- vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 39977] GRB250920C: LCOGT Optical Detection
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41911 SUBJECT: GRB250920C: LCOGT Optical Detection DATE: 25/09/20 17:10:36 GMT FROM: Robert Strausbaugh at Eastern Illinois University <rstrausbaugh(a)eiu.edu> R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the Swift GRB 250920C field (Gupta et al., GCN 41904) with the LCOGT 1-meter Sinistro instrument at the Siding Spring Observatory, Australia site, on September 20, from 16:29 to 16:51 UT (corresponding to 1.07 to 1.26 hours after the GRB trigger time) with the SDSS r and i filters. We performed a series of 3x200s exposures in i-band and r-band. We detect an uncatalogued source consistent with GOTO optical counterpart candidate (Wortley et al., GCN 41907) in both bands. The following magnitudes are calculated using the PanSTARRS catalog as reference: r = 18.54 +/- 0.05 i = 18.25 +/- 0.01 These magnitudes are not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41911. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39976] GRB 250920B: Enhanced Swift-XRT position
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41910 SUBJECT: GRB 250920B: Enhanced Swift-XRT position DATE: 25/09/20 17:03:19 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 1850 s of XRT Photon Counting mode data and 5 UVOT images for GRB 250920B, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 187.31688, +47.83750 which is equivalent to: RA (J2000): 12h 29m 16.05s Dec (J2000): +47d 50' 15.0" with an uncertainty of 1.9 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41910. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39975] GRB 250920B: Swift-XRT refined Analysis
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41909 SUBJECT: GRB 250920B: Swift-XRT refined Analysis DATE: 25/09/20 16:55:32 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> K.L. Page (U. Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.4 ks of XRT data for GRB 250920B, from 87 s to 22.3 ks after the trigger. The data comprise 395 s in Windowed Timing (WT) mode (the first 2 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The refined XRT position is RA, Dec = 187.3175, +47.8376 which is equivalent to: RA (J2000): 12h 29m 16.21s Dec(J2000): +47d 50' 15.2" with an uncertainty of 3.5 arcsec (radius, 90% confidence). The late-time light curve (from T0+3.8 ks) can be modelled with a power-law decay with a decay index of alpha=1.20 (+/-0.05). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.490 (+0.035, -0.017). The best-fitting absorption column is consistent with the Galactic value of 1.1 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.89 (+/-0.07) and a best-fitting absorption column of 3.3 (+1.5, -1.4) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (3.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.3 (+1.5, -1.4) x 10^20 cm^-2 Galactic foreground: 1.1 x 10^20 cm^-2 Excess significance: 2.5 sigma Photon index: 1.89 (+/-0.07) If the light curve continues to decay with a power-law decay index of 1.20, the count rate at T+24 hours will be 0.10 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.5 x 10^-12 (3.8 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01351008. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41909. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39974] GRB 250920B: SVOM/C-GFT optical observations
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41908 SUBJECT: GRB 250920B: SVOM/C-GFT optical observations DATE: 25/09/20 16:38:42 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei Qiu (NAOC), Jing Wang (NAOC), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC), report on behalf of the SVOM/C-GFT team: We observed the field of GRB 250920B detected by Fermi/GBM (Fermi Team, GCN 41897) and Swift/BAT (Gupta et al., GCN 41898) with LATIOS on SVOM/C-GFT. Observations started at 2025-09-20 11:22:32.815 UTC, ~2.60 hr after the trigger. The optical counterpart reported by Gupta et al.(GCN 41898) was clearly detected in our stacked images of band g, r, and i. The magnitudes are: | mid-time (T-T₀) / hr | exposure time / s | band | mag (AB) | mag err | |:---------------------|:------------------|:-----|:---------|:--------| | 2.76 | 10×30 | g | 17.15 | ±0.07 | | 2.64 | 10×30 | r | 17.05 | ±0.07 | | 2.85 | 9×30 | i | 17.01 | ±0.05 | The photometry was calibrated with nearby Pan-STARRS1 stars. Magnitudes were not corrected for dust extinction. We thank the observation assistants Shuai Liu and Chunlei Guo at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/41908. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39973] GRB 250920C: GOTO optical counterpart candidate
