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

[vsnet-grb-info 43481] GRB 260730B: AstroSat CZTI detection
by GCN Circulars 31 Jul '26

31 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45265 SUBJECT: GRB 260730B: AstroSat CZTI detection DATE: 26/07/31 10:25:34 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), 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 Bright, long GRB 260730B which was also detected by NuSTAR (G. Waratkar, GCN Circ. 45262). 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 2026-07-30 13:13:56.216 UTC. The measured peak count rate associated with the burst is 1201 (+58, -66) counts/s above the background in the combined data of three quadrants (out of four), with a total of 8451 (+206, -277) counts. The local mean background count rate was 243(+3, -3) counts/s. We measure a T90 of 16.0 (+0.3, -0.3) s from the cumulative CZT light curve. 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 2026-07-30 13:13:55.471 UTC. The measured peak count rate associated with the burst is 2594 (+88, -100) counts/s above the background in the combined data of all quadrants, with a total of 15878(+327, -466) counts. The local mean background count rate was 715 (+5, -5) counts/s. We measure a T90 of 15.6 (+0.4, -0.3) s from the cumulative Veto light curve. CZTI data products like interactive and downloadable light curves for this GRB can be found at:https://astrosat.iucaa.in/cift/cift_products/ET20260730T131406/ET20260730T131406_details.html 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/45265. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43480] EP260731a: COLIBRÍ optical upper limit
by GCN Circulars 31 Jul '26

31 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45264 SUBJECT: EP260731a: COLIBRÍ optical upper limit DATE: 26/07/31 07:24:07 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Fredd Sánchez Álvarez (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), 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), Benjamin Schneider (LAM), Alan M. Watson (UNAM) report: We imaged the field of EP260731a (Ni et al., GCN Circ. 45261) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-07-31 05:52:50 to 07:10:03 UTC (from 4.9739 to 6.2776 hours after the trigger) and obtained 39x60 s of simultaneous exposure in the z-band filter. Some further images obtained during this time window were lost due to passing clouds. The data were reduced, coadded and analysed with the COLIBRÍ ASU and CPPM pipelines. The photometry was calibrated using nearby stars from the PanSTARRS catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the FXT source position (Ni et al., GCN Circ. 45261) down to the following 5-sigma limit: z > 20.9 This upper limit is consistent with the one reported by Liu et al. (GCN Circ. 45263). Further observations are ongoing. 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/45264. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43479] EP260731a: NOT optical upper limit
by GCN Circulars 31 Jul '26

31 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45263 SUBJECT: EP260731a: NOT optical upper limit DATE: 26/07/31 04:39:27 GMT FROM: liuxing(a)nao.cas.cn X. Liu, J. An, Z.P. Zhu, S.Q. Jiang, L.B. He, D. Xu (NAOC), S.Y. Fu (HUST), J. P. U. Fynbo (DAWN/NBI), A. L. Bouquin, A. Schenone-Zanuzzi (NOT) report: We observed the field of EP260731a detected by EP (Ni et al., GCN 45261), using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observation started at 2026-07-31 03:16:25.90 UT, i.e., 2.37 hours post-trigger, and a series of z-band frames were obtained. The target was 16 deg from the moon at 98% illumination at the time of the observation. No uncatalogued optical transient is detected in the stacked image within the EP-FXT error circle (Ni et al., GCN 45261) down to a 5-sigma limiting magnitude of z ~ 19.8 at a median time of 2.46 hr post-trigger, calibrated with Pan-STARRS DR2 stars in the field. View this GCN Circular online at https://gcn.nasa.gov/circulars/45263. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43478] GRB 260730B: NuSTAR detection of prompt emission
by GCN Circulars 31 Jul '26

31 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45262 SUBJECT: GRB 260730B: NuSTAR detection of prompt emission DATE: 26/07/31 02:58:15 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 260730B 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 2026-07-30T13:13:45.0 UTC, shows a detection of GRB 260730B, also detected by SVOM-GRM (GCN notices). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a single episode with two peaks lasting for about 25-s. The peak count rate is ~3500-cps with a baseline rate of ~1000-cps during this time period. We also see a signal above 100 keV in the CZT detectors. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260730B 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/45262. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43477] EP260731a: Einstein Probe detection of an X-ray transient
by GCN Circulars 31 Jul '26

31 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45261 SUBJECT: EP260731a: Einstein Probe detection of an X-ray transient DATE: 26/07/31 02:15:53 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> K.R. Ni (CCNU) , Y.F. Liang (PMO, CAS), H.Y. Liu, and H.W. Pan (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 EP260731a. The transient triggered EP-WXT (ID: 01709277303) at 2026-07-31T00:54:24 (UTC). The WXT position of the source is R.A. = 344.424 deg, DEC = -11.764 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. = 344.4279 deg, DEC = -11.7623 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/45261. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43476] GRB 260727A: SVOM/ECLAIRs refined analysis
by GCN Circulars 30 Jul '26

