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[vsnet-grb-info 42689] GRB 260511B: GROWTH-India Telescope optical observations
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44561 SUBJECT: GRB 260511B: GROWTH-India Telescope optical observations DATE: 26/05/11 17:39:26 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Vijaykumar (IITB), A.P. Saikia (IITB), V. Swain (IITB), T. Mohan (IITB), S. Patil (IITB), V. Bhalerao (IITB), G.C. Anupama (IIA), S. Barway (IIA) and R. Norbu (IAO) report on behalf of the GIT team: We observed the field of GRB 260511B detected by Fermi (Fermi GBM Team, GCN 44542), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2026-05-11 16:19:32 (UTC), i.e., 5.32 hours after the trigger, and obtained multiple exposures in the SDSS r', g', and i' filters. We detect the optical counterpart in our images at the position reported by Wu et al., GCN 44547. The photometric upper limit is as follows: | MJD (mid) | Filter | tmid-t0 (hours) | Exposure Time (sec) | Magnitude (AB) | | -------------- | ------ | --------------- | ------------------- | ---------------- | | 61171.68255 | r' | 5.37 | 1x400 | 18.27 +/- 0.05 | | 61171.68758 | g' | 5.49 | 1x400 | 18.54 +/- 0.06 | | 61171.69242 | i' | 5.61 | 1x360 | 18.10 +/- 0.10 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our results are consistent with other optical observations (Wu et al., GCN 44547 and GCN 44552; Sasada et al. GCN 44549; Jiang et al., GCN 44551.) The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/44561. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42688] GRB 260511B: AstroSat CZTI detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44560 SUBJECT: GRB 260511B: AstroSat CZTI detection DATE: 26/05/11 17:32:28 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 260511B which is also detected by Fermi/GBM (Fermi GBM Team, GCN 44542), SVOM/ECLAIRs (Godet et al., GCN 44543), and NuSTAR (Waratkar et. al. , GCN Circ. 44556). The source was clearly detected in the CZT detectors in the 20-200 keV energy range.The light curve showed multiple peaks of emission with the strongest peak at 2026-05-11 11:01:02.99 UTC. The measured peak count rate associated with the burst is 398 (+41, -36) counts/s above the background in the combined data of all quadrants, with a total of 3131 (+342, -481) counts.The local mean background count rate was 282 (+2, -4) counts/s. We measure a T90 of 39 (+3, -2) s from the cumulative CZT light curve. The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.The light curve showed multiple peaks of emission with the strongest peak at 2026-05-11 11:01:02.74. The measured peak count rate associated with the burst is 1362 (+85, -90) counts/s above the background in the combined data of all quadrants, with a total of 7777 (+766, -805) counts.The local mean background count rate was 1287 (+4, -5) counts/s. We measure a T90 of 37 (+16, -3) s from the cumulative Veto light curve. 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 data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/516193231.75/S516193231.75_det… 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/44560. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42687] GRB 260506B: Glowbug gamma-ray detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44559 SUBJECT: GRB 260506B: Glowbug gamma-ray detection DATE: 26/05/11 17:12:04 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 260506B, which was also detected by Fermi/GBM (GCN 44484, 44485) and AstroSat/CZTI (GCN 44503). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-06 13:07:30.824 with a duration of 20.5 s and a total significance of about 34 sigma. The lightcurve comprises a faint initial peak at ~T0+1s, a complex structure from ~T0+7s to +15s, and a peak at ~T0+21s — the peaks correspond to the brightest features seen in the GBM lightcurve. Note that data from ~T0-1s to +1s suffered from deadtime in various detectors. 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 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/44559. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42686] GRB 260506A: Glowbug gamma-ray detection of a short burst
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44558 SUBJECT: GRB 260506A: Glowbug gamma-ray detection of a short burst DATE: 26/05/11 16:37:58 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 the short burst GRB 260506A, which was detected by Fermi/GBM (GCN 44481). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-06 06:28:47.264 with a duration of 0.32 s and a total significance of about 19.0 sigma. The lightcurve comprises a single peak. 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 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/44558. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42685] GRB 260511B: J-band observations by the SYSU 80 cm infrared telescope
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44557 SUBJECT: GRB 260511B: J-band observations by the SYSU 80 cm infrared telescope DATE: 26/05/11 16:10:48 GMT FROM: lijj328(a)mail2.sysu.edu.cn Jin-Ji Li, Chun Chen, Duo-Le Cao, Zhong-Nan Dong, Wei-Sen Huang, Jia-Qi Lin, Pu Lin, Yun Shi, Hao-Nan Yang, Yan Yu, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team: We observed the field of GRB 260511B (SVOM burst-id sb26051102) detected by SVOM/ECLAIRs (Godet et al., GCN 44543) and Fermi (Fermi GBM team, GCN 44542), using the Sun Yat-sen University (SYSU) 80 cm infrared telescope. Our observations started on 2026 May 11 at 13:51 UT, 2.9 hours after the GRB trigger, with a total exposure time of 1800 s in the J-band images. We clearly detect the source at the position of the optical counterpart (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Wu et al., GCN 44552), and we measure J = 16.02 +/- 0.07 Vega mag. The photometry was calibrated against nearby stars from the 2MASS catalog and is reported in the Vega system, without correction for Galactic extinction. Further observations are planned. The SYSU 80 cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University. View this GCN Circular online at https://gcn.nasa.gov/circulars/44557. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42684] GRB 260511B: NuSTAR detection of prompt emission
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44556 SUBJECT: GRB 260511B: NuSTAR detection of prompt emission DATE: 26/05/11 16:08:21 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 260511B in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-05-11T11:00:31.7 UTC, shows a detection of GRB 260511B, also detected by Fermi/GBM (Fermi GBM Team, GCN 44542) and SVOM (Godet et al., GCN 44532). The NuSTAR CsI shield data are recorded at 1 Hz. We detect an initial faint burst followed by a 20-s long brighter burst consistent with the Fermi/GBM lightcurve. The peak count rate is ~2500-cps with a baseline rate of ~1000-cps during this time period. We also see marginal evidence in the signal above 100 keV in the CZT detectors. The optical counterpart candidate (Wu et al., GCN 44547) at RA = 192.57345, Dec = 4.05512 implies an offset from the NuSTAR boresight of 93-deg (i.e. from the side of the instrument) and an offset from the geocenter of 164-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260511B 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/44556. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42683] GRB 260511A: NuSTAR detection of prompt emission
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44555 SUBJECT: GRB 260511A: NuSTAR detection of prompt emission DATE: 26/05/11 16:06:48 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 260511A in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm, triggered at 2026-05-11T06:13:30.0 UTC, shows a detection of GRB 260511A, also detected by Fermi/GBM (Fermi GBM Team, GCN 44529) and SVOM (Godet et al., GCN 44532). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a ~10-s burst consistent with Fermi/GBM. The peak count rate is ~3500-cps with a baseline rate of ~1000-cps during this time period. We do not see evidence in the signal above 100 keV in the CZT detectors. The optical counterpart candidate (Akl et al., GCN 44534) at RA = 197.8996, Dec = -33.80446 implies an offset from the NuSTAR boresight of 57-deg and an offset from the geocenter of 144-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260511A 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/44555. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42682] GRB 260511B: Fermi GBM Detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44554 SUBJECT: GRB 260511B: Fermi GBM Detection DATE: 26/05/11 15:37:39 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 11:00:31.70 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260511B (trigger 800190036 / 260511459), which was also detected by SVOM /ECLAIRs and MXT (Godet et al. 2026, GCN 44543), with an optical counterpart initially detected by C-GFT (Wu et al. 2026, GCN 44547). The GBM localization is consistent with the SVOM position. The angle from the Fermi LAT boresight is 100 degrees. The GBM light curve consists of a two bright emission episodes with a duration (T90) of about 41 s (50-300 keV). The time-averaged spectrum from T0-0.5 to T0+47.6 s is best fit by a Band function, with Epeak = 209 +/- 16 keV, alpha = -1.01 +/- 0.04, and beta = -2.14 +/- 0.08. The event fluence (10-1000 keV) in this time interval is (2.62 +/- 0.04) E-05 erg/cm^2. The 1-s peak photon flux measured starting from T0+33.5 s in the 10-1000 keV band is 18.3 +/- 0.4 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/44554. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42681] GRB 260511C: Fermi GBM Final Real-time Localization
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44553 SUBJECT: GRB 260511C: Fermi GBM Final Real-time Localization DATE: 26/05/11 15:26:25 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 15:15:49 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260511C (trigger 800205354.688558 / 260511636). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 219.4, Dec = 39.3 (J2000 degrees, equivalent to J2000 14h 37m, 39d 17'), with a statistical uncertainty of 14.9 degrees. The angle from the Fermi LAT boresight is 50.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511636/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511636/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511636/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44553. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42680] GRB 260511B: SVOM/VT optical observation with VHF data
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44552 SUBJECT: GRB 260511B: SVOM/VT optical observation with VHF data DATE: 26/05/11 15:08:48 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu, L. P. Xin, Y. L. Qiu, H. L. Li (NAOC), J. T. Palmerio (CEA/Irfu), L. Zhang (IHEP), D. Kong (GXU) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs at 2026-05-11T11:00:32 UTC (T0), SVOM performed an automatic slew on the burst of GRB 260511B location (Godet et al.,GCN 44543; The Fermi GBM team, GCN 44542;). SVOM/VT took images of the field in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, the candidate (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551) was clearly detected in VT-VHF data. The candidate's magnitude is : | date-obs (UTC) | mid-time (T-T0) | exposure | VT_B mag(AB) | VT_R mag(AB) | | -------------------- | ----------- | --------- | ------------- | ------------- | |2026-05-11T13:14:19 | 2.23 hr | 5*50 sec | 17.83 +/- 0.01 | -- | Magnitude was not corrected for Galactic reddening. (Note:The missing magnitude is likely caused by either onboard processing interference or saturation of the bright source at early epoch.） 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/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44552. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[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…

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[vsnet-grb-info 42669] GRB 260510C: EP-FXT follow-up observation
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44541 SUBJECT: GRB 260510C: EP-FXT follow-up observation DATE: 26/05/11 10:10:16 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.-Y. Fu (HUST), A. Li (BNU), C.-Y. Wang (THU), R. Shi (PMO), Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260510C (SVOM/sb26051004, Gotz et al., GCN 44521), which also triggered Fermi-GBM (Fermi GBM team, GCN 44520) and MAXI/GSC (Iwakiri et al., GCN 44526). The follow-up obervation started at 2026-05-10T18:03:40 UTC, approximately 50 minutes after the SVOM trigger, with a total exposure time of 5370 s. On-ground analysis of the FXT data found an uncatalogued fading source at R.A., Dec. = 157.9391, 2.837 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic) within the ECLAIRs error circle, which is spatially consistent with the optical counterpart (Angulo et al., GCN 44530; Li et al., GCN 44540). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power-law model, with the hydrogen column density fixed at the Galactic value and a photon index of 2.15 (-0.07/+0.07). The derived average unabsorbed flux in the 0.5-10 keV band is 4.1 (-0.1/+0.1)×10^-11 erg s^-1 cm^-2. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44541. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42668] GRB 260510C: SVOM/VT optical counterpart confirmation
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44540 SUBJECT: GRB 260510C: SVOM/VT optical counterpart confirmation DATE: 26/05/11 09:42:07 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. We refined the analysis of SVOM/VT images (Li et al., GCN 44527) on GRB 260510C (Gotz et al., GCN 44521; Fermi GBM team, GCN 44520; Iwakiri et al., GCN 44526) with more data available. The optical counterpart found by SVOM/COLIBRÍ (Angulo et al., GCN 44530) was clearly detected in both channels of SVOM/VT. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 1.79 h VT_B 40*50 sec 21.13 +/- 0.09 mag 1.18 h VT_R 41*50 sec 19.94 +/- 0.06 mag 8.06 h VT_B 9*100 sec 22.13 +/- 0.14 mag 8.14 h VT_R 3*100 sec 20.61 +/- 0.08 mag The source showed a fading slope of -0.45 during the observations above. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44540. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42667] EP260509a: EP-FXT non-detection and upper limit
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44539 SUBJECT: EP260509a: EP-FXT non-detection and upper limit DATE: 26/05/11 09:39:15 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.-Y. Fu (HUST), A. Li (BNU), C.-Y. Wang (THU), R. Shi (PMO), Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT observed the field of EP260509a (detected by EP-WXT, Wang et al., GCN 44517; and followed by MASTER-Net observations, Lipunov et al., GCN 44525) for 5475 seconds starting at 2026-05-10T10:15:44, around 20.5 hours after the detection by EP-WXT. No significant X-ray source is detected within the 2.78 arcmin radius of the EP-WXT position (Wang et al., GCN 44517) to a preliminary 0.5-10 keV upper limit of 3e-14 erg/cm2/s. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44539. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42666] GRB 260511A: SVOM/VT optical observation with VHF data
