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[vsnet-grb-info 41650] Fermi GRB 260127A: Global MASTER-Net observations report
by GCN Circulars 28 Jan '26

28 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43548 SUBJECT: Fermi GRB 260127A: Global MASTER-Net observations report DATE: 26/01/28 23:15:22 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope [1] located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 260127A ( Fermi GBM team, GCN 43528) errorbox 1 days 15723 sec after notice time and 1 days 15745 sec after trigger time at 2026-01-28 22:13:32 UT, with upper limit up to 16.8 mag. The observations began at zenith distance = 80 deg. The sun altitude is -63.0 deg. The galactic latitude b = 45 deg., longitude l = 357 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3117030 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 102175 | 2026-01-28 22:13:32 | MASTER-Kislovodsk | (14h 51m 08.24s , +02d 48m 33.2s) | C | 60 | 16.6 | 102578 | 2026-01-28 22:20:15 | MASTER-Kislovodsk | (15h 05m 19.35s , +04d 43m 03.8s) | C | 60 | 16.6 | 102789 | 2026-01-28 22:23:46 | MASTER-Kislovodsk | (15h 03m 14.11s , +02d 50m 18.9s) | C | 60 | 16.5 | 102901 | 2026-01-28 22:25:38 | MASTER-Kislovodsk | (14h 49m 55.15s , -00d 58m 21.9s) | C | 60 | 16.8 | 103234 | 2026-01-28 22:31:11 | MASTER-Kislovodsk | (15h 02m 06.17s , +00d 55m 55.7s) | C | 60 | 16.8 | 103454 | 2026-01-28 22:34:51 | MASTER-Kislovodsk | (14h 50m 37.84s , -02d 52m 07.1s) | C | 60 | 16.5 | 103569 | 2026-01-28 22:36:46 | MASTER-Kislovodsk | (15h 15m 11.23s , +02d 50m 27.3s) | C | 60 | 16.5 | 103928 | 2026-01-28 22:42:46 | MASTER-Kislovodsk | (15h 13m 59.01s , +00d 56m 55.7s) | C | 60 | 16.6 | 104040 | 2026-01-28 22:44:38 | MASTER-Kislovodsk | (14h 52m 27.85s , -04d 45m 35.0s) | C | 60 | 16.6 | 104156 | 2026-01-28 22:46:33 | MASTER-Kislovodsk | (15h 02m 42.73s , -02d 51m 50.3s) | C | 60 | 16.6 | 104268 | 2026-01-28 22:48:25 | MASTER-Kislovodsk | (15h 27m 17.10s , +02d 49m 26.6s) | C | 60 | 16.5 | 104390 | 2026-01-28 22:50:27 | MASTER-Kislovodsk | (15h 13m 49.40s , -00d 57m 33.9s) | C | 60 | 16.6 | 104620 | 2026-01-28 22:54:17 | MASTER-Kislovodsk | (15h 26m 00.01s , +00d 54m 54.2s) | C | 60 | 16.5 | 104726 | 2026-01-28 22:56:03 | MASTER-Kislovodsk | (15h 04m 25.84s , -04d 43m 38.4s) | C | 60 | 16.7 | 104959 | 2026-01-28 22:59:56 | MASTER-Kislovodsk | (14h 55m 16.13s , -06d 36m 58.7s) | C | 60 | 16.7 | 105183 | 2026-01-28 23:03:40 | MASTER-Kislovodsk | (15h 25m 53.63s , -00d 56m 48.2s) | C | 60 | 16.7 | 105413 | 2026-01-28 23:07:30 | MASTER-Kislovodsk | (15h 07m 22.73s , -06d 39m 00.3s) | C | 60 | 16.6 | 105526 | 2026-01-28 23:09:23 | MASTER-Kislovodsk | (15h 16m 34.84s , -04d 44m 35.6s) | C | 60 | 16.8 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/43548. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41649] IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
by GCN Circulars 28 Jan '26

28 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43547 SUBJECT: IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility DATE: 26/01/28 21:37:15 GMT FROM: Robert David Stein at JSI <rdstein(a)umd.edu> Robert Stein (JSI), Jannis Necker (Leiden University), Akshay Eranhalodi (DESY), and Anna Franckowiak (Ruhr University Bochum) report, On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: As part of the ZTF neutrino follow up program (Stein et al. 2023), we observed the localization region of the neutrino event IceCube-260125A (Zegarelli et. al, GCN 43512) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2026-01-25 11:15 UTC, approximately 1.1 hours after event time. We covered 100.0% (1.3 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each exposure was 300s with a typical depth of 21.0 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019). No candidate counterparts were detected. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan, and OKC, University of Stockholm, Sweden. Operations are conducted by Caltech's Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019). Alert filtering is performed with the nuztf (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf ). View this GCN Circular online at https://gcn.nasa.gov/circulars/43547. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41648] GRB 260127A: Fermi GBM Observation
by GCN Circulars 28 Jan '26

