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[vsnet-grb-info 43432] EP260723a: further EP-FXT follow-up observation
by GCN Circulars 26 Jul '26

26 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45216 SUBJECT: EP260723a: further EP-FXT follow-up observation DATE: 26/07/26 12:17:29 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> K. R. Ni (CCNU), Y. J. Zhang (PKU), X. H. Tang (THU), and H. Sun (NAOC) report on behalf of the Einstein Probe (EP) team: EP-FXT performed a second follow-up observation of EP260723a, which was detected by EP-WXT (Zhang et al., GCN 45201) and previously followed up by EP-FXT (Ni et al., GCN 45209). The observation started at 2026-07-25T11:52:47 UTC, about 40.9 hr after the WXT detection, with an exposure time of approximately 6.0 ks. On-ground analysis of the FXT data identified an uncatalogued X-ray source within the WXT error circle at R.A. (J2000) = 2.9759 deg and Dec. (J2000) = -12.1022 deg, with an uncertainty of 10 arcsec in radius (90% confidence level, including both statistical and systematic uncertainties). The source position is consistent with the optical counterpart reported by the Liverpool Telescope (Eyles-Ferris et al., GCN 45202, 45212), the Nordic Optical Telescope (He et al., GCN 45203), COLIBRÍ (Basa et al., GCN 45204), and SVOM/VT (Ma et al., GCN 45205), and also with the weak X-ray excess reported in the first EP-FXT follow-up observation (Ni et al., GCN 45209). The average FXT spectrum in the 0.5-10 keV band can be fitted with an absorbed power-law model, with the hydrogen column density fixed at the Galactic value of 2.0 x 10^20 cm^-2 and a photon index of 2.96 (+1.53, -1.21). The derived average unabsorbed 0.5-10 keV flux is 3.1 (+3.0, -1.4) x 10^(-14) erg cm^-2 s^-1. The uncertainties quoted above are at the 90% confidence level. Further EP-FXT follow-up observations will be arranged. Continued multi-band follow-up observations are encouraged. Launched on January 9, 2024, EP is a space X-ray observatory designed to monitor the dynamic soft X-ray sky and perform follow-up observations of newly discovered transients (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/45216. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43431] EP260725a: EP-FXT follow-up observation and association with a bright flaring star
by GCN Circulars 26 Jul '26

26 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45215 SUBJECT: EP260725a: EP-FXT follow-up observation and association with a bright flaring star DATE: 26/07/26 08:11:38 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. D. Liang (NAOC), Y. J. Zhang (PKU), W. Chen, H. W. Pan (NAOC), on behalf of the Einstein Probe (EP) team EP-FXT performed a follow-up observation of EP260725a, an X-ray transient detected by EP-WXT (GCN 45214), about 15 hrs after the WXT detection. The updated EP-FXT position is R.A. = 337.0689 deg and DEC = 50.7748 deg (J2000), with an uncertainty radius of 10 arcsec (90% confidence level, including statistical and systematic uncertainties), which is consistent with the known RS CVn-type variable star ZTF J222816.62+504629.8. The averaged unabsorbed flux in 0.5-10 keV is about 1.2 x 10^(-12) erg/cm^2/s. The corresponding EP-WXT X-ray luminosity is estimated to be approximately 1.1x 10^34 erg/s. Launched on 2024 January 9, Einstein Probe is a space-based X-ray observatory designed to monitor the dynamic soft X-ray sky with rapid 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/45215. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43430] EP260725a: EP-WXT detection of an X-ray transient
by GCN Circulars 25 Jul '26