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44538 SUBJECT: GRB 260511A: SVOM/VT optical observation with VHF data DATE: 26/05/11 09:18:19 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), Y.N. Ma, L. P. Xin, Y. L. Qiu, H. L. Li (NAOC), L. Zhang (IHEP), D. F. Kong (GXU) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs at 2026-05-11T06:13:32 UTC (T0), SVOM performed an automatic slew on the burst location ( Godet et al., GCN 44532; Fermi GBM team, GCN 44529;Preis et al., GCN44531). SVOM/VT took images of the field in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, the candidate (Jiang et al., GCN 44533; Akl et al., GCN 44534; Saccardi et al., GCN 44535; Zheng et al., GCN 44536) was clearly detected in VT-VHF data. This candidate was detected in both VT_R and VT_B, and was flagged as an uncatalogued source whose brightness faded over the course of the VT observations. The candidate's magnitudes are: | date-obs (UTC) | mid-time | exposure | VT_B mag(AB) | VT_R mag(AB) | | -------------------- | ----------- | --------- | ------------- | ------------- | |2026-05-11T06:26:52.000 | 13.32 min | 6*50 sec | -- | 18.61 ± 0.02 | |2026-05-11T07:42:49.000 | 89.27 min | 6*50 sec | 21.15 ± 0.08 | 19.65 ± 0.07 | Magnitudes were not corrected for Galactic reddening. ( Note: The missing VT_B magnitude is likely caused by onboard processing interference. ) The color of VT_B - VT_R = 1.5 is in line with the expectations of an event at redshift z < 4. Further follow-up is encouraged. 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/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44538. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42665] Fermi GRB 260511A: Global MASTER-Net observations report
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44537 SUBJECT: Fermi GRB 260511A: Global MASTER-Net observations report DATE: 26/05/11 08:30:44 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-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260511A ( Fermi GBM team, GCN 44529) errorbox 5184 sec after notice time and 5215 sec after trigger time at 2026-05-11 07:40:25 UT, with upper limit up to 20.5 mag. The observations began at zenith distance = 64 deg. The sun altitude is -45.2 deg. MASTER-OAGH robotic telescope located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260511A errorbox 6822 sec after notice time and 6853 sec after trigger time at 2026-05-11 08:07:44 UT, with upper limit up to 19.5 mag. The observations began at zenith distance = 77 deg. The sun altitude is -39.6 deg. The galactic latitude b = 29 deg., longitude l = 310 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3306895 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 5246 | 2026-05-11 07:40:25 | MASTER-OAFA | (13h 10m 55.69s , -33d 35m 27.4s) | C | 60 | 19.5 | 5306 | 2026-05-11 07:40:25 | MASTER-OAFA | (13h 10m 55.69s , -33d 35m 27.5s) | C | 180 | 20.0 | Coadd 5366 | 2026-05-11 07:40:25 | MASTER-OAFA | (13h 10m 55.68s , -33d 35m 27.5s) | C | 300 | 20.0 | Coadd 5636 | 2026-05-11 07:40:25 | MASTER-OAFA | (13h 10m 55.69s , -33d 35m 27.5s) | C | 840 | 20.5 | Coadd 5322 | 2026-05-11 07:41:42 | MASTER-OAFA | (13h 10m 55.74s , -33d 37m 08.5s) | C | 60 | 19.4 | 5400 | 2026-05-11 07:43:00 | MASTER-OAFA | (13h 10m 59.00s , -33d 35m 34.7s) | C | 60 | 19.2 | 5475 | 2026-05-11 07:44:14 | MASTER-OAFA | (13h 10m 53.33s , -33d 36m 24.9s) | C | 60 | 19.5 | 5535 | 2026-05-11 07:44:14 | MASTER-OAFA | (13h 10m 53.33s , -33d 36m 24.9s) | C | 180 | 20.0 | Coadd 5554 | 2026-05-11 07:45:34 | MASTER-OAFA | (13h 10m 53.06s , -33d 35m 26.1s) | C | 60 | 19.3 | 5631 | 2026-05-11 07:46:51 | MASTER-OAFA | (13h 10m 59.98s , -33d 36m 26.7s) | C | 60 | 19.4 | 5708 | 2026-05-11 07:48:07 | MASTER-OAFA | (13h 10m 53.23s , -33d 37m 28.2s) | C | 60 | 19.3 | 5768 | 2026-05-11 07:48:07 | MASTER-OAFA | (13h 10m 53.23s , -33d 37m 28.1s) | C | 180 | 19.9 | Coadd 5781 | 2026-05-11 07:49:21 | MASTER-OAFA | (13h 11m 00.12s , -33d 37m 27.8s) | C | 60 | 19.3 | 5858 | 2026-05-11 07:50:37 | MASTER-OAFA | (13h 10m 56.28s , -33d 35m 51.6s) | C | 60 | 19.4 | 5935 | 2026-05-11 07:51:54 | MASTER-OAFA | (13h 10m 56.39s , -33d 37m 16.0s) | C | 60 | 19.3 | 5995 | 2026-05-11 07:51:54 | MASTER-OAFA | (13h 10m 56.39s , -33d 37m 16.0s) | C | 180 | 19.9 | Coadd 6012 | 2026-05-11 07:53:11 | MASTER-OAFA | (13h 10m 58.63s , -33d 35m 39.5s) | C | 60 | 19.3 | 6087 | 2026-05-11 07:54:27 | MASTER-OAFA | (13h 10m 52.96s , -33d 36m 32.8s) | C | 60 | 19.2 | 6163 | 2026-05-11 07:55:43 | MASTER-OAFA | (13h 10m 53.42s , -33d 35m 33.6s) | C | 60 | 19.2 | 6223 | 2026-05-11 07:55:43 | MASTER-OAFA | (13h 10m 53.41s , -33d 35m 33.6s) | C | 180 | 19.9 | Coadd 6239 | 2026-05-11 07:56:59 | MASTER-OAFA | (13h 10m 59.31s , -33d 36m 35.2s) | C | 60 | 19.2 | 6313 | 2026-05-11 07:58:13 | MASTER-OAFA | (13h 10m 52.93s , -33d 37m 36.1s) | C | 60 | 19.2 | 6391 | 2026-05-11 07:59:31 | MASTER-OAFA | (13h 11m 00.57s , -33d 37m 29.1s) | C | 60 | 19.2 | 6451 | 2026-05-11 07:59:31 | MASTER-OAFA | (13h 11m 00.57s , -33d 37m 29.2s) | C | 180 | 19.8 | Coadd 6464 | 2026-05-11 08:00:44 | MASTER-OAFA | (13h 10m 57.03s , -33d 35m 54.4s) | C | 60 | 19.1 | 6541 | 2026-05-11 08:02:01 | MASTER-OAFA | (13h 10m 57.13s , -33d 37m 22.1s) | C | 60 | 19.1 | 6617 | 2026-05-11 08:03:16 | MASTER-OAFA | (13h 10m 59.39s , -33d 35m 57.2s) | C | 60 | 19.2 | 6677 | 2026-05-11 08:03:16 | MASTER-OAFA | (13h 10m 59.40s , -33d 35m 57.2s) | C | 180 | 19.8 | Coadd 6692 | 2026-05-11 08:04:32 | MASTER-OAFA | (13h 10m 53.41s , -33d 36m 41.7s) | C | 60 | 19.2 | 6766 | 2026-05-11 08:05:46 | MASTER-OAFA | (13h 10m 54.96s , -33d 35m 42.7s) | C | 60 | 19.0 | 6840 | 2026-05-11 08:07:00 | MASTER-OAFA | (13h 10m 59.75s , -33d 36m 43.9s) | C | 60 | 19.1 | 6900 | 2026-05-11 08:07:00 | MASTER-OAFA | (13h 10m 59.75s , -33d 36m 43.9s) | C | 180 | 19.7 | Coadd 6884 | 2026-05-11 08:07:44 | MASTER-OAGH | (13h 11m 20.18s , -33d 45m 22.0s) | C | 60 | 18.2 | 6944 | 2026-05-11 08:07:44 | MASTER-OAGH | (13h 11m 20.19s , -33d 45m 21.9s) | C | 180 | 19.0 | Coadd 6884 | 2026-05-11 08:07:44 | MASTER-OAGH | (13h 09m 49.25s , -33d 12m 34.9s) | C | 60 | 18.8 | 6944 | 2026-05-11 08:07:44 | MASTER-OAGH | (13h 09m 49.25s , -33d 12m 34.9s) | C | 180 | 19.5 | Coadd 6917 | 2026-05-11 08:08:17 | MASTER-OAFA | (13h 10m 54.11s , -33d 37m 45.2s) | C | 60 | 19.0 | 6953 | 2026-05-11 08:08:52 | MASTER-OAGH | (13h 11m 26.44s , -33d 45m 03.2s) | C | 60 | 18.4 | 6953 | 2026-05-11 08:08:52 | MASTER-OAGH | (13h 09m 55.72s , -33d 12m 16.6s) | C | 60 | 18.8 | 6990 | 2026-05-11 08:09:30 | MASTER-OAFA | (13h 11m 01.38s , -33d 37m 35.3s) | C | 60 | 19.0 | 7021 | 2026-05-11 08:10:01 | MASTER-OAGH | (13h 11m 22.36s , -33d 43m 39.0s) | C | 60 | 18.3 | 7021 | 2026-05-11 08:10:01 | MASTER-OAGH | (13h 09m 51.74s , -33d 10m 53.0s) | C | 60 | 18.7 | 7066 | 2026-05-11 08:10:46 | MASTER-OAFA | (13h 10m 57.89s , -33d 36m 10.1s) | C | 60 | 19.1 | 7126 | 2026-05-11 08:10:46 | MASTER-OAFA | (13h 10m 57.89s , -33d 36m 10.1s) | C | 180 | 19.6 | Coadd 7091 | 2026-05-11 08:11:11 | MASTER-OAGH | (13h 11m 22.26s , -33d 45m 14.7s) | C | 60 | 18.2 | 7151 | 2026-05-11 08:11:11 | MASTER-OAGH | (13h 11m 22.26s , -33d 45m 14.7s) | C | 180 | 18.9 | Coadd 7091 | 2026-05-11 08:11:11 | MASTER-OAGH | (13h 09m 51.67s , -33d 12m 28.6s) | C | 60 | 18.5 | 7151 | 2026-05-11 08:11:11 | MASTER-OAGH | (13h 09m 51.67s , -33d 12m 28.5s) | C | 180 | 19.4 | Coadd 7143 | 2026-05-11 08:12:03 | MASTER-OAFA | (13h 10m 58.00s , -33d 37m 28.1s) | C | 60 | 19.1 | 7161 | 2026-05-11 08:12:21 | MASTER-OAGH | (13h 11m 25.40s , -33d 43m 36.4s) | C | 60 | 18.2 | 7161 | 2026-05-11 08:12:21 | MASTER-OAGH | (13h 09m 54.89s , -33d 10m 50.9s) | C | 60 | 18.6 | 7217 | 2026-05-11 08:13:17 | MASTER-OAFA | (13h 11m 02.04s , -33d 35m 52.5s) | C | 60 | 18.9 | 7231 | 2026-05-11 08:13:31 | MASTER-OAGH | (13h 11m 18.85s , -33d 44m 19.2s) | C | 60 | 18.2 | 7231 | 2026-05-11 08:13:31 | MASTER-OAGH | (13h 09m 48.37s , -33d 11m 33.8s) | C | 60 | 18.6 | 7294 | 2026-05-11 08:14:34 | MASTER-OAFA | (13h 10m 54.24s , -33d 36m 51.2s) | C | 60 | 18.9 | 7354 | 2026-05-11 08:14:34 | MASTER-OAFA | (13h 10m 54.24s , -33d 36m 51.1s) | C | 180 | 19.6 | Coadd 7300 | 2026-05-11 08:14:40 | MASTER-OAGH | (13h 11m 19.17s , -33d 43m 17.9s) | C | 60 | 18.3 | 7360 | 2026-05-11 08:14:40 | MASTER-OAGH | (13h 11m 19.17s , -33d 43m 17.9s) | C | 180 | 18.8 | Coadd 7300 | 2026-05-11 08:14:40 | MASTER-OAGH | (13h 09m 48.71s , -33d 10m 32.7s) | C | 60 | 18.6 | 7360 | 2026-05-11 08:14:40 | MASTER-OAGH | (13h 09m 48.71s , -33d 10m 32.5s) | C | 180 | 19.2 | Coadd 7370 | 2026-05-11 08:15:49 | MASTER-OAGH | (13h 11m 25.51s , -33d 44m 17.0s) | C | 60 | 18.2 | 7370 | 2026-05-11 08:15:49 | MASTER-OAGH | (13h 09m 55.12s , -33d 11m 31.7s) | C | 60 | 18.6 | 7371 | 2026-05-11 08:15:51 | MASTER-OAFA | (13h 10m 55.41s , -33d 35m 51.5s) | C | 60 | 18.9 | 7438 | 2026-05-11 08:16:58 | MASTER-OAGH | (13h 11m 19.31s , -33d 45m 15.5s) | C | 60 | 18.1 | 7438 | 2026-05-11 08:16:58 | MASTER-OAGH | (13h 09m 48.97s , -33d 12m 30.0s) | C | 60 | 18.5 | 7449 | 2026-05-11 08:17:09 | MASTER-OAFA | (13h 11m 00.93s , -33d 36m 53.0s) | C | 60 | 18.9 | 7507 | 2026-05-11 08:18:07 | MASTER-OAGH | (13h 11m 24.61s , -33d 45m 00.1s) | C | 60 | 18.2 | 7567 | 2026-05-11 08:18:07 | MASTER-OAGH | (13h 11m 24.62s , -33d 44m 60.0s) | C | 180 | 18.8 | Coadd 7507 | 2026-05-11 08:18:07 | MASTER-OAGH | (13h 09m 54.39s , -33d 12m 14.6s) | C | 60 | 18.6 | 7567 | 2026-05-11 08:18:07 | MASTER-OAGH | (13h 09m 54.39s , -33d 12m 14.6s) | C | 180 | 19.4 | Coadd 7523 | 2026-05-11 08:18:23 | MASTER-OAFA | (13h 10m 55.99s , -33d 37m 53.5s) | C | 60 | 18.9 | 7583 | 2026-05-11 08:18:23 | MASTER-OAFA | (13h 10m 55.99s , -33d 37m 53.5s) | C | 180 | 19.6 | Coadd 7577 | 2026-05-11 08:19:17 | MASTER-OAGH | (13h 11m 21.64s , -33d 43m 38.5s) | C | 60 | 18.0 | 7577 | 2026-05-11 08:19:17 | MASTER-OAGH | (13h 09m 51.53s , -33d 10m 53.2s) | C | 60 | 18.5 | 7598 | 2026-05-11 08:19:38 | MASTER-OAFA | (13h 11m 00.75s , -33d 37m 31.6s) | C | 60 | 18.8 | 7647 | 2026-05-11 08:20:26 | MASTER-OAGH | (13h 11m 21.58s , -33d 44m 48.6s) | C | 60 | 18.1 | 7647 | 2026-05-11 08:20:26 | MASTER-OAGH | (13h 09m 51.49s , -33d 12m 02.7s) | C | 60 | 18.6 | 7676 | 2026-05-11 08:20:55 | MASTER-OAFA | (13h 10m 58.71s , -33d 36m 14.3s) | C | 60 | 18.9 | 7722 | 2026-05-11 08:21:42 | MASTER-OAGH | (13h 11m 24.04s , -33d 43m 24.1s) | C | 60 | 18.1 | 7782 | 2026-05-11 08:21:42 | MASTER-OAGH | (13h 11m 24.03s , -33d 43m 24.0s) | C | 180 | 18.6 | Coadd 7722 | 2026-05-11 08:21:42 | MASTER-OAGH | (13h 09m 54.00s , -33d 10m 38.6s) | C | 60 | 18.5 | 7782 | 2026-05-11 08:21:42 | MASTER-OAGH | (13h 09m 54.00s , -33d 10m 38.5s) | C | 180 | 19.1 | Coadd 7752 | 2026-05-11 08:22:12 | MASTER-OAFA | (13h 10m 58.85s , -33d 37m 45.7s) | C | 60 | 18.9 | 7792 | 2026-05-11 08:22:51 | MASTER-OAGH | (13h 11m 17.55s , -33d 44m 06.7s) | C | 60 | 18.0 | 7792 | 2026-05-11 08:22:52 | MASTER-OAGH | (13h 09m 47.49s , -33d 11m 21.0s) | C | 60 | 18.3 | 7826 | 2026-05-11 08:23:26 | MASTER-OAFA | (13h 11m 02.50s , -33d 36m 10.9s) | C | 60 | 18.9 | 7861 | 2026-05-11 08:24:01 | MASTER-OAGH | (13h 11m 18.56s , -33d 43m 05.0s) | C | 60 | 18.0 | 7861 | 2026-05-11 08:24:01 | MASTER-OAGH | (13h 09m 48.54s , -33d 10m 19.5s) | C | 60 | 18.4 | 7903 | 2026-05-11 08:24:43 | MASTER-OAFA | (13h 10m 56.54s , -33d 36m 58.6s) | C | 60 | 18.9 | 7931 | 2026-05-11 08:25:11 | MASTER-OAGH | (13h 11m 24.27s , -33d 44m 03.0s) | C | 60 | 18.1 | 7931 | 2026-05-11 08:25:11 | MASTER-OAGH | (13h 09m 54.32s , -33d 11m 17.1s) | C | 60 | 18.5 | 8000 | 2026-05-11 08:26:20 | MASTER-OAGH | (13h 11m 17.71s , -33d 45m 00.9s) | C | 60 | 18.1 | 8000 | 2026-05-11 08:26:20 | MASTER-OAGH | (13h 09m 47.79s , -33d 12m 14.9s) | C | 60 | 18.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44537. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42664] GRB 260511A: KAIT optical afterglow observations
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44536 SUBJECT: GRB 260511A: KAIT optical afterglow observations DATE: 26/05/11 07:56:17 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) 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 260511A (Fermi GBM Team, GCN Circ. 44529; Godet et al., GCN Circ. 44532) starting at 06:15:44, 132 seconds after SVOM trigger. Observations were performed in 3 x 3 tiling mode, and a set of clear (roughly R) filter images were obtained. The first image covered the optical afterglow (Jiang et al., GCN 44533; Akl et al. GCN 44534 Saccardi et al., GCN 44535) was at 06:16:57, 205 seconds after the burst, in which we measure the afterglow brightness to be 16.7 +/- 0.1 mag (Vega) calibrated to APASS catalog. Observations are on going. View this GCN Circular online at https://gcn.nasa.gov/circulars/44536. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42663] GRB 260511A: LCO optical afterglow detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44535 SUBJECT: GRB 260511A: LCO optical afterglow detection DATE: 26/05/11 07:20:44 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), L. Zhang (IHEP), D. Kong (GXU), report on behalf of the SVOM mission team: We observed the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260511A (Godet et al., GCN 44532; Fermi GBM Team, GCN 44529) with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument. Our observation started on 2026-05-11 at 06:24:46 UT (about 11 min after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. The optical counterpart (Jiang et al., GCN 44533; Akl et al. GCN 44534) is clearly detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: r = 18.88 +/- 0.02 AB (mid-time 21 min after the trigger); z = 18.05 +/- 0.04 AB (mid-time 15 min after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44535. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42662] GRB 260511A: SVOM/COLIBRÍ (FM-GFT) optical counterpart
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44534 SUBJECT: GRB 260511A: SVOM/COLIBRÍ (FM-GFT) optical counterpart DATE: 26/05/11 07:11:33 GMT FROM: Dalya Akl at New York University Abu Dhabi <dka2010(a)nyu.edu> Dalya Akl (NYUAD), Camila Angulo (UNAM), Alan M. Watson, Rosa L. Becerra (UNAM), (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM), L. Zhang (IHEP), and D. Kong (GXU) report: We imaged the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260511A (Fermi GBM Team, GCN Circ. 44529; Godet et al., GCN Circ. 44532) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-11 06:14:45 to 06:27:52 UTC (from 72 seconds to 14 minutes after the trigger) and obtained 520 seconds of simultaneous exposure in r and z filters. The data were reduced, coadded, calibrated, and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect a bright, fading source at: RA(J2000) = 13:11:35.90 = 197.89960 degrees Dec(J2000) = -33:48:16.1 = -33.80446 degrees with an uncertainty of 0.5 arcsec. The preliminary, unsubtracted magnitudes derived for that source are: r = 16.86 +/- 0.01, z = 16.43 +/- 0.01. This position is 3.25 arcmin and 0.87 arcmin away from the ECLAIRs and MXT positions, respectively, released via notices. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44534. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42661] GRB 260511A: TRT optical counterpart detection
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44533 SUBJECT: GRB 260511A: TRT optical counterpart detection DATE: 26/05/11 06:45:10 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), J. An, L.B. He, X. Liu, Z.P. Zhu, D. Xu (NAOC) report: We observed the field of GRB 260511A detected by Fermi GBM (GCN 44529) and SVOM (GCN 44532) using the 0.7-m telescope of the Thai Robotic Telescope network (TRT) located at Cerro Tololo Inter-American Observatory, Chile (CTO). We obtained a series of frames in the Sloan r-band. An uncatalogued and varing source is detected near the SVOM MXT error circle at coordinates R.A. (J2000) = 13:11:35.94 (197.8997 deg) Dec. (J2000) = -33:48:16.3 (-33.8045 deg) with an uncertainty of ~ 1.0 arcsec. The source had r ~ 17.9 mag at a median time of 2026-05-11T06:19:37.771, calibrated with Legacy DR10 and not corrected for Galactic extinction. No NEO would be at the above position at the observational time by checking MPC. We thus think the source could be the optical counterpart of GRB 260511A. View this GCN Circular online at https://gcn.nasa.gov/circulars/44533. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42660] GRB 260511A: SVOM detection of a bright burst
