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[vsnet-grb-info 40005] Konus-Wind detection of GRB 250911A
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41939 SUBJECT: Konus-Wind detection of GRB 250911A DATE: 25/09/22 16:37:08 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 250911A (Swift-BAT detection: Klingler et al., GCN 41781; Palmer et al., GCN 41812; GECAM-B detection: Zhang et al., GCN 41813; Insight-HXMT detection: Wang et al., GCN 41827) triggered Konus-Wind at T0=05370.240 s UT (01:29:30.240). The burst light curve shows a multipeaked structure which starts at ~T0-2.3 s and has a total duration of ~57 s. The weak precursor that triggered Swift-BAT is seen at ~T0-100 s. The emission is seen up to ~10 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250911_T05370/ As observed by Konus-Wind, the burst had the total fluence of 4.54(-0.29,+0.30)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+1.440 s, of 5.15(-0.88,+0.90)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+41.216 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.85(-0.11,+0.12), the high energy photon index beta = -2.58(-0.19,+0.14), the peak energy Ep = 196(-13,+14) keV (chi2 = 102/97 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.92(-0.11,+0.12), the high energy photon index beta = -2.44(-0.19,+0.14), the peak energy Ep = 257(-25,+26) keV (chi2 = 88/84 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/41939. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40004] GRB 250916A: Swift/UVOT Detection
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41938 SUBJECT: GRB 250916A: Swift/UVOT Detection DATE: 25/09/22 15:32:00 GMT FROM: Alice Breeveld at MSSL-UCL <a.breeveld(a)ucl.ac.uk> A. A. Breeveld (UCL-MSSL) and R. Caputo (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of the Fermi/GBM detected burst GRB 250916A 102120s after the trigger (Fermi GBM team, GCN Circ. 41839). The optical counterpart detected by 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, is detected in the initial white and u-band UVOT exposures. Preliminary magnitudes and upper limit using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u 102120 107275 968 20.5 ± 0.2 white 102446 102767 316 21.1 ± 0.3 v 102774 103051 273 >19.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.051 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41938. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40003] GRB 250920B: Glowbug gamma-ray detection
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41937 SUBJECT: GRB 250920B: Glowbug gamma-ray detection DATE: 25/09/22 14:59:17 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 250920B, which was also detected by Fermi/GBM (GCN 41897, 41919) and Swift/BAT (GCN 41898, 41923). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-09-20 08:46:28.344 with a duration of 129.5 s and a total significance of over 30 sigma. The observed light curve comprises an initial multi-peaked structure from ~T0 to T0+7.5s, followed by peaks at ~T0+76s, ~T0+107s, and ~T0+128s. 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/41937. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40002] GRB 250916A: CrAO ZTSh R-band optical observations
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41936 SUBJECT: GRB 250916A: CrAO ZTSh R-band optical observations DATE: 25/09/22 11:24:20 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), V. Rumyantsev (CrAO) report on behalf of IKI-GRB-FuN. We observed the field of the GRB 250916A (The Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855; Osborne et al., GCN 41862; Waratkar and Grefenstette, GCN 41871; Godwin and Meegan, GCN 41876) with the Shajn 2.65m telescope of CrAO, equipped with CCD-photometer. The observations in the R-filter were carried out on epochs 2025-09-19, 2025-09-20, and 2025-09-21. The OT (Belkin et al., GCN 41847; Mohan et al., GCN 41858; Burkhonov et al., GCN 41860; de Ugarte Postigo et al., GCN 41863; Moskvitin et al., GCN 41870; Zheng and Filippenko, GCN 41873; Pankov et al., GCN 41892; Hall et al., GCN 41921; Moskvitin et. al, GCN 41934) is clearly detected in the stacked images taken on each epoch. Preliminary results of our observations are given below: Date UT start t-T0 Exp. Filter OT Err. UL (mid, days) (n*s) (3sigma) 2025-09-19 21:40:39 3.42451 120*120 R 21.45 0.02 25.0 2025-09-20 23:47:56 4.48374 78*120 R 21.89 0.03 24.7 2025-09-21 22:21:48 5.44545 109*120 R 22.72 0.05 24.8 Preliminary photometry is based on the nearby objects from PanSTARRS (magnitudes converted via Lupton 2005 transformations) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41936. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40001] GRB 250920C: Swift-XRT refined Analysis
