GRB 260111A
GCN Circular 43426
Subject
GRB 260111A: COLIBRÍ fading of the optical counterpart candidate
Date
2026-01-16T17:02:10Z (2 months ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
Via
Web form
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.
GCN Circular 43388
Subject
GRB 260111A: Swift-XRT observations
Date
2026-01-13T11:01:35Z (2 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
S. Lanava (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester),
A.P. Beardmore (U. Leicester), M. Perri (SSDC & INAF-OAR), V. D'Elia
(SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), S. Dichiara (PSU), J.A.
Kennea (PSU) and P.A. Evans (U. Leicester) reports on behalf of the
Swift-XRT team:
Swift-XRT has performed follow-up observations of the Swift/BAT-GUANO
(Ronchini et al., GCN 43377) and Fermi/GBM (Fermi GBM team, GCN 43370;
Palafox et al., GCN 43384) detected burst GRB 260111A, collecting 2.8
ks of Photon Counting (PC) mode data between T0+94.3 ks and T0+104.8
ks.
One uncatalogued X-ray source has been detected within the estimated
3-sigma Swift/BAT error region (493 arcsec), it is below the RASS limit
and shows no definitive signs of fading. A source consistent with the
position of XRT source 2 has been reported in the optical with
COLIBRÍ, suggesting it could be the GRB afterglow (Ducoin et al., GCN
43386).
Details of this source are given below:
Source 2:
RA (J2000.0): 229.5858 = 15h 18m 20.60s
Dec (J2000.0): +51.9736 = +51d 58' 24.8"
Error: 6.3 arcsec (radius, 90% conf.)
Count-rate: (5.6 [+2.4, -1.9])e-3 ct s^-1
Distance: 27 arcsec from Swift/BAT position.
Flux: (1.56 [+0.66, -0.53])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
A catalogued source was also detected within the estimated 3-sigma
Swift/BAT error region (493 arcsec).
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/00021897.
This circular is an official product of the Swift-XRT team.
GCN Circular 43386
Subject
GRB 260111A: COLIBRÍ optical afterglow candidate
Date
2026-01-13T07:27:49Z (2 months ago)
From
J.-G. Ducoin at CPPM <ducoin@cppm.in2p3.fr>
Via
Web form
Jean-Grégoire Ducoin (CPPM), Diego López-Cámara (UNAM), Edilberto Aguilar-Ruiz (UNAM), Francesco Magnani (CPPM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (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), Kin Ocelotl López (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):
We imaged the field of the Swift/Fermi GRB 260111A (Fermi GBM Team, GCN 43370, GCN 43384; Ronchini et al., GCN 43377) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-12 10:06 to 13:26 UTC (from 17.55 to 20.88 hours after the trigger) and obtained 145 minutes of simultaneous exposure in the r and z filters.
The data were reduced, coadded, calibrated, and analyzed with the COLIBRÍ pipeline, and were also analyzed 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.
We detect an uncatalogued source revealed by image subtraction using Legacy Survey as template, consistent with the BAT/GUANO 5 arcmin error circle (Ronchini et al., GCN Circ. 43377) and the XRT source #2 (Evans et al., GCN 43379) at :
RA(J2000) = 15:18:20.830 = 229.58679 degrees
Dec(J2000) = +51:58:25.82 = 51.97384 degrees
with an uncertainty of 0.5 arcsec.
The preliminary magnitude derived for that source is:
r = 22.87 +/- 0.07
z = 22.33 +/- 0.14
We cannot confirm that the source is fading, however its proximity to XRT #2 suggests it could be the afterglow of GRB 260111A. This detection is very significantly fainter than the upper limit measured with GOTO (Gompertz et al., GCN 43381), and thus compatible with it.
We encourage further follow-up of this candidate.
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.
GCN Circular 43385
Subject
GRB 260111A: GECAM-B observation of a burst
Date
2026-01-13T06:22:50Z (2 months ago)
From
Xinghao Luo at IHEP <2952704891@qq.com>
Via
Web form
Xing-Hao Luo, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:
GECAM-B was triggered on-ground by GRB 260111A, at 2026-01-11T16:33:15.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43370).
