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[vsnet-grb-info 42049] EP260302a: Optical afterglow rebrightening
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43928 SUBJECT: EP260302a: Optical afterglow rebrightening DATE: 26/03/05 23:34:56 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), L. Cotter (UCD), J. Quirola-Vasquez (Radboud), A. Martin-Carrillo (UCD), R. A. J. Eyles-Ferris (Leicester), D. B. Malesani (DAWN/NBI and Radboud), P. G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the optical counterpart (Li et al., GCN 43898; Pérez-García et al., GCN 43903; Corcoran et al., GCN 43904) of the fast X-ray transient EP260302a (Zhang et al., GCN 43899; Zhang et al., GCN 43906) on two epochs. Our first observation was carried out with the Gemini South telescope located in Cerro Pachon (Chile); and the second with the LCO 1m telescope located in Sutherland (South Africa). The exposure times were 1x30 and 9x300 s, respectively, both in the SDSS r band, at mean epochs 2026-03-03 at 07:25:03 UT and 2026-03-05 at 19:05:14 UT (~7.8 and ~67.4 hr after trigger, respectively). The counterpart is clearly detected on both epochs. We measure magnitudes r = 22.06 +- 0.12 (Gemini) and r = 21.07 +/- 0.06 (LCO). Both values are calibrated against nearby stars from the SkyMapper catalog, and are not corrected for Galactic extinction. The observed fluxes imply a rebrightening by ~1 mag, which is uncommon for FXT and GRB afterglows around this epoch, and possibly indicates the emergence of an extra component (for another example, see e.g. van Dalen et al. 2025, doi:10.3847/2041-8213/adbc7e). We encourage further multiwavelength follow up of this unusual source. View this GCN Circular online at https://gcn.nasa.gov/circulars/43928. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42048] GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43927 SUBJECT: GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation DATE: 26/03/05 19:04:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), Y. Julakanti (Univ. Leicester), D. Turpin (CEA/Irfu), J.-L. Atteia (IRAP), D. B. Malesani (DAWN/NBI and Radboud), Y. H. Cheng (SWIFAR, YNU), R. A. J. Eyles-Ferris (Univ. Leicester) report on behalf of the SVOM and Einstein Probe teams: We performed a second observation at the location of the SVOM/ECLAIRs GRB 260228A (Julakanti et al., GCN 43882) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started on 2026-03-04 at 19:25:58 UT (3.94 days after the trigger) with a total exposure time of ~6000 s. All six sources detected by EP/FXT during the first visit (Cheng et al., GCN 43900) are detected in the second epoch data set. The brightest of them (EPF_J155124.0+262035; error radius of 10 arcsec) has faded by a factor of ~10, down to a flux of (1.92 +/- 0.47) x 10^-13 erg/s/cm^-2 (0.5-10 keV; 1-sigma uncertainty). The fading behavior of this X-ray source confirms it as the afterglow of GRB 260228A. The early deep optical limits measured by SVOM/VT (Li et al., GCN 43886), compared to the bright X-ray flux (Cheng et al., GCN 43900), suggest that this could be a dark GRB. We encourage multi-wavelength follow-up observation of this source. 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/43927. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42047] GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43927 SUBJECT: GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation DATE: 26/03/05 19:04:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), Y. Julakanti (Univ. Leicester), D. Turpin (CEA/Irfu), J.-L. Atteia (IRAP), D. B. Malesani (DAWN/NBI and Radboud), Y. H. Cheng (SWIFAR, YNU), R. A. J. Eyles-Ferris (Univ. Leicester) report on behalf of the SVOM and Einstein Probe teams: We performed a second observation at the location of the SVOM/ECLAIRs GRB 260228A (Julakanti et al., GCN 43882) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started on 2026-03-04 at 19:25:58 UT (3.94 days after the trigger) with a total exposure time of ~6000 s. All six sources detected by EP/FXT during the first visit (Cheng et al., GCN 43900) are detected in the second epoch data set. The brightest of them (EPF_J155124.0+262035; error radius of 10 arcsec) has faded by a factor of ~10, down to a flux of (1.92 +/- 0.47) x 10^-13 erg/s/cm^-2 (0.5-10 keV; 1-sigma uncertainty). The fading behavior of this X-ray source confirms it as the afterglow of GRB 260228A. The early deep optical limits measured by SVOM/VT (Li et al., GCN 43886), compared to the bright X-ray flux (Cheng et al., GCN 43900), suggest that this could be a dark GRB. We encourage multi-wavelength follow-up observation of this source. 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/43927. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42046] GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43927 SUBJECT: GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation DATE: 26/03/05 19:04:24 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), Y. Julakanti (Univ. Leicester), D. Turpin (CEA/Irfu), J.