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

[vsnet-grb-info 41530] Swift triggered on the HMXB 1A 1118-61
by GCN Circulars 17 Jan '26

17 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43435 SUBJECT: Swift triggered on the HMXB 1A 1118-61 DATE: 26/01/17 06:59:18 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> R. Gupta (NASA GSFC) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 06:28:58 UT, the Swift Burst Alert Telescope (BAT) triggered and located the HMXB 1A 1118-61 (trigger 1441823). Swift slewed soon after the event. The BAT on-board calculated location is RA, Dec 170.183, -61.905 which is RA(J2000) = 11h 20m 44s Dec(J2000) = -61d 54' 17" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure. This is an image-triggered event. The XRT began observing the field at 06:35:17.6 UT, 378.7 seconds after the BAT trigger. XRT found a bright X-ray source located at RA, Dec 170.2403, -61.9170 which is equivalent to: RA(J2000) = 11h 20m 57.67s Dec(J2000) = -61d 55' 01.2" with an uncertainty of 5.5 arcseconds (radius, 90% containment). This location is 106 arcseconds from the BAT onboard position, within the BAT error circle. This position is 4.3 arcseconds from a known X-ray source: LSXPS J112057.1-615459. This source is in the Swift XRT LSXPS catalogue with a mean 0.3-10 keV count-rate of 0.2537 +/- 0.0012 ct/sec; see https://www.swift.ac.uk/LSXPS/LSXPS%20J112057.1-615459 for details of these previous observations. No event data are yet available to determine the column density using X-ray spectroscopy. This trigger occurred just as Swift was exiting the SAA, so it is not clear at this time whether the source has actually brightened, or if the trigger was caused by the enhanced particle background. View this GCN Circular online at https://gcn.nasa.gov/circulars/43435. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41529] GRB 260115A: GECAM-B observation
by GCN Circulars 17 Jan '26

17 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43434 SUBJECT: GRB 260115A: GECAM-B observation DATE: 26/01/17 00:47:57 GMT FROM: zhangjinpeng(a)ihep.ac.cn Jin-Peng Zhang, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 260115A, at 2026-01-15T17:46:45.900 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43417). According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a bright pulse and some fainter emissions, with a duration (T90) of 4.8 +2.4/-1.4 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb260115A.png The time-averaged spectrum from T0 - 1.0 to T0 + 4.0 s is best fitted by a power law function. The power law index is -2.2 +0.3/-0.4. The event fluence (10-1000 keV) in this time interval is (2.8 +0.7/-0.4)E-06 erg/cm^2. Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/43434. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41528] FRB 20251229A: COLIBRÍ further inspection of the updated localization
by GCN Circulars 17 Jan '26

17 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43433 SUBJECT: FRB 20251229A: COLIBRÍ further inspection of the updated localization DATE: 26/01/17 00:23:03 GMT FROM: Rosa L. Becerra at Instituto de Astronomía, UNAM <rbecerra(a)astro.unam.mx> Rosa L. Becerra (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Edilberto Aguilar-Ruiz (UNAM), Dalya Akl (NYUAD), Camila Angulo (UNAM), 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 reinspected our previous observations of the field of FRB 20251229A (Mulyk et al., GCN Circ. 43334) reported by Globus et al. (GCN Circ. 43431), focusing on the updated baseband localization provided by the CHIME/FRB Collaboration (Mason et al., GCN Circ. 43431). We analysed the data and performed image subtraction using STDWeb/STDPipe (Karpov 2025), with templates from the Pan-STARRS DR2 catalog (Flewelling et al. 2020). In this further inspection, we do not detect any new source or evidence for brightness variability of any object within the localization uncertainty region (Mason et al., GCN Circ. 43431), down to the following 5-sigma limits: r > 22.5, z > 21.5. 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/43433. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41527] EP260116a: Liverpool Telescope upper limits
by GCN Circulars 16 Jan '26

