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[vsnet-grb-info 41630] GRB 260127A: LCO optical afterglow discovery
by GCN Circulars 27 Jan '26

27 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43530 SUBJECT: GRB 260127A: LCO optical afterglow discovery DATE: 26/01/27 19:06:16 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud) report on behalf of the SVOM mission team: We observed the field of GRB 260127A (Fermi GBM team, GCN 43528; Klingler et al., GCN 43529) with the LCO 1-m telescope at Siding Spring Observatory equipped with the Sinistro instrument. Our observation started on 2026-01-27 at 18:12:42 (about 22 min after the trigger) and we obtained 3x200 s exposures in the SDSS r filter. An uncatalogued optical transient is detected within the XRT error box at the following coordinates (J2000): RA = 15:27:31.14 Dec = +06:45:45.49 with an uncertainty of 0.3". No object is visible at these coordinates in the much deeper archival images from the Legacy Survey, indicating that this object is most likely the optical afterglow of GRB 260127A. We measure the following magnitude, calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction: r = 20.45 +/- 0.20 AB (mid-time of 27.3 min after the trigger). Further observations are planned. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/43530. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41629] GRB 260127A: Swift detection of a burst
by GCN Circulars 27 Jan '26

27 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43529 SUBJECT: GRB 260127A: Swift detection of a burst DATE: 26/01/27 18:17:19 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> N. J. Klingler (GSFC/UMBC/CRESSTII), R. Gupta (NASA GSFC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), K. L. Page (U Leicester), T. M. Parsotan (GSFC) and B. Sbarufatti (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team: At 17:50:34 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 260127A (trigger=1444088). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 231.857, +6.758 which is RA(J2000) = 15h 27m 26s Dec(J2000) = +06d 45' 30" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed no structure initially, typical of an image trigger, with a more classic pulse structure starting at ~T0+20 sec. The emission has a duration of about 50 sec. The peak count rate was ~1460 counts/sec (15-350 keV), at ~33 sec after the trigger. The XRT began observing the field at 17:54:00.1 UT, 205.3 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source located at RA, Dec 231.87885, 6.76345 which is equivalent to: RA(J2000) = 15h 27m 30.92s Dec(J2000) = +06d 45' 48.4" with an uncertainty of 3.5 arcseconds (radius, 90% containment). This location is 80 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (4.07 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.2 (+2.30/-2.03) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 4.58e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 213 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.049. Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.edu) Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43529. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41628] GRB 260127A: Fermi GBM Final Real-time Localization
by GCN Circulars 27 Jan '26

27 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43528 SUBJECT: GRB 260127A: Fermi GBM Final Real-time Localization DATE: 26/01/27 18:01:38 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 17:51:07 UT on 27 Jan 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260127A (trigger 791229072.735026 / 260127744). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 226.9, Dec = -2.2 (J2000 degrees, equivalent to J2000 15h 07m, -2d 12'), with a statistical uncertainty of 5.1 degrees. The angle from the Fermi LAT boresight is 79.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260127744/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260127744/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260127744/… View this GCN Circular online at https://gcn.nasa.gov/circulars/43528. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41627] GRB 260125A: Swift-XRT observations
by GCN Circulars 27 Jan '26

27 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43527 SUBJECT: GRB 260125A: Swift-XRT observations DATE: 26/01/27 15:36:17 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), S. Campana (INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Fermi/GBM-detected burst GRB 260125A (Fermi GBM Team, GCN 43510), collecting 3.1 ks of Photon Counting (PC) mode data between T0+64.9 ks and T0+86.3 ks. No X-ray sources have been detected consistent with the GOTO counterpart position (Gompertz et al., GCN 43514). The 3-sigma upper limit in the field is 0.003 ct s^-1, corresponding to a 0.3-10 keV observed flux of 1.0e-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum). Five uncatalogued sources were detected too far from the GOTO position, and not showing significant signs of fading to be likely afterglow candidates. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/ToO_GRBs/00021899. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43527. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41626] EP260126a: EP-FXT follow-up observation
by GCN Circulars 27 Jan '26

27 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43526 SUBJECT: EP260126a: EP-FXT follow-up observation DATE: 26/01/27 13:40:40 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: EP-FXT performed a follow-up observation of EP260126a (detected by EP-WXT, GCN 43520) about 19.1 hours after the WXT detection, with an exposure time of 5.8 ks. The FXT telemetry data show that an uncatalogued source was detected within the WXT error circle at R.A. = 103.7551, DEC = 37.7053 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT X-ray spectrum of this uncatalogued source can be fitted with an absorbed powerlaw with a hydrogen column density fixed at the Galactic value of 1.21 x 10^21 cm^-2 and a photon index of 1.76 (+/- 0.20). The derived unabsorbed 0.5-10 keV flux is approximately 5.65 (+1.0/-0.85) x 10^-13 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Multi-band follow-up 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/43526. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41625] EP260126a: Optical upper limit with Kinder observations
by GCN Circulars 27 Jan '26

27 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43525 SUBJECT: EP260126a: Optical upper limit with Kinder observations DATE: 26/01/27 12:48:50 GMT FROM: Amar Aryan at National Central University, Institute of Astronomy (NCUIA) <amararyan941(a)gmail.com> M.-H. Lee, A. Aryan, T.-W. Chen, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), J. H. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), Y.-H. Lee, A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, C.-H. Lai, W.-J. Hou, H.-Y. Hsiao, H.-C. Lin, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP260126a (Fu et al., GCN 43520) using the 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first SLT epoch of observations in r-band started at 13:53 UTC on the 26 January 2026 (MJD 61066.578), 9.46 hr after the EP-WXT trigger. We utilized the astroalign (Beroiz et al., 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al., 2022, ApJ, 935, 167) packages to align and stack the individual frames. Moreover, we used AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform PSF photometry. We do not detect any new or uncataloged sources within the 20" EP-FXT localization circle. The details of the observations and the measured 3-sigma upper limits (in the AB system) are as follows: Telescope | Filter | MJD (start)| t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass SLT | r | 61066.578 | 9.46 | 300 * 6 | >21.0 | 2".8 | 1.04 SLT | i | 61066.606 | 10.14 | 300 * 3 | >20.3 | 2".5 | 1.03 The non-detections in our observations are consistent with those reported by Zhu et al. (GCN 43521), Globus et al. (GCN 43522), Eyles-Ferris et al. (GCNs 43523 and 43524). The presented upper limits are calibrated using the field stars from the Pan-STARRS catalog and are not corrected for the expected Galactic foreground extinction of A_r = 0.24 and A_i = 0.18 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology, details on the Lulin observatory telescopes, and a compilation of our optical follow-up campaign for FXTs discovered within the first year of operation of the Einstein-Probe mission are presented in Aryan et al., 2025, ApJS, 281, 20, doi:10.3847/1538-4365/adfc69. View this GCN Circular online at https://gcn.nasa.gov/circulars/43525. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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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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