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[vsnet-grb-info 42722] EP260512a: Einstein Probe detection of an X-ray transient
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44594 SUBJECT: EP260512a: Einstein Probe detection of an X-ray transient DATE: 26/05/13 04:03:17 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. D. Liang, M. J. Liu (NAO, CAS), H. Z. Wu (HUST), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260512a. The transient was detected at 2026-05-12 08:31:32 (UTC). The signal-to-noise ratio is below the on-board trigger threshold and hence the transient was discovered by ground-based analysis. The WXT position of the source is R.A. = 223.899 deg, DEC = 28.432 deg (J2000) with an uncertainty of 2.6 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) is scheduled. 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/44594. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42721] GRB 260511B: further J-band observations by the SYSU 80 cm infrared telescope
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44593 SUBJECT: GRB 260511B: further J-band observations by the SYSU 80 cm infrared telescope DATE: 26/05/13 02:15:50 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 80 cm infrared telescope team: We further observed the field of GRB 260511B 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. The afterglow (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Wu et al., GCN 44552; Li et al., GCN 44557; Vijaykumar et al., GCN 44561; Lee et al., GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572; Adami et al., GCN 44573; Saccardi et al., GCN 44574; Rajabov et al., GCN 44576; Pérez-Fournon et al., GCN 44577; Novotný et al., GCN 44580; Moskvitin, GCN 44582; Calapai, GCN 44592) with the redshift of z=2.006 (Postigo et al., GCN 44565) was clearly detected in our stacked J-band images. The photometric results are summarized in the table below. The photometry was calibrated against nearby stars from the 2MASS catalog and is reported in the Vega system, without correction for Galactic extinction. Mid time |Band | Exposure | Mag (Vega) ------------|-------|-------------|------------------ 5.362 h | J | 700s | 16.66 +/- 0.14 5.568 h | J | 640s | 16.57 +/- 0.10 5.771 h | J | 640s | 16.85 +/- 0.13 5.985 h | J | 560s | 17.16 +/- 0.18 6.191 h | J | 660s | 17.10 +/- 0.19 7.011 h | J | 960s | 17.11 +/- 0.15 7.367 h | J | 1040s | 17.26 +/- 0.14 7.720 h | J | 1100s | 17.46 +/- 0.18 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/44593. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42720] GRB 260511B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44592 SUBJECT: GRB 260511B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation. DATE: 26/05/13 00:24:14 GMT FROM: Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy <giovannicalapai(a)tiscali.it> Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani. Report: We observed the field of GRB 260511B detected by Fermi/GBM (Fermi GBM Team, GCN 44542) and SVOM/ECLAIRs (Godet et al., GCN 44543) with the 14 inches Schmidt-Cassegrain (Celestron 14) telescope F/D=7. The observations were started at 2026-05-11 21:24:23 UT (approximately 10.40 hours after burst) stacking two sets of unfiltered CCD image. The observations were carried out with clear skies and good visibility conditions. The OT was detected at the following position: RA (J2000.0) 12h 50m 17.18s Decl. (J2000.0) +04° 03' 10.2" Photometry was obtained using nearby PanSTARRS stars as follows: Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Mag. err. 2026-05-11 21:54:50 UT 10.91 60x60s CR 18.85 +/-0.04 2026-05-11 23:01:52 UT 12.02 72x60s CR 18.95 +/-0.04 Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied. Our observations are consistent with other already reported Wu et al. (GCN 44547); Sasada et al. (GCN 44549); Jiang et al. (GCN 44551); Wu et al. (GCN 44552); Li et al. (GCN 44557); Vijaykumar et al. (GCN 44561); De Ugarte Postigo et al. (GCN 44565); Lee et al. (GCN 44567); Li et al. (44568); Belkin et al. (GCN 44572); Saccardi et al. (GCN 44574); Rajabov et al. (GCN 44576); Pérez-Fournon et al. (GCN 44577); Novotný et al. (GCN 44580); Moskvitin (GCN 44582). The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/44592. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42719] GRB 260512A: NuSTAR detection of prompt emission
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44591 SUBJECT: GRB 260512A: NuSTAR detection of prompt emission DATE: 26/05/12 23:53:06 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 260512A 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 2026-05-12T16:56:43.530 UTC, shows a detection of GRB 260512A, also detected by Fermi/GBM (Fermi GBM Team, GCN 44542). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a 10-s long 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 do not see evidence in the signal above 100 keV in the CZT detectors. The Fermi/GBM localization (GCN 44542) at RA = 153.56, Dec = -82.64 implies an offset from the NuSTAR boresight of 15-deg (i.e. near the boresight) and an offset from the geocenter of 96-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260512A 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/44591. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42718] GRB 260509A: Infrared J and Hs observations with MDM/MIRAGE
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44590 SUBJECT: GRB 260509A: Infrared J and Hs observations with MDM/MIRAGE DATE: 26/05/12 20:45:37 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Carnegie/Caltech), K. De, V. Karambelkar, S. Ibrahim, D. Schiminovich (Columbia University) report: We observed the field of GRB 260509A (Gotz et al., GCN 44504) in the near-infrared J and Hs bands with the MDM InfraRed Astronomy inGaas Explorer (MIRAGE) instrument on the MDM 1.3 m telescope. Observations began at 2026-05-10T04:00:51 (+6.2 hours after the GRB trigger) in the J band and 2026-05-10T03:27:31 (+5.6 hours) in the Hs band, lasting 1560 s in J and 1260 s in Hs. The optical counterpart (O’Neill et al., GCN 44505; Saccardi et al., GCN 44506; Wu et al., GCN 44507; Alvarez et al., 44509; Zheng et al., GCN 44510; Lipunov et al., GCN 44512; Belkin et al., GCN 44513; Corcoran et al., GCN 44514; Bochenek et al., GCN 44516; Moskvitin et al., GCN 44563) is detected in the J filter at low significance and undetected in H band, with the following AB magnitudes: J = 20.91 ± 0.40, Hs > 19.6. MIRAGE is a new YJHs-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44590. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42717] GRB 260510C: Infrared J and Hs detections with MDM/MIRAGE