28 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43546 SUBJECT: GRB 260127A: Fermi GBM Observation DATE: 26/01/28 18:26:39 GMT FROM: atrigg2(a)lsu.edu A. C. Trigg (NPP ORAU, NASA MSFC) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 17:51:07.74 UT on 27 January 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260127A (trigger 791229072/260127744), which was also detected by Swift BAT and XRT (N. J. Klingler et al. 2026, GCN 43529). The Fermi GBM real-time localization (GCN 43528) is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 88 degrees. The GBM light curve single emission episode with a duration (T90) of about 36 s (50-300 keV). The time-averaged spectrum from T0-15 to T0+32 s is best fit by a power law function. The power law index is -1.55 +/- 0.04. A Comptonized model fits the spectra equally well with power law index is -1.29 +/- 0.06 and the cutoff energy, parameterized as Epeak, is 490 +/- 25 keV. The event fluence (10-1000 keV) in this time interval is (3.8 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.32 s in the 10-1000 keV band is 2.7 +/- 0.5 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/43546. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41647] IceCube-260125A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 28 Jan '26

28 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43545 SUBJECT: IceCube-260125A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/01/28 17:45:24 GMT FROM: Sam Hori at IceCube/U Wisc-Madison <sahori(a)wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-260125A (https://gcn.nasa.gov/circulars/43512) in a time range of 1000 seconds centered on the alert event time (2026-01-25 10:01:19.880 UTC to 2026-01-25 10:17:59.880 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-260125A. We report a p-value of 1.00 in this time window. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, ranges from 1.3e-01 to 1.4e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260125A in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 3e+02 GeV and 1e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-01-24 10:09:39.880 UTC to 2026-01-26 10:09:39.880 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, is 1.5e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260125A in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/43545. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41646] GRB 260127A: COLIBRÍ optical observations
by GCN Circulars 28 Jan '26

28 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43544 SUBJECT: GRB 260127A: COLIBRÍ optical observations DATE: 26/01/28 17:12:02 GMT FROM: F. Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work(a)gmail.com> Francesco Magnani (CPPM), Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), 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 Swift/Fermi/GBM GRB 260127A (Fermi GBM Team, GCN Circ. 43528, Klingler et al., GCN Circ. 43529) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-28 09:48 to 13:24 UTC (from 16.0 to 19.5 hours after the trigger) and obtained 110 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. At the location of the optical counterpart reported by Saccardi et al. (GCN Circ. 43530), consistent with the X-ray counterpart reported by Evans et al. (GCN Circ. 43532) and Osborne et al. (GCN Circ. 43535), we marginally detect a source at a preliminary magnitude of: r = 22.80 +/- 0.28 At this same position, we measure the following 3-sigma upper limit: z > 21.6 Our observations suggest the candidate has faded since the observations reported by Saccardi et al. (GCN Circ. 43530), Wu et al. (GCN Circ. 43537), and Hagio et al. (GCN CIrc. 43540). 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/43544. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41645] GRB 260127A: NOT optical observations
by GCN Circulars 28 Jan '26

28 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43543 SUBJECT: GRB 260127A: NOT optical observations DATE: 26/01/28 16:53:18 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), J. An (NAOC), L. B He (NAOC), G. Corcoran (UCD), K. Valeckas (NOT & NBI), L. Izzo (INAF/OAC and DARK/NBI), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), B. Schneider (LAM) report on behalf of a larger collaboration: We observed the optical counterpart (Saccardi & Malesani, GCN 43530; Wu et al., GCN 43537; Hagio et al., GCN 43540) of GRB 260127A (Klingler et al., GCN 43529; Fermi GBM team, GCN 43528) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out in the SDSS i, z, and r filters (with exposure times 3x300, 5x200, and 3x300 s, respectively). The optical counterpart is detected in the stacked images for all bands. We report the following magnitudes: | Filter | Epoch (UT) | Time since GRB (hr) | Exp time (s) | Magnitude (AB) | | ------ | ---------- | ------------------- | ------------ | -------------- | | i | Jan 28.197 | 10.88 | 3x300 | 22.30 +- 0.08 | | z | Jan 28.209 | 11.18 | 5x200 | 22.05 +- 0.18 | | r | Jan 28.243 | 12.00 | 3x300 | 22.30 +- 0.06 | The above magnitudes are calibrated against the Pan-STARRS catalog and are not corrected for Galactic extinction. We note that at the coordinates of the optical counterpart a faint source is reported in the Legacy Survey catalogue. Considering its tabulated magnitudes (r = 23.3, i = 23.2, z = 22.3), the transient emission is thus significantly contaminated by the host flux. View this GCN Circular online at https://gcn.nasa.gov/circulars/43543. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41644] GRB 260127B: Swift ToO observations
by GCN Circulars 28 Jan '26

