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

[vsnet-grb-info 42679] GRB 260511B: TRT optical observation
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44551 SUBJECT: GRB 260511B: TRT optical observation DATE: 26/05/11 14:21:35 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), L.B. He, X. Liu, Z.P. Zhu, J. An, D. Xu (NAOC), S.Y. Fu (HUST) report: We observed the field of GRB 260511B detected by SVOM (Godet et al., GCN 44543) and Fermi (Fermi GBM team, GCN 44542), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observation started at 2026-05-11T12:52:30.855 UT, i.e., 1.867 hrs post-burst, and a series of R-band frames were obtained. The optical counterpart (Wu et al., GCN 44547; Sasada et al., GCN 44549) is clearly detected in our images with a brightness of R = 16.82 +/- 0.01 at a median time of 1.875 hrs since trigger, calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44551. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42678] GRB 260510B: SVOM/ECLAIRs refined analysis
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44550 SUBJECT: GRB 260510B: SVOM/ECLAIRs refined analysis DATE: 26/05/11 14:12:00 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> N. Dagoneau (CEA), A. Saccardi (CEA), B. Cordier (CEA), report on behalf of the SVOM/ECLAIRs team: Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 260510B (SVOM burst-id sb26051001). The burst that triggered ECLAIRs onboard (GCN 44515) consists of a multiple peaks lightcurve with a duration of T90 = 12.05 -3.49 / +2.22 s in the 4-120 keV energy band. The time-averaged spectrum (from T0-0.13s to T0+12.16s) in the energy range 5-120 keV is best fitted by a simple power-law model with a photon index -1.43 +/- 0.12. With this model,the 4-120 keV fluence is (4.604 ± 0.481)E-7 erg/cm² and the 4-120 keV photon flux is 0.93 ± 0.09 ph/cm²/s. 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. The SVOM/ECLAIRs point of contact for this burst is: Nicolas Dagoneau (CEA) (nicolas.dagoneau at cea.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44550. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42677] GRB 260511B : MITSuME Akeno optical afterglow candidate detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44549 SUBJECT: GRB 260511B : MITSuME Akeno optical afterglow candidate detection DATE: 26/05/11 13:40:52 GMT FROM: Mahito Sasada at Institute of Science Tokyo <sasada(a)hp.phys.titech.ac.jp> M. Sasada, I. Takahashi, H. Hagio, Y. Kubo, A. Ochi, R. Kato, N. Hosoya, J. Yonamine, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration: We observed the field of GRB 260511B detected by SVOM (Godet et al., GCN 44543) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. The observation started at 2026-05-11 11:11:58 UT (11.4 min after the trigger). We stacked the images taken under good conditions. We detected a candidate of the optical afterglow in all-band images at R.A. = 192.5739 deg and Dec. = 4.0554 deg, which is near the candidate position of SVOM/ECLAIRs reported by Wu et al., GCN 44547. Here we report the preliminary magnitudes of the source as follows. T0+[sec] | MID-UT | T-EXP[sec] | magnitudes --------------------------------------------------------------------------------------------------------------- 716 | 2026-05-11 11:12:28 | 60 | Rc=13.1+/-0.1, Ic=13.1+/-0.1 1337 | 2026-05-11 11:22:49 | 240 | g'=14.9+/-0.1, Rc=14.9+/-0.1, Ic=14.5+/-0.1 --------------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the trigger T-EXP: Total exposure time We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire) View this GCN Circular online at https://gcn.nasa.gov/circulars/44549. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42676] GRB 260511A: Fermi GBM Detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44548 SUBJECT: GRB 260511A: Fermi GBM Detection DATE: 26/05/11 13:25:00 GMT FROM: oliver.roberts(a)universityofgalway.ie O.J. Roberts (Uni. Of Galway, Ireland) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 06:13:30.286 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260511A (trigger 800172815/260511259), which was also detected by SVOM /ECLAIRs and MXT (Godet et al. 2026, GCN 44532), with an optical counterpart was initially detected by Colibri (Akl et al. 2026, GCN 44534). The angle from the Fermi LAT boresight is 118 degrees. The GBM light curve consists of a two bright emission episodes with a duration (T90) of about 14 s (50-300 keV). The time-averaged spectrum from T0-0.26 to T0+18.43 s is best fit by a Band function, with Epeak = 166 +/- 9 keV, alpha = -0.66 +/- 0.05, and beta = -2.31 +/- 0.07. The event fluence (10-1000 keV) in this time interval is (1.973 +/- 0.032) E-05 erg/cm^2. The 1-s peak photon flux measured starting from T0+2.6 s in the 10-1000 keV band is 27.3 +/- 0.5 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/44548. