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GRB 260127A

GCN Circular 43596

Subject
GRB 260127A: GECAM-B observation
Date
2026-02-02T03:09:30Z (a month ago)
From
renyz16607@163.com
Via
Web form
Yang-Zhao Ren, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:

GECAM-B was triggered on-ground by GRB 260127A, at 2026-01-27T17:51:07.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #43528) and Swift/BAT (Klingler et al., GCN #43529). 

According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a pulse with a duration (T90) of 6 +1/-1 s.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb260127A.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 43563

Subject
GRB 260127A: Swift-BAT refined analysis
Date
2026-01-29T21:16:56Z (a month ago)
From
D. R. Sadaula at NASA GSFC <dev.r.sadaula@nasa.gov>
Via
Web form
T. Parsotan (GSFC), S. D. Barthelmy (GSFC), 
R. Gupta (GSFC), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), M. J. Moss (GSFC),
D. M. Palmer (LANL), T. Parsotan (GSFC),
D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU)
(i.e. the Swift-BAT team)
 
Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 260127A (trigger #1444088)
(Kilingler et al., GCN Circ. 43529).  The BAT ground-calculated position is
RA, Dec = 231.879, 6.758 deg which is 
   RA(J2000)  =  15h 27m 30.9s 
   Dec(J2000) = +06d 45' 28.4" 
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 40%.
 
The classic pulse has a single peak that started around T+20 sec and has a structure before it at ~T+5 sec. The duration of the burst is ~100 sec.  T90 (15-350 keV) is 104.06 +- 19.41 sec (estimated error including systematics).
 
The time-averaged spectrum using multiple GTIs  from T-2.68 to T+7.62, T+9.00 to T+84.43 sec, and T+86.00 to T+117.04 sec is best fit by a simple power-law model.  The power law index of the time-averaged spectrum is 1.76 +- 0.15.  The fluence in the 15-150 keV band is 2.3 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+33.36 sec in the 15-150 keV band is 2.1 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence level. 
 
The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1444088

GCN Circular 43557

Subject
GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
Date
2026-01-29T15:04:48Z (a month ago)
From
Alina Volnova at IKI RAS <alinusss@gmail.com>
Via
Web form
A. Volnova (IKI), A. Moskvitin (SAO RAS), N. Pankov (IKI), A. Tarasenkov (INASAN), I.
Sokolov (INASAN, KIAM), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN collaboration:

We observed the field of the Swift/Fermi/GBM GRB 260127A (Fermi GBM Team, GCN Circ. 43528; Klingler et al., GCN Circ. 43529; Osborne et al., GCN 43535; D'Ai et al, GCN 43539; Trigg, GCN 43546) in R-band with the RC500 telescope of the INASAN-Kislovodsk observatory starting on 2026-01-27 (UT) 23:20:50, in Rc-band with the Zeiss-1000 of the SAO RAS starting on 2026-01-28 (UT) 01:01:40, and in clear light with the 0.8-meter K-800 telescope of the Terskol observatory of INASAN 2026-01-28 (UT) 01:46:18. The optical counterpart reported previously (Saccardi & Malesani, GCN 43530; Lipunov et al., GCNs 43531, 43548; Wu et al., GCN 43537; Hagio et al., GCN 43540; Malesani et al, GCN 43543; Magnani et al., GCN 43544) is clearly detected in the stacked frame of the Zeiss-1000 and is not detected in the stacked frames of the RC500 and K-800 telescopes. Preliminary photometry and observational details are the following:

Date           UT start  t-T0       Exp.    Filter Obj.   Err.   UL       Site/Telescope
                        (mid,days)  (n*s)                       (3sigma)
2026-01-27     23:20:50  0.30822    110*120 R      n/d    n/d    21.9     INASAN-Kislovodsk/RC500
2026-01-28     01:01:40  0.32599    15*300  Rc     22.00  0.22   22.7     SAO RAS/Zeiss-1000
2026-01-28     01:46:18  0.35748    94*30   Clear  n/d    n/d    21.2     Terskol/K800

The photometry is based on several nearby stars from the USNO-B1 catalogue (R2 magnitudes) and is not corrected for the Galactic extinction.

We would like to thank the SAO RAS engineering team: Afanasieva I. V., Pritychenko M. A., Egorov V. A., Shaldyrvan I. V. for their excellent support.

GCN Circular 43548

Subject
Fermi GRB 260127A: Global MASTER-Net observations report
Date
2026-01-28T23:15:22Z (a month 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-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

GCN Circular 43546

Subject
GRB 260127A: Fermi GBM Observation
Date
2026-01-28T18:26:39Z (a month ago)
From
atrigg2@lsu.edu
Via
Web form
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/"

GCN Circular 43544

Subject
GRB 260127A: COLIBRÍ optical observations
Date
2026-01-28T17:12:02Z (a month ago)
From
F. Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work@gmail.com>
Via
Web form
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.

