July 2026 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 43461] EP260727a: 1.5m OSN optical counterpart detection
by GCN Circulars 28 Jul '26

28 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45245 SUBJECT: EP260727a: 1.5m OSN optical counterpart detection DATE: 26/07/28 19:45:10 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct(a)iaa.es> S. Guziy, J. Rodrigo, E. Fernandez-Garcia, A. J. Castro-Tirado, S.-Y. Wu, I. Perez-Garcia, M.D. Caballero-Garcia and M. Gritsevich (IAA-CSIC), G. Garcia-Segura (UNAM) and Y.-D. Hu (GXI), on behalf of a larger collaboration, report: Following the detection of EP260727a by Einstein Probe (Hu et al. GCN 45235), we triggered the 1.5m telescope at Sierra Nevada Observatory (OSN) in Granada (Spain) starting on July 27, 23:51 UT (~3.24 h post trigger) in the Ic-band. The optical counterpart in the r-band proposed by He et al. (GCNC 45234) and also detected in z-band by Eyles-Ferris (GCNC 45239), and Adami et al. (GCNC 45243), is recorded in our images as well. We measure Ic=21.76+-0.26 on a 12x300s coadded image (July 28, 00:16 UT, mid exposure time). The additional candidate reported by Adami et al. (GCGC 45243) is not detected on our images (taken ~1 h earlier) down to Ic=21.9 limiting magnitude. Further optical monitoring is ongoing. We thank the staff at OSN for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/45245. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43460] EP260727a:refined analysis of the EP-WXT and EP-FXT observation
by GCN Circulars 28 Jul '26

28 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45244 SUBJECT: EP260727a:refined analysis of the EP-WXT and EP-FXT observation DATE: 26/07/28 15:59:03 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T. Wu, H. C. Ding (AHNU), J. W. Hu, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260727a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Hu et al., GCN 45235) and followed by several optical telescopes (He et al., GCN 45234; Maksut et al., GCN 45238; Eyles-Ferris et al., GCN 45239; Adami et al., GCN 45243) with z_phot = 1.03 +/- 0.24 (He et al., GCN 45234). The refined analysis of the WXT data shows that the event started at T0=2026-07-27T20:36:47Z (UTC) and lasted for about 70 s before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5–4 keV spectrum can be fitted with an absorbed power-law model (tbabs*ztbabs*powerlaw) with a fixed Galactic hydrogen column density of 4.76 × 10^20 cm^-2 and a fixed redshift of z = 1.03. The best-fit photon index is 0.5 (-0.6/+1.2), and the intrinsic hydrogen column density is 7.1 (-7.1/+240.0) × 10^20 cm^-2. The derived average unabsorbed 0.5–4 keV flux is 1.8 (-0.5/+0.8) × 10^-9 erg/s/cm^2, corresponding to a luminosity of 3.0 (-0.8/+1.3) × 10^48 erg/s. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-07-27T21:26:27 (UTC), about 50 minutes after T0. The exposure time of this observation is 2568 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 346.4612, 3.1939 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 with a fixed Galactic equivalent hydrogen column density of 4.76 × 10^20 cm^-2 and a photon index of 2.0 (-0.6/+1.1), and the intrinsic hydrogen column density is 0.15 (-0.15/+0.87)×10^22 cm^-2. The derived average unabsorbed 0.5-10 keV flux is 4.4 (-2.7/+0.2)×10^-13 erg/s/cm^2, corresponding to a luminosity of 3.0 (-1.8/+0.11) × 10^45 erg/s. 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/45244. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43459] EP260727a: OHP/T193 optical observations
by GCN Circulars 28 Jul '26

28 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45243 SUBJECT: EP260727a: OHP/T193 optical observations DATE: 26/07/28 13:56:48 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), B. Schneider (LAM), A. Saccardi (CEA/Irfu) report on behalf of a larger collaboration: We observed the field of EP260727a (Hu et al., GCN45235) using the T193cm telescope at Observatoire de Haute-Provence (France) with the MISTRAL spectro-imager. We obtained 14x4 + 1x5 + 1x2 minutes of exposure in the r-band under a 2.1arcsec seeing, starting at 20260728_005726UT (4.3 hr after the Hu et al. trigger) and ending at 20260728_024425UT (6.1 hr after the Hu et al. trigger). In the preliminary stacked images, we detect two potential optical counterparts. The first one is barely detected and consistent with the position of He et al. (GCN 45234), and Eyles-Ferris et al. (GCN 45239). See also Maksut et al. (GCN 45238). We detect it at a preliminar magnitude of: r = 22.82 +/- 0.28 mag We also detect another candidate not present in PanStarrs images at: RA (J2000): 23:05:48.7 DEC (J2000): +03:15:27.4 with preliminary magnitude of: r = 20.49 +/- 0.06 mag The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the STDWeb/STDPipe tools (Karpov 2025), is in the AB system, and is not corrected for Galactic extinction. We acknowledge the excellent support from Observatoire de Haute-Provence and in particular Yoann Degot-Longhi Larralde Erasun. We also thank the SOPHIE observer: Deepanshi Singh. View this GCN Circular online at https://gcn.nasa.gov/circulars/45243. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43458] Konus-Wind detection of GRB 260727A
by GCN Circulars 28 Jul '26

