained 3x200 s exposures using the SDSS r filter. In the stacked image, we did not detect any new optical source at the SVOM/ECLAIRs position (Cheng et al., GCN 42471), in agreement with the results reported by Dornic et al. (GCN 42480). We derived the following upper limit r > 22 AB mag (5-sigma) calibrated against Pan-STARRS1 catalogue and not corrected for Galactic extinction. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/42481. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40565] GRB 251027A: LCO optical upper limit
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42481 SUBJECT: GRB 251027A: LCO optical upper limit DATE: 25/10/27 15:13:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), L. P. Xin (NAOC), D. Turpin (CEA/Irfu), B. Cordier (CEA/Irfu), Y. H. Cheng (YNU), Y. F. Liang (PMO), report on behalf of the SVOM mission team: We observed the field of the GRB 251027A detected by SVOM/ECLAIRs (Cheng et al., GCN 42471) with the LCO 1m telescope at McDonald Observatory equipped with the Sinistro instrument. Our observation started on 2025-10-27 at 10:22:43 UT (~45 min after the trigger) and we obtained 3x200 s exposures using the SDSS r filter. In the stacked image, we did not detect any new optical source at the SVOM/ECLAIRs position (Cheng et al., GCN 42471), in agreement with the results reported by Dornic et al. (GCN 42480). We derived the following upper limit r > 22 AB mag (5-sigma) calibrated against Pan-STARRS1 catalogue and not corrected for Galactic extinction. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/42481. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40564] GRB 251027A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42480 SUBJECT: GRB 251027A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/10/27 14:47:37 GMT FROM: J.-G. Ducoin at CPPM <ducoin(a)cppm.in2p3.fr> Damien Dornic (CPPM), William H. Lee (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), 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), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), Y. H.Cheng (YNU) and Y. F. Liang (PMO) : We imaged the field of the SVOM GRB 251027A (Cheng et al., GCN Circ. 42471) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-10-27T10:08:34 to 2025-10-27T10:47:17 UTC (from 31 to 69 minutes after the trigger) and obtained 32x60 seconds of exposure in the r and z 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 (Av>2). In the stacked image, we do not detect any new source at the ECLAIRs source position (Cheng et al., GCN Circ. 42471) down to the following 5-sigma limit: r > 23.57 z > 22.26 Further analysis is 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/42480. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40563] GRB 251017A: Mondy AZT-33IK and Koshka Zeiss-1000 optical observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42479 SUBJECT: GRB 251017A: Mondy AZT-33IK and Koshka Zeiss-1000 optical observations DATE: 25/10/27 13:47:19 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), E. Klunko (ISTP), A. Novichonok (Petrozavodsk State University, KIAM), I. Nikolenko (INASAN), A. Pozanenko (IKI), N. Pankov (HSE, IKI), report on behalf of IKI-GRB-FuN: We observed the optical counterpart (Perez-Garcia et al., 42323; Antier et al., 42325; Sasada et al., 42329; Lipunov et al., 42330; Fu et al., 42331; Mo et al., 42336; Adami et al., 42339; Xin et al., 42341; Izzo et al., 42350; Shilling et al., 42355; Akl et al., 42368; Midavaine et al., 42370; Volnova et al., 42477) of the Swift GRB 251017A (Gupta et al., GCN 42322) in the R-filter with 1.5-meter AZT-33IK telescope of Sayan Solar Observatory (Mondy) on Oct. 17,18,23, 2025, and in the Rb filter with 1-meter Zeiss-1000 telescope of the Koshka Observatory (INASAN) on Oct. 20, 2025. Preliminary photometry and observation details are the following: Date UT start t-T0 Exp. Filter OT Err. UL Site/Instrum (mid,days) (n*s) (3sigma) 2025-10-17 11:25:01 0.14333 20*120 R 20.41 0.07 21.8 Mondy/AZT-33IK 2025-10-17 12:49:15 0.19065 26*120 R 20.88 0.07 22.3 Mondy/AZT-33IK 2025-10-18 11:40:09 1.14891 35*120 R 21.79 0.13 22.5 Mondy/AZT-33IK 2025-10-20 16:36:07 3.37307 40*180 R n/d n/d 21.1 Koshka/Zeiss-1000 2025-10-23 13:18:38 6.22425 45*120 R n/d n/d 22.5 Mondy/AZT-33IK The photometry is based on several nearby PS1 stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42479. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40562] GRB 251023B / EP251023b: Mondy optical upper limit
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42478 SUBJECT: GRB 251023B / EP251023b: Mondy optical upper limit DATE: 25/10/27 13:44:29 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), A. Pozanenko (IKI) , N. Pankov (HSE, IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN: We observed the field of the GRB 251023B / EP251023b (Kang et al., GCN Circ. 42392; Nakahira et al., GCN Circ. 42402; Wu et al., GCN Circ. 42415; Cheung et al., GCN Circ. 42407) in the R-filter with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) starting Oct. 25, 2025, 17:50:36 UT, and taking several frames with 120 s exposures. The optical candidate reported by Mandarakas et al. (GCN Circ. 42404) is not detected in the stacked frame. Photometry and observational details are the following: Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2025-10-25 17:50:36 2.40386 40*120 R n/d n/d 22.7 The photometry is based on several nearby SDSS stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42478. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40561] GRB 251017A: INASAN-Kislovodsk optical observations
by GCN Circulars 27 Oct '25

27 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42477 SUBJECT: GRB 251017A: INASAN-Kislovodsk optical observations DATE: 25/10/27 13:36:52 GMT FROM: Alina Volnova at IKI RAS <alinusss(a)gmail.com> A. Volnova (IKI), A.N. Tarasenkov (INASAN), A. Pozanenko (IKI), N. Pankov (HSE) report on behalf of IKI GRB-FuN: We observed the field of the Swift GRB 251017A (Gupta et al., GCN 42322) with RC500 telescope of the INASAN-Kislovodsk observatory. We took several 120-seconds frames in the R-band starting Oct. 17, 2025, 15:09:15 (UT). In the stacked image the optical counterpart (Perez-Garcia et al., 42323; Antier et al., 42325; Sasada et al., 42329; Lipunov et al., 42330; Fu et al., 42331; Mo et al., 42336; Adami et al., 42339; Xin et al., 42341; Izzo et al., 42350; Shilling et al., 42355; Akl et al., 42368; Midavaine et al., 42370) is clearly detected. Preliminary photometry is the following: Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2025-10-17 15:09:15 0.34348 100*120 R 21.45 0.16 22.0 The photometry is based on several nearby PS1 stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42477. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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