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[vsnet-grb-info 40502] GRB 251023B / EP251023b: COLIBRÍ Confirmation of the Fading Nature of the Optical Candidate
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42424 SUBJECT: GRB 251023B / EP251023b: COLIBRÍ Confirmation of the Fading Nature of the Optical Candidate DATE: 25/10/24 16:50:02 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Enrique Moreno Méndez (UNAM), Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), 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), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We reimaged the field of the GRB 251023B / EP251022b (Kang et al., GCN Circ. 42392; Nakahira et al., GCN Circ. 42402; Wu et al., GCN Circ. 42415; Cheung et al., GCN Circ. 42407), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-24 07:06 to 08:12 UTC (from 22.3 to 23.4 hours after the trigger) and obtained 16 minutes of exposure in each of the r and i filters and 32 minutes of exposure in the z filter. 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 our second epoch, we do not detect the optical candidate reported by Mandarakas et al. (GCN Circ. 42404) down to the following 3-sigma limits: r > 22.8 i > 22.4 z > 22.0 These values are consistent with the non-detection reported by Adami et al. (GCN Circ. 42421) and confirm the fading nature of the source, supporting its association with GRB 251023B / EP251022b. 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/42424. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40501] GRB 251022A: COLIBRÍ Further Multi-frequency Optical Observations
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42423 SUBJECT: GRB 251022A: COLIBRÍ Further Multi-frequency Optical Observations DATE: 25/10/24 15:05:07 GMT FROM: Rosa Leticia Becerra Godínez at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Enrique Moreno Méndez (UNAM), Nikos Mandarakas (LAM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), 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), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We reobserved the field of the Fermi GRB 251022A (Fermi GBM Team, GCN Circ. 42380; Di Lalla et al., GCN Circ. 42384) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-24 07:25 to 08:30 UTC (from 32.8 to 33.9 hours after the trigger) and obtained 10 minutes of exposure in each of the g, r, i, and z filters and 20 minutes of exposure in the y filter. 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 our second epoch, we still detect the optical counterpart firstly reported by GOTO (O’Neill et al. GCN Circ. 42386) and subsequently followed-up by DDOTI (Becerra et al. GCN Circ. 42394), MASTER (Lipunov et al. GCN Circ. 42395), COLIBRÍ (Mandarakas et al. GCN Circ. 42397), and GROWTH (Mohan et al. GCN Circ. 42413) at preliminary magnitudes and upper limits of: g = 22.52 +/- 0.23 r = 22.05 +/- 0.20 i = 21.99 +/- 0.31 z = 21.95 +/- 0.65 y > 20.7 (3-sigma) Compared with the values reported in our first epoch (Mandarakas et al. GCN Circ. 42397), we estimate a temporal decay index of ~-2, consistent with a jet break. Our detection in g suggests that this is not a high-redshift GRB, but instead has z < 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/42423. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40500] EP251023a: MAO/AZT-22 optical observations
