September 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 39943] The EP-WXT trigger 01709240768: Las Cumbres discovery of the optical counterpart
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41877 SUBJECT: The EP-WXT trigger 01709240768: Las Cumbres discovery of the optical counterpart DATE: 25/09/19 03:28:55 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> Wenxiong Li (NAOC), Iair Arcavi (TAU), Ido Keinan (TAU), David Sand (U of Arizona) We observed the position of EP-WXT trigger 01709240768 with a Las Cumbres 1m telescope at Cerro Tololo Inter-American Observatory 0.8 hours after the Einstein Probe WXT trigger. We took 2x300s exposures in the broad optical w band. We find an uncataloged source at RA=298.55383, Dec=-48.8378 within the EP/WXT error circle and measure the following preliminary photometry calibrated to the r band: MJD 60937.127 Mag 17.0 Additional followup is encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/41877. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39942] GRB 250916A: Fermi GBM Observation
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41876 SUBJECT: GRB 250916A: Fermi GBM Observation DATE: 25/09/19 02:43:19 GMT FROM: Matt Godwin <msg0028(a)uah.edu> Matt Godwin (UAH) and C. Meegan (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 13:29:21.01 UT on 16 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250916A (trigger 779722166/250916562). which was also detected by AstroSat ( Arya et al. 2025, GCN 41843) with an optical counterpart by GOTO (Belkin et al. 2025, GCN 41847). The angle from the Fermi LAT boresight is 66 degrees. GBM triggered on what appears to be precursor and the main emission episode begins about 150 seconds after the precursor. The lightcurve has a duration (T90) of about 80 s (50-300 keV). The time-averaged spectrum of the main emission from T0+230 to T0+290 s is best fit by a Band function with Epeak = 144 +/- 9 keV, alpha = -1.08 +/- 0.03, and beta = -2.00 +/- 0.03. The event fluence (10-1000 keV) within this time interval is (4.61 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+270 s in the 10-1000 keV band is 5.65 +/- 0.4 ph/s/cm^2. The time-averaged spectrum of the percursor from T0-12 to T0+05 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.92 +/- 0.3 and the cutoff energy, parameterized as Epeak, is 110 +/- 22 keV. The event fluence (10-1000 keV) within this time interval is (1.31 +/- 0.15)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+270 s in the 10-1000 keV band is 0.67 +/- 0.05 ph/s/cm^2. The localization for the preliminary pulse is uncertain, but consistent with the secondary pulse. The event fluence (10-1000 keV) within the whole time interval is (4.73 +/- 0.16)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+270 s in the 10-1000 keV band is 4.57 +/- 0.3 ph/s/cm^2. The localization for the preliminary pulse is uncertain, but consistent with the secondary pulse. 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/41876. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39941] Fermi GRB 250919A: Global MASTER-Net observations report
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41875 SUBJECT: Fermi GRB 250919A: Global MASTER-Net observations report DATE: 25/09/19 01:30:59 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250919A ( Fermi GBM team, GCN 41874) errorbox 557 sec after notice time and 592 sec after trigger time at 2025-09-19 00:38:44 UT, with upper limit up to 19.3 mag. The observations began at zenith distance = 63 deg. The sun altitude is -47.5 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 250919A errorbox 658 sec after notice time and 693 sec after trigger time at 2025-09-19 00:40:26 UT, with upper limit up to 20.3 mag. The observations began at zenith distance = 19 deg. The sun altitude is -28.7 deg. The galactic latitude b = -34 deg., longitude l = 350 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2994728 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 622 | 2025-09-19 00:38:44 | MASTER-SAAO | (20h 12m 52.30s , -49d 54m 57.2s) | C | 60 | 19.3 | 622 | 2025-09-19 00:38:44 | MASTER-SAAO | (20h 10m 02.82s , -49d 39m 38.7s) | C | 60 | 19.2 | 764 | 2025-09-19 00:40:26 | MASTER-OAFA | (20h 13m 10.49s , -49d 55m 27.8s) | C | 140 | 20.2 | 925 | 2025-09-19 00:42:52 | MASTER-OAFA | (20h 13m 10.79s , -49d 55m 23.7s) | C | 170 | 20.3 | 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/41875. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39940] GRB 250919A: Fermi GBM Final Real-time Localization