16 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43432 SUBJECT: EP260116a: Liverpool Telescope upper limits DATE: 26/01/16 23:35:52 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 EP260116a (Wang et al., GCN 43424) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 5x100s exposures in the SDSS r and i filters starting at 2026-01-16 21:52:40 UT, approximately 21.7 hours post trigger. Two exposures taken in i-band had to be discarded due to poor seeing. We performed image subtraction of the stacked images of remaining exposures in each filter 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 (Wang et al., GCN 43424). The 3-sigma limiting magnitude on the stacked images is r > 22.5 mag and i > 21.9 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/43432. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41526] FRB 20251229A: Updated CHIME/FRB Baseband Localization of FRB 20251229A
by GCN Circulars 16 Jan '26

16 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43431 SUBJECT: FRB 20251229A: Updated CHIME/FRB Baseband Localization of FRB 20251229A DATE: 26/01/16 21:59:12 GMT FROM: masonng(a)mit.edu Mason Ng (McGill University, Trottier Space Institute) on behalf of the CHIME/FRB Collaboration: In GCN 43334 (ATel 17574), we reported the discovery of the potentially hyperactive repeating fast radio burst source, FRB 20251229A. In that ATel, we published best-fit localization coordinates from an initial analysis of the raw voltage (baseband) data using an older version of the localization pipeline (Michilli et al. 2021). Here, we update the best-fit baseband localization for FRB 20251229A using a newer version of the pipeline, with the latest calibration methods. The new localization, which is approximately 35" away from the previously reported localization (GCN 43334, ATel 17574), is the following with errors quoted at 1-sigma uncertainty: RA (J2000): 20h 41m 23.9s +/- 1.8s, Dec. (J2000): 16d 01' 31" +/- 36" RA (J2000): 310.3494 +/- 0.0077 deg., Dec. (J2000): 16.0252 +/- 0.0099 deg. View this GCN Circular online at https://gcn.nasa.gov/circulars/43431. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41525] EP260116A: 1.3m DFOT optical upper limit
by GCN Circulars 16 Jan '26

16 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43430 SUBJECT: EP260116A: 1.3m DFOT optical upper limit DATE: 26/01/16 21:53:31 GMT FROM: ANSHIKA GUPTA at ARIES <anshika05180(a)gmail.com> Anshika Gupta, Kuntal Misra, Tarak Chand, Debalina Kar, Dhruv Jain, and Pankaj Pawar (ARIES) report: We observed the field of EP260116A detected by EP/WXT (EP Team, GCN 43424) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations began on 2026-01-16 at 19:01:13 UT, i.e., ~18.87 hours after the EP trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. No uncatalogued source is detected in our stacked image within the EP/WXT error box (EP Team, GCN 43424). We obtain the following 3-sigma upper limit in the stacked image: Date Start_UT T_start-T0 (hour) Filter Exp time (s) Magnitude =============================================================== 2026-01-16 19:01:13 ~18.87 R 300s*12 >23.0 The non-detection of the burst is consistent with Junjie-Jin et al. 2026 (GCN 43425); Lipunov et al. 2026 (GCN 43427). The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalogue. View this GCN Circular online at https://gcn.nasa.gov/circulars/43430. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41524] GRB 260114A: VLT/MUSE spectroscopic observations
by GCN Circulars 16 Jan '26