30 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45260 SUBJECT: GRB 260727A: SVOM/ECLAIRs refined analysis DATE: 26/07/30 23:55:12 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet (IRAP), R. Li (YNAO), Z. Wang (BNU) 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 260727A (SVOM burst-id sb26072701 – GCN 45220, trigger time T0 = 2026-07-27T00:22:02 UTC), which was also detected by SVOM/GRM (GCN 452457), AstroSat/CZTI (GCN 45225), Glowbug (GCN 45233), and Konus-Wind (GCN 45242). The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve. The burst duration is T90 = 66.5+/-2.5 s in the 4-120 keV energy band. The time-averaged spectrum from T0-3.5 s to T0+112 s in the 5-120 keV energy range is best fitted by a powerlaw with an exponential cutoff model with alpha = -1.03 +/-0.03 and a peak energy = 72 +4/-3 keV. With this model, the 4-120 keV fluence is (1.38 +/-0.02)e-5 erg/cm^2 and the 4-120 keV photon flux is 3.17 +/-0.03 ph/cm^2/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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/45260. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43475] GRB 260726A: SVOM/ECLAIRs refined analysis
by GCN Circulars 30 Jul '26

30 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45259 SUBJECT: GRB 260726A: SVOM/ECLAIRs refined analysis DATE: 26/07/30 23:53:05 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet (IRAP), W. Xie (NAOC), R. Li (YNAO), Z. Wang (BNU) 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 260726A (SVOM burst-id sb26072614 – GCN 45219 & GCN 45229, trigger time T0 = 2026-07-26T23:45:23UTC), which was also detected by Fermi/GBM (GCN 45218 & GC 45246). The burst that triggered ECLAIRs onboard shows a single peak lightcurve. The burst duration is T90 = 63 +9/-10 s in the 4-120 keV energy band. The time-averaged spectrum from T0-23.3 s to T0+35.9 s in the 5-120 keV energy range is best fitted by a powerlaw with an exponential cutoff model with alpha = -1.30 +0.23/-0.18 and a peak energy = 58 +57/-18 keV. With this model, the 4-120 keV fluence is (1.1 +/-0.1)e-6 erg/cm^2 and the 4-120 keV photon flux is 0.61+/-0.03 ph/cm^2/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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/45259. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43474] GRB260730A: Fermi GBM Final Localization
by GCN Circulars 30 Jul '26

30 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45258 SUBJECT: GRB260730A: Fermi GBM Final Localization DATE: 26/07/30 13:35:14 GMT FROM: oliver.roberts(a)universityofgalway.ie The Fermi GBM team reports the detection of a likely LONG GRB "At 04:28:34.96 UT on 30 July 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB260730A (trigger 807078519/260730187). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 290.97, Dec = +33.39 (J2000 degrees, equivalent to 19h 24', +33d 23'), with a statistical uncertainty of 11.61 degrees. The angle from the Fermi LAT boresight is 30 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260730187/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260730187/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260730187/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/45258. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43473] EP260728a: COLIBRÍ optical upper limit
by GCN Circulars 30 Jul '26

30 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45257 SUBJECT: EP260728a: COLIBRÍ optical upper limit DATE: 26/07/30 10:16:03 GMT FROM: J.-G. Ducoin at CPPM <ducoin(a)cppm.in2p3.fr> Jean-Grégoire Ducoin (CPPM), Fredd Sánchez Álvarez (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), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Alan M. Watson (UNAM) report: We imaged the field of the EP260728a (Yang et al., GCN Circ. 45248) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. 2026-07-30T05:58:16 to 2026-07-30T07:24:22 UTC (from 37.2 to 38.6 hours after the trigger) and obtained 64 minutes of exposure in the z filters. The data were reduced, coadded and analysed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the SkyMapper DR4 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the FXT source position (Yang et al., GCN Circ. 42250) down to the following 3-sigma limit: z > 21.5 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/45257. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43472] EP260727a: VLT/X-shooter spectroscopic redshift z = 2.817
by GCN Circulars 30 Jul '26

30 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45256 SUBJECT: EP260727a: VLT/X-shooter spectroscopic redshift z = 2.817 DATE: 26/07/30 08:38:35 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> B. Schneider (LAM), M. Garnichey (LUX-Paris Obs.), L. Xin (NAOC), D. Xu (NAOC), G. Corcoran (UCD), V. D'Elia (ASI-SSDC), L. Izzo (INAF/OACn & DARK/NBI), A. Rossi (INAF-OAS), A. Saccardi (CEA/Irfu), A. L. Thakur (INAF/IAPS), B. Topcu (University of Bath), S. D. Vergani (LUX-Paris Obs.) report on behalf of the Stargate collaboration: We observed the optical counterpart (He et al., GCN 45234; Maksut et al., GCN 45238; Eyles-Ferris et al., GCN 45239; Adami et al., GCN 45243; Guziy et al., GCN 45245) of the EP260727a (Hu et al., GCN 45235; Wu et al., GCN 45244) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-25000 AA, and consist of 4 exposures of 1200 s each. The observation mid time was 09:00:34 UT on 2026 July 28 (12.38 hr after the EP/WXT trigger). In a 3x60s acquisition image (taken 11.46 hr after the EP/WXT trigger), the optical counterpart is detected with a magnitude r = 22.51 +/- 0.06 AB mag, calibrated against Pan-STARRS objects, and not corrected for Galactic extinction. In a preliminary reduction of the spectra, we detect a faint continuum down to ~3800 AA. We identify a trough around 4639 AA, likely due to H I Lyman-alpha. Multiple absorption lines are also detected, which we interpret as due to Si II, O I, C II, Si IV, Mg II, all at a common redshift of z = 2.817. Additionally, at a consistent redshift (z = 2.817) we note the presence of several emission lines due to the [O II] doublet, [O III] doublet, and Hgamma from the faint host galaxy visible in Legacy Survey DR10 as noted by He et al. (GCN 45234). We acknowledge the excellent support from the observing staff in Paranal, in particular Florian Rodler and Marcela Espinoza. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/45256. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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