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41874 SUBJECT: GRB 250919A: Fermi GBM Final Real-time Localization DATE: 25/09/19 00:39:24 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 00:28:52 UT on 19 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250919A (trigger 779934537.284108 / 250919020). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 303.5, Dec = -49.8 (J2000 degrees, equivalent to J2000 20h 14m, -49d 47'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 57.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250919020/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250919020/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250919020/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41874. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39939] GRB 250916A: KAIT optical observations
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41873 SUBJECT: GRB 250916A: KAIT optical observations DATE: 25/09/18 22:13:06 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of GRB 250916A (Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855; Waratkar et al., GCN 41871) starting at ~0.783d and again at ~1.738d after the burst. A set of clear (roughly R) filter images were obtained. We clearly detected the optical afterglow (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) in our coadd images. We estimate the afterglow to be 19.35 +/- 0.1 and 20.10 +/- 0.1 mag (Vega) at a mid time of ~0.824d and ~1.807d respectively. View this GCN Circular online at https://gcn.nasa.gov/circulars/41873. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39938] GRB 250917B: VLT/HAWK-I near-infrared observations
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41872 SUBJECT: GRB 250917B: VLT/HAWK-I near-infrared observations DATE: 25/09/18 20:03:34 GMT FROM: muskan.yadav(a)students.uniroma2.eu Muskan Yadav (U. Rome), Rosa L. Becerra (U. Rome) and Eleonora Troja (U. Rome) report on behalf of the ERC BHianca team: We observed the field of GRB 250917B (Fermi GBM Team et al., GCN 41846; Caputo et al., GCN 41848) with the HAWKI imager on the ESO VLT UT4 (Yepun). Observations started on 2025-09-17 at 23:52:22 UT, approximately 0.7 days after the trigger, and were carried out in the Ks filter at an average seeing of 0.6". Image subtraction against 2MASS Catalogue (Skrutskie et al. 2006) shows no new uncataloged source down to K~18.5 AB. Several fainter objects are visible within the BAT refined position (Parsotan et al., GCN 41868), however additional observations are required to assess their variability. At the position of the Source 1 reported by Kennea et al. GCN 41851, our observation is dominated by the close bright star TYC 1059-317-1. We thank the staff at the VLT, for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41872. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39937] GRB 250916A: NuSTAR detection of the prompt emission
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41871 SUBJECT: GRB 250916A: NuSTAR detection of the prompt emission DATE: 25/09/18 19:45:02 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 250916A in both the NuSTAR CsI anti-coincidence shields. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm triggered at 2025-09-16 13:33:27.000 (with a resolution ~5-seconds). This is consistent with the detections by Fermi-GBM (Fermi GBM Team, GCN Circ., 41839), Astrosat-CZTI (Arya et al., GCN Circ. 41843), Glowbug (Cheung et al., GCN Circ. 41855), and CALET-GBM (Trig ID. 1442064382). The NuSTAR CsI shield data are recorded at 1 Hz. The burst appears to be composed of two significantly-detected peaks. We do not detect the initial faint burst detected by Fermi-GBM which occurred ~250-s before our detection. The total duration for the event is at roughly 50-s. The peak count rate is ~500-cps over a baseline rate of ~1,000-cps during this time period. We do not see clear evidence in the signal above 100 keV in the CdZnTe detectors. The localization from the optical counterpart candidate (Belkin et al., GCN Circ. 41847) at RA = 26.57, Dec = 36.16 implies an offset from the NuSTAR boresight of 69-deg (e.g., through the side of the instrument) and the offset from the geocenter of 142-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250916A/ Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/41871. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39936] GRB 250916A: further SAO RAS optical observations