16 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43429 SUBJECT: GRB 260114A: VLT/MUSE spectroscopic observations DATE: 26/01/16 21:38:14 GMT FROM: Andrea Saccardi at CEA/Irfu <andrea.saccardi(a)cea.fr> A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), B. Schneider (LAM), G. Corcoran (UCD), H. Fausey (Baylor), L. Izzo (INAF/OACn & DARK/NBI), A. J. Levan (Radboud and Warwick), A. Martin-Carrillo (UCD), G. Tagliaferri (INAF/OAB), N. R. Tanvir (Leicester) report on behalf of the Stargate collaboration: We observed the field of the short GRB 260114A (Eyles-Ferris et al., GCN 43396; Bissaldi, GCN 43400; Ren et al., GCN 43402; Wang et al., GCN 43404; Ridnaia et al., GCN 43413) using the ESO/VLT UT4 (Yepun) equipped with the MUSE integral-field spectrograph, covering 1'x1' centered around the XRT position. The observation mid time was 2026 Jan 15.155 UT (16.05 hr after the Swift/BAT trigger). In proximity of the X-ray localization (Beardmore et al., GCN 43412), several objects are visible in archival images of the field, for some of which we report redshifts. These measurements are based on identification of emission lines due to, among others, [O III], Hbeta, and the [O II] doublet. The redshift of the first object in the list has been already reported by Yang et al. (GCN 43410). Three of the objects have redshift close to z = 0.52, reinforcing that this is the likely GRB redshift. We note the presence of a star in chance alignment with the galaxy at z = 0.524. Its spectrum easily identifies it as an early M star, and its PSF is unresolved down to ~0.5" seeing in our HAWK-I image (Schneider et al., GCN 43423). | RA (J2000) | Dec (J2000) | Redshift | Comments | | ----------- | ----------- | -------- | --------- | | 04:58:23.43 | -08:00:50.5 | 0.524 | GCN 43410 | | 04:58:23.57 | -08:00:52.2 | 0.514 | | | 04:58:23.60 | -08:01:00.4 | 0.523 | | | 04:58:22.72 | -08:00:47.7 | 0.288 | | | 04:58:23.41 | -08:00:49.7 | 0 | M star | A finding chart showing the positions of the above objects is posted at the following link (the XRT position is taken from https://www.swift.ac.uk/xrt_positions/) https://sid.erda.dk/share_redirect/Ba6h5nsfin We thank Phil Evans (Leicester) for insightful clarifications about the XRT localization. We also acknowledge excellent support from the observing staff at Paranal, in particular Thomas Rivinius, Julien Drevon, Camila de Sa Freitas, Rodrigo Romero. View this GCN Circular online at https://gcn.nasa.gov/circulars/43429. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41523] IceCube-260115A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 16 Jan '26

16 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43428 SUBJECT: IceCube-260115A: Upper limits from a search for additional neutrino events in IceCube DATE: 26/01/16 21:03:16 GMT FROM: Yuhua Yao at IceCube/UW-Madison <yyao255(a)icecube.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-260115A (https://gcn.nasa.gov/circulars/43421) in a time range of 1000 seconds centered on the alert event time (2026-01-15 17:24:15.710 UTC to 2026-01-15 17:40:55.710 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-260115A. 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, is 1.3e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260115A 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 2e+02 GeV and 1e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2026-01-14 17:32:35.710 UTC to 2026-01-16 17:32:35.710 UTC). In this case, we report a p-value of 0.19, 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, ranges from 1.5e-01 to 1.6e-01 GeV cm^-2 within the 90% spatial containment region of IceCube-260115A 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/43428. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41522] EP260116a: Global MASTER-Net observations report
by GCN Circulars 16 Jan '26