-L. Atteia (IRAP), D. B. Malesani (DAWN/NBI and Radboud), Y. H. Cheng (SWIFAR, YNU), R. A. J. Eyles-Ferris (Univ. Leicester) report on behalf of the SVOM and Einstein Probe teams: We performed a second observation at the location of the SVOM/ECLAIRs GRB 260228A (Julakanti et al., GCN 43882) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started on 2026-03-04 at 19:25:58 UT (3.94 days after the trigger) with a total exposure time of ~6000 s. All six sources detected by EP/FXT during the first visit (Cheng et al., GCN 43900) are detected in the second epoch data set. The brightest of them (EPF_J155124.0+262035; error radius of 10 arcsec) has faded by a factor of ~10, down to a flux of (1.92 +/- 0.47) x 10^-13 erg/s/cm^-2 (0.5-10 keV; 1-sigma uncertainty). The fading behavior of this X-ray source confirms it as the afterglow of GRB 260228A. The early deep optical limits measured by SVOM/VT (Li et al., GCN 43886), compared to the bright X-ray flux (Cheng et al., GCN 43900), suggest that this could be a dark GRB. We encourage multi-wavelength follow-up observation of this source. 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/43927. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42045] GRB 260303A: 1.3m DFOT optical upper limit
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43926 SUBJECT: GRB 260303A: 1.3m DFOT optical upper limit DATE: 26/03/05 16:36:08 GMT FROM: Debalina Kar at ARIES <kardebalina2000(a)gmail.com> Debalina Kar, Pankaj Pawar, Anshika Gupta, Dhruv Jain and Kuntal Misra (ARIES) report: We observed the field of GRB 260303A triggered by SVOM/ECLAIRs (sb26030303, Wang et al., GCN 43901) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-03-03 at 14:54:29.000 UT, approximately 8.88 hours after the trigger. We obtained multiple exposures of 300 s each in the R filter . A total of 10 frames were aligned and stacked to improve the signal-to-noise ratio. In the stacked frame we do not detect any optical counterpart within the error box of SVOM/ECLAIRs (Brunet et al., GCN 43922, Wang et al., GCN 43901) as well as outside the ECLAIRs error circle as reported by Xin et al. (GCN 43916) and (Schneider et al., GCN 43902). This is consistent with the non-detection in the J band reported by Mo et al. (GCN 43915). We derive the following 3-sigma upper limit from the stacked image: Date (UT) Start Time T_start–T0 (hr) Filter Exposure Magnitude ---------------------------------------------------------------------------------- 2026-03-03 14:54:29 ~8.88 R 300 s × 10 > 20.29 The reported magnitude is not corrected for Galactic extinction. Photometric calibration was performed using standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/43926. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42044] GRB 260303A: 1.3m DFOT optical upper limit
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43925 SUBJECT: GRB 260303A: 1.3m DFOT optical upper limit DATE: 26/03/05 16:34:28 GMT FROM: Debalina Kar at ARIES <kardebalina2000(a)gmail.com> Debalina Kar, Pankaj Pawar, Anshika Gupta, Dhruv Jain and Kuntal Misra (ARIES) report: We observed the field of GRB 260303A triggered by SVOM/ECLAIRs (sb26030303, Wang et al., GCN 43901) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-03-03 at 14:54:29.000 UT, approximately 8.88 hours after the trigger. We obtained multiple exposures of 300 s each in the R filter . A total of 10 frames were aligned and stacked to improve the signal-to-noise ratio. In the stacked frame we do not detect any optical counterpart within the error box of SVOM/ECLAIRs (Brunet et al., GCN 43922, Wang et al., GCN 43901) as well as outside the ECLAIRs error circle as reported by Xin et al. (GCN 43916) and (Schneider et al., GCN 43902). This is consistent with the non-detection in the J band reported by Mo et al. (GCN 43915). We derive the following 3-sigma upper limit from the stacked image: Date (UT) Start Time T_start–T0 (hr) Filter Exposure Magnitude ---------------------------------------------------------------------------------- 2026-03-03 14:54:29 ~8.88 R 300 s × 10 > 20.29 The reported magnitude is not corrected for Galactic extinction. Photometric calibration was performed using standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/43925. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42043] GRB 260303A: 1.3m DFOT optical upper limit