25 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45214 SUBJECT: EP260725a: EP-WXT detection of an X-ray transient DATE: 26/07/26 02:25:45 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y.J. Zhang (PKU), R. D. Liang, W. Chen, H. W. Pan (NAOC) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient, designated EP260725a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient started at 2026-07-25 02:45:59 (UTC), with a peak flux of ~ 1 x 10^(-10) erg cm^-2 s^-1 in 0.5-4 keV. The position of the transient is R.A. = 337.069 deg, Dec. = 50.764 deg (J2000), with an uncertainty radius of 3 arcmin in radius (90% confidence level, including both statistical and systematic uncertainties). The average WXT 0.5-4 keV spectrum can be fitted by an absorbed power-law model with a fixed Galactic hydrogen column density of 7.0×10^20 cm^-2 and a photon index of 3.5 (-1.7/+2.2). The derived average unabsorbed 0.5-4 keV flux is 2.0(-0.8/+2.4) x 10^(-11) erg cm^-2 s^-1. The uncertainties are at the 90% confidence level for the above parameters. EP-FXT performed a follow-up observation of EP260725a detected by EP-WXT. The observation started at 2026-07-25 17:40:12 UTC, about 15 hr after the WXT detection, with a total exposure time of around 3.0 ks. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 337.0718 deg, DEC = 50.7757 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Launched on 2024 January 9, Einstein Probe is a space-based X-ray observatory designed to monitor the dynamic X-ray sky and perform rapid follow-up observations of newly discovered transients (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/45214. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43429] GRB 260616A: cubesat Avion detection
by GCN Circulars 25 Jul '26

25 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45213 SUBJECT: GRB 260616A: cubesat Avion detection DATE: 26/07/25 23:58:54 GMT FROM: Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> From Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> A. Bogomolov, V. Bogomolov, A. Iyudin, S. Svertilov, N. Vasiliev on behalf of the MSU “Sozvezdie-270” team, report: At 2026-06-16 ~03:21:40 UT the long-duration GRB 260616A (Fermi/GBM detection: GCN #44948, Fermi/LAT detection: GCN #44960, GECAM-B detection: GCN #44964, CALET detection: GCN #44966, Konus-Wind detection: GCN #44967, Insight HXMT detection: GCN #44980, NuSTAR detection: #44987, SVOM detection: #44995, AstroSat CZTI detection: GCN #44996) was detected by the DeCoR-1 and DeCoR-3 instruments on the cubesat Avion of the Moscow University project “Sozvezdie-270” [1]. Total amount of photons detected by Avion is 1688 (DeCoR-1, energy band >40 keV), it corresponds to a fluence of ~7.5*10^(-6) erg/cm^2 in the range 40-500 keV. LC in the energy range of 40-500 keV consists of multiple peaks of various intensity and duration, a maximum flux is ~4.5 phot/(cm^2*s). А total duration (T90) of the burst is ~80 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB260616A_LC_Avion.png Parameters of GRB 260616A as well as other GRBs detected by Moscow University cubesats are listed at: https://swx.sinp.msu.ru/models/grb_cat/grb.php?lang=en Avion is one of 5 cubesats of the Moscow University project “Sozvezdie-270” [1] launched on 2023 June 27. The payload of Avion is a set of scintillation gamma-ray detectors DeCoR [2], the energy range is >30 keV, the time resolution is 0.5s. [1] Svertilov et al. 2023 https://link.springer.com/chapter/10.1007/978-3-031-50248-4_21 [2] Bogomolov et al. 2022 Universe 8, 282 https://www.mdpi.com/2218-1997/8/5/282 View this GCN Circular online at https://gcn.nasa.gov/circulars/45213. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43428] EP260723a: Continued Liverpool Telescope observations suggest hours long optical plateau or rebrightening
by GCN Circulars 25 Jul '26

25 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45212 SUBJECT: EP260723a: Continued Liverpool Telescope observations suggest hours long optical plateau or rebrightening DATE: 26/07/25 22:02:47 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 the Einstein Probe fast X-ray transient EP260723a (Zhang et al., GCN 45201; Ni et al. GCN 45209) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 12x150 s and 12x150 s exposures in each of the SDSS r’ and z’ filters starting at 2026-07-25 03:26:08 UT, approximately 32.5 hours after the X-ray detection. We detect the optical counterpart (Eyles-Ferris et al., GCN 45202; He et al., GCN 45203; Basa et al., GCN 45204; Ma et al., GCN 45205) in both bands at AB magnitudes of r = 22.17 +/- 0.08 and z = 21.48 +/- 0.13. Our photometry is calibrated to PanSTARRS and not corrected for Galactic extinction. We note that these magnitudes are consistent with those reported by Basa et al. (GCN 45204) approximately 19 hours earlier, suggesting an extended optical plateau or rebrightening. Further observations are planned. View this GCN Circular online at https://gcn.nasa.gov/circulars/45212. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43427] GRB 260602B: cubesat Avion detection
by GCN Circulars 25 Jul '26