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41907 SUBJECT: GRB 250920C: GOTO optical counterpart candidate DATE: 25/09/20 16:16:16 GMT FROM: d.s.oneill(a)bham.ac.uk M. E. Wortley, D. O'Neill, B. P. Gompertz, G. Ramsay, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, A. Kumar, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 250920C (GCN #41903, Fermi GBM team, #41904, Gupta et al.). Targeted observations were performed at 2025-09-20 15:33:10 (starting 0.13 hours after trigger). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogues. Human vetting was carried out in real time on any candidates that passed the above checks. We identify a candidate optical counterpart GOTO25hju with L = 15.91±0.01 AB mag, within the Swift/BAT error region with coordinates: RA,DEC (J2000) = 51.465773, -29.65547 | 03:25:51.79, -29:39:19.67 We find no evidence of these sources prior to the GRB trigger time in previous GOTO observations taken at 2025-09-17 16:39:05 UT (2.95d pre-trigger) down to a depth of L<19.7 AB mag, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). There is a faint, point-like object coincident at the source location in the Legacy catalogue. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Observations are ongoing. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/41907. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39972] GRB 250919A / EP250919a: LCO optical observation
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41906 SUBJECT: GRB 250919A / EP250919a: LCO optical observation DATE: 25/09/20 16:06:37 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), D. Turpin (CEA/Irfu), J. T. Palmerio (CEA/Irfu), Z. Q. Wang (GXU), Y. F. Liang (PMO), report on behalf of the SVOM mission team: We observed the field of GRB 250919A / EP250919a detected by Fermi/GBM (Fermi GBM Team, GCN 41874), EP/WXT (Liang et al., GCN 41879), SVOM/GRM (Wang et al., GCN 41882), Fermi/LAT (Holzmann Airasca et al., GCN 41884), NuSTAR (Waratkar et al., GCN 41888), Glowbug (Cheung et al., GCN 41891), Insight-HXMT (Wang et al. GCN 41900), Konus-Wind (Frederiks et al. GCN 41905), with the LCO 1m telescope at Siding Spring Observatory equipped with the Sinistro instrument. We obtained 3x200 s exposures in each of the SDSS g, r and i filters. The optical counterpart (Li et al., GCN 41877; Levan et al., GCN 41883; Oates et al., GCN 41886; Lipunov et al., GCN 41893; Ma et al. GCN 41894) is clearly detected in our subtracted image (using the Legacy Survey DR10 image template) with the following magnitudes (calibrated against the SkyMApper DR4 catalogued stars, not corrected for Galactic extinction): g = 19.49 +/- 0.02 (AB), at a mid-time of 32.7 hr after the trigger; r = 19.19 +/- 0.03 (AB), at a mid-time of 32.5 hr after the trigger; i = 18.98 +/- 0.04 (AB), at a mid-time of 32.5 hr after the trigger. Further observations are planned. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/41906. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39971] Konus-Wind detection of GRB 250919A
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41905 SUBJECT: Konus-Wind detection of GRB 250919A DATE: 25/09/20 15:50:37 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> 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 GRB 250919A (Fermi-GBM detection: The Fermi GBM team, GCN 41874; Mukherjee & Meegan, GCN 41890; EP-WXT detection: Liang et al., GCN 41879; SVOM-GRM observaion: Wang et al., GCN 41882), Fermi-LAT detection: Holzmann Airasca et al., GCN 41884; Glowbug detection: Cheung et al., GCN 41891; AstroSat CZTI detection: Harsha et al., GCN 41899) triggered Konus-Wind (KW) at T0=1741.403 s UT (00:29:01.403). The burst consists of two separated emission pulses and had the total duration of ~240 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/GRB250919_T01741/ As observed by Konus-Wind, the burst had a fluence of (4.24 ± 0.25)x10^-4 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 23.168 s, of (1.33 ± 0.09)x10^-4 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+218 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.94 (-0.05,+0.05), the high energy photon index beta = -2.32 (-0.17,+0.11), the peak energy Ep = 452 (-33,+39) keV, chi2 = 101/97 