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42422 SUBJECT: EP251023a: MAO/AZT-22 optical observations DATE: 25/10/24 15:02:32 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 EP transient EP251023a (Wu et al., GCN 42388), with the AZT-22 1.5m telescope of the Maidanak Observatory (MAO) starting on 2025-10-23 at 22:52:18 UT, i.e. ~10.37 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 GOTO (Wortley et al., GCN 42387) and also observed (Li et al., GCN 42389; Liu et al., GCN 42391; Mandarakas et al., GCN 42400; Lipunov et al., GCN 42405; Selezneva et al., GCN 42406; Mohan et al., GCN 42411; Rakotondrainibe et al., GCN 42420) is detected in our individual and stacked frames. Preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope (nxs) (mid, days) 2025-10-23 23:08:31 6x300 0.85928 R 20.56 0.03 22.99 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/42422. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40499] GRB 251023B: OHP/T193 optical observations
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42421 SUBJECT: GRB 251023B: OHP/T193 optical observations DATE: 25/10/24 13:26:31 GMT FROM: Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe(a)gmail.com> C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), E. Le Floc'h (CEA/Irfu), report on behalf of the MISTRAL GRB collaboration: We carried out observations of GRB 251023B (Cheung et al., GCN 42407; Mandarakas et al., GCN 42404; Nakahira et al., GCN 42402; Evans et al., GCN 42401; Kang et al., GCN 42392) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 6 exposures of 15 min in the r-band at a midtime of 2025 10 24 01:51:23 UT, corresponding to T-T0 = 17.04 hours. We do not significantly detect the optical source identified by Mandarakas et al. (GCN 42404) at the 3-sigma upper limit of: r’ < 21.78 mag (AB) 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 Jean Balcaen. View this GCN Circular online at https://gcn.nasa.gov/circulars/42421. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40498] EP251023a: OHP/T193 optical observations
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42420 SUBJECT: EP251023a: OHP/T193 optical observations DATE: 25/10/24 13:25:17 GMT FROM: Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe(a)gmail.com> N.A. Rakotondrainibe (LAM), C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), report on behalf of the MISTRAL GRB collaboration: We carried out observations of EP251023a (Mohan et al., GCN 42411; Selezneva et al., GCN 42406; Lipunov et al., GCN 42405; Mandarakas et al., GCN 42400; Liu et al., GCN 42391; Li et al., GCN 42389; Wu et al., GCN 42388; Wortley et al., GCN 42387) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 4 exposures of 15 min in the r-band at a midtime of 2025 10 24 03:17:52UT corresponding to T-T0 = 24.78 hours. The afterglow is well detected in r’ and we measured the following preliminary magnitude: r’ = 21.55+/-0.10 mag (AB) 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 Jean Balcaen. View this GCN Circular online at https://gcn.nasa.gov/circulars/42420. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40497] GRB 251023C: AstroSat CZTI detection
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42419 SUBJECT: GRB 251023C: AstroSat CZTI detection DATE: 25/10/24 12:15:05 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), A. Arya (IITB), A. Goyal (IITB), 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 a long,bright GRB 251023C which was also detected by SWIFT BAT (DeLaunay et. al., GCN Circ. 42412), and CALET (Asaoka et. al., GCN Circ. 42414). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-10-23 16:24:32.50 UTC. The measured peak count rate associated with the burst is 682 (+55, -51) counts/s above the background in the combined data of all quadrants, with a total of 4344 (+401, -229) counts. The local mean background count rate was 294 (+1, -7) counts/s. Using cumulative rates, we measure a T90 of 18.2 (+2.8, -1.6) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-10-23 16:24:28.05 UTC. The measured peak count rate associated with the burst is 942 (+83, -89) counts/s above the background in the combined data of all quadrants, with a total of 5554 (+521, -528) counts. The local mean background count rate was 1676 (+7, -8) counts/s. We measure a T90 of 15.8 (+1.9, -6.2) s from the cumulative Veto light curve. 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/42419. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40496] GRB 251023C: AstroSat CZTI detection
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42419 SUBJECT: GRB 251023C: AstroSat CZTI detection DATE: 25/10/24 12:15:05 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), A. Arya (IITB), A. Goyal (IITB), 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 a long,bright GRB 251023C which was also detected by SWIFT BAT (DeLaunay et. al., GCN Circ. 42412), and CALET (Asaoka et. al., GCN Circ. 42414). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-10-23 16:24:32.50 UTC. The measured peak count rate associated with the burst is 682 (+55, -51) counts/s above the background in the combined data of all quadrants, with a total of 4344 (+401, -229) counts. The local mean background count rate was 294 (+1, -7) counts/s. Using cumulative rates, we measure a T90 of 18.2 (+2.8, -1.6) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-10-23 16:24:28.05 UTC. The measured peak count rate associated with the burst is 942 (+83, -89) counts/s above the background in the combined data of all quadrants, with a total of 5554 (+521, -528) counts. The local mean background count rate was 1676 (+7, -8) counts/s. We measure a T90 of 15.8 (+1.9, -6.2) s from the cumulative Veto light curve. 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/42419. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40495] EP251023b/GRB 251023B: JinShan optical observation
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42418 SUBJECT: EP251023b/GRB 251023B: JinShan optical observation DATE: 25/10/24 08:38:09 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He, J. An, S.Q. Jiang, X. Liu, Z.P. Zhu, D. Xu (NAOC), S.Y. Fu, A.D. Zhu, L. Lei, H.Z. Wu (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration: We observed the field of EP251023b/GRB 251023B (Kang et al., GCN 42392; Nakahira et al., GCN 42402; Wu et al., GCN 42415) using the 100C telescope of the JinShan project, located at Altay, Xinjiang, China. Observations started at 2025-10-23 16:01:41 UT, i. e. 7.3 hours after the trigger. The previously reported optical counterpart (Mandarakas et al., GCN 42404) was detected in our stacked z-band frame with a magnitude z~21.4 at a mid-time 9.75 hrs post-burst. The magnitude was callibrated with nearby PanSTARRS1 dr2 catalog 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/42418. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40494] GRB 251022A: Swift-XRT detection of GOTO25iym
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42417 SUBJECT: GRB 251022A: Swift-XRT detection of GOTO25iym DATE: 25/10/24 08:12:16 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Fermi/LAT-detected burst GRB 251022A in a series of observations tiled on the sky. The total exposure time is 4.6 ks, distributed over 4 tiles; the maximum exposure at a single sky location in the tiling was 2.5 ks. The data were collected between T0+26.7 ks and T0+71.7 ks, and are entirely in Photon Counting (PC) mode. Seven uncatalogued X-ray sources have been detected, however none of