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

[vsnet-grb-info 41939] EP260223a: Xinglong optical upper limit
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43826 SUBJECT: EP260223a: Xinglong optical upper limit DATE: 26/02/25 06:29:12 GMT FROM: Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong(a)nao.cas.cn> Yinan-Zhu (NAOC), Junjie-Jin (NAOC), Haiyang-Mu (NAOC), Feng-Xiao (NAOC), Yuguang-Sun (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration: Following the detection of EP260223a (GCN Circular 43817), we observed the field of EP260223a using the 2.16-m telescope at Xinglong Observatory, NAOC. We obtained 3x300s N-band frames by using 2.16-m with a median time of 2026-02-24 10:56:45 (UT), 4 hrs after the EP trigger and 3x300s clear-band frames by using 2.16-m with a median time of 2026-02-21T19:09:10, 8 hrs after the EP trigger. No uncatalogued optical transient is detected in the stacked images within the 20 arcsec EP/FXT error circle (GCN Circular 43817), down to 3-sigma limiting magnitudes of N-band ~19.11 mag for 2.16-m, calibrated with Pan-STARRS sources in the field. Also there is no apparent brightening for the catalogued sources within the error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/43826. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41938] The EP-WXT trigger 01709258631 is likely a flaring star
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43825 SUBJECT: The EP-WXT trigger 01709258631 is likely a flaring star DATE: 26/02/25 06:09:06 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> JiaYing Cao(IHEP), WenFeng Wen(SZTU), Guojiong Yang and Haiwu Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709258631 at 2026-02-25T03:33:22 is likely a stellar flare associated with RX J1220.4+1226. The estimated flux of the flare is around 4e-11 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 4e+31 erg/s. 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/43825. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41937] GRB 260223A: Glowbug gamma-ray detection
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43824 SUBJECT: GRB 260223A: Glowbug gamma-ray detection DATE: 26/02/25 05:26:59 GMT FROM: Richard S. Woolf at US Naval Research Laboratory <richard.s.woolf.civ(a)us.navy.mil> R. Woolf, C.C. Cheung, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260223A, which was also detected by Fermi GBM (GCN 43808) and SVOM/GRM (GCN 43815). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-02-23 04:11:09.520 with a duration of 20.5 s and a total significance of about 48.4 sigma. Following the initial event onset, the light curve comprises two main peaks at ~T0+11s and +18s. Note that data from ~T0+15s to T0+17s suffered from deadtime in various detectors. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/43824. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41936] EP260213a: Mephisto optical upper limits
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43823 SUBJECT: EP260213a: Mephisto optical upper limits DATE: 26/02/25 04:33:50 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Guowang Du, Ziwei Li, Zhenfei Qin, Jialong Zhou, Yu Pan, Xingzhu Zou, Xinlei Chen, Brajesh Kumar, Yuan Fang, Jinghua Zhang, Xufeng Zhu, Tao Wang, Xinzhong Er, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: The 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory, was triggered at 2026-02-13T20:05:57 (~7.2 min after the EP/WXT trigger) to observe the field of EP260213a (Yang et al., GCN 43729; Li et al., GCN 43730). A set of simultaneous multi-band (ugi and vrz) images was collected. In our stacked frames, no new candidate was detected within the EP/FXT localization (Li et al., GCN 43730) and the upper limits (3 sigma) are listed below. These results are consistent with previously reported non-detection by Cotter et al. (GCN 43728), Wu et al. (GCN 43731), Maksut et al. (GCN 43732), Pankov et al. (GCN 43733), Li et al. (GCN 43734), Aryan et al. (GCN 43735), Fortin et al. (GCN 43737), Lipunov et al. (GCN 43738) and Eyles-Ferris et al. (GCN 43739). --------------------------------------------------- Start_Time(UT) | Band | Exp(s) | LimMag (AB) --------------------------------------------------- 2026-02-13T20:11:30 | u | 45.0*8 | >22.68 2026-02-13T20:05:57 | v | 45.0*5 | >22.62 2026-02-13T20:11:33 | g | 45.0*8 | >23.51 2026-02-13T20:05:59 | r | 45.0*5 | >23.41 2026-02-13T20:13:07 | i | 45.0*8 | >22.84 2026-02-13T20:05:59 | z | 45.0*5 | >21.85 --------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. The facility is operated by the South-Western Institute for Astronomy Research (SWIFAR), Yunnan University. It provides real-time, high-quality colors of stellar objects. The Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025 and presently, these are under the commissioning phase. All the data have been reduced by the Mephisto data processing pipeline. Here, we note that the current data processing pipeline is still at a preliminary stage, with flux calibration precision in each band at the level of about 5% or even higher. View this GCN Circular online at https://gcn.nasa.gov/circulars/43823. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41935] EP260223a: EP-FXT follow-up observation
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43822 SUBJECT: EP260223a: EP-FXT follow-up observation DATE: 26/02/25 04:06:11 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. C. Liu (THU), J. W. Hu and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: We performed one follow-up observation of the X-ray transient EP260223a (Liu et al., GCN 43817, and followed by Álvarez et al., GCN 43818) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2026-02-24 04:45:40 (UTC), about 17.42 hours after the WXT detection, with an exposure of ~5.2 ks. No source was detected within the WXT error circle. The 0.5-10 keV flux upper limit is about 6e-14 erg/s/cm^2 (90% C. L.). 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/43822. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41934] sb26021801: SVOM/VT optical upper limits
by GCN Circulars 25 Feb '26

