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[vsnet-grb-info 43522] EP260806a: refined analysis of the EP-WXT and autonomous EP-FXT observations
by GCN Circulars 07 Aug '26

07 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45305 SUBJECT: EP260806a: refined analysis of the EP-WXT and autonomous EP-FXT observations DATE: 26/08/07 09:57:42 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO, CAS), Y.-H. Cheng (YNU), G.-J. Yang and W.-D. Zhang (NAOC) on behalf of the Einstein Probe (EP) team: The X-ray transient EP260806a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Li et al., GCN 45299), and followed up by LCO (He et al., GCN 45300), GTC (de Ugarte Postigo et al., GCN 45302), Liverpool Telescope (Eyles-Ferris et al., GCN 45303) and SVOM/VT (Ma et al., GCN 45304). We report the refined analysis of the EP-WXT observation during which the source was detected, and the autonomous EP-FXT follow-up observation. The WXT observation in which the source was detected started at 2026-08-06 22:57:37 (UTC) and lasted for ~290 seconds. No obvious variability or flaring activity of the source was seen in its lightcurve during the WXT observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 4.64 x 10^20 cm^-2, an intrinsic column density of 1.17 (+/- 0.51) x 10^18 cm^-2 and a photon index of 1.94 (-0.81/+2.7). The derived average unabsorbed 0.5-4 keV flux is 1.65 (-0.58/+5.7) x 10^-10 erg s^-1 cm^-2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously starting at 2026-08-06T23:03:51 (UTC, 374 seconds after the first WXT observation). The exposure time of this observation was 3950 s. On-ground analysis of the FXT data found an uncatalogued X-ray source at R.A. = 12.3066 deg, DEC = 35.5603 deg (J2000), with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 4.64 x 10^20 cm^-2, an intrinsic column density of 1.92 (+/-0.13) x 10^21 cm^-2 and a photon index of 2.02 (+/-0.04). The derived average unabsorbed 0.5-10 keV flux is 2.13 (+/-0.03) x 10^-10 erg s^-1 cm^-2. The peak luminosity is estimated to be 3.8 × 10^45 erg s^-1 in the 0.5-10 keV energy band, adopting a redshift of z = 0.089 (de Ugarte Postigo et al., GCN 45302). The source flux had been declining during the FXT observation. The uncertainties are at the 90% confidence level for the above spectral parameters. Further follow-up observations with EP/FXT are scheduled. 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/45305. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43521] EP260806a: SVOM/VT optical observation
by GCN Circulars 07 Aug '26

07 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45304 SUBJECT: EP260806a: SVOM/VT optical observation DATE: 26/08/07 09:39:44 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, H. L. Li, Y. L. Qiu, C. Wu, L. P. Xin, Z. H. Yao, J. R. Xu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of EP260806a detected by EP/WXT (Li et al., GCN 45299). SVOM/VT began observing the field at 2026-08-06T23:46:08 UTC, 43.667 minutes after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, no uncatalogued sources are found within the EP/FXT error circle (Li et al., GCN 45299). At the optical counterpart position reported by LCO (He et al., GCN 45300; de Ugarte Postigo et al., GCN 45302; Eyles-Ferris et al., GCN 45303), a bright cataloged galaxy is detected. Preliminary photometric analysis shows a brightening of ~0.1 mag from 0.728 h to 3.855 h in both bands. Further detailed analysis is still ongoing. 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/45304. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43520] EP260806a: Liverpool Telescope observations of the counterpart show a blue colour
by GCN Circulars 07 Aug '26

07 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45303 SUBJECT: EP260806a: Liverpool Telescope observations of the counterpart show a blue colour DATE: 26/08/07 09:33:18 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), J. N. D. van Dalen (Radboud) and A. Martin-Carrillo (UCD) report on behalf of a larger collaboration: We observed the field of the Einstein Probe fast X-ray transient EP260806a (Li et al., GCN 45299) 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 2026-08-07 01:24:49 UT, approximately 2.38 hours after the X-ray detection. We performed image subtraction on the stacked images using PanSTARRS templates and detect the optical counterpart (He at al., GCN 45300; de Ugarte Postigo et al., GCN 45302) in both bands. No other sources are detected within the EP/FXT error region (Li et al., GCN 45299). In our subtracted images, we measure r = 19.22 +/- 0.03 z = 19.53 +/- 0.04 Our photometry is calibrated to PanSTARRS and not corrected for Galactic extinction. The blue colour is broadly consistent with an AGN outburst as suggested by de Ugarte Postigo et al. (GCN 45302) but may also be evidence of a fast rising tidal disruption event origin. Further observations are encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/45303. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43519] EP260806a: OSIRIS+/GTC redshift z=0.089
by GCN Circulars 07 Aug '26

