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[vsnet-grb-info 41035] GRB251129A/EP251129a: Swift UVOT detection
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42959 SUBJECT: GRB251129A/EP251129a: Swift UVOT detection DATE: 25/12/02 18:31:14 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> N.P.M. Kuin (UCL-MSSL) and B. Cenko (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began observations of the field of GRB 251129A 16.8 ks after the SVOM trigger (Tan et al., GCN Circ. 42877). GRB251129A was also detected by the EP (Wu et al, GCN Circ. 16828). The optical afterglow consistent with the SVOM/COLIBRI position (Angulo et al. GCN Circ. 42880; Watson, GCN Circ. 42883) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits 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 16828 17147 315 19.63 +/- 0.07 white 27564 28089 502 19.69 +/- 0.12 white 111007 117142 1044 20.22 +/- 0.12 white 227072 234439 2745 20.92 +/- 0.17 u 16503 16823 315 20.06 +/- 0.30 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.025 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42959. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41034] GRB251129A/EP251129a: Swift UVOT detection
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42959 SUBJECT: GRB251129A/EP251129a: Swift UVOT detection DATE: 25/12/02 18:31:14 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> N.P.M. Kuin (UCL-MSSL) and B. Cenko (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began observations of the field of GRB 251129A 16.8 ks after the SVOM trigger (Tan et al., GCN Circ. 42877). GRB251129A was also detected by the EP (Wu et al, GCN Circ. 16828). The optical afterglow consistent with the SVOM/COLIBRI position (Angulo et al. GCN Circ. 42880; Watson, GCN Circ. 42883) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits 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 16828 17147 315 19.63 +/- 0.07 white 27564 28089 502 19.69 +/- 0.12 white 111007 117142 1044 20.22 +/- 0.12 white 227072 234439 2745 20.92 +/- 0.17 u 16503 16823 315 20.06 +/- 0.30 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.025 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42959. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41033] GRB 251129B: AstroSat CZTI detection
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42958 SUBJECT: GRB 251129B: AstroSat CZTI detection DATE: 25/12/02 18:22:35 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 short-duration GRB 251129B which was also detected by Konus Wind (IPN Notices). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed a peak of emission with the strongest peak at 2025-11-29T09:51:34 UTC. The measured peak count rate associated with the burst is 1480 (+927, -83) counts/s above the background in the combined data of three quadrants (out of four), with a total of 128 (+30, -29) counts. The local mean background count rate was 212 (+20, -44)) counts/s. Using cumulative rates, we measure a T90 of 0.14 (+0.04, -0.03) s. 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/42958. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41032] GRB 251202A: Fermi GBM Observation
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42957 SUBJECT: GRB 251202A: Fermi GBM Observation DATE: 25/12/02 16:57:29 GMT FROM: Suman Bala at USRA <sumanbala2210(a)gmail.com> S. Bala (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 01:50:52.31 UT on 02 December 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251202A (GCN trigger 786333057/251202077), which was also detected by Einstein Probe (Y. J. Zhang et al. 2025, GCN 42937), Swift XRT (B. Sbarufatti et al. 2025, GCN 42943), Swift UVOT (N.P.M. Kuin et al. 2025, GCN 42956) GOTO (D. O’Neill et al. 2025, GCN 42947) and LCO (J. Quirola-Vasquez et al. 2025, GCN 42948). The spectroscopic redshift of GRB 251202A is found to be 2.785 by NOT (Z.P. Zhu et al. 2025, GCN 42939). The Fermi GBM Final Real-time Localization (GCN 42933) is consistent with the position reported by other instruments. The angle from the Fermi LAT boresight is 73 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 43 s (50-300 keV). The time-averaged spectrum from T0-10 to T0+55 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.07 +/- 0.06 and the cutoff energy, parameterized as Epeak, is 350 +/- 50 keV. The event fluence (10-1000 keV) in this time interval is (9.9 +/- 0.6)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+8.8 s in the 10-1000 keV band is 4.2 +/- 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/42957. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41031] GRB 251202A: Swift/UVOT Detection
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42956 SUBJECT: GRB 251202A: Swift/UVOT Detection DATE: 25/12/02 16:35:43 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> N.P.M. Kuin (UCL-MSSL) and M. J. Moss (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of EP251202a/GRB 251202A 17,500s after the EP trigger (Zhang et al., GCN Circ. No 42937). A source consistent with Li et al. (GCN Circ No 42934) and the XRT position (Sbarufatti et al. GCN Circ. No. 42943) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 08:08:27.5 = 122.11420 (deg.) Dec (J2000) = 40:36:45.3 = 40.61244 (deg.) with an estimated uncertainty of 0.48 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u 17500 18104 509 19.80 +/- 0.20 u 23697 24044 342 20.26 +/- 0.39 u 28710 28841 129 20.06 +/- 0.53 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.043 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42956. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41030] GRB 251201B: Kilonova-Catcher optical afterglow detection