25 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45211 SUBJECT: GRB 260602B: cubesat Avion detection DATE: 26/07/25 12:55:55 GMT FROM: Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> From Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> A. Bogomolov, V. Bogomolov, A. Iyudin, S. Svertilov, N. Vasiliev on behalf of the MSU “Sozvezdie-270” team, report: At 2026-06-02 ~22:41:31 UT the short GRB 260602B (Fermi GBM detection: GCN #44779) was detected by the DeCoR-1 instrument on the cubesat Avion of the Moscow University project “Sozvezdie-270” [1]. Total amount of photons detected by Avion is 24 (energy band >40 keV), it corresponds to a fluence of ~1.1*10^(-7) erg/cm^2 in the range 40-500 keV. LC in the energy range of 40-500 keV is a single episode of ~0.5 sec duration with a maximum flux of ~2.3 phot/(cm^2*s). А total duration (T90) of the burst is ~0.5 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB260602B_LC_Avion.png Parameters of GRB 260602B as well as other GRBs detected by Moscow University cubesats are listed at: https://swx.sinp.msu.ru/models/grb_cat/grb.php?lang=en Avion is one of 5 cubesats of the Moscow University project “Sozvezdie-270” [1] launched on 2023 June 27. The payload of Avion is a set of scintillation gamma-ray detectors DeCoR [2], the energy range is >30 keV, the time resolution is 0.5s. [1] Svertilov et al. 2023 https://link.springer.com/chapter/10.1007/978-3-031-50248-4_21 [2] Bogomolov et al. 2022 Universe 8, 282 https://www.mdpi.com/2218-1997/8/5/282 View this GCN Circular online at https://gcn.nasa.gov/circulars/45211. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43426] GRB 260601A: cubesat Avion detection
by GCN Circulars 25 Jul '26

25 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45210 SUBJECT: GRB 260601A: cubesat Avion detection DATE: 26/07/25 12:55:07 GMT FROM: Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> From Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> A. Bogomolov, V. Bogomolov, A. Iyudin, S. Svertilov, N. Vasiliev on behalf of the MSU “Sozvezdie-270” team, report: At 2026-06-01 11:00:12UT the short GRB 260601A (Fermi GBM detection: GCN #44755, GCN #44760, Glowbug detection: GCN #44763, CALET detection: GCN #44773, GECAM-B detection: GCN #44778, SVOM detection: GCN #44793, IPN triangulation: GCN #44893, Konus-Wind detection: GCN #44894) was detected by the DeCoR-1 and DeCoR-3 instruments on the cubesat Avion of the Moscow University project “Sozvezdie-270” [1]. Total amount of photons detected by Avion is 43 (DeCoR-3, energy band >30 keV), it corresponds to a fluence of ~4*10^(-7) erg/cm^2 in the range 30-500 keV. LC in the energy range of 30-500 keV is a single episode of ~0.5 sec duration with a maximum flux of ~10 phot/(cm^2*s). А total duration (T90) of the burst is less than ~0.5 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB260601A_LC_Avion.png Parameters of GRB 260601A as well as other GRBs detected by Moscow University cubesats are listed at: https://swx.sinp.msu.ru/models/grb_cat/grb.php?lang=en Avion is one of 5 cubesats of the Moscow University project “Sozvezdie-270” [1] launched on 2023 June 27. The payload of Avion is a set of scintillation gamma-ray detectors DeCoR [2], the energy range is >30 keV, the time resolution is 0.5s. [1] Svertilov et al. 2023 https://link.springer.com/chapter/10.1007/978-3-031-50248-4_21 [2] Bogomolov et al. 2022 Universe 8, 282 https://www.mdpi.com/2218-1997/8/5/282 View this GCN Circular online at https://gcn.nasa.gov/circulars/45210. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43425] EP260723a: EP-FXT follow-up observation
by GCN Circulars 25 Jul '26