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44532 SUBJECT: GRB 260511A: SVOM detection of a bright burst DATE: 26/05/11 06:37:49 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 2026-05-11T06:13:32 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260511A (SVOM burst-id sb26051101). This transient was also detected by Fermi/GM (GCN Circular 44529). 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 16 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 55.22 in the [8-120] keV energy band over a time window of 10.20 seconds starting at 2026-05-11T06:13:32. The localization of the best alert is R.A., Dec. 197.929, -33.853 degrees (J2000) with a 90% confidence level (C.L.) radius of 2.44 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a single/multiple broad/narrow peak structure with a T90 duration of about 13.5 (-0.4/ +0.6) s in the 5-120 keV. This burst also triggered SVOM/GRM at 2026-05-11T06:13:30 on a timescale of 1 seconds with an SNR of 12.10. The SVOM/GRM light curve showed a multiple peak structure with a T90 duration of about 14.3 (-0.4 / +0.8) s in the 8-1100 keV. SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-05-11T06:16:38 UTC, 186 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 197.9145, -33.8120 degrees: R.A. (J2000) = 13h11m39.48s Dec. (J2000) = -33d48m43.09s with a 90% C.L. radius of 39.05 arcseconds. This location is 2.54 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/44532. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42659] GRB 260511A: BALROG localization (Fermi Trigger 800172815 / GRB 260511259)
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44531 SUBJECT: GRB 260511A: BALROG localization (Fermi Trigger 800172815 / GRB 260511259) DATE: 26/05/11 06:37:48 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 800172815 at 06:13:30 on 11 May 2026 were automatically 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) = 197.3 deg Decl.(2000.0) = -33.7 deg The 1 sigma statistical error radius is 1.3 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260511259/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260511259/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260511259/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44531. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42658] GRB 260510C: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44530 SUBJECT: GRB 260510C: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate DATE: 26/05/11 06:35:13 GMT FROM: Camila Angulo Valdez at UNAM <camiangulo(a)astro.unam.mx> Camila Angulo (UNAM), Dalya Akl (NYUAD), Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) and Andrea Saccardi (CEA/Irfu ) report: We imaged the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260510C (Fermi GBM Team, GCN Circ. 44520; Gotz et al., GCN Circ. 44521) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-11 04:46 to 05:39 UTC (from 11.54 to 12.44 hours after the trigger) and obtained 24 minutes of simultaneous exposure in r and z filters. The data were reduced, coadded, calibrated, and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect an uncatalogued source 1.06 arcmin away from the MXT position and slightly outside the 90% uncertainty region reported by SVOM, but still inside the ECLAIRs region (Gotz et al., GCN Circ. 44521), at: RA(J2000) = 10:31:45:49 = 157.9394 degrees Dec(J2000) = +02:50:15.5 = 2.83763 degrees with an uncertainty of 0.5 arcsec. The preliminary unsubtracted magnitudes derived for that source are: r = 21.32 + /- 0.03, z = 20.23 + /- 0.03. We suggest this is the optical counterpart of the GRB. The position of the candidate is consistent with a faint galaxy with reported magnitudes of g = 23.61 +/- 0.10, r = 23.49 +/- 0.14, i = 23.02 +/- 0.12 and z = 23.03 +/- 0.21 and a photo-z of =0.89 +/- 0.63 in the DESI Legacy Survey catalog (Dey et al. 2019), so our candidate is two magnitudes brighter than the galaxy. We suggest this galaxy may be the host. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44530. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42657] GRB 260511A: Fermi GBM Final Real-time Localization
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44529 SUBJECT: GRB 260511A: Fermi GBM Final Real-time Localization DATE: 26/05/11 06:22:11 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 06:13:30 UT on 11 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260511A (trigger 800172815.286154 / 260511259). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 199.1, Dec = -33.0 (J2000 degrees, equivalent to J2000 13h 16m, -33d 00'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 117.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511259/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511259/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260511259/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44529. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42656] GRB 260510B: SVOM/VT optical upper limits
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44528 SUBJECT: GRB 260510B: SVOM/VT optical upper limits DATE: 26/05/11 03:48:57 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed automatic observations of GRB260510B triggered by SVOM/ECLAIRs (sb26051001, Saccardi et al., GCN 44515). The burst was also detected at sub-threshold level by Fermi-GBM (Palafox et al., GCN 44524). VT observations started at 2026-05-10T12:23:54 UTC, 274 seconds post trigger, in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No uncatalogued sources were detected within the error box of SVOM/ECLAIRs (Saccardi et al., GCN 44515), compared to the Legacy Survey. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | 3-sigma upper limit 23.3 min VT_B 45*50 sec > 23.0 mag 23.3 min VT_R 45*50 sec > 23.0 mag Our non-detection is consistent with the non-detections reported by LCO (Saccardi et al., GCN 44518) and GOTO (Ramsay et al., GCN 44522). The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44528. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42655] GRB 260510C: SVOM/VT optical upper limits
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44527 SUBJECT: GRB 260510C: SVOM/VT optical upper limits DATE: 26/05/11 01:03:32 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed automatic observations of GRB260510C triggered by SVOM/ECLAIRs (sb26051004, Gotz et al., GCN 44521). The burst was also detected by Fermi GBM (Fermi GBM team, GCN 44520) and MAXI/GSC (Iwakiri et al., GCN 44526). The VT observations started at 2026-05-10T17:18:48 UTC, i.e., 304 seconds post trigger, in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No uncatalogued sources were detected within the error box of SVOM/MXT (Gotz et al., GCN 44521) and SVOM/ECLAIRs (Gotz et al., GCN 44521), compared to the Legacy Survey. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | 3 sigma upper limit 1.10 h VT_B 47*50 sec > 23.2 mag 1.18 h VT_R 41*50 sec > 23.1 mag Further analyses are ongoing. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44527. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42654] EP260507a: further Liverpool Telescope observations
by GCN Circulars 11 May '26

11 May '26

TITLE: GCN CIRCULAR NUMBER: 44495 SUBJECT: EP260507a: further Liverpool Telescope observations DATE: 26/05/08 01:20:37 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester) reports on behalf of a larger collaboration: We observed the field of EP260507a (Fu et al., GCN 44488) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x200s exposures in each of the SDSS r’ and z’ filters starting at 2026-05-07 22:51:45 UT, approximately 9.06 hours after the X-ray detection. We detect the optical counterpart (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491; Kumar et al., GCN 44492; Bochenek et al., GCN 44494) in both the r’ z’ bands and measure the following magnitudes: r’ = 22.76 +/- 0.21 z’ = 21.98 +/- 0.30 Our photometry is calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44495. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42653] GRB 260510C: MAXI/GSC detection
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44526 SUBJECT: GRB 260510C: MAXI/GSC detection DATE: 26/05/10 21:42:33 GMT FROM: Wataru Iwakiri at Chiba University <iwakiri.wataru.buz(a)gmail.com> W. Iwakiri (Chiba U.),　M. Serino(AGU), H. Negoro, M. Nakajima, K. Saito, T. Yokoyama, M. Wada (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), M. Shidatsu, C. Kang, M. Uenishi, T. Usuki, S. Yatsuzuka, H. Aoe (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U), S. Ogawa (TUS) report on behalf of the MAXI team: At 17:13:42 UT on 2026 May 10, the MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source. The trigger time and position are consistent with GRB 260510C reported by the Fermi team (GCN #44520) and the SVOM team (GCN #44521). The X-ray flux averaged over the scan was 338 +/- 36 mCrab (4.0-10.0 keV, 1-sigma error). Assuming that the source flux was constant over the transit, we obtain the source position at: (R.A., Dec) = (157.881 deg, 2.824 deg) = (10 31 31, +02 49 26) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.17 deg and 0.14 deg, respectively. The roll angle of the long axis is 73.0 deg counterclockwise from the north. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (157.267, 2.290) deg = (10 29 04, +02 17 24) (J2000) (157.477, 2.117) deg = (10 29 54, +02 07 01) (J2000) (158.505, 3.360) deg = (10 34 01, +03 21 35) (J2000) (158.295, 3.533) deg = (10 33 10, +03 31 58) (J2000) There was no significant excess flux in the previous transit at 15:40 UT with an upper limit of 20 mCrab. View this GCN Circular online at https://gcn.nasa.gov/circulars/44526. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42652] EP260509a: Global MASTER-Net observations report
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44525 SUBJECT: EP260509a: Global MASTER-Net observations report DATE: 26/05/10 21:36:20 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 [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP260509a ( EP Team et al., GCN 44517) errorbox 24957 sec after notice time and 1 days 27906 sec after trigger time at 2026-05-10 21:29:08 UT, with upper limit up to 17.9 mag. The observations began at zenith distance = 61 deg. The sun altitude is -29.1 deg. The galactic latitude b = 25 deg., longitude l = 353 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3305450 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 114336 | 2026-05-10 21:29:08 | MASTER-Kislovodsk | (15h 55m 47.13s , -18d 04m 15.2s) | C | 60 | 12.6 | 114336 | 2026-05-10 21:29:08 | MASTER-Kislovodsk | (15h 55m 58.90s , -18d 27m 08.8s) | C | 60 | 17.8 | 114426 | 2026-05-10 21:30:38 | MASTER-Kislovodsk | (15h 55m 42.18s , -18d 05m 11.2s) | C | 60 | 12.1 | 114426 | 2026-05-10 21:30:38 | MASTER-Kislovodsk | (15h 55m 53.95s , -18d 28m 02.6s) | C | 60 | 17.9 | 114514 | 2026-05-10 21:32:06 | MASTER-Kislovodsk | (15h 55m 55.18s , -18d 27m 07.8s) | C | 60 | 17.9 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44525. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42651] Fermi GBM Sub-Threshold Detection of GRB 260510B
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44524 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 260510B DATE: 26/05/10 21:21:21 GMT FROM: Eva MP at INAOE <eva.palafox(a)gmail.com> E. Palafox (INAOE) reports on behalf of the Fermi-GBM Team: SVOM/ECLAIRs detected GRB 260510B on 2026-05-10 at 12:19:20 UTC (A. Saccardi et al. 2026, [GCN 44515](https://gcn.nasa.gov/circulars/44515)) There was no Fermi-GBM onboard trigger around this event time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified no candidates. The GBM Targeted Search [1], the most sensitive coherent search for GRB-like signals in GBM, identified a transient approximately 3 s after the ECLAIRs best image SNR time of 2026-05-10T12:19:15. The Targeted Search candidate was found most significantly on the 8 s timescale using the "normal" spectral template (i.e., Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3) and has a false alarm rate of 1.1e-04 Hz. The Fermi-MET of the start time of this transient is 800108363.27 s. The Targeted Search localization is found to be spatially consistent with the ECLAIRs one, with a spatial association probability of 98.6%. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/44524. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42650] GRB 260510D: Fermi GBM Final Real-time Localization
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44523 SUBJECT: GRB 260510D: Fermi GBM Final Real-time Localization DATE: 26/05/10 20:48:45 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 SHORT GRB At 20:38:08 UT on 10 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260510D (trigger 800138293.771294 / 260510860). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 3.0, Dec = 37.4 (J2000 degrees, equivalent to J2000 00h 12m, 37d 23'), with a statistical uncertainty of 13.9 degrees. The angle from the Fermi LAT boresight is 61.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510860/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510860/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510860/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44523. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42649] GRB 260510B: GOTO early upper limit
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44522 SUBJECT: GRB 260510B: GOTO early upper limit DATE: 26/05/10 17:44:24 GMT FROM: d.s.oneill(a)bham.ac.uk G. Ramsay, D. O'Neill, S. Belkin, K. Ulaczyk, A. Kumar, K. Ackley, M. Dyer, J. Lyman, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, R. Starling, B. Gompertz, B. Godson, T. Killestein, M. Pursiainen, on behalf of GOTO collaboration. We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the SVOM/ECLAIRS alert GRB 260510B (sb26051001, Saccardi et al. GCN 44515). Observations covering the full extent of the localisation area were started at 2026-05-10 12:23:17 UT, (t0 +4 min) in the L band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations (Lyman et al. 2026). Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. Observations at 2026-05-10 12:23:17 UT (t0 +4 min) and 2026-05-10 13:30:27 UT (t0 +1.19h) did not reveal any new counterpart down to a localised 5-sigma limit of 20.3 and 20.5 AB mag respectively. The GOTO non-detection is consistent with that reported by Saccardi et al (GCN 44518). 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, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/44522. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42648] GRB 260510C: SVOM detection of a burst