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42955 SUBJECT: GRB 251201B: Kilonova-Catcher optical afterglow detection DATE: 25/12/02 16:14:17 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> 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 251201B detected by Swift/BAT (Moss et al., GCN 42924) and Fermi/GBM (Fermi GBM team, GCN 42923) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iTelescope 72 located in Chile and operated by M. Freeberg. Our observations started at TGRB+8.4h and were taken with Rc filter. In our stacked frames, subtracted from the Legacy Survey DR10 template image, we detect the optical counterpart reported by Swift/UVOT(Moss et al., GCN 42924, Kuin et al., GCN 42954), LCO/1m (Cerón et al., GCN 42929), MASTER (Buckley et al., GCN 42930), SVOM/VT (Li et al., GCN 42931). We report our follow-up results in the table below: +---------------+-----------+-----------+----------------+-------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+===========+================+=============+ | 8.89 | 17 x 180s | Rc (Vega) | 20.33 +/- 0.09 | iT72 | +---------------+-----------+-----------+----------------+-------------+ All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). 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/42955. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41029] GRB 251201B: Swift/UVOT Detection
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42954 SUBJECT: GRB 251201B: Swift/UVOT Detection DATE: 25/12/02 15:52:28 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> N.P.M. Kuin (UCL-MSSL) and M. J. Moss (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251201B 101 s after the BAT trigger (Moss et al., GCN Circ. 42924). A source consistent with the XRT position is detected in the initial UVOT exposures. Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 101 251 147 17.31 +/- 0.03 v 644 663 19 15.97 +/- 0.12 b 570 589 20 16.71 +/- 0.10 u 314 564 246 16.48 +/- 0.04 w1 693 1808 117 18.35 +/- 0.18 m2 668 1093 39 >18.7 w2 1196 1562 39 >18.8 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.008 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42954. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41028] GRB 251130B: Glowbug gamma-ray detection
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42953 SUBJECT: GRB 251130B: Glowbug gamma-ray detection DATE: 25/12/02 15:52:05 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 251130B, which was also detected by Fermi/GBM (GCN 42905, 42907) and AstroSat/CZTI (GCN 42925). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-11-30 15:33:27.216 with a duration of 82.0 s and a total significance of about 31.8 sigma. The light curve comprises an initial broad peak at ~T0+1s, a narrow peak ~T0+19s, followed by a dominant peak at ~T0+70s. An excess at the Fermi/GBM trigger time (15:33:18) may be present in the Glowbug data at low significance. 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 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/42953. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41027] GRB 251201B: GECAM-B observation of a long burst
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42952 SUBJECT: GRB 251201B: GECAM-B observation of a long burst DATE: 25/12/02 15:41:14 GMT FROM: Yue Wang <m18509381757(a)163.com> Yue Wang, Chen-Wei Wang, Hao-Xuan Guo, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 251201B, at 2025-12-01T16:26:32.950 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #42923). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a long pulse with a duration (T90) of 65 +6/-5 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb251201B.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/42952. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41026] EP251130a: continued NOT optical observations indicate steep fading phase
by GCN Circulars 02 Dec '25

02 Dec '25

TITLE: GCN CIRCULAR NUMBER: 42951 SUBJECT: EP251130a: continued NOT optical observations indicate steep fading phase DATE: 25/12/02 15:26:45 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), P. G. Jonker (Radboud), R. H. Rasmussen (NOT and Aarhus) report on behalf of a larger collaboration. We continued the monitoring of the optical counterpart (Dornic et al., GCN 42904; Evans et al., GCN 42908; He et al., GCN 42914; Gupta et al., GCN 42916; Zheng et al., GCN 42917; van Dalen et al., GCN 42918; Moskvitin et al., GCN 42919; Aryan et al., GCN 42921; Volnova et al., GCN 42922; Ma et al., GCN 42940) of EP251130a (Wu et al., GCN 42903; Zhang et al., GCN 42915) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations consisted of two epochs, the first consisting of 3 x 300 s exposures in SDSS-i and 5 x 200 s exposures in SDSS-z starting at 2025-12-01T23:32:00, with the second epoch being a repeat of the first i-band observation starting at 2025-12-02T05:56:48. The source was detected in all stacked images. We calibrated our photometry using nearby stars from the Pan-STARRS catalog and did not correct for Galactic extinction. We obtain the following i-band photometry: epoch 1: i = 20.84 +/- 0.07 (mid time: 2025-12-01T23:42:39, ~1.52 days post trigger); epoch 2: i = 21.23 +/- 0.04 (mid time: 2025-12-02T06:07:27, ~1.79 days post trigger). These measurements show that the re-brightening reported by Zheng et al. (GCN 42917), van Dalen et al. (GCN 42918) and Moskvitin et al. (GCN 42919) seems to have finished and the light curve is fading quickly with a power-law decay index of ~2.2. Further observations are planned and encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/42951. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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