25 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45209 SUBJECT: EP260723a: EP-FXT follow-up observation DATE: 26/07/25 09:24:56 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> K. R. Ni (CCNU), Y. J. Zhang (PKU), X. H. Tang (THU), H. Sun (NAOC) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of EP260723a detected by EP-WXT (Zhang et al., GCN 45201). The observation started at 2026-07-24 08:44:22 UTC, about 13.8 hr after the WXT detection, with a total exposure time of around 3.0 ks. On-ground analysis of the FXT data found no significant uncatalogued X-ray source in either the individual FXT-A or FXT-B image. After stacking the FXT-A and FXT-B data, a weak X-ray excess, with an S/N of approximately 2.2, was found at the position of the optical counterpart reported by the Nordic Optical Telescope (NOT; He et al., GCN 45203): R.A. (J2000) = 2.97518 deg Dec. (J2000) = −12.09851 deg The optical counterpart was initially reported by the Liverpool Telescope (Eyles-Ferris et al., GCN 45202) and was subsequently confirmed by NOT (He et al., GCN 45203), COLIBRÍ (Basa et al., GCN 45204), and SVOM/VT (Ma et al., GCN 45205). Given the low statistical significance, it is still unclear whether this weak X-ray excess is associated with EP260723a. The limited number of source counts does not allow meaningful spectral analysis. Further EP-FXT follow-up observations will be arranged. Launched on January 9, 2024, EP is a space X-ray observatory designed to monitor the dynamic soft X-ray sky and perform follow-up observations of newly discovered transients (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/45209. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43424] IPN triangulation of GRB 260706B
by GCN Circulars 24 Jul '26

24 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45208 SUBJECT: IPN triangulation of GRB 260706B DATE: 26/07/24 16:54:10 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, A.B. Sanin, and J. Benkhoff on behalf of the MGNS/BepiColombo and HEND/Mars-Odyssey teams, G. Jones on behalf of the BepiColombo team, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, D.J. Lawrence, J.O. Goldsten, P.N. Peplowski on behalf of the Psyche/GRNS team, E. Burns on behalf of the IPN, W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team report: The long-duration GRB 260706B was detected by Konus-Wind, Psyche (GRNS), Mars-Odyssey (HEND), and BepiColombo (MGNS) at about 84082 s UT (23:21:22). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: The correct preliminary 3-sigma error box is: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 130.509 (08h 42m 02s) +16.967 (+16d 58' 00") Corners: 130.752 (08h 43m 01s) +17.921 (+17d 55' 14") 130.743 (08h 42m 58s) +17.692 (+17d 41' 30") 130.183 (08h 40m 44s) +15.751 (+15d 45' 04") 130.232 (08h 40m 56s) +16.102 (+16d 06' 06") --------------------------------------------- The error box area is 352 sq. arcmin, and its maximum dimension is 2.2 deg (the minimum one is 3 arcmin). The Sun distance was 24 deg. This localization may be improved, as soon as the Psyche (GRNS) timing accuracy will be analyzed. A triangulation map and HEALPix FITS files are posted at http://www.ioffe.ru/LEA/GRBs/GRB260706_T84082/IPN The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/45208. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43423] GRB 260718A: SVOM/ECLAIRs refined analysis
by GCN Circulars 24 Jul '26

24 Jul '26

TITLE: GCN CIRCULAR NUMBER: 45207 SUBJECT: GRB 260718A: SVOM/ECLAIRs refined analysis DATE: 26/07/24 16:33:19 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, O. Godet (IRAP), R. Hamburg (USRA), W. Zhang (PMO), Y. Ma (NAOC), 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 260718A (SVOM burst-id sb26071802 – GCN 45177, trigger time T0 = 2026-07-18T11:16:34 UTC), which was also detected by Fermi/GBM (GCN 45181). The burst that triggered ECLAIRs onboard shows a single peak lightcurve. The burst duration is T90 = 17.4 -2.0/+4.1 s in the 4-120 keV energy band. The time-averaged spectrum from T0-2.15 s s to T0+15.0 s in the 5-120 keV energy range is best fitted by a powerlaw model with alpha = -1.95 +/- 0.05. With this model, the 4-120 keV fluence is (8.4 +/- 0.4)e-7 erg/cm^2 and the 4-120 keV photon flux is (2.16 ± 0.06) 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: M. Brunet (IRAP) (marius.brunet at utoulouse.fr). View this GCN Circular online at https://gcn.nasa.gov/circulars/45207. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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