December 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 41304] EP251221a: Liverpool Telescope upper limits
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43217 SUBJECT: EP251221a: Liverpool Telescope upper limits DATE: 25/12/23 15:21:03 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We observed the field of the fast X-ray transient EP251221a (Dai et al., GCN 43178) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 3x120s exposures in SDSS r and i filters starting at 2025-12-22 23:12:54 UT, approximately 25.6 hours after the trigger. We perform image subtraction of the stacked images against Pan-STARRS using PSF matching with the help of PSFEx. We do not detect any new objects within the EP/WXT error region of the transient (Dai et al., GCN 43178). We note the i-band Pan-STARRS reference image is affected by a small number of artefacts, covering in total less than 1% of the error region. The 3-sigma limiting magnitudes on the stacked images are r > 22.6 and i > 22.5. View this GCN Circular online at https://gcn.nasa.gov/circulars/43217. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41303] EP251222a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43216 SUBJECT: EP251222a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/12/23 14:23:50 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C.-L. Guo (NAO, CAS), R. Shi, Q.-J. Huang (PMO,CAS), X. Mao, and Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP251222a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Huang et al., GCN 43200), and followed by several telescopes (Li et al., GCN 43205, Kumar et al., GCN 43210, Malesani et al., GCN 43211). The refined analysis of the WXT data shows that this observation of the event started at T0=2025-12-22T14:59:14 (UTC). During the observation period of WXT (1100s), there was no significant short-timescale variability in the light curve. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 7.23 x 10^20 cm^-2 and a photon index of 1.58 (-0.4/+0.4). The derived average unabsorbed 0.5-4 keV flux is 6.35 (-4.9/+8.2) x 10^(-11) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2025-12-22T15:21:49 (UTC), about 22 minutes after T0. The exposure time of this observation is 4081s. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 62.5014, DEC = -1.4795 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent positionally with the WXT transient. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 7.23 x 10^20 cm^-2 and a photon index of 2.34 (-0.05/+0.05). The derived average unabsorbed 0.5-10 keV flux is 7.54 (-5.2/+16.7) x 10^(-12) 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/43216. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41302] EP251222b/GRB 251222A: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43215 SUBJECT: EP251222b/GRB 251222A: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/12/23 14:13:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R.Shi, Q. J. Huang (PMO, CAS), C. L. Guo, X. Mao, Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP251222b triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Guo et al., GCN 43201), which is associated with GRB 251222A (Yang et al., GCN 43188), and followed by several telescopes (Palmerio et al., GCN 43189, Evans et al., GCN 43191, An et al., GCN 43194, Li et al., GCN 43203, Saccardi et al., GCN 43204, Gupta et al., GCN 43207, Saccardi et al., GCN 43208, Kumar et al., GCN 43209, Pérez-Fournon et al., GCN 43212, Beardmore et al., GCN 43213). The refined analysis of the WXT data shows that the event started at T0=2025-12-22T17:04:52 (UTC) and lasted for ~350 s with the peak flux of 1.4e-8 erg/s/cm^2. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 9.81e20 cm^-2 and a photon index of 1.1 (-/+0.15). The derived average unabsorbed 0.5-4 keV flux is 2.8 (-0.2/+0.3) x 10^(-9) erg/s/cm^2. The observation by the Follow-up X-ray Telescope (FXT) was performed at 2025-12-23T05:11:10 (UTC), about 12.11 hours after T0. The exposure time of this observation is 1884 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 77.1954, -7.2139 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 9.81e20 cm^-2 and a photon index of 1.86 (-0.25/+0.26). The derived average unabsorbed 0.5-10 keV flux is 1.8 (-0.3/+0.4) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Further observations are encouraged. 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/43215. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41301] Konus-Wind detection of GRB 251222A / EP251222b
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43214 SUBJECT: Konus-Wind detection of GRB 251222A / EP251222b DATE: 25/12/23 12:47:21 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 251222A (Fermi-GBM detection: The Fermi GBM team, GCN 43186; SVOM detection: Yang et al., GCN 43188, Wang et al., GCN 43202), associated with the Einstein Probe X-ray transient EP251222b (Guo et al., GCN 43201), triggered Konus-Wind (KW) at T0=61605.670 s UT (17:06:45.670). The burst shows multiple emission pulses in the interval from T0-50 s to T0+33 s and has a total duration of ~83 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251222_T61605/ As observed by Konus-Wind, the burst had the fluence of (9.92 ± 0.94)x10^-6 erg/cm^2 and the 64-ms peak energy flux, measured from T0 + 4.864 s, of (2.51 ± 0.32)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the brightest part