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[vsnet-grb-info 41998] EP260227a: FTW optical and NIR observations
by GCN Circulars 28 Feb '26

28 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43881 SUBJECT: EP260227a: FTW optical and NIR observations DATE: 26/02/28 20:17:24 GMT FROM: Julius Gassert at Ludwig-Maximilians-Universität München <julius.gassert(a)campus.lmu.de> Julius Gassert (LMU/CMU), Malte Busmann (LMU), Christoph Ries (LMU), Xander J. Hall (CMU), Brendan O’Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report: We observed the optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris & Tanvir, GCN 43875; Malesani et al., GCN 43876; Eyles-Ferris et al., GCN 43877; Strausbaugh et al, GCN 43879, Bochenek et al. GCN 43880) of EP 20260227a (Wang et al., GCN 43869) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J bands for 19x 180s, starting at 2026-02-28T04:21:12 (0.34 days after the trigger). We detect the counterpart in all bands and measure an r-band magnitude of r = 21.69 +/- 0.10 AB mag The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43881. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41997] EP260227a: Liverpool Telescope optical observations
by GCN Circulars 28 Feb '26

28 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43880 SUBJECT: EP260227a: Liverpool Telescope optical observations DATE: 26/02/28 20:05:03 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU) report: We observed the field of EP260227a (Wang et al., GCN 43869) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x120s exposures in SDSS r and i filters and 3x100s + 2x120s in SDSS z, starting at 2026-02-28 02:54:00 UT, approximately 6.69 hours after trigger. We report detections in stacked images in all filters at the position first reported by Eyles-Ferris et al. (GCN 43867) and Li et al. (GCN 43868). MJD (mid) T_mid-T_0 Filter Mag. (AB) 61099.12483 6.79 h r 21.31 ± 0.19 61099.13319 6.99 h i 21.10 ± 0.12 61099.14035 7.16 h z 20.71 ± 0.11 Our results are consistent with the slower fading of the optical counterpart as reported by and Eyles-Ferris et al. (GCN 43875), comparing to the observations of Fu et al. (GCN 43873), Mandarakas et al. (GCN 43874) and Eyles-Ferris et al. (GCN 43875). The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43880. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41996] EP260227a: LCOGT Optical Observations
by GCN Circulars 28 Feb '26

28 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43879 SUBJECT: EP260227a: LCOGT Optical Observations DATE: 26/02/28 17:33:05 GMT FROM: Robert Strausbaugh at Eastern Illinois University <rstrausbaugh(a)eiu.edu> R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the EP260227a field (Wang et al., GCN 43869) with the LCOGT 1-meter Sinistro instrument at the Cerro Tololo Interamerican Observatory, Chile site, on February 28, from 05:39 to 06:00 UT (corresponding to 9.28 to 9.63 hours after the trigger time) with the SDSS r and i filters. We performed a series of 3x200s exposures in i-band and r-band. We marginally detect an uncatalogued sources in both bands, consistent with other optical detections (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris et al., GCN 43875; Malesani et al., GCN 43876). The following magnitudes are calculated using the PanSTARRS catalog as reference: r = 20.78 +/- 0.58 i = 21.47 +/- 0.52 These magnitudes are not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43879. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41995] GRB 260226A: Asiago r-band upper limit
by GCN Circulars 28 Feb '26

