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[vsnet-grb-info 43710] GRB 260831B / sb26083106: SVOM/VT optical variability of V* GK Per
by GCN Circulars 01 Sep '26

01 Sep '26

TITLE: GCN CIRCULAR NUMBER: 45489 SUBJECT: GRB 260831B / sb26083106: SVOM/VT optical variability of V* GK Per DATE: 26/09/01 14:33:23 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, Y. N. Ma, Y. L. Qiu, 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, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) and C. Guepin (LUPM) report on behalf of the SVOM/VT team. SVOM/VT performed observations with automatic slew of the SVOM/ECLAIRs trigger sb26083106 (Godet et al., GCN 45477, 45486) starting from 2026-08-31T18:46:36 UT, about 10 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The classical nova mentioned by Godet et al. (GCN 45486) during our observations showed a fluctuating variation with the amplitude of about 0.2 mag in both channels. We also searched for uncatalogued sources within the SVOM/ECLAIRs error box (Godet et al., GCN 45477). In our images no uncatalogued sources were detected down to 5-sigma upper limits of about 22.5 mag (AB) in both channels at the mid time of 18.3 minutes post trigger. 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/45489. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43709] NuSTAR Transient 260828: LCO Optical Upper Limits
by GCN Circulars 01 Sep '26

01 Sep '26

TITLE: GCN CIRCULAR NUMBER: 45488 SUBJECT: NuSTAR Transient 260828: LCO Optical Upper Limits DATE: 26/09/01 13:48:16 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> R. A. J. Eyles-Ferris (Leicester), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), J. A. Quirola-Vasquez (Radboud), A. Martin-Carrillo (UCD), J. Chacon (PUC), F. E. Bauer (SSI and UTA), M. Brightman (Caltech), P. G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient detected by NuSTAR (Brightman, GCN 45478) denoted as NuSTAR 260828 using the LCO 1m telescope located at Cerro Tololo Interamerican Observatory (Chile) and equipped with the SINISTRO instrument. Observations consisted of a sequence of 6 x 300 s exposures in SDSS r-band and 5 x 300 s exposures in SDSS z-band. We performed image subtraction on both stacked images against archival Pan-STARRS stacked images. We do not detect any new source in either band within the NuSTAR uncertainty (Brightman, GCN 45478), down to the following 3 sigma upper limits: r > 22.22 (midtime: 2026-09-01 08:52:05 UT, ~3.59 days post detection ); z > 21.31 (midtime: 2026-09-01 09:23:30 UT, ~3.61 days post detection). These upper limits are in AB magnitudes, calibrated using nearby stars from the Pan-STARRS catalogue, and are not corrected for the appreciable Galactic extinction (A_V = 1.74 mag). View this GCN Circular online at https://gcn.nasa.gov/circulars/45488. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43708] EP260901a: EP-WXT detection of a fast X-ray transient
by GCN Circulars 01 Sep '26

01 Sep '26

TITLE: GCN CIRCULAR NUMBER: 45487 SUBJECT: EP260901a: EP-WXT detection of a fast X-ray transient DATE: 26/09/01 13:16:31 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. F. Liang, J. Y. Liu (PMO), X. Mao, Q. H. Lao, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient, designated EP260901a (notice ID: 11900871682), by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient was identified in the telemetry data. The transient started about 2026-09-01T05:07:45(UTC) and lasted for about 500s. The position of the transient is R.A. = 260.845 deg, Dec. = -19.232 (J2000), with an uncertainty radius of 2.4 arcmin in radius (90% confidence level, including both statistical and systematic uncertainties). There are no known X-ray sources in the WXT error circle. 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 3.34 × 10^21 cm^-2 and a photon index of 1.12 (-0.07/+0.07). The derived average unabsorbed 0.5-4 keV flux is 3.96(-0.61/+0.68) x 10^(-10) erg cm^-2 s^-1. The peak flux is about 3.7 x 10^(-9) erg cm^-2 s^-1. The uncertainties are at the 90% confidence level for the above parameters. Follow-up observations by EP-FXT will be arranged. 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/45487. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43707] SVOM trigger sb26083106 is not a GRB
by GCN Circulars 01 Sep '26