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42675] GRB 260511B SVOM/C-GFT optical counterpart detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44547 SUBJECT: GRB 260511B SVOM/C-GFT optical counterpart detection DATE: 26/05/11 13:03:12 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), Z. Kang (CHO), L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC) ，O. Go-det, M. Brunet (IRAP), L. Zhang (IHEP), D. Kong (GXU) report on behalf of the SVOM/C-GFT team: We observed the field of GRB 260511B (SVOM burst-id sb26051102) detected by SVOM/ECLAIRs (Godet et al., GCN 44543) with LATIOS on SVOM/C-GFT. Observations start-ed at 2026-05-11T11:29:37 UTC, ~0.48 hr after the trigger. An uncatalogued optical source compared to Pan-STARRS1 is detected in our images within the ECLAIRs localization error circle. Its position is R.A., Dec. 192.57345, 4.05512 degrees: R.A. (J2000) = 12h50m17.63s Dec. (J2000) = +04d03m18.4s with an uncertainty of ~0.5 arcsec. The magnitudes is mag_r = 15.56 +/- 0.04 at 45.32 min post-trigger. The photometry was calibrated against nearby Pan-STARRS1 stars and no correction for Galactic dust extinction was applied. We propose that this source is the optical counterpart of GRB 260511B. Further analyses are ongoing. We thank the observation assistants Bo-Wen Li and Hong-Xv Xue 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/44547. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42674] EP260509a: LCO optical upper limits
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44546 SUBJECT: EP260509a: LCO optical upper limits DATE: 26/05/11 12:37:13 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester), G. Corcoran (UCD), P. G. Jonker (Radboud), J. A. Chácon (PUC), F. E. Bauer (SSI and UTA), report on behalf of a larger collaboration: We observed the field of the X-ray transient EP260509a (Wang et al., GCN 44517; Fu et al., GCN 44539) using LCO 1m telescopes located at the Cerro Tololo Inter-American Observatory (Chile) and McDonald Observatory (USA) equipped with SINISTRO instruments. A series of 6x300 s exposures were taken in each of the SDSS-r and SDSS-z filters, starting at 2026-05-10 08:04:39 UT and 2026-05-10 06:53:47 UT respectively (~17.2 and 18.3 hr after the first X-ray detection). No new source is detected within or at the border of the EP/WXT uncertainty region (Wang et al., GCN 44517) nor do we identify any significant residuals in subtractions using PanSTARRS DR1 templates. From the stacked images, we obtain the following 3-sigma upper limits:  r > 22.8 z > 21.4 These upper limits are in AB magnitudes, calibrated using nearby stars from the PanSTARRS catalogue, and are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44546. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42673] GRB 260511A: UTGO H50 optical afterglow observation
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44545 SUBJECT: GRB 260511A: UTGO H50 optical afterglow observation DATE: 26/05/11 12:13:03 GMT FROM: Harrison at University of Tasmania <hgharper9962(a)gmail.com> H. Harper (UTAS), K. Siellez (UTAS), B. Emptage (UTAS), K. Hill (UTAS), T. Plunkett (UTAS), A. Cole (UTAS), J.-P. Beaulieu (IAP/UTAS) report: We observed the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260511A (Godet et al., GCN [44532](gcn.nasa.gov/circulars/44532); Fermi GBM Team, GCN [44529](gcn.nasa.gov/circulars/44529)) with the Harlingten 50cm (H50) at Greenhill Observatory, University of Tasmania (UTGO). Our observation started on 2026-05-11 at 08:58:59UT, ~165 minutes after Fermi trigger Observations. We obtained 11 x 120s exposure in the SDSS r’ filter. The optical counterpart (Jiang et al., GCN [44533](gcn.nasa.gov/circulars/44533); Akl et al. GCN [44534](gcn.nasa.gov/circulars/44534); Saccardi et al. GCN [44535](gcn.nasa.gov/circulars/44535); Zheng et al. GCN [44536](gcn.nasa.gov/circulars/44536); Wu et al., GCN [44538](gcn.nasa.gov/circulars/44538)) is clearly detected in our images at RA = 13:11:35.9244 (J2000) (197.8996850 deg) and Dec = -33:48:15.887 (J2000) (-33.8044130 deg) with an uncertainty of ~0.4 arcsec. Image subtraction was performed using STDpipe. We measured the following magnitude not corrected for Galactic extinction: r = 20.68 +/- 0.12 AB (mid time ~176minutes after trigger) Refined processing and more observations are still ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/44545. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42672] GRB 260510C: AstroSat CZTI detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44544 SUBJECT: GRB 260510C: AstroSat CZTI detection DATE: 26/05/11 11:30:38 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (IITB), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), 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 long GRB 260510C which is also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 44520), SVOM/GRM (Gotz et al., GCN Circ. 44521), and MAXI/GSC (Iwari et al., GCN Circ. 44526). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-05-10 17:15:41.94 UTC. The measured peak count rate associated with the burst is 168 (+65, -24) counts/s above the background in the combined data of all quadrants, with a total of 1298 (+346, -375) counts. The local mean background count rate was 1125 (5, -6) counts/s. We measure a T90 of 14 (+3, -3) s from the cumulative Veto light curve. The source was also faintly detected in the CZT detectors in the 20-200 keV energy range. 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/44544. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42671] GRB 260511B: SVOM detection of a burst
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44543 SUBJECT: GRB 260511B: SVOM detection of a burst DATE: 26/05/11 11:25:44 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> O. Godet, M. Brunet (IRAP), L. Zhang (IHEP), D. Kong (GXU) report on behalf of the SVOM mission team: At 2026-05-11T11:00:32 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260511B (SVOM burst-id sb26051102). This transient was also detected by Fermi/GM (GCN Circular 44542). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 15 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 45.21 in the [8-120] keV energy band over a time window of 5.10 seconds starting at 2026-05-11T11:01:00. The localization of the best alert is R.A., Dec. 192.606, 4.094 degrees: R.A. (J2000) = 12h50m25.47s Dec. (J2000) = 4d05m40.00s with a 90% confidence level (C.L.) radius of 2.63 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a multiple peak structure with a T90 duration of about 41.2 -0.6/+1.0 (5-120 keV). This burst also triggered SVOM/GRM at 2026-05-11T11:00:31 on a timescale of 0.10 seconds with an SNR of 7. The SVOM/GRM light curve showed a multiple peak structure with a T90 duration of about 54.2 -5.2/+5.1 s (8-1100 keV). SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-05-11T11:03:32 UTC, 180 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 192.5735, 4.0405 degrees: R.A. (J2000) = 12h50m17.65s Dec. (J2000) = 4d02m25.68s with a 90% C.L. radius of 32.02 arcseconds. This location is 3.78 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is zhangli: zhangli at ihep.ac.cn Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44543. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0

[vsnet-grb-info 42670] GRB 260511B: Fermi GBM Final Real-time Localization
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44542 SUBJECT: GRB 260511B: Fermi GBM Final Real-time Localization DATE: 26/05/11 11:10:56 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 11:00:31 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260511B (trigger 800190036.70394 / 260511459). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 192.2, Dec = 5.0 (J2000 degrees, equivalent to J2000 12h 48m, 5d 00'), with a statistical uncertainty of 1.4 degrees. The angle from the Fermi LAT boresight is 101.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511459/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511459/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511459/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44542. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

1 0