07 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45302 SUBJECT: EP260806a: OSIRIS+/GTC redshift z=0.089 DATE: 26/08/07 08:25:50 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), L. Izzo (INAF/OACN and DARK/NBI), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), S. Geier (GTC), C. C. Thoene (AbAO), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC),G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), G. Gómez Velarde (GTC) and A. Tejero Caro (GTC) report: We observed the optical counterpart candidate (He et al. GCN 45300) of EP260806a (Li et al. GCN 45299) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ instrument. The 30-s acquisition r-band image (beginning on 2026-08-07 at 03:21:44 UT, that is 4.32 hr after trigger), shows the underlying galaxy mentioned by He et al. We performed image subtraction and photometry with respect to a PanSTARRS reference image using STDWeb (Karpov 2025). The residuals show a clear excess at r = 19.05 +/- 0.01 mag consistent with the core of the galaxy. This implies a 0.27+/-0.04 mag brightening with respect to the observation by He et al. The location of the counterpart and the galaxy core are consistent with a catalogued LOTSS and VLASS radio source, which could be indicative of an active galactic nucleus. A total of 3 spectra of 900 s were secured, starting on 2026-08-07 at 03:26:22 UT (4.40 hr after trigger), using grism R1000B. Continuum is visible over the wavelength range 3620 - 7800 AA. We detect strong emission lines due to [OII], [OIII], HeI, HII, [NII] and [SII], as well as CaII absorptions, all at a common redshift z = 0.089, which we suggest to be the redshift of the EP260806a event. We also note that this galaxy is part of an interacting system with another, larger galaxy, located 22” at the West-southwest of this one. This second galaxy also falls in the slit and we confirm a consistent redshift. This work has used the GRBspec database at http://grbspec.eu (de Ugarte Postigo et al. 2014, doi:10.1117/12.2055774). View this GCN Circular online at https://gcn.nasa.gov/circulars/45302. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43518] EP260731a: refined analysis of the EP-WXT and autonomous EP-FXT observations
by GCN Circulars 06 Aug '26

06 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45301 SUBJECT: EP260731a: refined analysis of the EP-WXT and autonomous EP-FXT observations DATE: 26/08/07 03:41:59 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: The X-ray transient EP260731a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Ni et al., GCN 45261), and followed up by NOT/ALFOSC and COLIBRÍ/DDRAGO (Liu et al., GCN 45263; de Ugarte Postigo et al., GCN 45264). We report the refined analysis of the EP-WXT and autonomous EP-FXT observations. The refined analysis of the WXT data shows that the event started at T0 = 2026-07-31T00:53:50 (UTC) and lasted for approximately 35 s. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 3.10 x 10^20 cm^-2 and a photon index of 0.89 (-0.50/+0.52). The derived average unabsorbed 0.5-4 keV flux is 2.30 (-0.70/+0.94) x 10^-9 erg s^-1 cm^-2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously starting at 2026-07-31T00:56:34 (UTC, T0+164 s). The exposure time of this observation was 2982 s. On-ground analysis of the FXT data found an uncatalogued X-ray source at R.A. = 344.4246 deg, DEC = -11.7626 deg (J2000), with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a free hydrogen column density of 1.83 (-1.83/+2.06) x 10^21 cm^-2 and a photon index of 2.34 (-0.68/+0.75). The derived average unabsorbed 0.5-10 keV flux is 1.15 (-0.21/+0.33) x 10^-12 erg s^-1 cm^-2. The uncertainties are at the 90% confidence level for the above spectral 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/45301. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43517] EP260806a: LCO likely optical counterpart
by GCN Circulars 06 Aug '26

06 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45300 SUBJECT: EP260806a: LCO likely optical counterpart DATE: 26/08/07 02:28:30 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He, J. An, S.Q. Jiang, X. Liu, Z.P. Zhu, Z. Fan, W.X. Li, D. Xu(NAOC), S.Y. Fu (HUST), Y.L. Hua (PMO) report: We observed the field of EP260806a detected by EP (Li et al., GCN 45299), using an LCO 1m telescope located at the Teide Observatory (Spain) equipped with the SINISTRO instrument. We obtained 6x200 s exposures in the SDSS-r filter at the mid time on 2026-08-07 at 01:06:30.678 UT (2.04 hr after the trigger). After subtracting the archival Pan-STARRS image, we found a point source lie in a brightened known galaxy, which has a redshift of ~0.136 in REGALADE (Hugo et al. 2026), within the EP/FXT error circle. The coordinates of the optical counterpart are as follows: R.A. (J2000) = 00:49:13.554 (12.30647 deg) Dec. (J2000) = +35:33:39.72 (35.56103 deg) with an uncertainty of ~ 0.5 arcsec. The source had r = 19.32 +/- 0.03 mag (background subtracted), calibrated with Pan-STARRS DR2 and not corrected for Galactic extinction. We thus think the source is likely the optical counterpart. View this GCN Circular online at https://gcn.nasa.gov/circulars/45300. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43516] EP260806a: Einstein Probe detection of an X-ray transient
by GCN Circulars 06 Aug '26