01 Sep '26

TITLE: GCN CIRCULAR NUMBER: 45486 SUBJECT: SVOM trigger sb26083106 is not a GRB DATE: 26/09/01 13:07:45 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> O. Godet (IRAP), C. Guepin (LUPM), S. Guillot (IRAP) report on behalf of the SVOM mission team: At 2026-08-31T18:36:12 UT SVOM issued an alert with burst-id sb26083106, which was reported in the circular GCN #45477. Using the event-by-event data downloaded through the X-band ground station, we determined a refined position for this event, concluding that it originated from the classical nova V* GK Per. We apologize for any inconvenience this may have caused. The Burst Advocate (BA) on shift for this alert is Claire Guepin: claire.guepin(a)lupm.in2p3.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/45486. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43706] GRB 260829A: AstroSat CZTI detection
by GCN Circulars 01 Sep '26

01 Sep '26

TITLE: GCN CIRCULAR NUMBER: 45485 SUBJECT: GRB 260829A: AstroSat CZTI detection DATE: 26/09/01 11:39:37 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 GRB 260829A which was also detected by Fermi (Fermi GBM team, GCN Circ. 45464), BALROG localization (Preis et.al., GCN Circ. 45465), GECAM-B (Hao-Xuan Guo et al., GCN Circ. 45470), and IPN triangulation (Kozyrev et.al., GCN Circ. 45476). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-08-29 06:08:31.7 UTC. The measured peak count rate associated with the burst is 614 (+58, -62) counts/s above the background in the combined data of all quadrants, with a total of 2357 (+429, -471) counts. The local mean background count rate was 643 (+6, -6) counts/s. We measure a T90 of 13.1 (+5.3, -6.5) s from the cumulative Veto light curve. The source was 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 2026-08-29 06:08:30.7 UTC. The measured peak count rate associated with the burst is 213 (+34, -27) counts/s above the background in the combined data of three quadrants (out of four), with a total of 708 (+180, -194) counts. The local mean background count rate was 227 (+2, -3) counts/s. Due to poor statistics, we cannot reliably estimate the T90 from it. CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/525679702.67/S525679702.67_det… 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/45485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43705] GRB 260831B: EP-FXT follow-up observation
by GCN Circulars 01 Sep '26

01 Sep '26

TITLE: GCN CIRCULAR NUMBER: 45484 SUBJECT: GRB 260831B: EP-FXT follow-up observation DATE: 26/09/01 08:56:27 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. F. Liang, J. Y. Liu(PMO), X. Mao, Q. H. Lao, Z. X. Ling (NAO,CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 260831B (SVOM/sb26083106) (Godet et al. GCN 45477; Guan et al. GCN 45482) at 2026-08-31T21:31:08 (UTC), about 3 hours after the SVOM/ECLAIRs trigger, with an exposure time of 3002s. There is no uncataloged source within ECLAIRs' error box. The upper limit of this observation is about 2 x 10^(-13) erg/s/cm^2. 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/45484. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43704] GRB 260830A: NuSTAR detection of prompt emission
by GCN Circulars 01 Sep '26

01 Sep '26

TITLE: GCN CIRCULAR NUMBER: 45483 SUBJECT: GRB 260830A: NuSTAR detection of prompt emission DATE: 26/09/01 07:06:48 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 260830A 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 2026-08-30T19:32:13.02 UTC, shows a detection of GRB 260830A, also detected by Konus-Wind (GCN notices). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a single episode with two peaks lasting for about 10-s. The peak count rate is ~1500-cps with a baseline rate of ~1000-cps during this time period. We do not see any evidence in the 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/2026/260830A 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/45483. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43703] GRB 260831B: LCO optical upper limits
by GCN Circulars 01 Sep '26