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41870 SUBJECT: GRB 250916A: further SAO RAS optical observations DATE: 25/09/18 15:39:58 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), A. Pozanenko (IKI), N. Pankov (HSE, IKI) 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) with the BTA, 6-m telescope of SAO RAS equipped with SCORPIO-1 focal reducer. We obtained 3 x 60 sec. images in Rc band under mediocre weather conditions on September 18, 00:07:09--00:15:29 UT (t_mid - T0 = 1.4458 days = 34.6994 hours). The OT (Belkin et al., GCN 41847; Mohan et al., GCN 41858; Burkhonov et al., GCN 41860) at the redshift z = 2.015 (de Ugarte Postigo et al., GCN 41863) is clearly detected in the stacked frame with a brightness of R = 19.72 +/- 0.05. The preliminary photometry is based on PanSTARRS data on nearby objects (magnitudes calculated using the Lupton 2005 transformations) and does not take into account Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41870. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39935] GRB 250912A: SVOM/ECLAIRs refined analysis
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41869 SUBJECT: GRB 250912A: SVOM/ECLAIRs refined analysis DATE: 25/09/18 15:09:27 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Hui Yang, Olivier Godet, Marius Brunet, Jean-Luc Atteia (IRAP), Floriane Cangemi (APC), Jean-Grégoire Ducoin, Damien Dornic (CPPM) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250912A (SVOM burst-id sb25091206, GCN 41820) detected at T0 = 2025-09-12T21:06:24.69, which was also detected by SVOM/GRM (GCN 41826) and Fermi/GBM (GCN 41819). The burst that triggered ECLAIRs consists of a short main peak starting from T0-1.19 s and lasting about 0.6 s in the 4-120 keV energy band, followed by extended emission continuing until T0+18.3 s. We note a weak precursor at T0-11.1 s, detected mainly in the 8-20 keV band by ECLAIRs and also by GRM, whose position is consistent with that of the main event. The spectrum of the main peak (from T0-1.19 s to T0-0.55 s) in the 4-120 keV energy range is well fitted by a power-law model with a photon index of 1.2 +/-0.2. With this model, the 4-120 keV flux is (1.7+/-0.4)e-07 erg/cm^2/s. The spectrum of the extended emission following the main peak (from T0-0.55 s to T0+18.31 s) in the 4-120 keV band is well fitted by a power-law model with a photon index of 1.4+/-0.1, yielding a 4-120 keV flux of (3.3+/-0.5)e-08 erg/cm^2/s. The spectral index is consistent with that measured by SVOM/GRM and Fermi/GBM (GCN 41828). The combined fluence of both components in the 4-120 keV is (7.3+/-1.0)e-07 erg/cm^2. The low count rates prevent a spectral analysis of the precursor and the time-resolved spectral analysis of the burst. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Hui Yang (IRAP) (hui.yang(a)irap.omp.eu) View this GCN Circular online at https://gcn.nasa.gov/circulars/41869. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39934] GRB 250917B: Swift-BAT refined analysis
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41868 SUBJECT: GRB 250917B: Swift-BAT refined analysis DATE: 25/09/18 13:56:31 GMT FROM: Amy <yarleen(a)gmail.com> T. Parsotan (GSFC), S. D. Barthelmy (GSFC), R. Caputo (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250917B (trigger #1350381) (Caputo et al., GCN Circ. 41848). The BAT ground-calculated position is RA, Dec = 291.382, 11.117 deg which is RA(J2000) = 19h 25m 31.8s Dec(J2000) = +11d 06' 59.9" with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 48%. The mask-weighted light curve shows a single FRED-like structure that starts at ~T-0.1, peaks at ~T0, and ends at ~T+0.4. T90 (15-350 keV) is 0.29 +- 0.08 sec (estimated error including systematics). The time-averaged spectrum from T+0.00 to T+0.37 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.66 +- 0.17. The fluence in the 15-150 keV band is 1.7 +- 0.2 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T-0.31 sec in the 15-150 keV band is 2.4 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1350381 View this GCN Circular online at https://gcn.nasa.gov/circulars/41868. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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