According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 33 +13/-12 s.
The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb260111A.png
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).
GCN Circular 43384
Subject
GRB 260111A: Fermi GBM Observation
Date
2026-01-13T02:51:56Z (2 months ago)
From
Eva MP at INAOE <eva.palafox@gmail.com>
Via
Web form
Eva Palafox (INAOE) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 16:33:14.01 UT on 11 January 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260111A (trigger 789841999/260111690).
which was also detected by Swift/BAT (S. Ronchini et al. 2026, GCN 43377).
The Fermi GBM on-ground location (GCN 43370) is consistent with the Swift/BAT position.
The angle from the Fermi LAT boresight is 14.4 degrees.
The GBM light curve consists of a single emission episode with a duration (T90)
of about 31 s (50-300 keV). The time-averaged spectrum
from T0-18 to T0+52 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.7 +/- 0.3 and the cutoff energy,
parameterized as Epeak, is 140 +/- 30 keV.
The event fluence (10-1000 keV) in this time interval is
(2.3 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.70 s in the 10-1000 keV band is 2.4 +/- 0.2 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/"
GCN Circular 43381
Subject
GRB 260111A: GOTO optical upper limits
Date
2026-01-12T21:35:29Z (2 months ago)
From
Ben Gompertz at U of Birmingham <b.gompertz@bham.ac.uk>
Via
email
B. P. Gompertz, D. O’Neill, A. Kumar, G. Ramsay, R. Starling, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, S. Belkin, and M. Pursiainen report on behalf of GOTO collaboration:
We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 260111A (Fermi GBM Team, GCN 43370; Ronchini et al., GCN 43377).
Observations of the GBM localisation region began at 2026-01-12 02:58:56 UT, (+10.4h post trigger) and continued through to 2026-01-12 06:46:03 UT (+14.2h post trigger). Each observation consisted of 4x90 s exposures in the GOTO L-band (400-700 nm). 109 images were taken, across 9 unique pointings, covering 209.3 square degrees within the 90% localisation contour. ~78.4% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.0 mag.
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks.
The GUANO localisation region (Ronchini et al., GCN 43377) was fully covered in an epoch taken at 06:37:29 UT on 2026-01-12 (+14.1h post trigger). No new sources were identified to a 5-sigma limiting AB magnitude of L > 20.1 mag.
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).
GCN Circular 43379
Subject
GRB 260111A: Swift ToO observations
Date
2026-01-12T18:44:34Z (2 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Swift/BAT-detected event
GRB 260111A. Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021897
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 Swift/BAT 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.
GCN Circular 43377
Subject
GRB 260111A: Swift/BAT-GUANO arcminute localization of a burst
Date
2026-01-12T08:48:14Z (2 months ago)
From
Samuele Ronchini at PSU <sjs8171@psu.edu>
Via
Web form
Samuele Ronchini (GSSI), Aaron Tohuvavohu (Cosmic Frontier), James DeLaunay (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (Northwestern) report:
Swift/BAT did not localize GRB 260111A onboard (T0: 2026-01-11T16:33:14.01 UTC, Fermi GCN 43370).
The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
The position is found with the newly developed pipeline BAT-GLIMPSE: Gamma-ray Localization using Imaging and Mosaic techniques for Pointing and Slew Epochs (Ronchini et. al, in prep). The pipeline makes use of the tools from BatAnalysis (Parsotan et al. 2025). The source was detected with an SNR = 19.7 in a 8.192 s analysis time bin starting at t0 - 4.096 s.
Independently, the BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), confirms the detection and position of the burst in a 8.192 s analysis time bin starting at T0 - 4.096 s with a sqrt(TS) of 36.98. An arcminute localization is found with DeltaLLHOut of 317.21 and a DeltaLLHPeak of 302.45. See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut. The NITRATES and BAT-GLIMPSE positions are compatible.