28 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45242 SUBJECT: Konus-Wind detection of GRB 260727A DATE: 26/07/28 12:56:48 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, V. Panteleeva, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 260727A (SVOM-ECLAIRs detection: Li et al., GCN 45220; AstroSat-CZTI detection: Harsha et al., GCN 45225; Glowbug detection: Cheung et al., GCN 45233) triggered Konus-Wind at T0=1327.631 s UT (00:22:07.631). The burst light curve shows a multi-peaked structure which starts at ~T0-11 s and has a total duration of ~30 s (75-1200 keV). The emission is seen up to ~300 keV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260727_T01327/ As observed by Konus-Wind, the burst had the total fluence of 1.15(-0.03,+0.03)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+1.072 s, of 1.61(-0.30,+0.30)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 = -0.20(-0.11,+0.11) and Ep = 85(-2,+2) keV (chi2 = 107/98 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -4.2 (chi2 = 107/97 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: with alpha = 0.02(-0.14,+0.14) and Ep = 93(-3,+3) keV (chi2 = 80/82 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.8 (chi2 = 80/81 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/45242. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43457] GRB 260726A: Liverpool Telescope optical observations
by GCN Circulars 28 Jul '26

28 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45241 SUBJECT: GRB 260726A: Liverpool Telescope optical observations DATE: 26/07/28 11:04:58 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 260726A (Fermi GBM team, GCN 45218; Liang et al., GCN 45219; Brunet et al., GCN 45229) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 8x120s exposures in SDSS r and i filters, starting at 2026-07-28 01:48:36 UT, approximately 26.06 hours after Fermi trigger. We detect a source in the i-band stacked image at the candidate counterpart position reported by Brunet et al. (GCN 45229) and Li et al. (GCN 45230), and a non-detection in the stacked r-band image, with photometry given below: MJD (mid) T_mid-T_0 Filter Mag. (AB) 61249.08219 26.23 h r > 22.03 61249.09609 26.56 h i 22.58 ± 0.16 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/45241. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43456] GRB 260727A: Liverpool Telescope optical upper limits
by GCN Circulars 28 Jul '26

28 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45240 SUBJECT: GRB 260727A: Liverpool Telescope optical upper limits DATE: 26/07/28 11:03:43 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 260727A (Li et al. GCN 45220) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 8x120s exposures in SDSS r and i filters, starting at 2026-07-28 01:07:14 UT, approximately 24.75. hours after trigger. The images were stacked, and the stacks were subtracted from PanSTARRS reference images, using PSF matching through PSF convolution, with the help of PSFEx. We do not detect any new sources in the SVOM/IMT error region (Li et al. GCN 45220) down to 3-sigma limiting magnitudes of r > 22.17 and i > 22.05 mag. We note that the image subtraction is partially affected by two bright stars located close to the edge of the error region. 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/45240. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43455] EP260727a: Liverpool Telescope confirmation of optical counterpart
by GCN Circulars 28 Jul '26

28 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45239 SUBJECT: EP260727a: Liverpool Telescope confirmation of optical counterpart DATE: 26/07/28 10:23:11 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), D. B. Malesani (DAWN/NBIA and Radboud) and P. T. O’Brien (Leicester) report on behalf of a larger collaboration: We observed the field of the Einstein Probe fast X-ray transient EP260727a (Hu et al., GCN 45235) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x150 s and 6x150 s exposures in each of the SDSS r’ and z’ filters starting at 2026-07-28 02:34:17 UT, approximately 5.9 hours after the X-ray detection. We detect the optical counterpart (identified by He et al. (GCN 45234) in the r band) in the z band at an AB magnitude of z = 21.66 +/- 0.17. This is significantly brighter than the historical magnitude for the underlying source of z = 23.46 +/- 0.08 derived from archival HSC imaging. This underlying source was also identified by He et al. in the r band. In the r band, we obtain an upper limit of r > 22.85. As this upper limit is less deep than the detection reported in He et al. (GCN 45234), we cannot assess if the source is fading. Our photometry is calibrated to PanSTARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/45239. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43454] EP260727a: NUTTELA-TAO Early Optical Limits
by GCN Circulars 28 Jul '26