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41935 SUBJECT: GRB 250920C: Swift-XRT refined Analysis DATE: 25/09/22 10:15:36 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 5.1 ks of XRT data for GRB 250920C, from 110 s to 131.0 ks after the trigger. The data comprise 64 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+7.1 ks) can be modelled with a power-law decay with a decay index of alpha=1.53 (+/-0.09). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.94 (+/-0.10). The best-fitting absorption column is 4.8 (+2.1, -2.0) x 10^20 cm^-2, in excess of the Galactic value of 1.4 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.89 (+0.16, -0.15) and a best-fitting absorption column of 6.7 (+4.0, -3.5) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 6.7 (+4.0, -3.5) x 10^20 cm^-2 Galactic foreground: 1.4 x 10^20 cm^-2 Excess significance: 2.5 sigma Photon index: 1.89 (+0.16, -0.15) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01351039. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41935. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40000] GRB 250916A: SAO RAS Zeiss-1000 optical observations
by GCN Circulars 22 Sep '25

22 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41934 SUBJECT: GRB 250916A: SAO RAS Zeiss-1000 optical observations DATE: 25/09/22 09:39:39 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova (SAO), N. Pankov (HSE), 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 250916A (Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855; Osborne et al., GCN 41862; Waratkar and Grefenstette, GCN 41871; Godwin and Meegan, GCN 41876) with the 1-m SAO RAS telescope Zeiss-1000 equipped with the CCD-photometer. We obtained 9 x 300 sec. images Rc band on September 21, 23:36:57 -- September 22, 00:47:22 UT (t_mid - T0 = 5.44639 days). The optical transient (Belkin et al., GCN 41847; Mohan et al., GCN 41858; Moskvitin et al., GCN 41859; Burkhonov et al., GCN 41860; de Ugarte Postigo et al., GCN 41863; Moskvitin et al., GCN 41870; Zheng and Filippenko, GCN 41873; Pankov et al., GCN 41892; Hall et al., GCN 41921) is clearly detected in the stacked frame with the brightness of R = 22.6 +/- 0.1. Date UT start t-T0 Exp. Filter OT Err. UL (3sigma) (mid, d) (s) 2025.09.21 23:36:57 5.44639 9 x 300 Rc 22.6 +/- 0.1 23.3 Preliminary photometry is based on the nearby objects from PanSTARRS (magnitudes converted with Lupton 2005 equations) and has not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41934. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39999] GRB 250921A: Fermi GBM Final Localization
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41933 SUBJECT: GRB 250921A: Fermi GBM Final Localization DATE: 25/09/22 04:52:19 GMT FROM: rhamburg(a)usra.edu The Fermi GBM team reports the detection of a likely LONG GRB "At 03:07:21.46 UT on 22 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250921A (trigger 780203246/250922130). This trigger was initially classified as Below Horizon by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 353.54, Dec = 0.42 (J2000 degrees, equivalent to J2000 23h 34m, +0d 25'), with a statistical uncertainty of 6.13 degrees. The angle from the Fermi LAT boresight is 86 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250922130/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250922130/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250922130/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41933. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39998] GRB 250920B: Asiago optical observations