The BAT position is:
RA, Dec = 229.57340, 51.97470 deg which is
RA(J2000) = 15h 18m 17.6s
Dec(J2000) = 51d 58' 28.9"
with an estimated uncertainty of 5 arcmin radius.
More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=789842031
XRT and UVOT follow-up has been requested. Results of follow-up observations will be reported in future circulars.
GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/
GCN Circular 43371
Subject
Fermi GRB 260111A: Global MASTER-Net observations report
Date
2026-01-11T17:15:39Z (2 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
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) started inspect of the Fermi GRB 260111A ( Fermi GBM team, GCN 43370) errorbox 201 sec after notice time and 236 sec after trigger time at 2026-01-11 16:37:10 UT, with upper limit up to 19.5 mag. The observations began at zenith distance = 70 deg. The sun altitude is -59.9 deg.
The galactic latitude b = 56 deg., longitude l = 85 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3100149
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
262 | 2026-01-11 16:37:10 | MASTER-Tunka | (14h 52m 29.86s , +46d 07m 42.6s) | C | 50 | 17.8 |
262 | 2026-01-11 16:37:10 | MASTER-Tunka | (14h 52m 01.47s , +46d 14m 15.0s) | C | 50 | 18.3 |
320 | 2026-01-11 16:38:04 | MASTER-Tunka | (14h 52m 01.36s , +46d 14m 14.7s) | C | 60 | 18.5 |
320 | 2026-01-11 16:38:04 | MASTER-Tunka | (14h 52m 29.78s , +46d 07m 43.0s) | C | 60 | 18.1 |
384 | 2026-01-11 16:39:07 | MASTER-Tunka | (14h 52m 01.23s , +46d 14m 15.1s) | C | 60 | 18.3 |
384 | 2026-01-11 16:39:07 | MASTER-Tunka | (14h 52m 29.72s , +46d 07m 43.8s) | C | 60 | 18.0 |
607 | 2026-01-11 16:42:51 | MASTER-Tunka | (14h 58m 24.98s , +50d 10m 13.5s) | C | 60 | 18.8 |
667 | 2026-01-11 16:42:51 | MASTER-Tunka | (14h 58m 24.98s , +50d 10m 13.5s) | C | 180 | 19.5 | Coadd
607 | 2026-01-11 16:42:51 | MASTER-Tunka | (14h 58m 56.47s , +50d 03m 31.9s) | C | 60 | 18.4 |
670 | 2026-01-11 16:43:54 | MASTER-Tunka | (14h 58m 56.32s , +50d 03m 33.3s) | C | 60 | 18.4 |
670 | 2026-01-11 16:43:54 | MASTER-Tunka | (14h 58m 24.82s , +50d 10m 13.4s) | C | 60 | 18.7 |
734 | 2026-01-11 16:44:58 | MASTER-Tunka | (14h 58m 24.70s , +50d 10m 13.5s) | C | 60 | 18.7 |
734 | 2026-01-11 16:44:58 | MASTER-Tunka | (14h 58m 56.28s , +50d 03m 33.8s) | C | 60 | 18.3 |
797 | 2026-01-11 16:46:01 | MASTER-Tunka | (14h 58m 24.72s , +50d 10m 13.7s) | C | 60 | 18.6 |
797 | 2026-01-11 16:46:01 | MASTER-Tunka | (14h 58m 56.30s , +50d 03m 33.8s) | C | 60 | 18.3 |
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
GCN Circular 43370
Subject
GRB 260111A: Fermi GBM Final Real-time Localization
Date
2026-01-11T16:43:36Z (2 months ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB
At 16:33:14 UT on 11 Jan 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260111A (trigger 789841999.012866 / 260111690).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 224.7, Dec = 50.4 (J2000 degrees, equivalent to J2000 14h 58m, 50d 23'), with a statistical uncertainty of 2.7 degrees.
The angle from the Fermi LAT boresight is 12.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260111690/quicklook/glg_skymap_all_bn260111690.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260111690/quicklook/glg_healpix_all_bn260111690.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260111690/quicklook/glg_lc_medres34_bn260111690.gif