28 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43878 SUBJECT: GRB 260226A: Asiago r-band upper limit DATE: 26/02/28 12:43:06 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> A. Reguitti (INAF/OAPd), P. D'Avanzo (INAF/OAB), D. B. Malesani (DAWN/NBI and Radboud), L. Tomasella (INAF/OAPd) report on behalf of the CIBO collaboration: We observed the field of the bright GRB 260226A (Depalo et al., GCN 43850; Bissaldi et al., GCN 43851; Harsha et al., GCN 43846; Waratkar & Grefenstette, GCN 43854; Woolf et al.. GCN 43855; Kobayashi et al., GCN 43860; Svinkin et al., GCN 43864; Yu et al., GCN 43865) using the 67/92 Schmidt Telescope located at the Asiago observatory (Italy). Observations consisted of five r-band exposures of 240 s each, with a mid time Feb 26.766 UT (7.77 hr after the Fermi/GBM trigger). Image subtraction was carried out using the DESI Legacy survey (Dey et al. 2019, doi:10.3847/1538-3881/ab089d) as template. No new source is detected within the revised Fermi/LAT error circle (Depalo et al., GCN 43850) down to a limiting magnitude r > 20.4 AB (calibrated against nearby objects from the Pan-STARRS catalog). Our non detection is consistent with other reports from the literature (Konno et al., GCN 43852; Saikia et al., GCN 43853; Strausbaugh & Cucchiara, GCN 43858; Angulo et al., GCN 43859). View this GCN Circular online at https://gcn.nasa.gov/circulars/43878. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41994] EP260227a: Thai National Telescope observations
by GCN Circulars 28 Feb '26

28 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43877 SUBJECT: EP260227a: Thai National Telescope observations DATE: 26/02/28 12:41:42 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester), S. Littlefair (Sheffield), V. Dhillon (Sheffield), I. Pelisoli (Warwick), J. van Dalen (Radboud), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), D. Mata-Sanchez (IAC and ULL), report on behalf of a larger collaboration: We observed the position of the fast X-ray transient EP260227a (Wang et al., GCN 43869) with the 2.4m Thai National Telescope equipped with the ULTRASPEC instrument. Observations were conducted in the KG5 wideband filter which approximately covers the wavebands of the SDSS ugr filters (https://tinyurl.com/kg5filter; Hardy et al. 2017). The total exposure time was 62 minutes with a mid time of 2026-02-27 22:28:00 UT (2.52 hr after trigger). We clearly detect the optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris & Tanvir, GCN 43875; Malesani et al., GCN 43876) at a magnitude m_KG5 = 23.57 +/- 0.07 (AB) calibrated to Pan-STARRS and not corrected for Galactic extinction. The faint magnitude compared to other photometry is likely attributable to the peak response of the adopted filter in the blue and the red colour of the source, broadly consistent with the DLA suggested by Malesani et al (GCN 43876). View this GCN Circular online at https://gcn.nasa.gov/circulars/43877. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41993] EP260227a: likely GTC/OSIRIS+ redshift z = 2.714
by GCN Circulars 28 Feb '26

28 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43876 SUBJECT: EP260227a: likely GTC/OSIRIS+ redshift z = 2.714 DATE: 26/02/28 12:12:32 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD), R. A. J. Eyles-Ferris (Leicester), J. van Dalen (Radboud), D. Mata-Sanchez (IAC and ULL), A. de Ugarte Postigo (LAM), N. Castro Rodríguez (GTC), A. L. Cabrera Lavers (GTC) report on behalf of a larger collaboration: We observed the optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874; Eyles-Ferris & Tanvir, GCN 43875) of EP260227a (Wang et al., GCN 43869) using the Gran Telescopio Canarias (GTC) equipped with the OSIRIS+ spectrograph. Our observations consisted of 4 exposures of 900 s each, using grism R1000B which covers the wavelength range 3670 - 7700 Å. The observation start time was 2026-02-28 at 03:16 UT (~7.1 hr after the trigger). In the acquisition magnitude, we measure r = 21.55 +/- 0.07 AB at mid time 6.89 hr after trigger (consistent with the NOT measurement; Fu et al., GCN 43873). This value is calibrated against nearby objects from the Pan-STARRS catalog and not corrected for Galactic extinction. A faint trace is detected down to ~4000 Å, with an apparent spectral break around 4500 Å which is interpreted as due to H I and the onset of the Lyman forest. A few weak, narrow features, due to Si II 1259, Si II 1304, C II 1334, C IV 1548/1550, allow us to measure a redshift z = 2.714. View this GCN Circular online at https://gcn.nasa.gov/circulars/43876. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41992] EP260227a: Liverpool Telescope observations
by GCN Circulars 28 Feb '26