GCN Circular 43543

Subject
GRB 260127A: NOT optical observations
Date
2026-01-28T16:53:18Z (a month ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
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.

GCN Circular 43540

Subject
GRB 260127A : MITSuME Akeno optical afterglow candidate detection
Date
2026-01-28T11:16:16Z (a month ago)
From
hagio.h.ffca@m.isct.ac.jp
Via
Web form
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).

GCN Circular 43539

Subject
GRB 260127A: Swift-XRT refined Analysis
Date
2026-01-28T10:27:05Z (a month ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
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.

GCN Circular 43537

Subject
GRB 260127A: SVOM/C-GFT optical observations
Date
2026-01-28T04:44:46Z (a month ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form

C. Wu (NAOC), Z. Kang (CHO), L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC) report on behalf of the SVOM/C-GFT team:

We observed the field of GRB 260127A detected by Fermi/GBM (Fermi GBM team, GCN 43528

Loading...
 
 
) and Swift/BAT (Klingler et al., GCN 43529) with LATIOS on SVOM/C-GFT. Observations started at 2026-01-27T19:07:40 UTC, ~76.55 min after the trigger.

The optical counterpart (Saccardiet et al., GCN 43530

Loading...
 
 
), consistent with XRT position (Evans et al., GCN 43532; Osborne et al., GCN 43535), was detected in our stacked i-band image. The magnitude is:

Mid_t-T0(hr)exposure time (s)bandmag (AB)mag_err
2.2430x90si20.370.20

Our detection is deeper than the upper limit reported by Lipunov et al. (GCN 43532

Loading...
 
 
).

The photometry was calibrated against nearby stars from UCAC4 catalog and no correction for Galactic dust extinction was applied.

We thank the observation assistants Yin-Huai Hao Chun-Lei Guo at Jilin observatory for their excellent support.

The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching.

GCN Circular 43535

Subject
GRB 260127A: Enhanced Swift-XRT position
Date
2026-01-27T21:35:45Z (a month ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 1612 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 260127A, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 231.87939, +6.76215 which is equivalent
to:

RA (J2000): 15h 27m 31.05s
Dec (J2000): +06d 45' 43.7"

with an uncertainty of 2.1 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at https://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

GCN Circular 43532

Subject
GRB 260127A: Prompt enhanced Swift-XRT position
Date
2026-01-27T19:08:40Z (a month 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-XRT team:

Using 1.6 ks of promptly downlinked XRT event data for GRB 260127A, we
find an enhanced XRT position of the afterglow: RA, Dec: 231.87962,
6.76262 which is equivalent to:
   RA (J2000)  = 15h 27m 31.11s
   Dec (J2000) = 00h 27m 03.03s
with an uncertainty of 1.9 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/1444088.

Position enhancement is described by Goad et al. (2007, A&A, 476, 1401)
and Evans et al. (2009, MNRAS, 397, 1177).

This circular is an official product of the Swift-XRT team.

GCN Circular 43531

Subject
Swift GRB 260127A: Global MASTER-Net observations report
Date
2026-01-27T19:08:27Z (a month 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) was pointed to the Swift GRB 260127A ( N. J. Klingler et al., GCN 43529) errorbox  3854 sec after notice time and 3972 sec after trigger time at 2026-01-27 18:56:47 UT, with upper limit up to  17.1 mag. The observations began at zenith distance = 77 deg. The sun  altitude  is -52.1 deg. 

The galactic latitude b = 47 deg., longitude l = 12 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3117002

We obtain a following upper limits.  

Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

    3988 |        MASTER-Tunka |   C |    30 | 17.1 |        
    4030 |        MASTER-Tunka |   C |    30 | 17.1 |        
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 43530

Subject
GRB 260127A: LCO optical afterglow discovery
Date
2026-01-27T19:06:16Z (a month ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
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.

GCN Circular 43529

Subject
GRB 260127A: Swift detection of a burst
Date
2026-01-27T18:17:19Z (a month ago)
From
K.L. Page at U Leicester <klp5@leicester.ac.uk>
Via
email
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/)

GCN Circular 43528

Subject
GRB 260127A: Fermi GBM Final Real-time Localization
Date
2026-01-27T18:01:38Z (a month 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 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/quicklook/glg_skymap_all_bn260127744.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/bn260127744/quicklook/glg_healpix_all_bn260127744.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260127744/quicklook/glg_lc_medres34_bn260127744.gif
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