01 Sep '26

TITLE: GCN CIRCULAR NUMBER: 45482 SUBJECT: GRB 260831B: LCO optical upper limits DATE: 26/09/01 06:56:51 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y.X. Guan (GXU), A. Saccardi, D. Turpin (CEA/Irfu), C. Wu, L.P. Xin (NAOC), C.Guepin (LUPM), C. Plasse (HKU) report on behalf of the SVOM mission team: We observed the field of GRB 260831B (SVOM burst-id sb26083106 detected by SVOM (Godet et al., GCN 45477) with the LCO 1m telescope at Tenerife equipped with the Sinistro instrument. Our observation started on 2026-09-01 at 01:31:26 UT (about 6.92 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. In the stacked image, we do not detect any new source within the SVOM/ECLAIRs error box. We measure the following upper limit calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: r > 21.5 AB (5-sigma, mid-time 7.22 hr after the trigger); z > 20.2 AB (5-sigma, mid-time 7.01 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/45482. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43702] EP260830a: Global MASTER-Net observations report
by GCN Circulars 01 Sep '26

01 Sep '26

TITLE: GCN CIRCULAR NUMBER: 45481 SUBJECT: EP260830a: Global MASTER-Net observations report DATE: 26/09/01 06:36:34 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> M. Segura, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA) V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya..Kechin, V.Senik, A.Chasovnikov, K.Labsina (Lomonosov MSU) D.Buckley (SAAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) A.Sosnovskij (CrAO RAS) A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory) L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) R.Rebolo (The Instituto de Astrofisica de Canarias) O.Gress, N.Budnev(ISU) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) was pointed to the EP260830a ( EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> et al., GCN 45480) errorbox 245 sec after notice time and 1 days 53772 sec after trigger time at 2026-09-01 06:26:35 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 49 deg. The sun altitude is -55.3 deg. The galactic latitude b = -45 deg., longitude l = 109 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3497638 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 140203 | 2026-09-01 06:26:35 | MASTER-OAFA | (00h 07m 26.40s , +16d 48m 31.6s) | C | 60 | 18.5 | 140280 | 2026-09-01 06:27:53 | MASTER-OAFA | (00h 07m 25.14s , +16d 49m 34.6s) | C | 60 | 18.6 | 140357 | 2026-09-01 06:29:09 | MASTER-OAFA | (00h 07m 32.14s , +16d 48m 37.1s) | C | 60 | 18.5 | 140434 | 2026-09-01 06:30:27 | MASTER-OAFA | (00h 07m 26.13s , +16d 47m 39.6s) | C | 60 | 18.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/45481. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43701] EP260830a: EP-WXT detection of a fast X-ray transient
by GCN Circulars 01 Sep '26

01 Sep '26

TITLE: GCN CIRCULAR NUMBER: 45480 SUBJECT: EP260830a: EP-WXT detection of a fast X-ray transient DATE: 26/09/01 06:21:48 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> X. Mao (NAO, CAS), Y. F. Liang, J. Y. Liu (PMO), Q. H. Lao, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient, designated EP260830a (notice ID: 01709295827), by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient was identified in the telemetry data. The transient started about 2026-08-30T15:30:23(UTC) and lasted for about 500s. The position of the transient is R.A. = 2.055 deg, Dec. = 16.919 (J2000), with an uncertainty radius of 2.4 arcmin in radius (90% confidence level, including both statistical and systematic uncertainties). There are no known X-ray sources in the WXT error circle. 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 4.21×10^20 cm^-2 and a photon index of 1.03 (-0.92/+1.02). The derived average unabsorbed 0.5-4 keV flux is 3.69 (-1.65/+2.93) x 10^(-11) erg cm^-2 s^-1. The uncertainties are at the 90% confidence level for the above parameters. Follow-up observations by EP-FXT will be arranged. 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/45480. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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