them is above the RASS limit or shows definitive signs of fading in the X-rays. Source 4 is 2.6 arcsec from the reported optical transient GOTO25iym (O'Neill et al., GCN Circ. 42386) and thus is likely the counterpart to that transient and the GRB afterglow, though we cannot at present confirm fading in X-rays. The details of this source are: Source 4: RA (J2000.0): 65.4968 = 04h 21m 59.23s Dec (J2000.0): -18.9188 = -18d 55' 07.8" Error: 4.8 arcsec (radius, 90% conf.) Count-rate: 0.0110 [+0.0026, -0.0025] ct s^-1 Distance: 1463 arcsec from Fermi/LAT position. Flux: (2.96 [+0.71, -0.67])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) The other 6 uncatalogued sources detected are enumerated below: Source 1: RA (J2000.0): 65.0135 = 04h 20m 03.25s Dec (J2000.0): -19.3306 = -19d 19' 50.1" Error: 6.3 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: 0.0173 [+0.0061, -0.0050] ct s^-1 Distance: 1247 arcsec from Fermi/LAT position. Flux: (3.5 [+1.2, -1.0])e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 2: RA (J2000.0): 65.0984 = 04h 20m 23.62s Dec (J2000.0): -19.2625 = -19d 15' 45.2" Error: 5.4 arcsec (radius, 90% conf.) Count-rate: 0.0115 [+0.0046, -0.0037] ct s^-1 Distance: 971 arcsec from Fermi/LAT position. Flux: (4.4 [+1.8, -1.4])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 5: RA (J2000.0): 65.3796 = 04h 21m 31.10s Dec (J2000.0): -18.9857 = -18d 59' 08.4" Error: 6.0 arcsec (radius, 90% conf.) Count-rate: (7.7 [+2.6, -2.1])e-3 ct s^-1 Distance: 1167 arcsec from Fermi/LAT position. Flux: (2.17 [+0.72, -0.60])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 6: RA (J2000.0): 65.5456 = 04h 22m 10.93s Dec (J2000.0): -19.1086 = -19d 06' 30.8" Error: 6.5 arcsec (radius, 90% conf.) Count-rate: (6.0 [+2.5, -2.0])e-3 ct s^-1 Distance: 917 arcsec from Fermi/LAT position. Flux: (9.1 [+3.9, -3.0])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 8: RA (J2000.0): 65.4382 = 04h 21m 45.16s Dec (J2000.0): -19.0268 = -19d 01' 36.6" Error: 7.8 arcsec (radius, 90% conf.) Count-rate: (3.2 [+1.8, -1.3])e-3 ct s^-1 Distance: 1038 arcsec from Fermi/LAT position. Flux: (6.8 [+3.9, -2.8])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 9: RA (J2000.0): 65.3956 = 04h 21m 34.95s Dec (J2000.0): -19.0576 = -19d 03' 27.4" Error: 6.3 arcsec (radius, 90% conf.) Count-rate: (3.6 [+2.1, -1.5])e-3 ct s^-1 Distance: 910 arcsec from Fermi/LAT position. Flux: (1.15 [+0.65, -0.48])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Two catalogued sources were also detected. The results of the XRT-team automatic analysis of the tiled XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00139. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42417. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40493] EP251023b: Global MASTER-Net observations report
by GCN Circulars 24 Oct '25

24 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42416 SUBJECT: EP251023b: Global MASTER-Net observations report DATE: 25/10/24 06:18:23 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 EP251023b ( EP Team et al., GCN 42415) errorbox 40434 sec after trigger time at 2025-10-23 20:02:41 UT, with upper limit up to 20.1 mag. The observations began at zenith distance = 38 deg. The sun altitude is -34.7 deg. The galactic latitude b = -18 deg., longitude l = 187 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3022366 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 40494 | 2025-10-23 20:02:41 | MASTER-Tunka | (04h 53m 57.12s , +12d 53m 42.1s) | C | 120 | 16.4 | 40494 | 2025-10-23 20:02:41 | MASTER- | (04h 53m 27.18s , +12d 59m 22.7s) | C | 120 | 18.8 | 40627 | 2025-10-23 