of the burst (measured from T0 to T0+33.024 s) is best fit in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.45 (-0.21, + 0.24) and Ep = 102(-16,+17) keV, chi^2 = 94/98 dof. The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 15 MeV range by a CPL model with alpha = -1.23 (-0.20, + 0.23)and Ep = 131(-14,+18) keV, chi^2 = 69/83 dof. Assuming the redshift z=3.121 (Saccardi et al., GCN 43204) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the burst isotropic energy release E_iso to (2.15 ± 0.20)x10^53 erg, the isotropic peak luminosity L_iso to (2.24 ± 0.28)x10^53 erg/s, the rest-frame peak energy of the time-integrated spectrum Ep,i,z to (420 ± 68) keV, and the rest-frame peak energy at the peak of the emission Ep,p,z to (540 ± 66) keV. With the obtained estimates, GRB 251222A is consistent with 68% prediction bands of both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB251222_T61605/GRB251222A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/43214. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41300] Konus-Wind detection of GRB 251222A / EP251222b
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43214 SUBJECT: Konus-Wind detection of GRB 251222A / EP251222b DATE: 25/12/23 12:47:21 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 251222A (Fermi-GBM detection: The Fermi GBM team, GCN 43186; SVOM detection: Yang et al., GCN 43188, Wang et al., GCN 43202), associated with the Einstein Probe X-ray transient EP251222b (Guo et al., GCN 43201), triggered Konus-Wind (KW) at T0=61605.670 s UT (17:06:45.670). The burst shows multiple emission pulses in the interval from T0-50 s to T0+33 s and has a total duration of ~83 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251222_T61605/ As observed by Konus-Wind, the burst had the fluence of (9.92 ± 0.94)x10^-6 erg/cm^2 and the 64-ms peak energy flux, measured from T0 + 4.864 s, of (2.51 ± 0.32)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the brightest part of the burst (measured from T0 to T0+33.024 s) is best fit in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.45 (-0.21, + 0.24) and Ep = 102(-16,+17) keV, chi^2 = 94/98 dof. The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 15 MeV range by a CPL model with alpha = -1.23 (-0.20, + 0.23)and Ep = 131(-14,+18) keV, chi^2 = 69/83 dof. Assuming the redshift z=3.121 (Saccardi et al., GCN 43204) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the burst isotropic energy release E_iso to (2.15 ± 0.20)x10^53 erg, the isotropic peak luminosity L_iso to (2.24 ± 0.28)x10^53 erg/s, the rest-frame peak energy of the time-integrated spectrum Ep,i,z to (420 ± 68) keV, and the rest-frame peak energy at the peak of the emission Ep,p,z to (540 ± 66) keV. With the obtained estimates, GRB 251222A is consistent with 68% prediction bands of both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB251222_T61605/GRB251222A_rest_frame.pdf All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/43214. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41299] GRB 251222A: Swift-XRT afterglow detection
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43213 SUBJECT: GRB 251222A: Swift-XRT afterglow detection DATE: 25/12/23 11:12:39 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), J.P. Osborne (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected burst GRB 251222A. We searched for X-ray sources in 2.0 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 2.0 ks, obtained between T0+10.7 ks and T0+17.4 ks. An uncatalogued X-ray source is detected within the estimated 3-sigma SVOM/ECLAIRs error region (49 arcsec) and is above the RASS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. Using 1130 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 77.19502, -7.21354 which is equivalent to: RA (J2000): 05h 08m 46.81s Dec(J2000): -07d 12' 48.7" with an uncertainty of 2.5 arcsec (radius, 90% confidence). This position is 36 arcsec from the SVOM/ECLAIRs position. The light curve can be modelled with a power-law decay with a decay index of alpha=1.9 (+0.8, -0.7). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.92 (+0.31, -0.20). The best-fitting absorption column is 1.05 (+0.91, -0.12) x 10^21 cm^-2, consistent with the Galactic value of 9.3 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.05 (+0.91, -0.12) x 10^21 cm^-2 Galactic foreground: 9.3 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.92 (+0.31, -0.20) If the light curve continues to decay with a power-law decay index of 1.9, the count rate at T+24 hours will be 4.7 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x 10^-13 (2.0 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis of the likely afterglow are at https://www.swift.ac.uk/ToO_GRBs/00021895/Source1.php. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021895. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43213. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41298] GRB 251222A / EP251222b: LCO detection of the optical counterpart
