GRB 260105B

Matt Godwin (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 23:21:36.55 UT on 05 January 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260105B (trigger 789348101/260105973).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 259.71, Dec = 1.74 (J2000 degrees, equivalent to
J2000 17h 18m, +1d 44'), with a statistical uncertainty of 2.03 degrees.
(radius, 1-sigma containment, statistical only; there is additionally a
systematic error which we have characterized as a mixture of two Gaussians,
one with a radius of 1.8 degrees (52% contribution) and one with a radius
of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]).

The angle from the Fermi LAT boresight is 68 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 11 s (50-300 keV). The time-averaged spectrum
from T0-1.9 to T0+12.5 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.96 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 232 +/- 2 keV.

The event fluence (10-1000 keV) in this time interval is
(8 +/- 0.4)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+2.4 s in the 10-1000 keV band is 156 +/- 2 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 178 +/- 2 keV, alpha = -0.83 +/- 0.01 and beta = -2.19 +/- 0.03.


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/"

T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report:

The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger
789348101 at 23:21:36 on 05 Jan. 2026 were automatically fitted for spectrum
and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427;
Berlato et al. 2019, ApJ 873, 60).

The best-fit position is:
RA(2000.0) = 258.7 deg
Decl.(2000.0) = 7.9 deg
The 1 sigma statistical error radius is 2.1 deg.
We estimate an additional systematic error of 1 deg.

Further details are available at:
https://grb.mpe.mpg.de/grb/GRB260105973/

The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB260105973/healpix

The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB260105973/json

                        

SVOM/GRM team: Yue Wang, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)

SVOM/ECLAIRs team: Sebastien Guillot (IRAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight by GRB 260105B (SVOM trigger reference: sb26010502) at 2026-01-05T23:21:37.000 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43336
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 ). 

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 6.8 +1.8/-1.4 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260105B.png

In addition, the position of this burst, as determined by Fermi/GBM (RA = 259.7, Dec = 1.7, Error = 2.0, GCN #43336
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 ), is located at about 91 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. 

With this localization, the time-averaged spectrum from T0-1 to T0+7 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.61 +0.12/-0.13 and the cutoff energy, parameterized as Epeak, is 177 +15/-13 keV. The event fluence (10-1000 keV) in this time interval is (9.34+0.47/-0.44)E-06 erg/cm^2.  

The 1s peak spectrum, measured from T0-1.5 to T0+2.5 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -0.81 +0.15/-0.17 and the cutoff energy, parameterized as Epeak, is 242 +45/-33 keV. The flux (10-1000 keV) in this time interval is (2.53 +0.22/-0.20)E-06 erg/cm^2/s.

The localization of GRB 260105B in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260105B_amati.png
The localization of GRB 260105B in the 'Yonetoku' relation diagram is shown at: 
https://www.bursthub.cn//admin/static/svgrb260105B_yonetoku.png

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.

The SVOM/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang@ihep.ac.cn)

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 260105B ( Fermi GBM team, GCN 43336
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 ) errorbox  11975 sec after notice time and 12000 sec after trigger time at 2026-01-06 02:41:37 UT, with upper limit up to  15.8 mag. The observations began at zenith distance = 76 deg. The sun  altitude  is -21.3 deg. 

The galactic latitude b = 21 deg., longitude l = 24 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3096822

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   12031 | 2026-01-06 02:41:37 |   MASTER-Kislovodsk | (17h 22m 13.00s , +01d 20m 58.9s) |   C |    60 | 15.1 |        
   12031 | 2026-01-06 02:41:37 |   MASTER-Kislovodsk | (17h 26m 08.53s , +00d 57m 53.4s) |   C |    60 | 15.2 |        
   12121 | 2026-01-06 02:43:08 |   MASTER-Kislovodsk | (17h 10m 08.21s , +01d 21m 09.6s) |   C |    60 | 14.9 |        
   12128 | 2026-01-06 02:43:14 |   MASTER-Kislovodsk | (17h 14m 04.52s , +00d 58m 08.3s) |   C |    60 | 15.3 |        
   12226 | 2026-01-06 02:44:52 |   MASTER-Kislovodsk | (17h 11m 25.82s , +03d 16m 06.5s) |   C |    60 | 15.1 |        
   12226 | 2026-01-06 02:44:52 |   MASTER-Kislovodsk | (17h 15m 22.74s , +02d 53m 06.6s) |   C |    60 | 15.5 |        
   12321 | 2026-01-06 02:46:27 |   MASTER-Kislovodsk | (17h 23m 33.99s , +03d 14m 28.1s) |   C |    60 | 14.8 |        
   12322 | 2026-01-06 02:46:28 |   MASTER-Kislovodsk | (17h 27m 29.97s , +02d 51m 24.2s) |   C |    60 | 15.0 |        
   12414 | 2026-01-06 02:48:00 |   MASTER-Kislovodsk | (17h 13m 55.29s , +05d 08m 02.6s) |   C |    60 | 15.4 |        
   12414 | 2026-01-06 02:48:00 |   MASTER-Kislovodsk | (17h 17m 53.06s , +04d 45m 03.0s) |   C |    60 | 15.5 |        
   12510 | 2026-01-06 02:49:36 |   MASTER-Kislovodsk | (17h 10m 02.76s , -00d 33m 18.0s) |   C |    60 | 14.2 |        
   12510 | 2026-01-06 02:49:36 |   MASTER-Kislovodsk | (17h 13m 58.54s , -00d 56m 23.5s) |   C |    60 | 15.1 |        
   12604 | 2026-01-06 02:51:10 |   MASTER-Kislovodsk | (17h 21m 59.11s , -00d 32m 11.6s) |   C |    60 | 15.0 |        
   12605 | 2026-01-06 02:51:11 |   MASTER-Kislovodsk | (17h 25m 53.95s , -00d 55m 21.3s) |   C |    60 | 15.3 |        
   12703 | 2026-01-06 02:52:49 |   MASTER-Kislovodsk | (17h 26m 04.82s , +05d 09m 14.6s) |   C |    60 | 15.8 |        
   12812 | 2026-01-06 02:54:38 |   MASTER-Kislovodsk | (17h 03m 25.00s , +02d 54m 15.4s) |   C |    60 | 13.8 |        
   13208 | 2026-01-06 03:01:14 |   MASTER-Kislovodsk | (17h 34m 09.17s , +01d 21m 41.1s) |   C |    60 | 13.3 |        
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

The Fermi GBM team reports the detection of a likely LONG GRB

At 23:21:36 UT on 5 Jan 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260105B (trigger 789348101.546602 / 260105973).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 259.7, Dec = 1.7 (J2000 degrees, equivalent to J2000 17h 18m, 1d 42'), with a statistical uncertainty of 2.0 degrees.

The angle from the Fermi LAT boresight is 68.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260105973/quicklook/glg_skymap_all_bn260105973.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/bn260105973/quicklook/glg_healpix_all_bn260105973.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260105973/quicklook/glg_lc_medres34_bn260105973.gif