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[vsnet-grb-info 42727] GRB 260513A: Fermi GBM Final Real-time Localization
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44599 SUBJECT: GRB 260513A: Fermi GBM Final Real-time Localization DATE: 26/05/13 21:34:57 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 21:24:18 UT on 13 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260513A (trigger 800400263.713514 / 260513892). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 320.8, Dec = -36.4 (J2000 degrees, equivalent to J2000 21h 23m, -36d 23'), with a statistical uncertainty of 2.3 degrees. The angle from the Fermi LAT boresight is 65.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260513892/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260513892/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260513892/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44599. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42726] GRB 260509A: SVOM/VT optical observations
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44598 SUBJECT: GRB 260509A: SVOM/VT optical observations DATE: 26/05/13 15:17:36 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. L. Qiu, C. Wu, L. P. Xin, 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, D. Götz and D. Adrien (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations of GRB260509A triggered by SVOM/ECLAIRs (sb26050905, Götz et al., GCN 44504). The observation started at 2026-05-09T22:12:49 UTC, about 21.66 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The afterglow (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; Mo et al., GCN 44590) was detected clearly in both channels. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 22.08 m VT_B 50 s 20.05 +/- 0.07 mag 22.08 m VT_R 50 s 19.47 +/- 0.06 mag 8.17 h VT_B 16*100 s 21.76 +/- 0.09 mag 8.24 h VT_R 11*100 s 21.48 +/- 0.09 mag The light curves shows fading and brightening at early epochs, followed by a temporal decay with a slope of −1 in the late phase during our observations. 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/44598. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42725] Konus-Wind detection of GRB 260511B
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44597 SUBJECT: Konus-Wind detection of GRB 260511B DATE: 26/05/13 12:12:06 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 260511B (Fermi-GBM detection: Fermi GBM team, GCN 44542; Roberts et al., GCN 44554; SVOM detection: Godet et al., GCN 44543; NuSTAR detection: Waratkar & Grefenstette, GCN 44556; AstroSat-CZTI detection: Arya et al., GCN 44560) triggered Konus-Wind at T0=39635.267 s UT (11:00:35.267). The burst light curve shows two separate multipeaked episodes: the first from ~T0-1.1 s to ~T0+10 s, and the second, which is brighter and spectrally harder, from ~T0+26 s to ~T0+42 s. The total duration of the burst is ~43.4 s. The burst light curve shows two multipeaked episodes started at ~T0-1.1 s with a total duration of ~43.4 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_T39635/ As observed by Konus-Wind, the burst had a fluence of 2.48(-0.11,+0.12)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+30.512 s, of 6.82(-0.83,+0.84)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+41.216 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 = -1.12(-0.09,+0.10) and Ep = 259(-20,+24) keV (chi2 = 92/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.4 (chi2 = 92/98 dof). The spectrum near the maximum count rate (measured from T0+24.832 to T0+33.024 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.87(-0.23,+0.17), the high energy photon index beta = -2.26(-0.66,+0.13), the peak energy Ep = 273(-40,+102) keV (chi2 = 93/81 dof). Assuming the redshift z=2.006 (de Ugarte Postigo et al., GCN 44565; Wang et al., GCN 44571) and a standard cosmology model with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is 2.53(-0.11,+0.12)x10^53 erg, the peak luminosity L_iso is 2.09(-0.25,+0.26)x10^53 erg/s, the rest-frame peak energy of the time-averaged spectrum, Ep,i,z is 778(-60,+72) keV and the spectrum near the maximum count rate Ep,p,z is 821(-120,+307) keV. With the obtained estimates, GRB 260511B is inside 68% prediction bands for both the 'Amati' and the 'Yonetoku' relations derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB260511_T39635/GRB260511B_rest_frame.pdf 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/44597. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42724] The EP-WXT trigger 01709262036 is likely a flaring star
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44596 SUBJECT: The EP-WXT trigger 01709262036 is likely a flaring star DATE: 26/05/13 09:18:58 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M. J. Liu, R. D. Liang (NAO, CAS), H. Z. Wu (HUST), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709262036 at the time of 2026-05-13 08:45:48 (UTC), is likely a stellar flare associated with LP 497-99. The estimated flux of the flare is around 1×10^(-10) erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 3.5×10^31 erg/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/44596. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42723] EP260512a: COLIBRÍ optical upper limits
by GCN Circulars 13 May '26

13 May '26

TITLE: GCN CIRCULAR NUMBER: 44595 SUBJECT: EP260512a: COLIBRÍ optical upper limits DATE: 26/05/13 06:18:56 GMT FROM: J.-G. Ducoin at CPPM <ducoin(a)cppm.in2p3.fr> Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Camila Angulo (UNAM), Rosa L. Becerra (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), 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), Nikos Mandarakas (LAM), 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 EP260312a (Liang et al., GCN Circ. 44594), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-13 04:09 to 04:25 UTC (from 19.6 to 19.9 hours after the trigger and 6 minutes after the release of the GCN) and obtained 14 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ ASU pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked images and after performing image subtraction using templates from the DESI Legacy Survey (Dey et al. 2019), we do not detect any new source within the WXT error region we do not detect any new source at the WXT error position (Liang et al., GCN Circ. 44594) down to the following 5-sigma limits: r > 23.1 z > 21.9 We note the presence of the quasar 2MASS J14554420+282524 within the WXT region and, considering our upper limits and the low SNR reported by the Einstein Probe Team (Liang et al., GCN Circ. 44594), we cannot rule out the possibility that the trigger is related to this source. 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/44595. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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