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44521 SUBJECT: GRB 260510C: SVOM detection of a burst DATE: 26/05/10 17:42:51 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> D. Gotz (CEA/Irfu), A. Saccardi (CEA/Irfu), S. Schanne (CEA/Irfu), N. Dagoneau (CEA/Irfu) report on behalf of the SVOM mission team: At 2026-05-10T17:13:44 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260510C (SVOM burst-id sb26051004), also detected by Fermi/GBM (Fermi GRB Team, GCN #44520). 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 11 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 12.18 in the [8-120] keV energy band over a time window of 10.20 seconds starting at 2026-05-10T17:13:38. The localization of the best alert is R.A., Dec. 157.9595, 2.8711 degrees (J2000) with a 90% confidence level (C.L.) radius of 6.63 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs light curve showed a double peaked structure with a total duration of about 150 s. This burst was also detected by SVOM/GRM with a significance of 7.50. The SVOM/GRM light curve showed two separated peaks with a total duration of about 150 s. SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-05-10T17:16:44 UTC, 179 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 157.941, +2.820 degrees: R.A. (J2000) = 10h31m45.8s Dec. (J2000) = 02d49m12.0s with a 90% C.L. radius of 45 arcseconds. This location is 3.26 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 Andrea Saccardi: andrea.saccardi(a)cea.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44521. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42647] GRB 260510C: Fermi GBM Final Real-time Localization
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44520 SUBJECT: GRB 260510C: Fermi GBM Final Real-time Localization DATE: 26/05/10 17:24:27 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 17:13:43 UT on 10 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260510C (trigger 800126028.99095 / 260510718). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 174.6, Dec = 8.6 (J2000 degrees, equivalent to J2000 11h 38m, 8d 35'), with a statistical uncertainty of 10.4 degrees. The angle from the Fermi LAT boresight is 66.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510718/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510718/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510718/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44520. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42646] GRB 260510A: GECAM-B observation
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44519 SUBJECT: GRB 260510A: GECAM-B observation DATE: 26/05/10 16:30:03 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 260510A, at 2026-05-10T02:46:35.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44508). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 38 +6/-5 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260510A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44519. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42645] GRB 260510B: LCO optical upper limits
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44518 SUBJECT: GRB 260510B: LCO optical upper limits DATE: 26/05/10 15:18:38 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), L. Zhang (IHEP), Y. H. Cheng (YNU), report on behalf of the SVOM mission team: We observed the field of GRB 260510B detected by SVOM (Saccardi et al., GCN 44515) with the LCO 1m telescope at Siding Spring Observatory equipped with the Sinistro instrument. Our observation started on 2026-05-10 at 12:33:06 UT (about 14 min after the trigger) and we obtained 2x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. In the stacked images, we do not detect any new source within the SVOM/ECLAIRs error box. We measure the following upper limits calibrated against the DESI DR10 catalog, and not corrected for Galactic extinction: r > 20.7 AB (5-sigma, mid-time 1.9 hr after the trigger); z > 20.0 AB (5-sigma, mid-time 19 min after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44518. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42644] EP260509a: Einstein Probe detection of an X-ray transient
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44517 SUBJECT: EP260509a: Einstein Probe detection of an X-ray transient DATE: 26/05/10 14:32:36 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C.-Y. Wang (THU), S.-Y. Fu (HUST), A. Li (BNU)Y, R. Shi (PMO), Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260509a. The transient was identified during ground-based telemetry analysis. It was started at 2026-05-09T13:44:02 (UTC). The WXT position of the source is R.A. = 239.4813 deg, DEC = -18.4328 deg (J2000) with an uncertainty of 2.78 arcmin in radius (90% C.L. statistical and systematic). The duration of the event is ~ 250 s. The WXT spectrum can be fitted with an absorbed power-law, with the absorption fixed at the Galactic value of 1.05 x 10^21 cm^-2, and a photon index of 2.0 (-0.8, +0.9). The unabsorbed 0.5-4 keV flux is 6.0 (-2.0, +3.1) x 10^-11 erg/s/cm2. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed at 2026-05-10T09:52:54. Further information will be updated when the telemetry data is received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44517. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42643] GRB 260509A: Liverpool Telescope optical observations
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44516 SUBJECT: GRB 260509A: Liverpool Telescope optical observations DATE: 26/05/10 13:20:53 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU), report: We observed the field of GRB 260509A (Götz et al., GCN 44504) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 4x100s exposures in SDSS griz filters, starting at 2026-05-09 23:08:01 UT, approximately 1.28 hours after trigger. We detect a source in all filters at the position reported by O'Neill et al. (GCN 44505), observed also by Saccardi et al. (GCN 44506), Wu et al. (GCN 44507), Sánchez Álvarez et al. (GCN 44509), Zheng et al. (GCN 44510), Lipunov et al. (GCN 44512), and Belkin et al. (GCN 44513): MJD (mid) T_mid-T_0 Filter Mag. (AB) 61169.96654 1.34 h g 20.00 ± 0.05 61169.97218 1.48 h r 19.83 ± 0.06 61169.97779 1.61 h i 19.81 ± 0.09 61169.98272 1.73 h z 19.61 ± 0.09 The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44516. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42642] GRB 260510B: SVOM detection of a burst
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44515 SUBJECT: GRB 260510B: SVOM detection of a burst DATE: 26/05/10 12:49:03 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), B. Cordier (CEA/Irfu), N. Dagoneau (CEA/Irfu), Li. Zhang(IHEP), Y. H. Cheng (SWIFAR, YNU), report on behalf of the SVOM mission team: At 2026-05-10T12:19:20 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260510B (SVOM burst-id sb26051001). 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 11 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.71 in the [8-50] keV energy band over a time window of 10.20 seconds starting at 2026-05-10T12:19:15. The localization of the best alert is R.A., Dec. 173.2168, -34.5756 degrees: R.A. (J2000) = 11h32m52.04s Dec. (J2000) = -34d34m32.07s with a 90% confidence level (C.L.) radius of 8.18 arcmin (including systematic error of 2 arcmin added in quadrature). This burst was also detected by SVOM/GRM with a significance of 7.40. SVOM slewed to the burst. MXT and VT began observing the field after the slew. The analysis of the data will be published in future circulars. 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(a)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/44515. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42641] GRB 260509A: NOT spectroscopic redshift upper limit z < 1.95
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44514 SUBJECT: GRB 260509A: NOT spectroscopic redshift upper limit z < 1.95 DATE: 26/05/10 11:07:26 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), A. Saccardi (CEA/Irfu), B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud), N. R. Tanvir (Univ. Leicester), Kostas Valeckas (NOT and NBI), V. Vuolteenaho (NOT and Oulu Univ.), report on behalf of a larger collaboration: We observed the optical counterpart (O'Neill et al., GCN 44505; Saccardi et al. GCN 44506; Wu et al. GCN 44507; Sánchez Álvarez et al. GCN 44509; Zheng et al. GCN 44510; Lipunov et al. GCN 44512; Belkin GCN 44513) of the SVOM/ECLAIRs GRB 260509A (Götz et al., GCN 44504) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC spectrograph. A spectrum consisting of 4x1200 s exposures was secured starting on 2026 May 10 at 00:22:16 UT (2.52 hr after the SVOM trigger), using grism #4 with the WG345 356_LP order blocker which covers the wavelength range 3400-9600 AA. Based on a preliminary reduction of the spectra using PyLongslit (Valeckas et al. 2025 10.21105/joss.09264), a continuum is detected down to ~3600 AA, setting an upper limit to the redshift z < 1.95 based on the lack of HI absorption. We do not identify clear metal absorption features despite good S/N. Further analysis is ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/44514. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42640] GRB 260509A: LCO optical observations
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44513 SUBJECT: GRB 260509A: LCO optical observations DATE: 26/05/10 09:43:56 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> S. Belkin (Monash U) reports: We observed the optical counterpart candidate GOTO26emi of GRB 260509A, detected by SVOM/ECLAIRs (Götz et al., GCN 44504), with the Las Cumbres Observatory 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument. In the stacked images, we clearly detect the reported optical counterpart candidate GOTO26emi, first identified by GOTO (O'Neill et al., GCN 44505) and subsequently reported by Saccardi et al. (GCN 44506), Wu et al. (GCN 44507), Sánchez Álvarez et al. (GCN 44509), Zheng et al. (GCN 44510), and Lipunov et al. (GCN 44512). The preliminary photometry from the stacked images is: Date (UT) T-T0 (days) Filter Exp. time (s) Magnitude ============================================================================ 2026-05-10 01:53:25 0.16825 r 60 x 5 20.67 +/- 0.13 2026-05-10 02:00:37 0.17324 i 60 x 5 20.51 +/- 0.17 2026-05-10 02:07:48 0.17823 g 60 x 5 20.88 +/- 0.12 The photometry was calibrated against Pan-STARRS field stars. The quoted magnitudes are in the AB system and are not corrected for Galactic extinction. Our r-band measurement is consistent with the fading behaviour reported by Saccardi et al. (GCN 44506) and Sánchez Álvarez et al. (GCN 44509). Further follow-up is encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/44513. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42639] SVOM GRB 260509A: MASTER-OAFA optical observation
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44512 SUBJECT: SVOM GRB 260509A: MASTER-OAFA optical observation DATE: 26/05/10 08:23:16 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> Ya.Kechin (Lomonosov MSU), F.Podesta, M.J. Segura, C.Francile, R.Podesta, E. Gonzalez (OAFA, SJNU), A.Kuznetsov, V.Lipunov, I.Panchenko, P.Balanutsa, G.Antipov, N.Tiurina,K.Zhirkov, E.Gorbovskoy, V.Senik, A.Chasovnikov, V.Topolev, D.Vlasenko,A.Sankovich, I.Gorbunov(Lomonosov MSU), N.Budnev, O.Gress (ISU), D.Buckley (SAAO), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich (Blagoveschensk Educational StateUniversity) R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope of MASTER Global Robotic Net [1-4] was pointed to the SVOM GRB260509A (trigger No 1778363469,11h 47m 32.88s , +00d 12m 34.2s, R=0.0786667 Gotz et al. GCN 44504) errorbox 8054 sec after notice time and 10202 sec after trigger time at 2026-05-10 00:41:11 UT, with upper limit up to 20.5 mag. The observations began at zenith distance = 31 deg. The sun altitude is -36.5 deg. MASTER-OAGH robotic telescope located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) was pointed to the SVOM GRB260509.91 errorbox 24424 sec after notice time (26572 sec after trigger time at 2026-05-10 05:14:01 UT), with upper limit up to 19.3 mag. The observations began at zenith distance = 36 deg. The sun altitude is -33.4 deg. The galactic latitude b = 59 deg., longitude l = 272 deg. There is MASTER OT J114735.9135.91+001717.7 optical counterpart at first images with m_OT~20.9 at 2026-05-10 00:41:11UT discovered by GOTO (O'Neill et al. GCN 44505) and observed by LCO (Saccardi et al. GCN 44506), SVOM|VT (Wu et al. GCN 44507), KAIT (Zheng et al. GCN 44510) Real time updated cover map and OT are available here: https://master.sai.msu.ru/site/master2/observ.php?id=3303991 MASTER upper limits: Tmid-T0 | Date Time | Site | Coord J2000) |Filt.| Expt. | Limit| Comment 10233 | 2026-05-10 00:41:11 | MASTER-OAFA | (11h 44m 48.88s , -00d 51m 54.0s) | C | 60 | 20.2 | 10293 | 2026-05-10 00:41:11 | MASTER-OAFA | (11h 44m 48.87s , -00d 51m 54.0s) | C | 180 | 20.5 | Coadd 10311 | 2026-05-10 00:42:29 | MASTER-OAFA | (11h 44m 48.21s , -00d 50m 56.7s) | C | 60 | 20.2 | 10389 | 2026-05-10 00:43:47 | MASTER-OAFA | (11h 44m 52.24s , -00d 51m 59.4s) | C | 60 | 20.2 | 10465 | 2026-05-10 00:45:03 | MASTER-OAFA | (11h 44m 46.21s , -00d 53m 02.8s) | C | 60 | 20.2 | 10525 | 2026-05-10 00:45:03 | MASTER-OAFA | (11h 44m 46.20s , -00d 53m 02.8s) | C | 180 | 20.5 | Coadd 10540 | 2026-05-10 00:46:19 | MASTER-OAFA | (11h 44m 52.06s , -00d 52m 51.7s) | C | 60 | 20.2 | 10618 | 2026-05-10 00:47:36 | MASTER-OAFA | (11h 44m 49.58s , -00d 51m 21.4s) | C | 60 | 20.2 | 10697 | 2026-05-10 00:48:55 | MASTER-OAFA | (11h 44m 49.29s , -00d 53m 05.6s) | C | 60 | 20.2 | 10757 | 2026-05-10 00:48:55 | MASTER-OAFA | (11h 44m 49.28s , -00d 53m 05.6s) | C | 180 | 20.4 | Coadd 10774 | 2026-05-10 00:50:12 | MASTER-OAFA | (11h 44m 52.95s , -00d 51m 27.6s) | C | 60 | 20.2 | 10852 | 2026-05-10 00:51:31 | MASTER-OAFA | (11h 44m 45.40s , -00d 52m 20.8s) | C | 60 | 20.2 | 10930 | 2026-05-10 00:52:48 | MASTER-OAFA | (11h 44m 45.82s , -00d 51m 24.8s) | C | 60 | 20.2 | 10990 | 2026-05-10 00:52:48 | MASTER-OAFA | (11h 44m 45.81s , -00d 51m 24.8s) | C | 180 | 20.4 | Coadd 11007 | 2026-05-10 00:54:06 | MASTER-OAFA | (11h 44m 49.85s , -00d 52m 28.2s) | C | 60 | 20.2 | 11086 | 2026-05-10 00:55:24 | MASTER-OAFA | (11h 44m 45.55s , -00d 53m 32.1s) | C | 60 | 20.2 | 11160 | 2026-05-10 00:56:39 | MASTER-OAFA | (11h 44m 49.59s , -00d 53m 31.6s) | C | 60 | 20.2 | 11220 | 2026-05-10 00:56:39 | MASTER-OAFA | (11h 44m 49.59s , -00d 53m 31.6s) | C | 180 | 20.4 | Coadd [1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L [2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271 [3] Lipunov et a. 2019, ARep, vol.63, 293 [4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/44512. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42638] Fermi GRB 260510A: Global MASTER-Net observations report
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44511 SUBJECT: Fermi GRB 260510A: Global MASTER-Net observations report DATE: 26/05/10 06:30:25 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-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260510A ( Fermi GBM team, GCN 44508) errorbox 12795 sec after notice time and 12848 sec after trigger time at 2026-05-10 06:20:28 UT, with upper limit up to 17.6 mag. The observations began at zenith distance = 80 deg. The sun altitude is -61.8 deg. The galactic latitude b = -73 deg., longitude l = 333 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3304437 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 12879 | 2026-05-10 06:20:28 | MASTER-OAFA | (00h 01m 07.12s , -42d 06m 59.6s) | C | 60 | 17.0 | 12956 | 2026-05-10 06:21:45 | MASTER-OAFA | (00h 01m 04.44s , -42d 05m 38.2s) | C | 60 | 16.9 | 13034 | 2026-05-10 06:23:03 | MASTER-OAFA | (00h 01m 02.62s , -44d 07m 12.4s) | C | 60 | 17.4 | 13109 | 2026-05-10 06:24:18 | MASTER-OAFA | (00h 01m 04.74s , -44d 05m 38.9s) | C | 60 | 17.5 | 13186 | 2026-05-10 06:25:35 | MASTER-OAFA | (00h 00m 59.38s , -44d 06m 16.7s) | C | 60 | 17.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44511. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42637] GRB 260509A: KAIT optical observations