28 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45238 SUBJECT: EP260727a: NUTTELA-TAO Early Optical Limits DATE: 26/07/28 09:23:05 GMT FROM: Zhanat Maksut at Nazarbayev University <zhanat.maksut(a)nu.edu.kz> Z. Maksut (NU), T. Komesh (NU), D. Berdikhan (NU), E. Abdikamalov (NU), M. Krugov (FAI), K. Baigarin (NU), M. Coughlin (UMN), P. Hello (IJCLAB), S. Antier (IJCLAB), M. Pillas (IAP), and S. Karpov (FZU) on behalf of the GRANDMA/NUTTelA-TAO: The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTELA-TAO) pointed at EP 260727a on receipt of an automated GCN / EP position alert, observing in Sloan g' and i' bands. We started observations at 21:40:12 UT on 2026-07-27, 1.05 hour after the EP/WXT trigger (J. Hu et al., GCN 45235). No optical source consistent with the NOT optical counterpart (L. He et al., GCN 45234) was detected. We report the following results: start time t-t0(s) UL g' UL i' exposure_time (im x s) -------------------------------------------------------------- 21:40:12 3879 20.3 19.75 10x30 sec Where t is the middle time, t0 is the EP/WXT trigger time, t-t0 is given in seconds. UL gives the 5 sigma upper limit sensitivity in magnitudes, for images of the given exposure time. No color or other corrections were applied to the values above. The data were reduced by a single data processing pipeline, STDWeb (Karpov et al., 2022). Images obtained with the Sloan filters were calibrated using the PanSTARRS DR1 catalog. ---------------------------------- This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26103591). The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazakhstan. GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/45238. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43453] GRB 260728A: Fermi GBM Final Localization
by GCN Circulars 28 Jul '26

28 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45237 SUBJECT: GRB 260728A: Fermi GBM Final Localization DATE: 26/07/28 06:52:53 GMT FROM: oliver.roberts(a)universityofgalway.ie The Fermi GBM team reports the detection of a likely LONG GRB "At 04:37:01.48 UT on 28 July 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260728A (trigger 806906226/260728192). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 262.86, Dec = -48.57 (J2000 degrees, equivalent to J2000 17h 31m, -48d 34'), with a statistical uncertainty of 3.53 degrees. The angle from the Fermi LAT boresight is 64 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260728192/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260728192/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260728192/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/45237. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43452] GRB 260727A: EP/FXT follow-up observations
by GCN Circulars 28 Jul '26

28 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45236 SUBJECT: GRB 260727A: EP/FXT follow-up observations DATE: 26/07/28 02:53:14 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Ruizhi Li (YNAO), Ziming Wang (BNU), An Li (BNU), Yifang Liang (PMO), Wenjin Xie (NAOC), Donghua Zhao (NAOC), Clara Plasse (HKU) and Andrea Saccardi (CEA) report on behalf of the SVOM mission team: EP-FXT performed a follow-up observation of GRB 260727A detected by SVOM/ECLAIRs (Li et al., GCN 45220), which also triggered AstroSat CZTI (Harsha K. H. et al., GCN 45225) and Glowbug (Cheung et al., GCN 45233). The follow-up observation started at 2026-07-27T05:27:41 (UTC), about 5.09 hours after the SVOM-ECLAIRs trigger, with a total exposure time of around 6.1 ks. An uncatalogued X-ray source was found within the ECLAIRs error circle. The position of the source is at R.A., Decl. = 331.7702, 74.5296 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The 0.5-10 keV spectrum can be fitted by an absorbed powerlaw model with a Galactic hydrogen column density of (0.55 +/-0.10) x 10^22 cm^-2 and a photon index of 2.61 +/- 0.07. The average unabsorbed flux is 2.65 (+0.55, -0.35) x 10^(-12) erg/s/cm^2 in the 0.5-10 keV energy band (90% C.L.). Optical follow-up observations of the burst were carried out by LCO (Shi et al., GCN 45223), Kilonova-Catcher (Freeberg et al., GCN 45224), GOTO (Starling et al., GCN 45226), RAPAS (Lechapelain et al., GCN 45228), and WINTER (Mohan et al., GCN 45231). The Burst Advocate (BA) on shift for this alert is Ziming Wang: 202421101144(a)mail.bnu.edu.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/45236. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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