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[vsnet-grb-info 41624] EP260126a: Liverpool Telescope optical upper limits
by GCN Circulars 27 Jan '26

27 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43524 SUBJECT: EP260126a: Liverpool Telescope optical upper limits DATE: 26/01/27 09:58:21 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris and N. Habeeb (Leicester) report on behalf of a larger collaboration: We observed the field of EP260126a (Fu et al., GCN 43520) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x150s exposures in each of the SDSS i’ and SDSS g’ filters starting at 2026-01-26 23:48:56 UT, approximately 19.4 hours after the X-ray detection. We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. Within the EP/FXT localisation, and across the field, we detect no new sources in either the subtractions or stacked images consistent with the results of Zhu et al. (GCN 43521), Globus et al. (GCN 43522) and Eyles-Ferris et al. (GCN 43523). We derive 3-sigma upper limits of i’ > 23.3 and g’ > 23.0 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43524. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41623] EP260126a: Further NOT optical upper limits
by GCN Circulars 27 Jan '26

27 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43523 SUBJECT: EP260126a: Further NOT optical upper limits DATE: 26/01/27 09:56:26 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris (Leicester), D. B. Malesani (DAWN/NBI and Radboud), J. A. Quirola-Vasquez (Radboud), J. N. D. van Dalen (Radboud), G. Corcoran (UCD), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD) and A. J. Levan (Radboud) report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP260126a (Fu et al., GCN 43520) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were obtained in the SDSS r and z bands, consisting of 3x300 s and 5x200 s exposures, respectively, starting on 2026-01-26 at 23:08:13 UTC (~18.7 hr after the WXT trigger). No new source is detected within or at the border of the EP/FXT uncertainty region (Fu et al., GCN 43520) compared to Legacy DR10. From the stacked images, we obtain the following 3-sigma upper limits:  r > 24.3 z > 23.2 These upper limits are in AB magnitudes, calibrated using nearby stars from the Pan-STARRS catalog, and are not corrected for Galactic extinction. Our non-detection is consistent with the results of Zhu et al. (GCN 43521) and Globus et al. (GCN 43522). View this GCN Circular online at https://gcn.nasa.gov/circulars/43523. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41622] EP260126a: COLIBRÍ optical upper limits
by GCN Circulars 27 Jan '26

27 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43522 SUBJECT: EP260126a: COLIBRÍ optical upper limits DATE: 26/01/27 04:44:01 GMT FROM: globus(a)astro.unam.mx Noémie Globus (UNAM), Jean-Luc Atteia (IRAP), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), 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 EP 260126a (Fu et al., GCN Circ. 43520) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-27 02:21 to 04:06 UTC (from 21.9 to 23.7 hours after the trigger) and obtained 79 minutes of exposure in the r and z filters. The data were reduced, coadded, calibrated and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and was not corrected for Galactic extinction. In the stacked image, comparing to LS (Dey et al. 2019), we do not detect any new source at the FXT uncertainty region (Fu et al., GCN Circ. 43520) down to the following preliminary 5-sigma limits: r > 24.0, z > 23.1. 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/43522. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41621] EP260126a: NOT optical observations
by GCN Circulars 27 Jan '26

27 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43521 SUBJECT: EP260126a: NOT optical observations DATE: 26/01/27 04:35:07 GMT FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn> Z.P. Zhu, J. An, X. Liu, S.Q. Jiang, L.B. He, D. Xu (NAOC), S.Y. Fu (HUST), J.P.U. Fynbo (DAWN/NBI), S. Bijavara (NOT) report on behalf of a large collaboration: We observed the field of EP260126a (Fu et al., GCN 43520) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started at 22:13:05 UT on 2026-01-26, i.e., 17.8 hr after the EP trigger, and we obtained 5 x 180 s frames in the Sloan r-band and 5 x 200 s frames in the Sloan z- band. No new optical source is detected within the EP/FXT error circle (Fu et al., GCN 43520), down to 5-sigma upper limits of r ~ 23.6 and z ~ 22.5, calibrated with nearby Pan-STARRS stars and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43521. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41620] EP260126a: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 27 Jan '26

27 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43520 SUBJECT: EP260126a: Einstein Probe detection of a fast X-ray transient DATE: 26/01/27 02:36:26 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S.Y. Fu (HUST), Z.M. Wang (BNU), J.H. Wu (GZHU), H.Y. Liu, H.W. Pan (NAOC, 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 EP260126a. The event started at 2026-01-26T04:25:01 (UTC) and lasted for about 1400 seconds. The WXT position of the source is R.A. = 103.737 deg, DEC = 37.699 deg (J2000) with an uncertainty of 2.1 arcmin in radius (90% C.L. statistical and systematic). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 1.16(-/+0.17) and with a fixed galactic hydrogen column density of 1.21 x 10^21 cm^-2. The derived average unabsorbed 0.5-4 keV flux is 2.77 (-0.26/+0.29) x 10^-10 erg/s/cm^2. The peak flux in the 0.5-4 keV band reaches 1.49(-0.14/+0.16) x 10^-9 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed at 2026-01-26T23:08:05 (UTC), about 19 hours after the trigger. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 103.7537 deg, DEC = 37.7067 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. 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/43520. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41619] Fermi-LAT Gamma-ray Observations of IceCube-260125A
by GCN Circulars 26 Jan '26

