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

[vsnet-grb-info 39543] GRB 250821A: Swift-XRT refined Analysis
by GCN Circulars 21 Aug '25

21 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41479 SUBJECT: GRB 250821A: Swift-XRT refined Analysis DATE: 25/08/21 22:32:18 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M.A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), J.A. Kennea (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 7.4 ks of XRT data for GRB 250821A, from 150 s to 29.3 ks after the trigger. The data are entirely in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=1.32 (+/-0.20). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.59 (+0.42, -0.28). The best-fitting absorption column is 3 (+13, -2) x 10^20 cm^-2, consistent with the Galactic value of 1.6 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.2 x 10^-11 (4.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3 (+13, -2) x 10^20 cm^-2 Galactic foreground: 1.6 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.59 (+0.42, -0.28) If the light curve continues to decay with a power-law decay index of 1.32, the count rate at T+24 hours will be 1.0 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.3 x 10^-15 (4.6 x 10^-15) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01344131. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41479. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39542] Swift GRB 250821A: Global MASTER-Net observations report
by GCN Circulars 21 Aug '25

21 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41478 SUBJECT: Swift GRB 250821A: Global MASTER-Net observations report DATE: 25/08/21 22:28:53 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB 250821A ( S. Dichiara et al., GCN 41462) errorbox 41464 sec after notice time and 41495 sec after trigger time at 2025-08-21 22:17:52 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 72 deg. The sun altitude is -33.2 deg. The galactic latitude b = -78 deg., longitude l = 24 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2974552 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 41585 | MASTER-Kislovodsk | C | 180 | 17.4 | 41585 | MASTER-Kislovodsk | C | 180 | 16.6 | 41787 | MASTER-Kislovodsk | C | 180 | 18.0 | 41787 | MASTER-Kislovodsk | C | 180 | 17.2 | 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/41478. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39541] GRB 250821B: Fermi GBM Detection
by GCN Circulars 21 Aug '25

21 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41477 SUBJECT: GRB 250821B: Fermi GBM Detection DATE: 25/08/21 21:02:40 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: At 16:07:47.46 UT on 21 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250821B (trigger 777485272/250821672). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 39.95, Dec = -77.13 (J2000 degrees, equivalent to J2000 2h 39m, -77d 7'), with a statistical uncertainty of 1.00 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg systematic error [Connaughton et al. 2015, ApJS, 216, 32]). The angle from the Fermi LAT boresight is 67 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 2.3 s (50-300 keV). The time-averaged spectrum from T0-0.06 to T0+2.62 s is best fit by a Band function with Epeak = 250 +/- 10 keV, alpha = -0.67 +/- 0.03, and beta = -2.24 +/- 0.06. The event fluence (10-1000 keV) in this time interval is (1.19 +/- 0.01)E-05 erg/cm^2. The 0.064-sec peak photon flux measured starting from T0+0.576 s in the 10-1000 keV band is 58 +/- 1.9 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/41477. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39540] LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
by GCN Circulars 21 Aug '25