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44510 SUBJECT: GRB 260509A: KAIT optical observations DATE: 26/05/10 06:13:38 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) 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 260509A (Götz et al., GCN 44504 starting at 04:56 UT, 7.08 hours after the burst. A set of clear (roughly R) filter images were obtained. We detected the afterglow (O'Neill et al., GCN 44505; Saccardi et al., GCN 44506; Wu et al., GCN 44507; Álvarez et al., GCN 44509) in our coadd image. We measure its brightness to be 21.1 +/- 0.2 mag (Vega) at mid time of 7.37 hours after the burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/44510. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42636] GRB 260509A: SVOM/COLIBRÍ (FM-GFT) observations
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44509 SUBJECT: GRB 260509A: SVOM/COLIBRÍ (FM-GFT) observations DATE: 26/05/10 04:54:27 GMT FROM: freddalvarez(a)astro.unam.mx Fredd Sánchez Álvarez (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM),Nikos Mandarakas (LAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and D. Adrien (CEA/Irfu) report: We imaged the field of the SVOM/ECLAIRs GRB 260509A (Götz et al. GCN 44504) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-10 03:31 to 03:59 UTC and obtained 8 minutes of exposure in g, r, and i, and simultaneously 24 minutes of exposure in z. The data were reduced, coadded, calibrated, and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect the optical counterpart reported by O’Neill et al.(GCN 44505), Saccardi et al. (GCN 44506), and Wu et al. (GCN 44507) with preliminary magnitudes of: g = 21.25 +/- 0.05 r = 21.31 +/- 0.08 i = 20.97 +/- 0.08 z = 20.81 +/- 0.09 Our strong detection of the source in g suggests that the redshift is less than 3.0. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44509. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42635] GRB 260510A: Fermi GBM Final Real-time Localization
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44508 SUBJECT: GRB 260510A: Fermi GBM Final Real-time Localization DATE: 26/05/10 02:57:06 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 02:46:19 UT on 10 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260510A (trigger 800073984.34868 / 260510115). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 0.5, Dec = -41.9 (J2000 degrees, equivalent to J2000 00h 02m, -41d 53'), with a statistical uncertainty of 6.1 degrees. The angle from the Fermi LAT boresight is 84.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510115/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510115/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510115/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44508. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42634] GRB 260509A: SVOM/VT optical candidate with VHF data
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44507 SUBJECT: GRB 260509A: SVOM/VT optical candidate with VHF data DATE: 26/05/10 01:47:02 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu, H. L. Li, Y. L. Qiu, L. P. Xin (NAOC), J. T. Palmerio (CEA/Irfu), D. Götz (CEA/Irfu), A. Saccardi (CEA/Irfu), L. Zhang (IHEP), Y. H. Cheng (YNU) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs (SVOM burst-id sb26050905) at 2026-05-09T21:51:09 UTC (T0), SVOM/VT began observing the field after the automatic slew on the burst (Götz et al., GCN 44504) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. From a preliminary analysis of the 1-bit subimage and source list generated by on-board data processing and downloaded via VHF network, one credible candidate is identified, the details of which are presented below. VT_ID 722: The position of this candidate is R.A., Dec. 176.8997, 0.2882 degrees, corresponding to: R.A. (J2000) = 11:47:35.9 Dec. (J2000) = 00:17:17.6 with an uncertainty of 0.50 arcsec. This candidate was detected in both VT_R and VT_B, and was flagged as an uncatalogued source whose brightness faded during the VT observations. The candidate's magnitudes are: | date-obs (UTC) | mid-time | exposure | VT_B mag(AB) | VT_R mag(AB) | | -------------------- | ----------- | --------- | ------------- | ------------- | | 2026-05-09T23:18:31 | 89.87 min | 6x50 sec | 20.38 ± 0.03 | 19.80 ± 0.04 | | 2026-05-09T23:58:59 | 129.08 min | 3x50 sec | 20.67 ± 0.05 | 20.18 ± 0.06 | Magnitudes were not corrected for Galactic extinction. The mean color of VT_B - VT_R = 0.54 is in line with the expectations of an event at redshift z < 4. The position of this candidate is consisent with the reports (O'Neill et al., GCN 44505; Saccardi et al., GCN 44506) . 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/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44507. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42633] GRB 260509A: LCO optical counterpart detection
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44506 SUBJECT: GRB 260509A: LCO optical counterpart detection DATE: 26/05/10 01:00:45 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), D. Adrien (CEA/Irfu), L. Zhang (IHEP), Y. H. Cheng (YNU), report on behalf of the SVOM mission team: We observed the field of GRB 260509A detected by SVOM (Götz et al., GCN 44504) with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument. Our observation started on 2026-05-09 at 23:41:26 UT (about 1.84 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. The optical candidate reported by O'Neill et al. (GCN 44505) is clearly detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: r = 19.79 +/- 0.05 AB (mid-time 1.92 hr after the trigger); z = 19.76 +/- 0.15 AB (mid-time 2.65 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44506. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42632] GRB 260509A: GOTO optical counterpart candidate
by GCN Circulars 09 May '26

09 May '26

TITLE: GCN CIRCULAR NUMBER: 44505 SUBJECT: GRB 260509A: GOTO optical counterpart candidate DATE: 26/05/09 23:23:47 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> D. O'Neill, S. Belkin, K. Ulaczyk, A. Kumar, K. Ackley, M. Dyer, J. Lyman, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, R. Starling, B. Gompertz, B. Godson, T. Killestein, M. Pursiainen, on behalf of GOTO collaboration. We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the SVOM/ECLAIRS alert GRB 260509A (sb26050905, Götz et al. GCN 44504). Observations covering the localisation area were taken at 2026-05-09 21:56:19 UT, (t0 +0.09h) with an average 5-sigma depth of 20.8 mag. Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations (Lyman et al. 2026). Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. A new optical source GOTO26emi is identified near the edge of the ECLAIRS localisation region, at an angular separation of 4.79 arcmin from the reported GRB position, marginally outside the quoted 4.72 arcmin error radius. The source coordinates: RA,DEC (J2000) = 176.899834, 0.288276, 11:47:35.96, +00:17:17.80 The rapidly rising source was detected with average L = 20.13 ± 0.16 AB mag (+0.09h). We find no evidence of the source prior to the GRB trigger time in previous GOTO observations taken at 2026-05-09 10:38:10 (-11.21h) down to a depth of >20.40 AB mag, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). 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, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/44505. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42631] GRB 260509A: SVOM detection of a burst
by GCN Circulars 09 May '26

09 May '26

TITLE: GCN CIRCULAR NUMBER: 44504 SUBJECT: GRB 260509A: SVOM detection of a burst DATE: 26/05/09 22:26:24 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> GRB 260509A: SVOM detection of a burst D. Götz (CEA/Irfu), A. Saccardi (CEA/Irfu), H. Goto (RIKEN), F. Lacreu (IAP), D. Adrien (CEA/Irfu), report on behalf of the SVOM mission team: At 2026-05-09T21:51:09 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260509A (SVOM burst-id sb26050905). 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 18 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 18.00 in the [5-20] keV energy band over a time window of 20.40 seconds starting at 2026-05-09T21:51:03. The localization of the best alert is R.A., Dec. 176.8870, 0.2095 degrees: R.A. (J2000) = 11h47m32.9s Dec. (J2000) = 0d12m34.2s with a 90% confidence level (C.L.) radius of 4.72 arcmin (including systematic error of 2 arcmin added in quadrature). We note the presence of a high proper motion star G 10-49 at a distance of 4.48 arcmin from the ECLAIRs position. The SVOM/ECLAIRs light curve showed a single peak structure with a T90 duration of about 14.7 +/-0.6 s. This burst was also detected by SVOM/GRM with a significance of 6.40. The SVOM/GRM light curve showed a double peak structure with a T90 duration of about 18 (-6/+10) s. SVOM slewed to the burst. MXT and VT began observing the field after the slew. The analysis of the data will be published in future circulars. 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 Dylan Adrien: dylan.adrien(a)cea.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44504. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42630] GRB 260506B: AstroSat CZTI detection
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44503 SUBJECT: GRB 260506B: AstroSat CZTI detection DATE: 26/05/08 19:22:25 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> S. Salunke (IUCAA), Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), A. Goyal (IITB), A. Arya (IITB), 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 CIFT2 framework showed the detection of GRB 260506B which is also detected by the Fermi/GBM (Fermi GBM team, GCN Circ. 44484). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-05-06 13:07:41.9 UTC. The measured peak count rate associated with the burst is 129 (+37, -17) counts/s above the background in the combined data of all four quadrants, with a total of 899 (+239, -328) counts. The local mean background count rate was 289 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 22 (+12, -15) s. We caution that there is a 0.3 s dead time in the CZTI data in the burst, hence the actual T90 may be slightly longer. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-05-06 13:07:42.0 UTC. The measured peak count rate associated with the burst is 440 (+67, -69) counts/s above the background in the combined data of all quadrants, with a total of 3325 (+520, -551) counts. The local mean background count rate was 1313 (+4, -4) counts/s. We measure a T90 of 36 (+3, -7) s from the cumulative Veto light curve. 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 data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/515768858.51/S515768858.51_det… 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/44503. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42629] IceCube-260504A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44502 SUBJECT: IceCube-260504A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/05/08 18:08:49 GMT FROM: Alicia Mand at IceCube/UW-Madison <aemand(a)wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-260504A (https://gcn.nasa.gov/circulars/44464) in a time range of 1000 seconds centered on the alert event time (2026-05-04 21:03:00.958 UTC to 2026-05-04 21:19:40.958 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-260504A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.6e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260504A in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 5e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-05-03 21:11:20.958 UTC to 2026-05-05 21:11:20.958 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, ranges from 1.9e-01 to 2.0e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260504A in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/44502. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42628] EP260507a: REM optical/NIR observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44501 SUBJECT: EP260507a: REM optical/NIR observations DATE: 26/05/08 15:30:56 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of EP260507a, detected by EP (Fu et al., GCN 44488) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried out in the g, r, i, z, and H bands, started on 2026-05-07 at 22:56:01 UT (i.e. 9.1 hr after the burst) and lasted for about 1 hour. From preliminary photometry, we do not detect the optical/NIR counterpart (Corcoran et al., GCN Circ. 44489; Sankar et al., GCN Circ. 44490; Jiang et al., GCN Circ. 44491; Kumar et al., GCN Circ. 44492; Eyles-Ferris et al., GCN Circ. 44495; Jiang et al., GCN Circ. 44496; Li et al., GCN 44497; Globus et al., GCN 44498) down to the following 3sigma limits: r > 19.8 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 10.0 hr after the trigger; H > 14.5 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 9.2 hr after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/44501. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42627] EP260507a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44500 SUBJECT: EP260507a: refined analysis of the EP-WXT and EP-FXT observations DATE: 26/05/08 13:33:09 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.Y.Fu (HUST), Y. L. Wang (NAO, CAS; ICE, CSIC), C.L.Guo (NAO, CAS), X. Tian (GXU), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260507a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Fu et al., GCN 44488). The refined analysis of the WXT data shows that the event started at T0=2026-05-07T13:47:44.0 (UTC) and lasted for 15 s before the observation was interrupted by the autonomous follow-up observation (i.e. T90 > 15 s). The average 0.5–4 keV spectrum of WXT can be modeled with an absorbed power law, adopting a fixed Galactic hydrogen column density of 5.55 x 10^20 cm^-2 and an additional column density of 5.77 x 10^21 cm^-2. This additional absorption significantly improves the fit quality, yielding a photon index of 1.47 (+-0.79). The derived average unabsorbed 0.5-4 keV flux is 1.98 (-0.70/+2.20) x 10^(-8) erg/s/cm^2. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-05-07T13:51:52 (UTC), about 4 minutes after T0. The exposure time of this observation is 5046 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 206.899, -22.2364 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law adopting a fixed Galactic equivalent hydrogen column density of 5.55 x 10^20 cm^-2 and an additional column density of 8.33 x 10^20 cm^-2，yielding a photon index of 2.10 (+-0.06). The derived average unabsorbed 0.3-10 keV flux is 1.82 (-0.07/+0.08) x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44500. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42626] GRB 260507B / EP260507a: Fermi-GBM Sub-Threshold Detection