20:04:54 | MASTER- | (04h 53m 23.22s , +13d 00m 50.4s) | C | 120 | 19.8 | 40628 | 2025-10-23 20:04:54 | MASTER-Tunka | (04h 53m 53.26s , +12d 55m 10.3s) | C | 120 | 16.4 | 40761 | 2025-10-23 20:07:07 | MASTER-Tunka | (04h 53m 53.45s , +12d 53m 31.3s) | C | 120 | 16.9 | 40761 | 2025-10-23 20:07:07 | MASTER- | (04h 53m 23.36s , +12d 59m 11.7s) | C | 120 | 19.9 | 41086 | 2025-10-23 20:13:02 | MASTER-Tunka | (04h 53m 57.11s , +12d 54m 43.4s) | C | 60 | 19.7 | 41176 | 2025-10-23 20:13:02 | MASTER-Tunka | (04h 53m 57.11s , +12d 54m 43.3s) | C | 240 | 20.0 | Coadd 41086 | 2025-10-23 20:13:02 | MASTER- | (04h 53m 26.63s , +13d 00m 28.7s) | C | 60 | 19.7 | 41159 | 2025-10-23 20:14:15 | MASTER-Tunka | (04h 53m 50.19s , +12d 54m 07.5s) | C | 60 | 19.7 | 41159 | 2025-10-23 20:14:15 | MASTER- | (04h 53m 19.72s , +12d 59m 52.6s) | C | 60 | 19.7 | 41263 | 2025-10-23 20:15:30 | MASTER-Tunka | (04h 53m 51.71s , +12d 55m 04.5s) | C | 120 | 19.8 | 41263 | 2025-10-23 20:15:30 | MASTER- | (04h 53m 21.21s , +13d 00m 49.4s) | C | 120 | 19.8 | 41398 | 2025-10-23 20:17:44 | MASTER-Tunka | (04h 53m 57.01s , +12d 54m 00.3s) | C | 120 | 19.8 | 41518 | 2025-10-23 20:17:44 | MASTER-Tunka | (04h 53m 57.02s , +12d 54m 00.4s) | C | 360 | 20.0 | Coadd 41398 | 2025-10-23 20:17:44 | MASTER- | (04h 53m 26.46s , +12d 59m 45.2s) | C | 120 | 19.8 | 41530 | 2025-10-23 20:19:57 | MASTER-Tunka | (04h 53m 50.71s , +12d 52m 55.2s) | C | 120 | 19.7 | 41530 | 2025-10-23 20:19:57 | MASTER- | (04h 53m 20.15s , +12d 58m 40.0s) | C | 120 | 19.7 | 41663 | 2025-10-23 20:22:10 | MASTER-Tunka | (04h 53m 57.82s , +12d 53m 08.0s) | C | 120 | 19.7 | 41663 | 2025-10-23 20:22:10 | MASTER- | (04h 53m 27.32s , +12d 58m 52.6s) | C | 120 | 19.7 | 41796 | 2025-10-23 20:24:22 | MASTER-Tunka | (04h 53m 54.06s , +12d 54m 19.5s) | C | 120 | 19.7 | 41916 | 2025-10-23 20:24:22 | MASTER-Tunka | (04h 53m 54.06s , +12d 54m 19.5s) | C | 360 | 20.1 | Coadd 41796 | 2025-10-23 20:24:22 | MASTER- | (04h 53m 23.57s , +13d 00m 03.9s) | C | 120 | 19.6 | 41929 | 2025-10-23 20:26:35 | MASTER-Tunka | (04h 53m 54.16s , +12d 52m 58.5s) | C | 120 | 19.8 | 41929 | 2025-10-23 20:26:35 | MASTER- | (04h 53m 23.66s , +12d 58m 43.0s) | C | 120 | 19.8 | 42062 | 2025-10-23 20:28:48 | MASTER-Tunka | (04h 53m 57.79s , +12d 54m 17.4s) | C | 120 | 19.9 | 42062 | 2025-10-23 20:28:48 | MASTER- | (04h 53m 27.25s , +13d 00m 01.6s) | C | 120 | 19.9 | 42195 | 2025-10-23 20:31:02 | MASTER-Tunka | (04h 53m 52.11s , +12d 53m 34.1s) | C | 120 | 19.9 | 42315 | 2025-10-23 20:31:02 | MASTER-Tunka | (04h 53m 52.11s , +12d 53m 34.1s) | C | 360 | 20.1 | Coadd 42195 | 2025-10-23 20:31:02 | MASTER- | (04h 53m 21.54s , +12d 59m 18.5s) | C | 120 | 19.9 | 42327 | 2025-10-23 20:33:13 | MASTER-Tunka | (04h 53m 50.56s , +12d 54m 30.9s) | C | 120 | 20.0 | 42327 | 2025-10-23 20:33:13 | MASTER- | (04h 53m 19.95s , +13d 00m 15.1s) | C | 120 | 19.9 | 42460 | 2025-10-23 20:35:27 | MASTER-Tunka | (04h 53m 57.26s , +12d 53m 27.1s) | C | 120 | 19.9 | 42460 | 2025-10-23 20:35:27 | MASTER- | (04h 53m 26.58s , +12d 59m 11.0s) | C | 120 | 19.9 | 42595 | 2025-10-23 20:37:41 | MASTER-Tunka | (04h 53m 52.25s , +12d 52m 22.4s) | C | 120 | 19.9 | 42685 | 2025-10-23 20:37:41 | MASTER-Tunka | (04h 53m 52.25s , +12d 52m 22.4s) | C | 300 | 20.1 | Coadd 42595 | 2025-10-23 20:37:41 | MASTER- | (04h 53m 21.54s , +12d 58m 06.1s) | C | 120 | 19.9 | 42730 | 2025-10-23 20:39:56 | MASTER-Tunka | (04h 53m 57.37s , +12d 52m 45.8s) | C | 120 | 20.0 | 42730 | 2025-10-23 20:39:56 | MASTER- | (04h 53m 26.63s , +12d 58m 29.3s) | C | 120 | 20.0 | 42833 | 2025-10-23 20:42:09 | MASTER-Tunka | (04h 53m 54.47s , +12d 53m 48.3s) | C | 60 | 19.9 | 42833 | 2025-10-23 20:42:09 | MASTER- | (04h 53m 23.67s , +12d 59m 31.7s) | C | 60 | 19.9 | 42907 | 2025-10-23 20:43:24 | MASTER-Tunka | (04h 53m 54.53s , +12d 52m 27.5s) | C | 60 | 19.8 | 42967 | 2025-10-23 20:43:24 | MASTER-Tunka | (04h 53m 54.54s , +12d 52m 27.5s) | C | 180 | 20.0 | Coadd 42907 | 2025-10-23 20:43:24 | MASTER- | (04h 53m 23.70s , +12d 58m 10.7s) | C | 60 | 19.8 | 42980 | 2025-10-23 20:44:36 | MASTER-Tunka | (04h 53m 56.90s , +12d 54m 01.3s) | C | 60 | 19.7 | 42980 | 2025-10-23 20:44:36 | MASTER- | (04h 53m 26.04s , +12d 59m 44.2s) | C | 60 | 19.7 | 43052 | 2025-10-23 20:45:49 | MASTER-Tunka | (04h 53m 52.30s , +12d 53m 09.6s) | C | 60 | 19.5 | 43052 | 2025-10-23 20:45:49 | MASTER- | (04h 53m 21.42s , +12d 58m 52.8s) | C | 60 | 19.5 | 43134 | 2025-10-23 20:47:11 | MASTER-Tunka | (04h 53m 51.00s , +12d 54m 07.5s) | C | 60 | 19.2 | 43194 | 2025-10-23 20:47:11 | MASTER-Tunka | (04h 53m 50.99s , +12d 54m 07.5s) | C | 180 | 19.7 | Coadd 43135 | 2025-10-23 20:47:11 | MASTER- | (04h 53m 20.10s , +12d 59m 50.4s) | C | 60 | 19.1 | 43208 | 2025-10-23 20:48:25 | MASTER-Tunka | (04h 53m 58.03s , +12d 53m 05.4s) | C | 60 | 19.2 | 43208 | 2025-10-23 20:48:25 | MASTER- | (04h 53m 27.12s , +12d 58m 48.7s) | C | 60 | 19.1 | 43284 | 2025-10-23 20:49:41 | MASTER-Tunka | (04h 53m 50.96s , +12d 52m 02.9s) | C | 60 | 19.0 | 43284 | 2025-10-23 20:49:41 | MASTER- | (04h 53m 20.05s , +12d 57m 45.8s) | C | 60 | 19.0 | 43358 | 2025-10-23 20:50:54 | MASTER-Tunka | (04h 53m 58.58s , +12d 52m 08.7s) | C | 60 | 18.8 | 43418 | 2025-10-23 20:50:54 | MASTER-Tunka | (04h 53m 58.58s , +12d 52m 08.7s) | C | 180 | 19.3 | Coadd 43358 | 2025-10-23 20:50:54 | MASTER- | (04h 53m 27.65s , +12d 57m 51.3s) | C | 60 | 18.7 | 43435 | 2025-10-23 20:52:12 | MASTER-Tunka | (04h 53m 54.73s , +12d 53m 32.9s) | C | 60 | 18.7 | 43435 | 2025-10-23 20:52:12 | MASTER- | (04h 53m 23.76s , +12d 59m 15.7s) | C | 60 | 18.7 | 43507 | 2025-10-23 20:53:24 | MASTER-Tunka | (04h 53m 54.77s , +12d 52m 13.3s) | C | 60 | 18.3 | 43507 | 2025-10-23 20:53:24 | MASTER- | (04h 53m 23.79s , +12d 57m 56.2s) | C | 60 | 18.2 | 43579 | 2025-10-23 20:54:36 | MASTER-Tunka | (04h 53m 57.61s , +12d 53m 34.0s) | C | 60 | 18.7 | 43639 | 2025-10-23 20:54:36 | MASTER-Tunka | (04h 53m 57.62s , +12d 53m 34.0s) | C | 180 | 19.9 | Coadd 43579 | 2025-10-23 20:54:36 | MASTER- | (04h 53m 26.61s , +12d 59m 16.6s) | C | 60 | 18.7 | 43654 | 2025-10-23 20:55:50 | MASTER-Tunka | (04h 53m 52.49s , +12d 52m 52.2s) | C | 60 | 19.6 | 43654 | 2025-10-23 20:55:50 | MASTER- | (04h 53m 21.48s , +12d 58m 34.6s) | C | 60 | 19.5 | 43727 | 2025-10-23 20:57:04 | MASTER-Tunka | (04h 53m 51.37s , +12d 53m 50.1s) | C | 60 | 19.5 | 43727 | 2025-10-23 20:57:04 | MASTER- | (04h 53m 20.37s , +12d 59m 32.4s) | C | 60 | 19.4 | 43800 | 2025-10-23 20:58:16 | MASTER-Tunka | (04h 53m 57.11s , +12d 52m 48.1s) | C | 60 | 19.6 | 43890 | 2025-10-23 20:58:16 | MASTER-Tunka | (04h 53m 57.11s , +12d 52m 48.2s) | C | 240 | 20.0 | Coadd 43800 | 2025-10-23 20:58:16 | MASTER- | (04h 53m 26.13s , +12d 58m 30.3s) | C | 60 | 19.6 | 43873 | 2025-10-23 20:59:30 | MASTER-Tunka | (04h 53m 52.86s , +12d 51m 46.0s) | C | 60 | 19.6 | 43873 | 2025-10-23 20:59:30 | MASTER- | (04h 53m 21.87s , +12d 57m 27.9s) | C | 60 | 19.5 | 43984 | 2025-10-23 21:00:51 | MASTER-Tunka | (04h 53m 58.73s , +12d 51m 48.7s) | C | 120 | 19.2 | 43984 | 2025-10-23 21:00:51 | MASTER- | (04h 53m 27.73s , +12d 57m 30.8s) | C | 120 | 19.2 | 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/42416. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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