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41932 SUBJECT: GRB 250920B: Asiago optical observations DATE: 25/09/21 17:57:22 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> A. Reguitti (INAF/OAPd), L. Tomasella (INAF/OAPd), D. B. Malesani (DAWN/NBI and Radboud) report on behalf of a larger collaboration: We observed the field of GRB 250920B (Gupta et al., GCN 41898; Sonawane & Meegan, GCN 41919) using the 67/92 Schmidt Telescope located at the Asiago observatory (Italy). Observations were carried out using a clear filter, which covers roughly the r and i bands. The optical counterpart (Gupta et al., GCN 41898; Wu et al., GCN 41908; Hall et al., GCN 41914; Kuin & Gupta, GCN 41915) is well detected in our frames. At a mean epoch 2025 Sep 20.771 UT (9.74 hr after the GRB), we measure an AB magnitude r = 18.62 +- 0.06 (calibrated directly against r-band magnitudes from the Pan-STARRS catalog). Considering the filter difference, our measurement is consistent with the nearly simultaneous observation by Hall et al. (GCN 41914). View this GCN Circular online at https://gcn.nasa.gov/circulars/41932. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39997] GRB 250920B: Kitab-ISON optical upper limit
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41931 SUBJECT: GRB 250920B: Kitab-ISON optical upper limit DATE: 25/09/21 17:38:23 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Novichonok (Petrozavodsk State University, KIAM) report on behalf of GRB-IKI-FuN: We observed the field of a long GRB 250920B detected by Fermi/GBM (The Fermi GBM team GCN 41897), Swift (Gupta et. al, GCN 41898), with the RC-36 telescope of Kitab-ISON. The series of unfiltered 325x15 sec exposures was obtained starting on 2025-09-20 at 14:31 UT, i.e. ~0.26 days since Fermi/GBM trigger. The optical afterglow initially detected by Swift/UVOT (Gupta et. al, GCN 41898) and further observed by (WU et. al, GCN 41908; Hall et. al, GCN 41914) is not visible in our stacked image of 298x15 sec. Preliminary results of our observations provided below: Date UTstart Exptime t-T0 Filter OT Err. UL (nxs) (mid, days) (3sigma) 2025-09-20 14:31:30 298x15 0.26550 Clear n/d n/d 15.4 The photometry was calibrated against nearby USNO-B1.0 stars (R2 mags) and not corrected for the Galactic extinction. Ref. stars USNO-B1.0 RA Dec R2 187.73536 47.71878 13.75 187.52490 47.74643 13.74 View this GCN Circular online at https://gcn.nasa.gov/circulars/41931. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39996] GRB 250917B: Mondy and Zeiss-1000 SAO RAS optical observations, optical observations, afterglow candidate
by GCN Circulars 21 Sep '25

21 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41930 SUBJECT: GRB 250917B: Mondy and Zeiss-1000 SAO RAS optical observations, optical observations, afterglow candidate DATE: 25/09/21 13:38:53 GMT FROM: Alexei Pozanenko at IKI, Moscow <grb.alex(a)gmail.com> N. Pankov (HSE), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), E. Klunko (ISTP), O. Spiridonova (SAO RAS) report on behalf of GRB IKI FuN: We observed the field of Swift XRT of GRB 250917B (Fermi GBM team GCN 41846; Caputo et al. GCN 41848 ) with AZT-33IK telescope of Mondy observatory in R-filter on 2025-09-17 starting (UT) 13:36:18(epoch 1) and Zeiss-1000 of SAO RAS starting on 2025-09-17 (UT) 16:24:04 (epoch 2). We do not detect any new sources within S1, S5, S6 XRT localisation (Kennea et al., GCN 41851). This is consistent with optical observations (Hu et al, GCN 41854; Breeveld et al, GCN 41864; Yadav et al., GCN 41872; Zheng et al., GCN 41927). However, at the boundary of the S5 XRT circle, we found an object (coordinates are (J2000) 19:25:33.74 +11:04:24.85) that was significantly brighter in epoch 1 compared to epoch 2. The photometry of the object is the following Date UT start t-T0 Filter OT Err. UL(3sigma) Telescope (mid, days) (s) 2025-09-17 13:36:18 0.31845 R 19.97 +/- 0.08 21.4 AZT-33IK 2025-09-17 16:24:04 0.42394 Rc 20.79 +/- 0.12 21.3 Zeiss-1000 We suggest the source is an afterglow candidate of GRB 250917B. The object is a diffuse one and most likely is the galaxy. View this GCN Circular online at https://gcn.nasa.gov/circulars/41930. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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