25 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43821 SUBJECT: sb26021801: SVOM/VT optical upper limits DATE: 26/02/25 03:59:02 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, Y. Xu, J. Wang, 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), W. J. TAN (IHEP) report on behalf of the SVOM/VT team. SVOM/VT performed ToO osbervation on the long faint X-ray transient sb26021801 reported by SVOM/Eclairs (Tan et al., GCN 43778). The observation started at about 7.75 hours after trigger in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. No credible sources are detected in single or stacked images within error box of SVOM/Eclairs (Tan et al., GCN 43778) with the 3 sigma limit magnitudes of VT_B ~ 23.8 mag and VT_R ~ 23.5 mag at 9.42 hours post trigger. Our non-detection is consistent with the reports from LCO (Wu et al., GCN 43792), COLIBRÍ (Fortin et al., GCN 43783), LAST (Konno et al., GCN 43784) and C-GFT (Wu et al, GCN 43819). Our photometry was in AB magnitude and 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/43821. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41933] GRB 260223A: COLIBRÍ optical afterglow decay confirmation
by GCN Circulars 24 Feb '26

24 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43820 SUBJECT: GRB 260223A: COLIBRÍ optical afterglow decay confirmation DATE: 26/02/24 09:24:20 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Fredd Sánchez Álvarez (UNAM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Nikos Mandarakas (LAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Benjamin Schneider (LAM) report: We continued to observe the field of the Fermi GRB 260223A (Fermi GBM team et al., GCN Circ. 43808) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed in two epochs between 2026-02-24 02:23:16 and 07:15:39 UTC (between 22.20 and 27.07 hours after the trigger) obtaining images in the grizy filters on the first and rz on the second. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR2, is in the AB system, and is not corrected for Galactic extinction. The optical counterpart reported by Becerra et al. (GCN Circ. 43811) and confirmed by our earlier observations (de Ugarte Postigo et al. GCN Circ 43812) has decayed after the early rebrightnening (de Ugarte Postigo et al. GCN Circ 43814). On our latest stack, we detect the afterglow of GRB 260223A at r = 20.93 +/- 0.07 mag. Between our last observation obtained yesterday and today’s observations, we measure a decay slope of alpha ~ -1.1 (where F_nu ~ t ^ alpha). This is consistent with the observations obtained by SVOM/VT a few hours before (Li et al. GCN Circ. 43816) and serves to confirm that this object is indeed the afterglow of GRB 260223A. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. 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/43820. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41932] sb26021801: SVOM/C-GFT upper limit
by GCN Circulars 24 Feb '26

24 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43819 SUBJECT: sb26021801: SVOM/C-GFT upper limit DATE: 26/02/24 08:27:40 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), Z. Kang (CHO), L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC), Wenjin TAN (IHEP) report on behalf of the SVOM/C-GFT team: We observed the field of sb26021801 detected by SVOM/ECLAIRs (Tan et al., GCN 43778) with LATIOS on SVOM/C-GFT. Observations started at 2026-02-18T16:23:38 UTC, ~11.14 hr after the trigger. We obtained g, r, and i-band follow-up imaging. After preliminary analysis, no credible candidate was detected within the error box provided by SVOM/ECLAIRs (Tan et al., GCN 43778) in our images. The 5-sigma upper limits are: | Mid_t - T0 (hr)| Exposure Time (s) | Band | Upper Limit (AB) | |----------------|-------------------|------|------------------| | 11.67 | 20×90 | i | 20.7 | | 11.95 | 20×90 | g | 20.7 | | 12.23 | 20×90 | r | 20.9 | The photometry was calibrated against nearby Pan-STARRS1 stars and no correction for Galactic dust extinction was applied. This result is consistent with Fortin et al.(GCN 43783), Konno et al.(GCN 43784), and Wu et al. (GCN 43792). We thank the observation assistants Yin-Huai Hao and Chun-Lei Guo at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/43819. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41931] EP260223a: COLIBRÍ optical upper limits
by GCN Circulars 24 Feb '26

24 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43818 SUBJECT: EP260223a: COLIBRÍ optical upper limits DATE: 26/02/24 06:15:59 GMT FROM: freddalvarez(a)astro.unam.mx Fredd Sánchez Álvarez (UNAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Camila Angulo (UNAM), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Nikos Mandarakas (LAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Benjamin Schneider (LAM) report: We observed the field of the EP260223a (Liu et al., GCN Circ. 43817) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-24 04:07 to 05:22 UTC (from 16.79 to 18.03 hours after the trigger and 17 minutes after the GCN Circular) and obtained 57 minutes of simultaneous exposure in the r and z filters. The data were reduced, coadded, calibrated, and analysed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the Pan-STARRS-DR2 catalog, is in the AB system, and is not corrected for Galactic extinction. We used STDWeb (Karpov 2025) to perform image subtraction against Legacy Survey DR10 templates (Dey et al. 2019). We do not detect any new source in the WXT uncertainty region (Liu et al., GCN Circ. 43817) down to the following 5-sigma limits: r > 23.7 z > 22.9 We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. 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/43818. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41930] EP260223a: Einstein Probe detection of an X-ray transient
by GCN Circulars 24 Feb '26

24 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43817 SUBJECT: EP260223a: Einstein Probe detection of an X-ray transient DATE: 26/02/24 03:53:43 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. C. Liu (THU), J. W. Hu and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260223a. The transient did not trigger the WXT onboard unit due to the limited number of counts. The WXT position of the source is R.A. = 92.774 deg, DEC = 56.577 deg (J2000) with an uncertainty of 2.7 arcmin in radius (90% C.L. statistical and systematic). The preliminary analysis of the WXT data shows that the event started at T0=2026-02-23T11:20:27 (UTC), and lasted for approximately 130 seconds. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.7×10^21 cm^-2 and a photon index of 2.6 (+1.1/-0.9). The derived average unabsorbed 0.5-4 keV flux is 4.1 (+1.7/-1.3) x 10^-10 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Further FXT follow-up observations have been arranged. 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/43817. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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