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44499 SUBJECT: GRB 260507B / EP260507a: Fermi-GBM Sub-Threshold Detection DATE: 26/05/08 06:22:37 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (ICE-CSIC and Radboud Univ.), P.G. Jonker (Radboud Univ.) and E. Burns (LSU), R. Hamburg (USRA), and P. Veres (UAH) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial and temporal coverage of the transient EP260507a detected by EP (Fu et al., GCN 44488). There was no Fermi-GBM onboard trigger around the EP trigger time (T0 = 2026-05-07T13:47:57 UTC). The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+250] s from EP T0, seeking signals between 64 ms and 32.768 s in duration. A weak transient signal was found most significantly at ~T0-4 s on a 16 s timescale, with a false alarm rate of 1.7e-03 Hz. The localisation is consistent with the EP one, with a spatial association probability of 93.5%. Among the three spectral templates tested, the transient was best fit with a “soft” spectral template (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/44499. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42625] EP260507a: COLIBRÍ optical observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44498 SUBJECT: EP260507a: COLIBRÍ optical observations DATE: 26/05/08 06:07:02 GMT FROM: globus(a)astro.unam.mx Noémie Globus (UNAM), Francis Fortin (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260507a (Fu et al., GCN Circ. 44488) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-08 04:59 to 05:50 UTC (from 15.19 to 16.06 hours after the trigger) and obtained 39 minutes of exposure in the r and z filters, respectively. The data were reduced and coadded with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect the optical candidate reported previously (Corcoran et al., GCN Circ. 44489; Sankar et al., GCN Circ. 44490; Jiang et al., GCN Circ. 44491; Kumar et al., GCN Circ. 44492; Bochenek et al., GCN Circ. 44494; Eyles-Ferris et al., GCN Circ. 44495; Jiang et al., GCN Circ. 44496) with preliminary magnitudes of: r = 23.37 +/- 0.14, z = 22.44 +/- 0.21. From a combined power-law fit including our data and previously reported GCN Circular measurements, we derive a temporal decay index of α ≈ 0.6. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44498. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42624] EP260507a: SVOM/VT optical observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44497 SUBJECT: EP260507a: SVOM/VT optical observations DATE: 26/05/08 03:08:14 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed observations with automatic follow-up observations to the Xray transient EP260507a triggered by Einstein Probe (Fu et al., GCN 44488). The observation started at 2026-05-07T14:45:27 UTC, i.e. 57.5 minutes post trigger and lasted for 2 orbits (about 1.9 hours) in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical counterpart (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491; Kumar et al., GCN 44492; Eyles-Ferris et al., GCN 44495; Jiang et al., GCN 44496) was clearly detected in both channels. The measurements in AB magnitude are as follows: Mid time | Band | Exposure Time | Brightness 1.35 h VT_B 56*50 s 21.92 +/- 0.12 mag 1.35 h VT_R 55*50 s 20.91 +/- 0.08 mag 2.96 h VT_B 56*50 s 22.29 +/- 0.14 mag 2.96 h VT_R 55*50 s 21.25 +/- 0.10 mag Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44497. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42623] EP260507a: NOT optical observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44496 SUBJECT: EP260507a: NOT optical observations DATE: 26/05/08 01:42:18 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang, L.B. He, Z.P. Zhu, J. An, X. Liu, D. Xu (NAOC), S.Y. Fu (HUST), J. P. U. Fynbo (DAWN/NBI), A. L. Bouquin (NOT) report: We observed the field of EP260507a detected by EP (Fu et al., GCN 44488), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 3 x 300 s frames in the Sloan g, r, i-band, respectively. The optical afterglow (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491; Kumar et al., GCN 44492; Eyles-Ferris et al., GCN 44495) is detected in our stacked images. Preliminary photometry results are as follows: Tmid-T0(hr) Mag MagErr Filter 9.54 23.04 0.12 r 9.82 23.61 0.17 g 10.10 22.77 0.17 i 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/44496. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42622] EP260507a: further Liverpool Telescope observations
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44495 SUBJECT: EP260507a: further Liverpool Telescope observations DATE: 26/05/08 01:20:37 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester) reports on behalf of a larger collaboration: We observed the field of EP260227a (Fu et al., GCN 44488) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x200s exposures in each of the SDSS r’ and z’ filters starting at 2026-05-07 22:51:45 UT, approximately 9.06 hours after the X-ray detection. We detect the optical counterpart (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491; Kumar et al., GCN 44492; Bochenek et al., GCN 44494) in both the r’ z’ bands and measure the following magnitudes: r’ = 22.76 +/- 0.21 z’ = 21.98 +/- 0.30 Our photometry is calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44495. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42621] EP260507a: Liverpool Telescope optical upper limits
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44494 SUBJECT: EP260507a: Liverpool Telescope optical upper limits DATE: 26/05/07 23:34:35 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU), report: We observed the field of EP260507a (Fu et al., GCN 44488) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x100s exposures in SDSS g, r, and i filters, starting at 2026-05-07 22:20:09 UT, approximately 8.54 hours after trigger. We do not detect any sources at the position of the optical counterpart (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491, Kumar et al., GCN 44492) down to the 3-sigma limiting magnitude of g > 22.05, r > 21.92 and i > 22.07. Further observations are planned. The photometry is in the AB magnitude system, was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44494. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42620] GRB 260507A: Fermi GBM Final Real-time Localization
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44493 SUBJECT: GRB 260507A: Fermi GBM Final Real-time Localization DATE: 26/05/07 20:38:34 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 20:28:00 UT on 7 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260507A (trigger 799878485.453562 / 260507853). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 287.5, Dec = -21.3 (J2000 degrees, equivalent to J2000 19h 10m, -21d 18'), with a statistical uncertainty of 2.4 degrees. The angle from the Fermi LAT boresight is 79.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260507853/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260507853/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260507853/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44493. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42619] EP260507a: GOTO optical counterpart detection
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44492 SUBJECT: EP260507a: GOTO optical counterpart detection DATE: 26/05/07 19:02:11 GMT FROM: Amit Kumar at The Open University, UK <amitkundu515(a)gmail.com> A. Kumar, S. Belkin, D. O'Neill, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, J. Casares, B. Godson, T. Killestein and M. Pursiainen on behalf of 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 EP-WXT triggered EP260507a (Fu et al., GCN 44488). The observations were conducted with GOTO-South at 2026-05-07 13:57:30 UT and 2026-05-07 15:04:48 UT (9.5 and 76.8 mins post-trigger, respectively), consisting of 4x90s exposures in the GOTO L-band (400-700 nm). Difference imaging was performed using deeper template observations of the same pointings. We detect the optical counterpart of EP260507a (Corcoran et al., GCN 44489; Sankar et al., GCN 44490; Jiang et al., GCN 44491) in the GOTO L-band at 2026-05-07 13:57:30 UT (9.5 mins post-trigger), with a measured magnitude of 19.56 ± 0.11 AB. The source is no longer detected at the next epoch obtained at 2026-05-07 15:04:48 UT (76.8 mins post-trigger), with a 3-sigma upper limit of 20.4 AB mag. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. 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, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/44492. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42618] EP260507a: TRT optical counterpart detection
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44491 SUBJECT: EP260507a: TRT optical counterpart detection DATE: 26/05/07 18:11:13 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), X. Liu, Z.P. Zhu, J. An, L.B. He, D. Xu (NAOC) report: We observed the field of EP260507a detected by EP (Fu et. al, GCN 44488), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observation started at 2026-05-07T14:27:55.509 UT, i.e., 39.98 mins post-burst, and a series of R-band frames were obtained. The optical afterglow (Corcoran et. al, GCN 44489; Sankar et. al, GCN 44490) is marginally detected in our stacked images with a brightness of R = 20.8 +/- 0.36 at a median time of 45.88 mins 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/44491. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42617] EP260507a: Kinder optical counterpart candidate
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44490 SUBJECT: EP260507a: Kinder optical counterpart candidate DATE: 26/05/07 15:19:55 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> A. Sankar.K, A. Aryan, Y.-H. Lee, T.-W. Chen, W.-J. Hou (all NCU), A. K. H. Kong (NTHU), S. J. Smartt, J. Gillanders (both Oxford), S. Yang(HNAS), M.-H. Lee, A. Dutta, K. N.-T. Ho, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, H.-C. Lin, H.-Y. Hsiao, C.-S. Lin, J.-K. Guo (all NCU), Z. N. Wang, D. C. Qiang, L. L. Fan (all HNAS), Y. J. Yang (NYUAD), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, K. W. Smith, C. Angus, A. Aamer (all QUB), T. Moore (STScI), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260507a (Fu et al., GCN 44488) using the 40cm SLT at the Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86). The first SLT epoch of observations started at 14:06 UTC on 7th May 2026 (MJD 61167.5837), 0.30 hr after the EP-WXT trigger. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 image using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm. In the stacked frame as well as in the difference image, we detect an uncatalogued optical counterpart candidate at RA, DEC = 13:47:35.567, -22:14:08.38 with an uncertainty of 1". The optical counterpart candidate is well inside the EP-FXT error circle of 20". The details of the observations and measured PSF magnitude with template subtraction (in the AB system) of the possible counterpart of EP260507a are as follows: -------------------------------------------------------------------------------------------------- Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | r | 61167.5837 | 0.30 | 300 * 6 | 20.64 +/- 0.07 | 2".07 | 1.44 The presented magnitudes are calibrated using the field stars from ATLAS-RefCat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). The reported magnitudes/upper-limits are not corrected for an expected galactic extinction of A_r = 0.16 mag, in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al. 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/44490. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42616] EP260507a: LCO optical counterpart
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44489 SUBJECT: EP260507a: LCO optical counterpart DATE: 26/05/07 15:16:19 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), J. A. Chácon (PUC), J. N. D. van Dalen (Radboud), F. E. Bauer (SSI and UTA), P. G. Jonker (Radboud), A. J. Levan (Radboud & Warwick) and D. B. Malesani (DAWN/NBI and Radboud) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP260507a (Fu et al., GCN 44488) using an LCO 1m telescope located at the Siding Spring Observatory (Australia) equipped with the SINISTRO instrument. We obtained 6x300s exposures in the SDSS-r filter starting at 2026-05-07 14:34:48 (~47 minutes after the trigger). Within the EP/FXT error region (Fu et al., GCN 44488), we detect a likely optical counterpart at a position of (J2000): RA 13:47:35.57 (206.89822) Dec -22:14:08.40 (-22.23566) We measure a magnitude of r = 21.21 +/- 0.07 (AB) calibrated to PanSTARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44489. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42615] EP260507a: Einstein Probe detection of an X-ray transient
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44488 SUBJECT: EP260507a: Einstein Probe detection of an X-ray transient DATE: 26/05/07 14:40:02 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Y. Fu (HUST), Y. L. Wang (NAO, CAS; ICE, CSIC), C. L. Guo (NAO, CAS), X. Tian (GXU), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260507a. The transient triggered EP-WXT (ID: 01709261593) at 2026-05-07T13:47:57 (UTC). The WXT position of the source is R.A. = 206.895 deg, DEC = -22.243 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 206.8963 deg, DEC = -22.2361 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44488. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42614] GRB 260504B: AstroSat CZTI detection
by GCN Circulars 07 May '26

07 May '26

TITLE: GCN CIRCULAR NUMBER: 44487 SUBJECT: GRB 260504B: AstroSat CZTI detection DATE: 26/05/07 14:19:14 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (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 GRB 260504B which is also detected by SVOM/GRM (Saccardi et al., GCN Circ. 44454), GECAM-B (Wang et al., GCN Circ. 44473), and Konus-Wind (Frederiks et. al., GCN Circ. 44474). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-05-04 09:31:16.450 UTC. The measured peak count rate associated with the burst is 1150 (+201, -203) counts/s above the background in the combined data of all four quadrants, with a total of 162 (+33, -36) counts. The local mean background count rate was 319 (+9, -11) counts/s. Using cumulative rates, we measure a T90 of 0.22 (+0.11, -0.07) s. 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/44487. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42613] GRB 260504B: SVOM/ECLAIRs refined analysis
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44486 SUBJECT: GRB 260504B: SVOM/ECLAIRs refined analysis DATE: 26/05/06 16:54:33 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> F. Piron (LUPM), M. Brunet (IRAP), N. Dagoneau (CEA), Y. Wang (PMO,CAS; UCB), W. J. Xie (NAO,CAS), 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 SVOM/ECLAIRs observations of GRB 260504B (SVOM burst-id sb26050402 – GCN 44454, trigger time T0 = 2026-05-04T09:31:19 UTC), which was also detected by SVOM/GRM (GCN 44470), GECAM-B (GCN 44473) and Konus-Wind (GCN 44474). The burst that triggered ECLAIRs onboard shows a single peak lightcurve. The burst duration is T90 = 0.46 -0.06/+0.09 s in the 4-120 keV energy band. The time-averaged spectrum from T0+0.40 s to T0+0.86 s in the energy range 5-120 keV is best fitted by a powerlaw model with best-fit parameters: alpha = -0.72 +/-0.06. With this model, the 4-120 keV fluence is (1.87 ± 0.09) e-7 erg/cm^2 and the 4-120 keV photon flux is 6.0 ± 0.3 ph/cm²/s. We note that the photon index is consistent with the one found by SVOM/GRM (GCN 44470). 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: Frédéric Piron (LUPM) (piron at in2p3.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/44486. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42612] GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547)
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44485 SUBJECT: GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547) DATE: 26/05/06 14:01:40 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 799765648 at 13:07:23 on 06 May 2026 were automatically 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) = 280.7 deg Decl.(2000.0) = -6.1 deg The 1 sigma statistical error radius is 1.5 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260506547/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260506547/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260506547/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42611] GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547)
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44485 SUBJECT: GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547) DATE: 26/05/06 14:01:40 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 799765648 at 13:07:23 on 06 May 2026 were automatically 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) = 280.7 deg Decl.(2000.0) = -6.1 deg The 1 sigma statistical error radius is 1.5 deg. We estimate an additional systematic error of 1 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB260506547/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB260506547/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB260506547/json View this GCN Circular online at https://gcn.nasa.gov/circulars/44485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42610] GRB 260506B: Fermi GBM Final Real-time Localization