26 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43519 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-260125A DATE: 26/01/26 21:49:24 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and S. Garrappa (Weizmann Institute of Science) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC260125A neutrino event (GCN 43512) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2026-01-25 at 10:09:39.88 UTC (T0) with J2000 position RA = 243.72 (+0.52, -0.56) deg, Decl. = 6.69 (+0.62, -0.61) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC260125A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC260125A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC260125A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1.4e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <5.3e-09 (<8.8e-08) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this analysis, the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/43519. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41618] GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
by GCN Circulars 26 Jan '26

26 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43518 SUBJECT: GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf DATE: 26/01/26 14:19:11 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), B. P. Gompertz (Birmingham), G. Corcoran (UCD), L. Izzo (INAF/OAC and DARK/NBI), A. Martin-Carrillo (UCD), S. Bijavara Seshashayana (NOT), report on behalf of a larger collaboration: We observed the optical candidate GOTO26acv / AT 2026bjf (Gompertz et al., GCN 43514) of the Fermi GRB 260125A (Fermi GBM team, GCN 43510) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out using the SDSS griz filters, and started on 2026 Jan 25.995 UT (16.27 hr after the Fermi/GBM trigger). Visual inspection reveals no obvious point source at the coordinates of GOTO26acv / AT 2026bjf, on top of the galaxy PGC 139241 (LEDA 139241), in any of the observed bands, though we note that the bright and complex morphology of the galaxy makes a clear identification tough. Image subtraction against the Legacy survey archival images yields an upper limit r > 22.75 (AB) at a mean time of 16.47 hr after trigger (5x150 s exposure time). This value is calibrated against the Pan-STARRS catalog and is not corrected for Galactic extinction. Our limit is notionally deeper than the extrapolation of the power-law decay reported by Gompertz et al. (GCN 43514), even after accounting for a GOTO/ALFOSC color term and the quoted decay index uncertainty. View this GCN Circular online at https://gcn.nasa.gov/circulars/43518. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41617] Konus-Wind detection of GRB 260120B
by GCN Circulars 26 Jan '26

26 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43517 SUBJECT: Konus-Wind detection of GRB 260120B DATE: 26/01/26 13:06:35 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260120B (Fermi GBM detection: Fermi GBM team, GCN 43477; Godwin & Meegan, GCN 43489; Swift-BAT detection: Ferro et al., GCN 43479; Palmer et al., GCN 43493; AstroSat CZTI detection: Goyal et al., GCN 43504) triggered Konus-Wind at T0=64826.649 s UT (18:00:26.649). The burst light curve shows a single pulse, which starts at ~T0-3.2 s and has a total duration of ~5.9 s. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260120_T64826/ As observed by Konus-Wind, the burst had a fluence of 3.41(-0.52,+0.58)x10^-6 erg/cm2, and a 64-ms peak flux, measured from T0-0.064 s, of 1.97(-0.58,+0.60)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). Since a major part of the burst emission was detected before the trigger, the spectral analysis was performed using the KW 3-channel light curve data. Modelling the KW 3-channel time-integrated spectrum (measured from T0-3.173 s to T0+2.720 s) by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), yields alpha = -0.56(-0.23,+0.30) and Ep = 246(-53,+67) keV. All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/43517. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41616] GRB 251222A: SVOM/ECLAIRs refined analysis
by GCN Circulars 26 Jan '26

26 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43516 SUBJECT: GRB 251222A: SVOM/ECLAIRs refined analysis DATE: 26/01/26 11:12:41 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Hui Yang, Sebastien Guillot, Olivier Godet, Marius Brunet, Guangxuan Lan (IRAP) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 251222A (SVOM burst-id sb25122206, GCN 43188). The burst that triggered ECLAIRs consists of multiple peaks, and is detected for more than 200 s in the 4-120 keV energy band. The time-averaged spectrum before the slew from T0-14 s to T0+37 s (T0 = 2025-12-22T17:05:46) in the energy range 5-120 keV is best fitted by a cutoff power-law model with a photon index of 1.3+/-0.1, an Ecut of 54(+29/-15) keV, giving a corresponding 4-120 keV flux of (4.9+/-0.3)e-8 erg/cm^2/s. The spectrum from T0+162 s to T0+192 s after the slew in the energy range 5-120 keV is well fitted by a power-law model with a photon index of 2.4 +/-0.2 giving a corresponding 4-120 keV flux of (9+/-1)e-9 erg/cm^2/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: Hui Yang (IRAP) (hyang(a)irap.omp.eu) View this GCN Circular online at https://gcn.nasa.gov/circulars/43516. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41615] GRB 260125A: Swift ToO observations
by GCN Circulars 26 Jan '26

26 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43515 SUBJECT: GRB 260125A: Swift ToO observations DATE: 26/01/26 02:44:30 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the Fermi/GBM-detected event GRB 260125A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021899 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Fermi/GBM event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43515. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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