21 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41476 SUBJECT: LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz DATE: 25/08/21 20:58:24 GMT FROM: Andrew Levan at Radboud University <a.levan(a)astro.ru.nl> Smaranika Banerjee (Stockholm University), Maria-Teresa Botticella (INAF - Capodimonte Obs.), Seán J. Brennan (MPE), Enrico Cappellaro (Padua Obs.), Ting-Wan Chen (NCU Taiwan), Paolo D'Avanzo (INAF - Brera Obs.), Max De Pasquale (Univ. Messina), Rob A. J. Eyles-Ferris (Leicester), Morgan Fraser (UCD), James H. Gillanders (Oxford), Ben Gompertz (Birmingham), Nusrin Habeeb (Leicester), Luca Izzo (INAF/OAC and DARK/NBI), Peter G. Jonker (Radboud), Andrew J. Levan (Radboud and Warwick), Daniele Bjørn Malesani (DAWN/NBI and Radboud), Antonio Martin-Carrillo (UCD), Sam Oates (Lancaster U.), Matt Nicholl (QUB), Andrea Rossi (INAF - Bologna), Om Sharan Salafia (INAF - Brera Obs.), Nikhil Sarin (Cambridge), Steve Schulze (Northwestern), Stephen J. Smartt (Oxford), Danny Steeghs (Warwick), Nial R. Tanvir (Leicester), Aishwarya L. Thakur (INAF-IAPS) report for the ENGRAVE collaboration: “We report preliminary analysis of ESO VLT observations obtained by the ENGRAVE collaboration of AT 2025ulz (Stein et al., GCN 41414), which was discovered within the 3D localization of the GW alert S250818k (LVK Collaboration, GCNs 41437, 41440). Following the announcement of the discovery of AT 2025ulz, we triggered optical imaging and spectroscopy, as well as NIR imaging using FORS2, X-shooter and HAWK-I. Using X-shooter, we obtained total exposure times of 3480, 3600, 3600 s in the UVB, VIS and NIR arms respectively, between 2025 Aug 20.99 and Aug 21.04 UT. As AT 2025ulz is faint, we acquired the target using a blind offset. We see no obvious broad features in our extracted spectrum that would be suggestive of either a KN or a SN. We do, however, see galaxy features, with prominent lines from the Balmer series (alpha, beta, gamma and delta), Paschen-alpha, [OII], [OIII], [OI], [NII], [SII] in emission, and Ca II in absorption, which securely place the redshift at z = 0.0848 (consistent with Karambelkar et al., GCN 41436). With HAWK-I we obtained 690 s of Ks-band imaging between Aug 20.96 and Aug 20.98 UT. While the host galaxy of AT 2025ulz is well detected, we see no obvious point source corresponding to the transient itself. We note that, in the optical, template subtraction is required to detect AT 2025ulz, and, as we have no deep templates, we are currently unable to do this in the NIR. We estimate a limiting magnitude of K > 23 (AB mag) for the image, and K > 22 at the location of AT 2025ulz. We obtained 3000 s of FORS2 long-slit spectroscopy using the 300I grism at the position of AT 2025ulz between Aug 21.01 and Aug 21.05 UT, but again see no obvious signal from the transient. We also examined the 3x60 s I-band FORS2 acquisition images, but see no clear point source. With the data in hand, we cannot confirm a signal that is kilonova-like. Neither of the two VLT spectra show signatures of a transient source and there is no detectable K-band emission to around -16 (AB mag) absolute magnitude. The host galaxy contamination makes faint object observations challenging without deep templates. If AT 2025ulz is associated with a KN, then preliminary modeling of the optical fluxes reported (Busman et al. GCN 41421, Hall et al. GCN 41433, O'Connor et al. GCN 41452, Hall et al. GCN 41453, Gillanders et al. GCN 41454, Mo et al. GCN 41456, Lui et al. GCN 45461) indicate that it must have a fairly large ejecta mass (of perhaps ~0.05 Msun) and the lack of K-band detection indicates it may be lanthanide-poor. If AT 2025ulz is a cooling tail following shock breakout in a core-collapse supernova (as seen for example in SN 1993J), then we should expect the lightcurve to begin to rise again approximately four days from now. Further ENGRAVE observations of AT 2025ulz will be carried out at the VLT. We acknowledge Célia Desgrange, Lorena Faundez, Camila de Sa Freitas, Elisa Garro, Cecilia Bustos, Claudia Cid, Miguel Lopez, Francesca Lucertini and the observing staff in Paranal for their excellent support.“ View this GCN Circular online at https://gcn.nasa.gov/circulars/41476. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39539] GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
by GCN Circulars 21 Aug '25

21 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41475 SUBJECT: GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672) DATE: 25/08/21 19:57:25 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger at 16:07:47 on 21 Aug. 2025 were manually fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 60.0 deg Decl.(2000.0) = -84.7 deg The 1 sigma statistical error radius is 2.0 deg. We estimate an additional systematic error of 2 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB250821672/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB250821672/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB250821672/json View this GCN Circular online at https://gcn.nasa.gov/circulars/41475. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39538] GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
by GCN Circulars 21 Aug '25