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44589 SUBJECT: GRB 260510C: Infrared J and Hs detections with MDM/MIRAGE DATE: 26/05/12 20:44:36 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Carnegie/Caltech), K. De, V. Karambelkar, S. Ibrahim, D. Schiminovich (Columbia University) report: We observed the field of GRB 260510C (Fermi GBM Team, GCN 44520; Gotz et al., GCN 44521; Iwakiri et al., GCN 44526; Fu et al., GCN 44541; Arya et al., GCN 44544; Palafox et al., GCN 44564) in the near-infrared J and Hs bands with the MDM InfraRed Astronomy inGaas Explorer (MIRAGE) instrument on the MDM 1.3 m telescope. Observations began at 2026-05-11T03:31:14 (+10.3 hours after the GRB trigger) in the J band and 2026-05-11T04:04:31 (+10.8 hours) in the Hs band, lasting 1620 s in each filter. The optical counterpart (Li et al, GCN 44527; Angulo et al., GCN 44530; Li et al., GCN 44540; Lee et al., GCN 44570) is detected in both filters, with the following AB magnitudes: J = 19.64 ± 0.16, Hs = 19.42 ± 0.24. MIRAGE is a new YJHs-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44589. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42716] EP260507a: Infrared J and Hs upper limits with MDM/MIRAGE
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44588 SUBJECT: EP260507a: Infrared J and Hs upper limits with MDM/MIRAGE DATE: 26/05/12 20:43:26 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Carnegie/Caltech), K. De, V. Karambelkar, S. Ibrahim, D. Schiminovich (Columbia University) report: We observed the field of EP260507a (Fu et al., GCN 44488, GCN 44500) in the near-infrared J and Hs bands with the MDM InfraRed Astronomy inGaas Explorer (MIRAGE) instrument on the MDM 1.3 m telescope. Observations began at 2026-05-08T05:49:04 (+16.0 hours after the GRB trigger) in the J band and 2026-05-08T06:22:36 (+16.6 hours) in the Hs band, lasting 1620 s in each filter. 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; Eyles-Ferris et al., GCN 44495; Jiang et al., GCN 44496; Li et al., GCN 44497; Globus et al., GCN 44498; Brivio et al., GCN 44501) is not detected in either band, with the following 5-sigma upper limits in AB magnitudes: J > 19.84, Hs > 19.2. MIRAGE is a new YJHs-band near-infrared imager for the MDM 1.3m telescope. We thank the MDM Observatory staff for supporting the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/44588. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42715] GRB 260512A: Fermi GBM Final Real-time Localization
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44587 SUBJECT: GRB 260512A: Fermi GBM Final Real-time Localization DATE: 26/05/12 17:07:17 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 16:56:43 UT on 12 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260512A (trigger 800297808.529848 / 260512706). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 153.6, Dec = -82.6 (J2000 degrees, equivalent to J2000 10h 14m, -82d 35'), with a statistical uncertainty of 2.0 degrees. The angle from the Fermi LAT boresight is 136.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260512706/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260512706/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260512706/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44587. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42714] GRB 260511A: Glowbug gamma-ray detection
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44586 SUBJECT: GRB 260511A: Glowbug gamma-ray detection DATE: 26/05/12 17:03:10 GMT FROM: Richard S. Woolf at US Naval Research Laboratory <richard.s.woolf.civ(a)us.navy.mil> R. Woolf, C.C. Cheung, 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 260511A, which was also detected by Fermi GBM (GCN 44529), SVOM (GCN 44532), NuSTAR (GCN 44555), and Konus–Wind (GCN 44585). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-05-11 06:13:28.904 with a duration of 11.3 s and a total significance of about 41.6 sigma. The light curve comprises three primary peaks from T0 to ~T0+11s. 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/44586. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42713] Konus-Wind detection of GRB 260511A
by GCN Circulars 12 May '26

12 May '26

TITLE: GCN CIRCULAR NUMBER: 44585 SUBJECT: Konus-Wind detection of GRB 260511A DATE: 26/05/12 16:55:02 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: The long-duration GRB 260511A (Fermi-GBM detection: Fermi GBM team, GCN 44529; Roberts et al., GCN 44548; BALROG localization: Preis & Greiner, GCN 44531; SVOM detection: Godet et al., GCN 44532; NuSTAR detection: Waratkar et al., GCN 44555) triggered Konus-Wind at T0=22416.401 s UT (06:13:36.401). The burst light curve shows a multipeaked structure which starts at ~T0-4.6 s and has a total duration of ~20.5 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/GRB260511_T22416/ As observed by Konus-Wind, the burst had a fluence of 1.72(-0.05,+0.05)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+0.482 s, of 6.96(-0.71,+0.71)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+16.640 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.79(-0.08,+0.09) and Ep = 187(-8,+8) keV (chi2 = 107/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.1 (chi2 = 107/98 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.66(-0.08,+0.08) and Ep = 187(-6,+7) keV (chi2 = 88/86 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.9 (chi2 = 87/85 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/44585. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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