06 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45299 SUBJECT: EP260806a: Einstein Probe detection of an X-ray transient DATE: 26/08/07 00:18:42 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.-Z. Li (YNAO, CAS), Y.-H. Cheng (YNU), G.-J. Yang and W.-D. Zhang (NAOC) 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 EP260806a. The transient triggered EP-WXT (ID: 01709277716) at 2026-08-06T23:02:28 (UTC). The WXT position of the source is R.A. = 12.278 deg, DEC = 35.588 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. = 12.3098 deg, DEC = 35.5614 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/45299. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43515] GRB 260715A: cubesat Avion detection
by GCN Circulars 06 Aug '26

06 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45298 SUBJECT: GRB 260715A: cubesat Avion detection DATE: 26/08/06 08:51:32 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 2026-07-15 ~11:10:14 UT the long-duration GRB 260715A (Fermi/GBM detection: GCN #45167) was detected by the DeCoR-3 instrument on the cubesat Avion of the Moscow University project “Sozvezdie-270” [1]. Total amount of photons detected by Avion is 198 (energy band >30 keV), it corresponds to a fluence of ~1.75*10^(-6) erg/cm^2 in the range 30-500 keV. LC in the energy range of 30-500 keV consists of a single episode with a rapid front and a smoother decline, a maximum flux is ~3.8 phot/(cm^2*s). There is probably another increase ~13 s after the start of the burst. А total duration (T90) of the burst is ~15 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB260715A_LC_Avion.png Parameters of GRB 260715A 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. 2026 Cosmic Research 64, 262 https://link.springer.com/article/10.1134/S0010952526600071 View this GCN Circular online at https://gcn.nasa.gov/circulars/45298. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43514] GRB 260709A: cubesat Avion detection
by GCN Circulars 06 Aug '26

06 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45297 SUBJECT: GRB 260709A: cubesat Avion detection DATE: 26/08/06 08:49:20 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> At 2026-07-09 ~01:07:32 UT the long-duration GRB 260709A (Fermi/GBM detection: GCN #45121, GECAM-B detection: GCN #45136, SVOM/GRM detection: GCN #45137, AstroSat detection: GCN #45164) 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 100 (energy band >40 keV), it corresponds to a fluence of ~4.5*10^(-7) erg/cm^2 in the range 40-500 keV. LC in the energy range of 40-500 keV consists of several peaks of various intensity, a maximum flux is ~2 phot/(cm^2*s) at the central peak at 01:07:32 UT. А total duration (T90) of the burst is ~18 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB260709A_LC_Avion.png Parameters of GRB 260709A 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. 2026 Cosmic Research 64, 262 https://link.springer.com/article/10.1134/S0010952526600071 View this GCN Circular online at https://gcn.nasa.gov/circulars/45297. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43513] GRB 260708A: cubesat Avion detection
by GCN Circulars 06 Aug '26

06 Aug '26

TITLE: GCN CIRCULAR NUMBER: 45296 SUBJECT: GRB 260708A: cubesat Avion detection DATE: 26/08/06 08:47:21 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 2026-07-08 ~10:11:16 UT the long-duration GRB 260708A (Fermi/GBM detection: GCN #45115, Fermi/LAT detection: GCN #45117, GCN #45145, IceCube observation: GCN #45120, GCN #45134, GCN #45171, GECAM-B detection: GCN #45126, Glowbug detection: GCN #45130) 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 403 (energy band >40 keV), it corresponds to a fluence of ~1.8*10^(-6) erg/cm^2 in the range 40-500 keV. LC in the energy range of 40-500 keV is a single episode, a maximum flux is ~2.6 phot/(cm^2*s) at ~10 s after the start of the burst. А total duration (T90) of the burst is ~25 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB260708A_LC_Avion.png Parameters of GRB 260708A 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. 2026 Cosmic Research 64, 262 https://link.springer.com/article/10.1134/S0010952526600071 View this GCN Circular online at https://gcn.nasa.gov/circulars/45296. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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