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44484 SUBJECT: GRB 260506B: Fermi GBM Final Real-time Localization DATE: 26/05/06 13:18:06 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 13:07:23 UT on 6 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260506B (trigger 799765648.964258 / 260506547). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 280.5, Dec = -0.5 (J2000 degrees, equivalent to J2000 18h 41m, 0d 30'), with a statistical uncertainty of 1.8 degrees. The angle from the Fermi LAT boresight is 44.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260506547/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260506547/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260506547/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44484. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42609] EP260502a is likely a flaring star
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44483 SUBJECT: EP260502a is likely a flaring star DATE: 26/05/06 10:24:37 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T.Y. Liu (NAO,CAS), Y. Q. Zhao(PRIC,USTC), Y. F. Liang (PMO, CAS), Y. Wang (PMO, CAS; UCB), H. W. Pan (NAO,CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260502a (GCN #44440) at the time of 2026-05-02T06:08:51, is likely a stellar flare associated with SIPS J1809-7613. The estimated flux of the flare is around 1.1×10^(-9) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 9.8×10^(30) erg/s. The telemetry WXT data show that the flare started around 2026-05-02T05:58:08 (UTC) and exhibits no obvious flux variation later in the WXT exposure. The average WXT 0.5-4 keV spectrum of the burst period can be fitted with an absorbed power law with a hydrogen column density of 3.68×10^(-9)（-3.68×10^(-9)/+0.361 ）×10^22 cm^-2 and a photon index of 0.52(-0.52/+1.70). The derived average unabsorbed 0.5-4 keV flux is 9.96 (-3.89/+11.51) ×10^(-11) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source at 2026-05-02T06:19:45 (UTC). The exposure time of this observation is 3.0ks. The flux show a rapid fading of around 5 times in 1ks. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 0.66 (-0.21/+0.25) × 10^22 cm^-2 and a photon index of 5.44 (-1.02/+1.23). The derived average unabsorbed 0.5-10 keV flux is 8.29 (-4.61/+15.56) × 10^(-12) erg/s/cm^2. The optical follow-up observations were performed by Li et al. (GCN 44441), Sharma et al. (GCN 44442, GCN 44444), and catch a fading of 0.7mag of SIPS J1809-7613 in 30min starting from 2026-05-02 06:24:42, consistent with the X-ray fading detected by the FXT autumatic follow-up. A follow-up observation around 3ks with the EP/FXT was carried out starting at 2026-05-02T06:19:45, and no FXT trigger was received during the observation. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44483. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42608] Fermi GRB 260506A: Global MASTER-Net observations report
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44482 SUBJECT: Fermi GRB 260506A: Global MASTER-Net observations report DATE: 26/05/06 07:00:25 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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260506A ( Fermi GBM team, GCN 44481) errorbox 224 sec after notice time and 230 sec after trigger time at 2026-05-06 06:32:38 UT, with upper limit up to 19.3 mag. The observations began at zenith distance = 58 deg. The sun altitude is -41.5 deg. The galactic latitude b = 36 deg., longitude l = 136 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3296217 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 260 | 2026-05-06 06:32:38 | MASTER-OAGH | (08h 44m 39.72s , +75d 23m 45.7s) | C | 60 | 18.5 | 260 | 2026-05-06 06:32:38 | MASTER-OAGH | (08h 37m 44.58s , +75d 59m 45.8s) | C | 60 | 18.7 | 333 | 2026-05-06 06:33:51 | MASTER-OAGH | (09h 16m 22.00s , +75d 24m 42.7s) | C | 60 | 18.8 | 333 | 2026-05-06 06:33:51 | MASTER-OAGH | (09h 09m 15.33s , +76d 01m 00.1s) | C | 60 | 18.9 | 406 | 2026-05-06 06:35:04 | MASTER-OAGH | (08h 52m 23.52s , +77d 19m 08.0s) | C | 60 | 19.1 | 406 | 2026-05-06 06:35:04 | MASTER-OAGH | (08h 44m 14.66s , +77d 55m 18.4s) | C | 60 | 19.3 | 479 | 2026-05-06 06:36:17 | MASTER-OAGH | (09h 28m 38.58s , +77d 18m 24.2s) | C | 60 | 18.3 | 479 | 2026-05-06 06:36:17 | MASTER-OAGH | (09h 20m 26.78s , +77d 54m 22.8s) | C | 60 | 18.6 | 553 | 2026-05-06 06:37:31 | MASTER-OAGH | (09h 32m 43.22s , +73d 30m 24.2s) | C | 60 | 18.8 | 553 | 2026-05-06 06:37:31 | MASTER-OAGH | (09h 26m 27.66s , +74d 06m 31.2s) | C | 60 | 18.9 | 626 | 2026-05-06 06:38:44 | MASTER-OAGH | (10h 00m 45.91s , +73d 28m 55.8s) | C | 60 | 18.7 | 626 | 2026-05-06 06:38:44 | MASTER-OAGH | (09h 54m 25.86s , +74d 05m 06.5s) | C | 60 | 19.0 | 699 | 2026-05-06 06:39:57 | MASTER-OAGH | (09h 44m 54.95s , +75d 25m 08.4s) | C | 60 | 19.0 | 699 | 2026-05-06 06:39:57 | MASTER-OAGH | (09h 37m 45.79s , +76d 01m 15.0s) | C | 60 | 19.2 | 773 | 2026-05-06 06:41:11 | MASTER-OAGH | (10h 16m 39.45s , +75d 23m 04.3s) | C | 60 | 19.0 | 773 | 2026-05-06 06:41:11 | MASTER-OAGH | (10h 09m 25.61s , +75d 59m 15.1s) | C | 60 | 19.2 | 1010 | 2026-05-06 06:45:08 | MASTER-OAGH | (08h 44m 32.03s , +75d 26m 03.2s) | C | 60 | 18.9 | 1010 | 2026-05-06 06:45:08 | MASTER-OAGH | (08h 37m 39.30s , +75d 57m 59.1s) | C | 60 | 18.9 | 1083 | 2026-05-06 06:46:21 | MASTER-OAGH | (09h 16m 23.42s , +75d 24m 39.6s) | C | 60 | 18.8 | 1083 | 2026-05-06 06:46:21 | MASTER-OAGH | (09h 09m 18.88s , +76d 00m 58.5s) | C | 60 | 19.0 | 1156 | 2026-05-06 06:47:34 | MASTER-OAGH | (08h 52m 15.20s , +77d 18m 04.3s) | C | 60 | 19.1 | 1156 | 2026-05-06 06:47:34 | MASTER-OAGH | (08h 44m 14.12s , +77d 54m 09.0s) | C | 60 | 19.1 | 1230 | 2026-05-06 06:48:47 | MASTER-OAGH | (09h 28m 45.20s , +77d 17m 37.2s) | C | 60 | 18.7 | 1230 | 2026-05-06 06:48:47 | MASTER-OAGH | (09h 20m 32.90s , +77d 53m 53.1s) | C | 60 | 19.0 | 1303 | 2026-05-06 06:50:00 | MASTER-OAGH | (09h 32m 40.96s , +73d 31m 11.3s) | C | 60 | 18.9 | 1303 | 2026-05-06 06:50:00 | MASTER-OAGH | (09h 26m 24.09s , +74d 07m 34.1s) | C | 60 | 19.0 | 1376 | 2026-05-06 06:51:14 | MASTER-OAGH | (10h 00m 49.53s , +73d 29m 34.1s) | C | 60 | 18.9 | 1376 | 2026-05-06 06:51:14 | MASTER-OAGH | (09h 54m 31.45s , +74d 05m 45.0s) | C | 60 | 19.2 | 1448 | 2026-05-06 06:52:26 | MASTER-OAGH | (09h 44m 56.50s , +75d 25m 43.2s) | C | 60 | 19.0 | 1448 | 2026-05-06 06:52:26 | MASTER-OAGH | (09h 37m 49.83s , +76d 01m 49.5s) | C | 60 | 19.1 | 1523 | 2026-05-06 06:53:41 | MASTER-OAGH | (10h 16m 36.92s , +75d 24m 10.7s) | C | 60 | 18.9 | 1523 | 2026-05-06 06:53:41 | MASTER-OAGH | (10h 09m 24.89s , +76d 00m 21.4s) | C | 60 | 19.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44482. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42607] GRB 260506A: Fermi GBM Final Real-time Localization
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44481 SUBJECT: GRB 260506A: Fermi GBM Final Real-time Localization DATE: 26/05/06 06:39:24 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 SHORT GRB At 06:28:48 UT on 6 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260506A (trigger 799741733.38117 / 260506270). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 145.7, Dec = 76.1 (J2000 degrees, equivalent to J2000 09h 42m, 76d 05'), with a statistical uncertainty of 7.2 degrees. The angle from the Fermi LAT boresight is 18.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260506270/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260506270/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260506270/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44481. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42606] GRB 260503A: GECAM-B observation of a burst
by GCN Circulars 06 May '26

06 May '26

TITLE: GCN CIRCULAR NUMBER: 44480 SUBJECT: GRB 260503A: GECAM-B observation of a burst DATE: 26/05/06 05:19:05 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260503A, at 2026-05-03T20:40:18.050 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44451). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 21 +4/-3 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260503A.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44480. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42605] IceCube Alert 260505A: Global MASTER-Net observations report
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44479 SUBJECT: IceCube Alert 260505A: Global MASTER-Net observations report DATE: 26/05/05 22:26:33 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 [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the IceCube Alert 260505A (trigger No 58544625,16h 27m 57.60s , +54d 52m 12.0s, R=0.67) errorbox 1 days 3353 sec after notice time and 1 days 3411 sec after trigger time at 2026-05-05 22:08:12 UT, with upper limit up to 19.2 mag. The observations began at zenith distance = 13 deg. The sun altitude is -29.0 deg. The galactic latitude b = 42 deg., longitude l = 84 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3293437 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 89842 | 2026-05-05 22:08:12 | MASTER-Kislovodsk | (16h 26m 24.62s , +55d 13m 07.6s) | C | 60 | 13.2 | 89842 | 2026-05-05 22:08:12 | MASTER-Kislovodsk | (16h 26m 52.94s , +54d 49m 59.4s) | C | 60 | 19.1 | 89940 | 2026-05-05 22:09:50 | MASTER-Kislovodsk | (16h 26m 58.23s , +54d 48m 57.5s) | C | 60 | 19.1 | 90036 | 2026-05-05 22:11:26 | MASTER-Kislovodsk | (16h 26m 12.84s , +55d 11m 17.5s) | C | 60 | 13.3 | 90037 | 2026-05-05 22:11:27 | MASTER-Kislovodsk | (16h 26m 52.47s , +54d 47m 56.7s) | C | 60 | 19.1 | 90125 | 2026-05-05 22:12:56 | MASTER-Kislovodsk | (16h 26m 24.80s , +55d 12m 02.6s) | C | 60 | 13.6 | 90125 | 2026-05-05 22:12:56 | MASTER-Kislovodsk | (16h 26m 56.65s , +54d 48m 13.7s) | C | 60 | 19.2 | 90215 | 2026-05-05 22:14:25 | MASTER-Kislovodsk | (16h 26m 17.07s , +55d 12m 10.3s) | C | 60 | 12.9 | 90215 | 2026-05-05 22:14:25 | MASTER-Kislovodsk | (16h 26m 52.12s , +54d 49m 38.8s) | C | 60 | 19.2 | 90303 | 2026-05-05 22:15:54 | MASTER-Kislovodsk | (16h 26m 16.58s , +55d 10m 30.3s) | C | 60 | 13.1 | 90303 | 2026-05-05 22:15:54 | MASTER-Kislovodsk | (16h 26m 51.53s , +54d 48m 00.8s) | C | 60 | 19.1 | 90391 | 2026-05-05 22:17:21 | MASTER-Kislovodsk | (16h 26m 20.13s , +55d 12m 14.8s) | C | 60 | 12.7 | 90391 | 2026-05-05 22:17:21 | MASTER-Kislovodsk | (16h 26m 54.99s , +54d 49m 43.2s) | C | 60 | 19.0 | 90479 | 2026-05-05 22:18:50 | MASTER-Kislovodsk | (16h 26m 12.86s , +55d 11m 27.4s) | C | 60 | 12.7 | 90479 | 2026-05-05 22:18:50 | MASTER-Kislovodsk | (16h 26m 47.70s , +54d 48m 56.2s) | C | 60 | 19.2 | 90568 | 2026-05-05 22:20:18 | MASTER-Kislovodsk | (16h 26m 47.19s , +54d 49m 56.1s) | C | 60 | 19.2 | 90656 | 2026-05-05 22:21:46 | MASTER-Kislovodsk | (16h 26m 19.15s , +55d 11m 26.0s) | C | 60 | 12.7 | 90656 | 2026-05-05 22:21:46 | MASTER-Kislovodsk | (16h 26m 53.95s , +54d 48m 57.0s) | C | 60 | 19.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44479. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42604] GRB 260430B: Glowbug gamma-ray detection
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44478 SUBJECT: GRB 260430B: Glowbug gamma-ray detection DATE: 26/05/05 16:06:39 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 260430B, which was also detected by AstroSat/CZTI (GCN 44469) and SVOM/GRM (sb26043004). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-04-30 16:04:22.184 with a duration of 49.2 s and a total significance of about 113 sigma. The light curve comprises a complex series of peaks throughout the burst duration. 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 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/44478. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42603] GRB 260504B: SVOM/VT optical upper limits
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44477 SUBJECT: GRB 260504B: SVOM/VT optical upper limits DATE: 26/05/05 15:53:02 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), Y. Wang (PMO,CAS; UCB) report on behalf of the SVOM/VT team. SVOM/VT performed observations with an automatic slew to GRB 260504B detected by SVOM/ECLAIRs (sb26050402, Saccardi et al., GCN 44454), SVOM/GRM (Wang et al., GCN 44470), GECAM-B (Wang et al., GCN 44473) and Konus-Wind (Frederiks et al., GCN 44474). The observation started at 2026-05-04T09:34:59 UTC, 220 seconds post trigger and lasted for 6 orbits (about 8 hours), in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No uncatalogued sources were detected within the error box of SVOM/ECLAIRs (Saccardi et al., GCN 44454) or SVOM/MXT (Maggi et al., GCN 44468), compared to the Legacy Survey. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | 5-sigma upper limit 670 s VT_B 18*50 s > 22.5 mag 670 s VT_R 18*50 s > 22.5 mag 2.59 h VT_B 34*100 s > 23.0 mag 2.59 h VT_R 33*100 s > 23.0 mag Our result is consistent with the results from the rapid decay in SVOM/MXT (Saccardi et al., GCN 44454), upper limit of EP-FXT (Zhou et al., GCN 44467), optical non-detections by MASTER-OAFA(Podesta et al., GCN 44455), LCO (Turpin et al., GCN 44456), AST3-2 (Sun et al., GCN 44457) and REM (Brivio et al., GCN 44460). The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44477. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42602] GRB 260421B: radio observation with the VLA
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44476 SUBJECT: GRB 260421B: radio observation with the VLA DATE: 26/05/05 15:50:44 GMT FROM: Stefano Giarratana at INAF-OAB <s.giarratana(a)ira.inaf.it> S. Giarratana (INAF-OAB), M. Giroletti (INAF-IRA), G. Ghirlanda (INAF-OAB), N. Di Lalla (Stanford Univ.), N. Omodei (Stanford Univ.), O. S. Salafia (INAF-OAB), L. Nava (INAF-OAB) At 05:08:16 UT on 2026 April 22 (T_mid = 1.07 days post-burst) the Karl G. Jansky VLA observed the field of GRB 260421B (Fermi GBM team, GCN 44360, 44382; SVOM mission team, GCN 44362, GCN 44389, 44397; Insight-HXMT team, GCN 44401) at central frequencies of 6, 10 and 15 GHz. The standard 3C286 was used as bandpass and flux density calibrator, while J1239-1023 was used as phase calibrator. From a preliminary analysis, we do not detect the radio counterpart of GRB 260421B. We derive the following upper limits (UL; 3sigma): ================================================================ T_mid Freq UL r.m.s. Beam PA [days] [GHz] [uJy] [uJy/b] [arcsec^2] [deg] ================================================================ 1.07 6 24 8 0.47x0.28 11 1.07 10 24 8 0.30x0.18 11 1.07 15 27 9 0.20x0.11 -2 ================================================================ We would like to thank the staff of the VLA for approving, executing, and processing the observations. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. These observations were carried out as part of project SF181027, approved in the framework of the Fermi - NRAO joint program agreement. View this GCN Circular online at https://gcn.nasa.gov/circulars/44476. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42601] Konus-Wind detection of a burst from SGR 1E1841-045 on 2026 May 2