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43925 SUBJECT: GRB 260303A: 1.3m DFOT optical upper limit DATE: 26/03/05 16:34:28 GMT FROM: Debalina Kar at ARIES <kardebalina2000(a)gmail.com> Debalina Kar, Pankaj Pawar, Anshika Gupta, Dhruv Jain and Kuntal Misra (ARIES) report: We observed the field of GRB 260303A triggered by SVOM/ECLAIRs (sb26030303, Wang et al., GCN 43901) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-03-03 at 14:54:29.000 UT, approximately 8.88 hours after the trigger. We obtained multiple exposures of 300 s each in the R filter . A total of 10 frames were aligned and stacked to improve the signal-to-noise ratio. In the stacked frame we do not detect any optical counterpart within the error box of SVOM/ECLAIRs (Brunet et al., GCN 43922, Wang et al., GCN 43901) as well as outside the ECLAIRs error circle as reported by Xin et al. (GCN 43916) and (Schneider et al., GCN 43902). This is consistent with the non-detection in the J band reported by Mo et al. (GCN 43915). We derive the following 3-sigma upper limit from the stacked image: Date (UT) Start Time T_start–T0 (hr) Filter Exposure Magnitude ---------------------------------------------------------------------------------- 2026-03-03 14:54:29 ~8.88 R 300 s × 10 > 20.29 The reported magnitude is not corrected for Galactic extinction. Photometric calibration was performed using standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/43925. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42042] EP260214b: ATCA 6 GHz observations
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43924 SUBJECT: EP260214b: ATCA 6 GHz observations DATE: 26/03/05 15:31:04 GMT FROM: Giulia Gianfagna at INAF-IAPS <giulia.gianfagna(a)inaf.it> G. Gianfagna, G. Bruni, A. L. Thakur, L. Piro (INAF-IAPS) report: We observed the Fast X-ray Transient EP260214b (J Yang et al., GCN 43744, H Yang et al., GCN 43779) with the Australian Telescope Compact Array radio telescope using the 4-cm receiver. Observations were performed on March 3 2026 (at a mean epoch of ~17 days after the EP trigger) for a total of 6 hours. Data were reduced and imaged with standard CASA procedures. The final 6 GHz image has an RMS of ~15 uJy/beam. No radio emission is apparent at the position of the optical counterpart (He et al. GCN 43745, Watson et al. GCN 43747, Le Floch et al. GCN 43749, Pérez-Fournon et al. GCN 43750, Russeil et al. 43752,Li et al. GCN 43755, Vijayjumar et al. GCN 43757, Becerra et al. GCN 43758, Yang et al. GCN 43760, Aaryan et al. GCN 43762, Bochenek et al. GCN 43764, Kar et al. GCN 43774, Volnova et al. GCN 43775). The corresponding 3-sigma upper limit is thus ~50 uJy. Further ATCA observations are planned. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (grid.421683.a), which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. View this GCN Circular online at https://gcn.nasa.gov/circulars/43924. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42041] GRB 260211A: SVOM/VT optical rebrightening at 20 days after the burst, SN candidate
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43923 SUBJECT: GRB 260211A: SVOM/VT optical rebrightening at 20 days after the burst, SN candidate DATE: 26/03/05 15:06:48 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, L. P. Xin, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed further ToO observations of GRB 260211A detected by SVOM/Eclairs and SVOM/GRM (sb26021102, Gotz et al., GCN 43705). Also there was a sub-threshold detection by Fermi GBM (Hamburg et al., GCN 43713). The observations were performed on 2026-03-03 and 2026-03-05 in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical counterpart (Li et al., GCN 43720, GCN 43748) was measured to have a brightness of VT_R=22.91+/-0.25 mag at 19.36 days post trigger and VT_R=22.85+/-0.25 mag at 21.31 days respectively. These measurements show that the counterpart is rebrightening, relative to the reported brightness (Li et al. GCN 43748). We suggest that it is likely the supernova associated with the burst. Further follow-up observations are encouraged. Our photometry was in AB magnitude and was not corrected for Galactic extinction. 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/43923. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42040] GRB 260303A: SVOM/ECLAIRs refined analysis
by GCN Circulars 05 Mar '26

05 Mar '26

TITLE: GCN CIRCULAR NUMBER: 43922 SUBJECT: GRB 260303A: SVOM/ECLAIRs refined analysis DATE: 26/03/05 09:11:45 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> M. Brunet, L. Bouchet (IRAP), Z. Wang, D. Kong(GXU) 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 260303A (SVOM burst-id sb26030303 – GCN 43901, trigger time T0 = 2026-03-03T06:01:47 UTC). The burst that triggered ECLAIRs shows a single peak lightcurve. The burst duration is estimated to be around 14.5s (from T0-19.5s to T0-5s) in the 4-120 keV energy band through imaging. The refined burst localization is RA, Dec = 93.1458, 41.1727 degrees: RA (J2000) = 06h12m34.99s Dec (J2000) = 41d10m21.72s with a 90% C.L. radius of 9.6 arcmin (including systematic error of 6 arcmin added in quadrature). The time-averaged spectrum from T0-19.5 s to T0-5 s in the energy range 5-120 keV is best fitted by a powerlaw model with a photon index of 1.67 +0.14/-0.13. With this model, the 4-120 keV fluence is (1.19 +0.11/-0.20) e-6 erg/cm² and the 4-120 keV photon flux is 2.73 +0.16/-0.31 ph/cm²/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/43922. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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