28 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43542 SUBJECT: GRB 260127B: Swift ToO observations DATE: 26/01/28 15:34:04 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 260127B. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021900 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/43542. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41643] EP260126a: Seimei/TriCCS optical upper limit
by GCN Circulars 28 Jan '26

28 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43541 SUBJECT: EP260126a: Seimei/TriCCS optical upper limit DATE: 26/01/28 14:52:16 GMT FROM: Kenta Taguchi <kentagch(a)kusastro.kyoto-u.ac.jp> Kenta Taguchi (Kyoto University) reports on behalf of a larger collaboration: We observed the field of EP260126a detected by the Einstein Probe (Fu et al., GCN 43520) using the Tricolor CMOS Camera and Spectrograph (TriCCS) on the 3.8-m Seimei Telescope at the Okayama Observatory of Kyoto University. Our observation started at 13:30:04 UT on 2026-01-26 (MJD = 61066.5625). For each band, we took 30-second exposures 62 times (i.e., the total exposure time is 1860 s = 31 min). From our preliminary analysis, the 5-sigma limiting magnitudes are 21.74, 21.36, and 21.33 AB mag for g, r, and i-band, respectively. We detected no transient sources in the FXT error circle. View this GCN Circular online at https://gcn.nasa.gov/circulars/43541. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41642] GRB 260127A : MITSuME Akeno optical afterglow candidate detection
by GCN Circulars 28 Jan '26

28 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43540 SUBJECT: GRB 260127A : MITSuME Akeno optical afterglow candidate detection DATE: 26/01/28 11:16:16 GMT FROM: hagio.h.ffca(a)m.isct.ac.jp H. Hagio, I. Takahashi, M. Sasada, H. Seki, Y. Kubo, A. Ochi, R. Kato, S. Joshima, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration: We observed the field of GRB 260127A detected by Fermi (Fermi GBM team et al., GCN 43528) and Swift ( Klingler et al., GCN 43529) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. The observation started at 2026-01-27 17:52:58 UT (2.4 min after the trigger). We stacked the images taken under good conditions. We detected a point source in the Rc-band image at a position of the reported candidate (Saccardi et al., GCN 43530; Wu et al., GCN 43537). Here we report the preliminary magnitude of the source and the 5-sigma upper-limits as follows. T0+[sec] | MID-UT | T-EXP[sec] | magnitudes --------------------------------------------------------------------------------------------------------------- 1245 | 2026-01-27 18:11:19 | 1620 | g'>19.2,Rc=19.4+/-0.2, Ic>18.7 --------------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the trigger T-EXP: Total exposure time We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire) View this GCN Circular online at https://gcn.nasa.gov/circulars/43540. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41641] GRB 260127A: Swift-XRT refined Analysis
by GCN Circulars 28 Jan '26

28 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43539 SUBJECT: GRB 260127A: Swift-XRT refined Analysis DATE: 26/01/28 10:27:05 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A. D'Ai (INAF-IASFPA), J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), S. Campana (INAF-OAB), A. Melandri (INAF-OAR) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 9.4 ks of XRT data for GRB 260127A, from 226 s to 51.7 ks after the trigger. The data comprise 102 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+5.2 ks) is consistent with a constant source of mean count rate 3.6e+00 ct/sec. A power-law fit gives an index of 3.08 (+0.03, -3.08). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.14 (+0.20, -0.19). The best-fitting absorption column is 8.0 (+4.6, -3.9) x 10^20 cm^-2, in excess of the Galactic value of 4.1 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.75 (+/-0.06) and a best-fitting absorption column of 1.32 (+0.21, -0.20) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.32 (+0.21, -0.20) x 10^21 cm^-2 Galactic foreground: 4.1 x 10^20 cm^-2 Excess significance: 7.6 sigma Photon index: 1.75 (+/-0.06) The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01444088. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43539. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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