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44475 SUBJECT: Konus-Wind detection of a burst from SGR 1E1841-045 on 2026 May 2 DATE: 26/05/05 15:28:39 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: A bright burst from SGR 1E1841-045 (IPN triangulation: Ridnaia et al., GCN 44448; SVOM-GRM detection: Zao et al., GCN 44450) triggered Konus-Wind at T0=20396.052 s UT (05:39:56.052) on 2026 May 2. The burst light curve shows a single pulse, which starts at ~T0-50 ms and has a total duration of ~96 ms. The emission is seen up to ~200 keV. The Konus-Wind light curve of this burst is available at http://www.ioffe.ru/LEA/SGRs/260502_T20396/ As observed by Konus-Wind, the burst had a fluence of 8.64(-0.45,+0.46)x10^-7 erg/cm2, and a 16-ms peak flux, measured from T0-0.004 s, of 1.93(-0.16,+0.16)x10^-5 erg/cm2/s (both in the 20 - 500 keV energy range). The spectrum of the burst (measured from T0 to T0+0.064 s) is best fit in the 20 - 500 keV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = 0.16(-0.69,+0.76) and Ep = 48(-4,+3) keV (chi2 = 12/15 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/44475. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42600] Konus-Wind detection of GRB 260504B (short/hard)
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44474 SUBJECT: Konus-Wind detection of GRB 260504B (short/hard) DATE: 26/05/05 14:25:39 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 short GRB 260504B (SVOM/ECLAIRs detection: Saccardi et al., GCN 44454; SVOM/GRM detection: Wang et al., GCN 44470; GECAM-B detection: Wang et al., GCN 44473) triggered Konus-Wind (KW) at T0=34281.198 s UT (09:31:21.198). The burst light curve shows a single pulse, which starts at ~T0-0.05 s and has a duration of ~0.21 s. The emission is seen up to ~6 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260504_T34281/ As observed by Konus-Wind, the burst had the total fluence of (2.39 ± 0.52)x10^-6 erg/cm^2 and a 16-ms peak energy flux, measured from T0-0.032, of (2.06 ± 0.45)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+0.192 s) is best fitted in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.00 (-0.12, + 0.14) and Ep = 1461(-398,+584) keV, chi^2 = 34/32 dof. Fitting this spectrum by a Band GRB function yields the same values of alpha and Ep, and only an upper limit on the high energy photon index beta of -2.1 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/44474. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42599] GRB 260504B: GECAM-B detection
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44473 SUBJECT: GRB 260504B: GECAM-B detection DATE: 26/05/05 13:41:13 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong, Chao Zheng (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a hard burst GRB 260504B at 2026-05-04T09:31:19.450 UTC (denoted as T0). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 0.20 +0.02/-0.06 s, which is also detected by SVOM/ECLAIRs and SVOM/GRM (A. Saccardi et al., GCN # 44454). The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260504B.png The time-averaged spectrum from T0-0.07 s to T0+0.1 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.07 +0.29/-0.27 and the cutoff energy, parameterized as Epeak, is 1240 +730/-400 keV. The event fluence (10-1000 keV) in this time interval is (1.06 +0.13/-0.10)E-06 erg/cm^2. Thus GRB 260504B is consistent with Type I GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/gecambgrb260504B_amati.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/44473. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42598] Fermi-LAT Gamma-ray Observations of IceCube-260504A
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44472 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-260504A DATE: 26/05/05 12:53:40 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC260504A neutrino event (GCN 44464) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2026-05-04 21:11:20.90 UTC (T0) with J2000 position RA = 246.99 (+0.86, -0.80) deg, Decl. = 54.87 (+0.46, -0.47) deg 90% PSF containment. One cataloged >100 MeV gamma-ray source is located within the 90% IC260504A localization error, at a distance of roughly 0.38 deg (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). This is the object 4FGL J1626.0+5436 associated with 87GB 162528.4+544848. Based on a preliminary analysis of the LAT data over the timescale of 1-day and 1-month prior to T0, this object is not significantly detected at gamma-rays. We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC260504A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260504A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.3e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <4.6e-09 (<4.7e-08) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this source the Fermi-LAT contact person is Leonard Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/44472. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42596] GRB 260504C: SVOM/GRM observation of short GRB
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44471 SUBJECT: GRB 260504C: SVOM/GRM observation of short GRB DATE: 26/05/05 12:42:20 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Frédéric Piron (LUPM) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a short burst GRB 260504C (SVOM trigger reference: sb26050401) at 2026-05-04T07:10:06.60 UTC (T0). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple spikes with a T90 of 0.26 +0.06/-0.08 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260504C.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44471. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42597] GRB 260504B: SVOM/GRM spectral analysis
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44470 SUBJECT: GRB 260504B: SVOM/GRM spectral analysis DATE: 26/05/05 12:31:40 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Stéphane Schanne (CEA) Report on behalf of the SVOM team: With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 260504B. With the localization of ECLAIRs (RA= 351.2451 deg, DEC= -80.3291 deg, GCN#44454), the time-averaged spectrum from T0-0.10 to T0+0.34 s can be fitted by a power law function with an exponential high-energy cutoff adequately. The power law index is -0.72 +0.11/-0.10 and the cutoff energy, parameterized as Epeak, is 1340 +590/-380 keV. The event fluence (10-1000 keV) in this time interval is (1.46 +0.10/-0.09)E-06 erg/cm^2. Thus GRB 260504B is consistent with Type I GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/svgrb260504B_amati.png The SVOM/GRM light curve was updated using the X-band data： https://www.bursthub.cn//admin/static/svgrb260504B.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Chen-Wei Wang (IHEP) (cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44470. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42595] GRB 260430B: AstroSat CZTI detection of a long burst
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44469 SUBJECT: GRB 260430B: AstroSat CZTI detection of a long burst DATE: 26/05/05 11:53:54 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), A. Goyal (IITB), A. Arya (IITB), 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 260430B. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-04-30 16:04:26.34 UTC. The measured peak count rate associated with the burst is 100 (+32, -10) counts/s above the background in the combined data of three quadrants (out of four), with a total of 1436 (+290, -227) counts. The local mean background count rate was 219 (+1, -2) counts/s. Using cumulative rates, we measure a T90 of 47 (+2, -4) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-04-30 16:04:22.5 UTC. The measured peak count rate associated with the burst is 417 (+77, -26) counts/s above the background in the combined data of all quadrants, with a total of 6007 (+912, -928) counts. The local mean background count rate was 1271 (+6, -6) counts/s. We measure a T90 of 40 (+11, -6) s from the cumulative Veto light curve. 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 data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/515261050.0/S515261050.0_detai… 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/44469. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42594] GRB 260504B: SVOM/MXT refined analysis and potential detection
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44468 SUBJECT: GRB 260504B: SVOM/MXT refined analysis and potential detection DATE: 26/05/05 09:32:52 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> P. Maggi (ObAS), D. Götz (CEA), H. Goto (RIKEN/CEA), M. Moita (CEA), C. Plasse (UHK), F. Robinet (IJCLab), C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team: GRB 260504B (Saccardi et al. GCN 44454) was observed by SVOM/MXT after an automatic SVOM slew, starting at T_MXT = 2026-05-04T09:33:16, 117 s after trigger time T0. MXT observed for the remainder of the orbit for 730s and the subsequent 5 orbits. Using the full X-band dataset, an uncatalogued X-ray source is only detected significantly at the very start of the MXT observation. Restricting the analysis until T_MXT+60s, the position of the MXT candidate afterglow is refined to: R.A. (J2000) = 23h24m10.8s Dec (J2000) = -80d17m01s with a 90% C.L. radius of 113” (including 25 arcseconds systematic error added in quadrature). This position is compatible with the SVOM/ECLAIRS position, but not with the SVOM/MXT position using the onboard processed data, initially reported. This position supersedes the one published in the GCN 44454. The light curve exhibits a fast decay with temporal index alpha < -6 (with count rate proportional to t^alpha). At t >T_MXT + 60s the source is no longer detected by MXT. The source is below the MXT detection limit in subsequent orbits. We analysed the spectrum extracted from the first 60s of observation, modelled with an absorbed power-law. The absorbing column was fixed to the Galactic NH of 7x1e20 /cm². A photon index Gamma = 1.3 +/- 0.4 is measured. We measure a 0.3-8 keV flux of 2.6 (-1.6/ +2.28) x 1e-10 erg/s/cm² (all uncertainties at 90% C. L.; these preliminary results may be improved) The Space 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. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. The Burst Advocate (BA) on shift for this alert is Yun Wang: wangyun(a)pmo.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44468. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42593] GRB 260504B: EP-FXT upper limit
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44467 SUBJECT: GRB 260504B: EP-FXT upper limit DATE: 26/05/05 04:30:12 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Zhou (PMO, CAS), Y.Q. Zhao (PRIC, USTC), T.Y. Liu, Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team: The Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission observed GRB 260504B (Saccardi, GCN 44454) autonomously at 2026-05-04 11:46:16 (UTC, ~ 2.25 hours after the burst). The exposure time of this observation is 1472s. On-ground analysis of the FXT data did not found any significant source within the error circle (90% C.L. radius of 167 arcsec) of GRB 260504B. The 5-sigma upper limit of EP-FXT observation is 4.8 x 10^-13 erg/s/cm^2 in the 0.5-10 keV band. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/44467. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42592] GRB 260502A: SVOM/GRM observation of a short GRB
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44466 SUBJECT: GRB 260502A: SVOM/GRM observation of a short GRB DATE: 26/05/05 03:09:45 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> SVOM/GRM team: Xing-Hao Luo, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Hui Yang (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by GRB 260502A at 2026-05-02T05:01:00.300 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44447). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.61 +0.28/-0.15 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260502A.png In addition, the position of this burst, as determined by Fermi/GBM (RA=283.76 , DEC=57.62, with a statistical uncertainty of 13.77 degrees, Fermi GBM team, GCN #44447), is located at about 82 degrees form the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-0.04 to T0+0.01 s is best fitted by a power law function. The power law index is -1.12 +/-0.10. The event fluence (10-1000keV) in this time interval is (2.3 +0.37/-0.33)E-07 erg/cm^2. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Xing-Hao Luo (luoxh(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44466. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42591] GRB 260503A: SVOM/GRM observation of a GRB
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44465 SUBJECT: GRB 260503A: SVOM/GRM observation of a GRB DATE: 26/05/05 03:08:00 GMT FROM: Xinghao Luo at IHEP <2952704891(a)qq.com> SVOM/GRM team: Xing-Hao Luo, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Marius Brunet (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 260503A (SVOM trigger reference: sb26050309) at 2026-05-03T20:40:20.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44451). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 21 +7/-3 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260503A.png In addition, the position of this burst, as determined by Fermi/GBM (RA=287.1 , DEC=-2.0, with a statistical uncertainty of 2.6 degrees, Fermi GBM team, GCN #44451), is located at about 87 degrees form the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-3 to T0+17 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.12 +0.17/-0.16 and the cutoff energy, parameterized as Epeak, is 128 +21/-15 keV. The event fluence (10-1000keV) in this time interval is (6.65 +0.53/-0.46)E-06 erg/cm^2. The localization of GRB 260503A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260503A_amati.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Xing-Hao Luo (luoxh(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/44465. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42590] IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 05 May '26

05 May '26

TITLE: GCN CIRCULAR NUMBER: 44464 SUBJECT: IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 26/05/05 01:46:29 GMT FROM: jliao(a)icecube.wisc.edu The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 26-05-04 at 21:11:20.90 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_BRONZE alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of None events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/142545_58544625.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 26-05-04 Time: 21:11:20.90 UT RA: 246.99 (+0.86/-0.80 deg 90% PSF containment) J2000 Dec: 54.87 (+0.46/-0.47 deg 90% PSF containment) J2000 One gamma-ray source from the Fermi 4FGL-DR4 catalog is located within the 90% uncertainty region of this event: 4FGL J1626.0+5436 , at RA = 246.51° and Dec = 54.61° (J2000), with an angular separation of 0.38° from the best-fit event position. As announced in GCN Circular 43419 (https://gcn.nasa.gov/circulars/43419) IceCube alert notices for high-energy track alerts are now also streamed via Kafka. IceCube Gold/Bronze track alerts are available on the Kafka topic 'gcn.notices.icecube.gold_bronze_track_alerts'. The probability distribution of the true neutrino direction, allowing the extraction of precise 90% containment regions around the best-fit direction, is now available for revised reconstruction of high-energy track alerts. The corresponding sky map is distributed as a FITS file and follows the explicit naming convention IceCube-YYMMDDX, where YYMMDD indicates the date of the event and X is a letter distinguishing multiple alerts on the same day. The download link is provided through the GCN schema distributed via Kafka. Detailed documentation describing the alert distribution, schemas, and probability maps is available at: https://gcn.nasa.gov/missions/icecube. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/44464. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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