16 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43427 SUBJECT: EP260116a: Global MASTER-Net observations report DATE: 26/01/16 17:09:27 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-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the EP260116a ( EP Team et al., GCN 43424) errorbox 16387 sec after notice time and 59243 sec after trigger time at 2026-01-16 16:36:14 UT, with upper limit up to 19.6 mag. The observations began at zenith distance = 44 deg. The sun altitude is -58.9 deg. The galactic latitude b = 13 deg., longitude l = 213 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3104022 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 59273 | 2026-01-16 16:36:14 | MASTER-Tunka | (07h 33m 54.24s , +06d 54m 24.5s) | C | 60 | 18.3 | 59273 | 2026-01-16 16:36:14 | MASTER-Tunka | (07h 34m 21.60s , +06d 48m 07.1s) | C | 60 | 18.8 | 59333 | 2026-01-16 16:36:14 | MASTER-Tunka | (07h 34m 21.60s , +06d 48m 07.2s) | C | 180 | 19.5 | Coadd 59351 | 2026-01-16 16:37:32 | MASTER-Tunka | (07h 34m 00.18s , +06d 53m 22.7s) | C | 60 | 18.3 | 59351 | 2026-01-16 16:37:32 | MASTER-Tunka | (07h 34m 27.46s , +06d 47m 05.3s) | C | 60 | 18.8 | 59425 | 2026-01-16 16:38:45 | MASTER-Tunka | (07h 33m 55.76s , +06d 52m 20.0s) | C | 60 | 18.5 | 59425 | 2026-01-16 16:38:45 | MASTER-Tunka | (07h 34m 23.07s , +06d 46m 03.1s) | C | 60 | 18.8 | 59499 | 2026-01-16 16:39:59 | MASTER-Tunka | (07h 34m 01.62s , +06d 52m 23.8s) | C | 60 | 18.5 | 59499 | 2026-01-16 16:39:59 | MASTER-Tunka | (07h 34m 28.91s , +06d 46m 06.5s) | C | 60 | 19.0 | 59559 | 2026-01-16 16:39:59 | MASTER-Tunka | (07h 34m 28.91s , +06d 46m 06.5s) | C | 180 | 19.6 | Coadd 59572 | 2026-01-16 16:41:13 | MASTER-Tunka | (07h 33m 57.80s , +06d 54m 14.6s) | C | 60 | 18.5 | 59572 | 2026-01-16 16:41:13 | MASTER-Tunka | (07h 34m 25.14s , +06d 47m 57.4s) | C | 60 | 19.0 | 59647 | 2026-01-16 16:42:27 | MASTER-Tunka | (07h 33m 57.89s , +06d 52m 28.8s) | C | 60 | 18.5 | 59647 | 2026-01-16 16:42:27 | MASTER-Tunka | (07h 34m 25.22s , +06d 46m 11.7s) | C | 60 | 19.0 | 59721 | 2026-01-16 16:43:41 | MASTER-Tunka | (07h 34m 01.50s , +06d 53m 59.9s) | C | 60 | 18.6 | 59721 | 2026-01-16 16:43:41 | MASTER-Tunka | (07h 34m 28.85s , +06d 47m 42.9s) | C | 60 | 19.0 | 59795 | 2026-01-16 16:44:56 | MASTER-Tunka | (07h 33m 55.46s , +06d 53m 09.1s) | C | 60 | 18.4 | 59795 | 2026-01-16 16:44:56 | MASTER-Tunka | (07h 34m 22.81s , +06d 46m 52.3s) | C | 60 | 18.9 | 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/43427. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41521] GRB 260111A: COLIBRÍ fading of the optical counterpart candidate
by GCN Circulars 16 Jan '26

16 Jan '26

TITLE: GCN CIRCULAR NUMBER: 43426 SUBJECT: GRB 260111A: COLIBRÍ fading of the optical counterpart candidate DATE: 26/01/16 17:02:10 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Enrique Moreno Méndez (UNAM), 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), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM): We imaged the field of the Fermi/Swift GRB 260111A (Fermi GBM Team, GCN 43370, GCN 43384; Ronchini et al., GCN 43377, Luo et al., GCN 43385, Pfeiffer et al., GCN 43397) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-16 10:52 to 13:22 UTC (from 4.77 to 4.87 days after the trigger) and obtained 89 and 75 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 is not corrected for Galactic extinction. The optical afterglow candidate reported by Ducoin et al., GCN 43386, consistent with the XRT #2 source (Lanava et al., GCN 43388), is no longer detected in the images down to the following 3-sigma limit: r > 24.4 z > 23.0 Our measurements indicate fading, and we propose this source as the optical afterglow of GRB 260111A. 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/43426. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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