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43212 SUBJECT: GRB 251222A / EP251222b: LCO detection of the optical counterpart DATE: 25/12/23 10:34:06 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon (IAC and ULL), F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia, E. Lekaroz-Urriza, M. Quintana-Ansaldo (all ULL), and A. López-Oramas (IAC and ULL) Following the detection of the long GRB 251222A / EP251222b detected by Fermi/GBM (The Fermi GBM team, GCN #43186; and Preis and Greiner, GCN #43190), SVOM ECLAIRs, GRM, and MXT (Yang et al., GCN #43188), EP/WXT (Guo et al., GCN #43201), SVOM/GRM (Wang et al., GCN 43202) and Swift-XRT (Evans, GCN #43191, source 1 of https://www.swift.ac.uk/ToO_GRBs/00021895/) we observed the field with one of the three Las Cumbres Observatory (LCO) 1-m telescopes equipped with Sinistro cameras located at the LCO node at Sutherland Observatory, South Africa. The observation, a single exposure of 300 sec in the SDSS r' filter, started on 2025-12-22 at 18:48:07 UT, about 1.7 hours after the SVOM and Fermi triggers. The optical counterpart detected by SVOM/VT (Palmerio et al., GCN #43189; and Li et al., GCN #43203) is clearly detected in our image with a magnitude of r' = 18.55 +/- 0.03 (AB), calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction. Our result is consistent with other optical and near-IR detections (Palmerio et al., GCN #43189; An et al., GCN #43194; Calapai et al., GCN #43195; Durbak et al., GCN #43197; Li et al., GCN #43203; Saccardi et al., GCN #43204; Gupta et al., GCN #43207; Saccardi et al., GCN #43208; and Kumar et al., GCN #43209). We notice a minimum in the light curve at the time of our LCO r'-band and the Calapai Observatory (Calapai et al., GCN #43195) observations. Saccardi et al. (GCN #43204) have reported a spectroscopic redshift of z = 3.171. This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2025B-008, SGLF and Superluminous Supernovae surveys). This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5). View this GCN Circular online at https://gcn.nasa.gov/circulars/43212. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41297] EP251222a: NTT/ULTRACAM optical observations
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43211 SUBJECT: EP251222a: NTT/ULTRACAM optical observations DATE: 25/12/23 08:11:19 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), M. Stepney (CATA), D. Sahman (Sheffield), L. Cotter (UCD), G. Corcoran (UCD), P. G. Jonker (Radboud) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP251222a (Huang et al., GCN 43200) using the ULTRACAM instrument on the ESO NTT telescope in La Silla (Chile). Observations consisted of 120 exposures by 15 s each, taken at a mean epoch 2025 December 23, 03:07:14 UT (11.81 hr after the EP trigger). The optical counterpart identified by Li et al. (GCN 43205) is well detected in our coadded image, for which we measure a magnitude r = 21.56 +- 0.08 (AB), calibrated against nearby stars from the Pan-STARRS catalog and not corrected for Galactic extinction. This confirms the rebrightening reported by Li et al. (GCN 43205). The consistency with the EP/FXT X-ray position (Huang et al., GCN 43200) makes this source the likely counterpart of EP251222a. Further follow-up is encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/43211. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41296] EP251222a: GOTO optical upper limit
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43210 SUBJECT: EP251222a: GOTO optical upper limit DATE: 25/12/23 08:03:47 GMT FROM: Amit Kumar at The Open University, UK <amitkundu515(a)gmail.com> A. Kumar, G. Ramsay, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, S. Belkin, D. O'Neill, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022; Dyer et al. 2024) in response to EP251222a (Huang et al., GCN 43200). Two sets of targeted observations were performed by GOTO-North at 2025-12-22 22:19:38 UT and 2025-12-23 01:14:12 UT, corresponding to 7.0 and 9.9 hours post-trigger, respectively. Each observation consisted of 4x90 s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogues. We do not identify any new optical source within the EP/WXT localisation uncertainty region after the trigger time, down to a 5-sigma limiting magnitude for the two sets of observations of L >20.4 (AB) and L >20.5 (AB). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/43210. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41295] GRB 251222A / EP251222b: GOTO optical counterpart detection
by GCN Circulars 23 Dec '25

23 Dec '25

TITLE: GCN CIRCULAR NUMBER: 43209 SUBJECT: GRB 251222A / EP251222b: GOTO optical counterpart detection DATE: 25/12/23 07:19:23 GMT FROM: Amit Kumar at The Open University, UK <amitkundu515(a)gmail.com> A. Kumar, G. Ramsay, D. O’Neill, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) that serendipitously covered the field of GRB 251222A / EP251222b, detected by Fermi/GBM (The Fermi GBM team, GCN 43186), SVOM/ECLAIRs (Yang et al., GCN 43188), EP/WXT (Guo et al., GCN 43201) and SVOM/GRM (Wang et al., GCN 43202). Targeted observations were performed by GOTO-North at 2025-12-22 23:02:47 UT (5.95 hours post-trigger). The observation consisted of 4x45s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. The optical afterglow (Palmerio et al., GCN 43189; An et al., GCN 43194; Calapai et al., GCN 43195; Durbak et al., GCN 43197; Li et al., GCN 43203; Saccardi et al., GCN 43204; Gupta et al., GCN 43207; Saccardi et al., GCN 43208) detected with an L-band magnitude of 19.51 ± 0.11 (AB). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Observations are ongoing. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/43209. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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