dof. The spectrum near the peak count rate (measured from T0+23.04 to T0+23.296 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.07 (-0.09,+0.10), the high energy photon index beta = -2.15 (-0.07,+0.06), the peak energy Ep = 515 (-38,+42) keV, chi2 = 63/62 dof. Assuming the redshift z=1.145 (Levan et al., GCN 41883) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the burst isotropic energy release E_iso to (1.53 ± 0.09)x10^54 erg, the isotropic peak luminosity L_iso to (1.03 ± 0.07)x10^54 erg/s, and the rest-frame peak spectral energy Ep,z to (970 ± 80) keV. With the obtained estimates, GRB 250919A is consistent with 68% prediction bands of both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB250919_T01741/GRB250919A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/41905. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39970] GRB 250920C: Swift detection of a burst
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41904 SUBJECT: GRB 250920C: Swift detection of a burst DATE: 25/09/20 15:39:55 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> R. Gupta (NASA GSFC), S. Dichiara (PSU), C. Gronwall (PSU), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 15:25:17 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250920C (trigger=1351039). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 51.459, -29.646 which is RA(J2000) = 03h 25m 50s Dec(J2000) = -29d 38' 44" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 40 sec. The peak count rate was ~8500 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 15:27:21.2 UT, 123.8 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 51.4644, -29.6566 which is equivalent to: RA(J2000) = 03h 25m 51.46s Dec(J2000) = -29d 39' 23.8" with an uncertainty of 5.3 arcseconds (radius, 90% containment). This location is 41 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 1.50e-09 erg cm^-2 s^-1 (0.2-10 keV). There are no UVOT data available at this time. Burst Advocate for this burst is R. Gupta (rahulbhu.c157 AT gmail.com) Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41904. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39969] GRB 250920C: Fermi GBM Final Real-time Localization
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41903 SUBJECT: GRB 250920C: Fermi GBM Final Real-time Localization DATE: 25/09/20 15:36:01 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 15:25:17 UT on 20 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250920C (trigger 780074722.062672 / 250920643). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 47.6, Dec = -26.7 (J2000 degrees, equivalent to J2000 03h 10m, -26d 41'), with a statistical uncertainty of 1.2 degrees. The angle from the Fermi LAT boresight is 93.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920643/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920643/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920643/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41903. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39968] LIGO/Virgo/KAGRA S250920bq: Coverage and upper limits from MAXI/GSC observations
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41902 SUBJECT: LIGO/Virgo/KAGRA S250920bq: Coverage and upper limits from MAXI/GSC observations DATE: 25/09/20 14:43:37 GMT FROM: Satoshi Sugita at Aoyama Gakuin U. <sugita(a)phys.aoyama.ac.jp> Y. Kawakubo, S. Sugita, M. Serino, H. Hiramatsu, Y. Kondo (AGU) H. Negoro, M. Nakajima, K. Takagi (Nihon U.), N. Kawai, T. Mihara, (RIKEN), report on behalf of the MAXI team: We examined MAXI/GSC all-sky X-ray images (2-20 keV) after compact binary merger candidate S250920bq at 2025-09-20 10:27:39.063 UTC. At the trigger time of S250920bq, the high-voltage of MAXI/GSC was on, but the FOV was out of the 90% credible region of the bayestar skymap. The first one-orbit (92 min) scan observation with GSC after the event covered 100% of the 90% credible region of the bayestar skymap from 10:30:54 to 10:46:39 UTC (T0+195 to T0+1140 sec). No significant new source was found in the region in the one-orbit scan observation. A typical 1-sigma averaged upper limit obtained in one scan observation is 20 mCrab at 2-20 keV. If you require information about X-ray flux by MAXI/GSC at specific coordinates, please contact the submitter of this circular by email. View this GCN Circular online at https://gcn.nasa.gov/circulars/41902. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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