28 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43875 SUBJECT: EP260227a: Liverpool Telescope observations DATE: 26/02/28 10:29:52 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris and N. R. Tanvir (Leicester) report on behalf of a larger collaboration: We observed the field of EP260227a (Wang et al., GCN 43869) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x150s exposures in each of the SDSS g’ r’ i’ z’ filters starting at 2026-02-28 04:25:03 UT, approximately 8.21 hours after the X-ray detection. We detect the optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868; Fu et al., GCN 43873; Mandarakas et al., GCN 43874) in the r’, i’ and z’ bands. We measure the following magnitudes calibrated to Pan-STARRS and not corrected for Galactic extinction. | t_mid (hours) | Filter | AB magnitude | | ------------- | ------ | ---------------- | | 8.35 | g’ | >22.28 (3-sigma) | | 8.63 | i’ | 21.12 +/- 0.08 | | 8.92 | r’ | 21.61 +/- 0.22 | | 9.21 | z’ | 20.74 +/- 0.11 | Compared to the photometry tabulated by Fu et al. (GCN 43873) and Mandarakas et al. (GCN 43874), our observations suggest the source has not faded significantly between these three epochs. View this GCN Circular online at https://gcn.nasa.gov/circulars/43875. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41991] EP260227a: COLIBRÍ optical observations
by GCN Circulars 28 Feb '26

28 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43874 SUBJECT: EP260227a: COLIBRÍ optical observations DATE: 26/02/28 09:50:46 GMT FROM: nikos.mandarakas(a)lam.fr Nikos Mandarakas (LAM), Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), 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), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260227a (Wang et al., GCN Circ. 43869) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-28 07:51:00 to 08:49:14 UTC (from 11.64 to 12.61 hours after the trigger) and obtained 44 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 PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart reported by Eyles-Ferris et al. (GCN 43867), Li et al. (GCN 43868), Fu et al. (GCN 43873), at a preliminary magnitude of: r = 21.4644 +/- 0.0680 z = 20.8905 +/- 0.0745 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/43874. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41990] EP260227a: NOT optical observations
by GCN Circulars 28 Feb '26

28 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43873 SUBJECT: EP260227a: NOT optical observations DATE: 26/02/28 06:51:11 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> S.Y. Fu (HUST), L.B. He, Z.P. Zhu, J. An, X. Liu, S.Q. Jiang, D. Xu (NAOC), J. P. U. Fynbo (DAWN/NBI), A. L. Bouquin (NOT) report on behalf of a large collaboration: We observed the field of EP260227a (Wang et al., GCN 43869) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. The observations started at 02:20:46 UT, 2026-02-28, i.e. 6.14 hrs after the trigger, and we obtained 3x120 s frames each in Sloan g', r' and i' bands. The previously reported optical counterpart (Eyles-Ferris et al., GCN 43867; Li et al., GCN 43868) was detected in our stacked frames with the following AB magnitudes: | t-mid (hrs) | filter | mag | | ----------- |--------| ------------ | | 6.21 | g' | 21.40 ± 0.20 | | 6.33 | r' | 21.50 ± 0.20 | | 6.46 | i | 21.37 ± 0.12 | calibrated using nearby Pan-STARRS1 dr2 catalog, and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43873. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41989] GRB 260225A: SVOM/VT optical continued observations and upper limit
by GCN Circulars 28 Feb '26

28 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43872 SUBJECT: GRB 260225A: SVOM/VT optical continued observations and upper limit DATE: 26/02/28 05:02:37 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, Z. H. Yao, H. L. Li, Y. L. Qiu, C. Wu, L. P. Xin, 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), L. Zhang (IHEP) report on behalf of the SVOM/VT team. SVOM/VT continued observations of GRB 260225A (sb26022501) triggered by SVOM/ECLAIRs (Ma et al., GCN 43829). With X-band data available, the optical counterpart (Ducoin et al., GCN 43837; Li et al., GCN 43838; Schneider et al., GCN 43861) within EP/FXT error box (Yang et al., GCN 43839) was detected in VT_B band. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) -------------|-------------------|------|------------ 35.08 | 37*70 | VT_B | 23.6+/-0.3 35.04 | 27*70 | VT_R | >23.3 Our photometry 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/43872. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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