21 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41475 SUBJECT: GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672) DATE: 25/08/21 19:57:25 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger at 16:07:47 on 21 Aug. 2025 were manually fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 60.0 deg Decl.(2000.0) = -84.7 deg The 1 sigma statistical error radius is 2.0 deg. We estimate an additional systematic error of 2 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB250821672/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB250821672/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB250821672/json View this GCN Circular online at https://gcn.nasa.gov/circulars/41475. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39537] LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
by GCN Circulars 21 Aug '25

21 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41474 SUBJECT: LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits DATE: 25/08/21 19:06:59 GMT FROM: Sylvio Klose at TLS Tautenburg <klose(a)tls-tautenburg.de> S. Klose, B. Stecklum, A. Nicuesa Guelbenzu, and F. Ludwig (all Tautenburg) report: We observed the optical transient ZTF25abjmnps/AT2025ulz (Stein et al., GCN 41414), possibly associated with the gravitational wave event S250818k (GCN 41437), with the Tautenburg 1.34-m Schmidt telescope using the Sloan filter set. Observations were performed on 20-08-2025 between 20:06 and 20:39 UT as well as between 21:57 and 22:30 UT. They reached a 3-sigma upper limit in r and i of 22.3 and 22.4 mag (AB), respectively. Photometric calibration was performed using Pan-STARRS DR2. At the position of the optical transient (OT) discovered by Stein et al. (GCN 41414; see also Busmann et al., GCN 41421; Hall et al., GCN 41433), no point source superimposed the underlying host galaxy was detected / could be identified. Given the closeness of the OT to the host galaxy's nucleus (Liu et al., GCN 41461) we caution that the photometric limits are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/41474. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39536] GRB 250821B: Fermi GBM Final Localization of a Bright Burst
by GCN Circulars 21 Aug '25

21 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41473 SUBJECT: GRB 250821B: Fermi GBM Final Localization of a Bright Burst DATE: 25/08/21 19:00:29 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> The Fermi GBM team reports the detection of a likely LONG GRB "At 16:07:47.46 UT on 21 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250821B (trigger 777485272/250821672). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 39.95, Dec = -77.13 (J2000 degrees, equivalent to J2000 2h 39m, -77d 7'), with a statistical uncertainty of 1.00 degrees. The angle from the Fermi LAT boresight is 67 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250821672/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250821672/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250821672/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41473. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39535] GRB 250821A: Enhanced Swift-XRT position
by GCN Circulars 21 Aug '25

21 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41472 SUBJECT: GRB 250821A: Enhanced Swift-XRT position DATE: 25/08/21 18:23:49 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 1629 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250821A, 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 = 358.43974, -28.65327 which is equivalent to: RA (J2000): 23h 53m 45.54s Dec (J2000): -28d 39' 11.8" with an uncertainty of 2.6 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/41472. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39534] GRB 250821A: Swift/UVOT Upper Limits
by GCN Circulars 21 Aug '25

21 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41471 SUBJECT: GRB 250821A: Swift/UVOT Upper Limits DATE: 25/08/21 17:55:04 GMT FROM: Samantha Oates at University of Birmingham <samantha.oates(a)alumni.ucl.ac.uk> S. R. Oates (Lancaster U.) and S. Dichiara (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250821A 147 s after the BAT trigger (Dichiara et al., GCN Circ. 41462). No optical afterglow consistent with the XRT position (Evans et al., GCN Circ. 41463) 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) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag/3sigUL white (FC) 147 297 148 >20.8 u (FC) 455 475 19 >18.3 white 147 1715 281 >21.1 v 381 1593 136 >19.1 b 480 1692 127 >19.9 u 455 1667 136 >19.6 uvw1 431 1643 58 >18.7 uvm2 406 1618 136 >19.1 uvw2 357 1569 136 >19.4 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.015 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41471. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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