GRB 260120B

A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long-duration GRB 260120B
(Fermi GBM detection: Fermi GBM team, GCN 43477
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 ;
Godwin & Meegan, GCN 43489
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 ;
Swift-BAT detection: Ferro et al., GCN 43479
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 ;
Palmer et al., GCN 43493
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 ;
AstroSat CZTI detection: Goyal et al., GCN 43504
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 )
triggered Konus-Wind at T0=64826.649 s UT (18:00:26.649).

The burst light curve shows a single pulse,
which starts at ~T0-3.2 s and has a total duration of ~5.9 s.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260120_T64826/

As observed by Konus-Wind, the burst
had a fluence of 3.41(-0.52,+0.58)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0-0.064 s,
of 1.97(-0.58,+0.60)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

Since a major part of the burst emission was 
detected before the trigger, the spectral analysis
was performed using the KW 3-channel light curve data.

Modelling the KW 3-channel time-integrated spectrum
(measured from T0-3.173 s to T0+2.720 s)
by a power law with exponential cutoff (CPL) model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep),
yields alpha = -0.56(-0.23,+0.30) and Ep = 246(-53,+67) keV.

All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.

SVOM/GRM team: Yang-Zhao Ren, 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 on-ground by GRB 260120B at 2026-01-20T18:00:26.200 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #43477
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 ) and Swift/BAT (Ferro et al., GCN #43479
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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 pulse with a T90 of 8.5 +5.0/-3.5 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260120B.png

In addition, the position of this burst, as determined by Swift/BAT (RA = 284.666, Dec = 61.912, GCN #43479
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 ), is located at about 89 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view.

With this localization, the time-averaged spectrum from T0 to T0+5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.16 +0.16/-0.18 and the cutoff energy, parameterized as Epeak, is 307 +106/-62 keV. The event fluence (10-1000 keV) in this time interval is (3.78 +0.32/-0.33)E-06 erg/cm^2. 

The localization of GRB 260120B in the 'Amati' relation diagram is shown at: 
https://www.bursthub.cn//admin/static/svgrb260120B_amati.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 point of contact for this burst is: Yang-Zhao Ren (IHEP)(renyz@ihep.ac.cn)

A. Goyal (IITB), A. Arya (IITB), M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), Harsha K. H. (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 260120B which was also detected by Swift BAT (M. Ferro et. ala, GCN Circ. 43479
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 ), Fermi GBM (Fermi GBM Team, GCN Circ. 43477
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 ), Swift XRT (Goad et al., GCN Circ. 43484
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 ), and SVOM/C-GFT (Wu et al., GCN Circ. 43483
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 ).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-01-20 18:00:23.85 UTC. The measured peak count rate associated with the burst is  312 (+129, -23) counts/s above the background in the combined data of three quadrants (out of four), with a total of 622 (+153, -176) counts. The local mean background count rate was  174 (+4, -6) counts/s. Using cumulative rates, we measure a T90 of 5.0 (+1.5, -1.5) s. 

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-01-20 18:00:22.68 UTC. The measured peak count rate associated with the burst is 333 (+65, -44) counts/s above the background in the combined data of all quadrants, with a total of 1026 (+266, -251) counts. The local mean background count rate was 1065 (+7, -9) counts/s. We measure a T90 of 4.3 (+1.6, -1.8) s from the cumulative Veto light curve.

CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.

CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb

D. M. Palmer (LANL), 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),
T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC),
T. Sakamoto (AGU) (i.e. the Swift-BAT team):
 
Using the data set from T-769 to T+303 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 260120B (trigger #1442454)
(Ferro et al., GCN Circ. 43479
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 ).  The BAT ground-calculated position is
RA, Dec = 284.701, 61.905 deg which is 
   RA(J2000)  =  18h 58m 48.3s 
   Dec(J2000) = +61d 54' 19.2" 
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 9%.
 
The BAT light curve showed a single-peaked structure with a duration of about 10 sec.
T90 (15-350 keV) is 4.48 +- 0.94 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.34 to T+4.59 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index -0.93 +- 1.35, 
and Epeak of 103.9 +- 38.6 keV (chi squared 48.41 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.2 +- 0.1 x 10^-06 erg/cm2
and the 1-sec peak flux measured from T+0.48 sec in the 15-150 keV band is
3.1 +- 0.8 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 0.95 +- 0.21 (chi squared 57.22 for 57 d.o.f.).  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/1442454

M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S.
Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and
P.A. Evans report on behalf of the Swift-XRT team:

We have analysed 5.6 ks of XRT data for GRB 260120B, from 130 s to 29.5
ks after the   trigger. The data comprise 13 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 light curve can be modelled with a power-law decay with a decay
index of alpha=0.84 (+/-0.06).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.97 (+0.29, -0.27). The
best-fitting absorption column is  2.1 (+1.2, -1.0) x 10^21 cm^-2, in
excess of the Galactic value of 7.4 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.7 x 10^-11 (5.1 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.1 (+1.2, -1.0) x 10^21 cm^-2
Galactic foreground: 7.4 x 10^20 cm^-2
Excess significance: 2.4 sigma
Photon index:	     1.97 (+0.29, -0.27)

The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01442454.

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

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

"At 18:00:26.05 UT on 20 January 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260120B (trigger 790624831/260120750),
which was also detected by Swift BAT (Ferro et al. 2026, GCN 43479
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 ), Swift XRT (Goad et al. 2026, GCN 43484
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 ),
 and SVOM/C-GFT (Wu et al. 2026, GCN 43483
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 ).
The Fermi GBM real-time localization (GCN 43477
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 ) is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 10 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 7 s (50-300 keV). The time-averaged spectrum
from T0-1.1 to T0+9.9 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.19 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 214 +/- 4 keV.

The event fluence (10-1000 keV) in this time interval is
(3.1 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.38 s in the 10-1000 keV band is 5.8 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 152 +/- 2 keV, alpha = 0.36 +/- 0.02 and beta = -2.26 +/- 0.05.

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/"

A.A. Breeveld (UCL-MSSL) and M. Ferro (INAF-OAB) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 260120B 149 s after the BAT trigger (Ferro et al., GCN Circ. 43479
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 ).
A fading source consistent with the optical counterpart position given by Wu et al., (GCN Circ. 43483
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 ) and also the enhanced XRT position (Goad et al., GCN Circ. 43484
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 ) is detected in the initial UVOT exposures.

Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white              149          299          147         18.38 ± 0.06
white              588          776           35        >19.4
v                  637          657           19        >17.4
b                  563          755           39        >18.7
u                  307          557          246         18.80 ± 0.14
w1                 686          705           19        >17.4
m2                 661          681           19        >17.1
w2                 613          633           19        >17.5

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.063 in the direction of the burst (Schlegel et al. 1998).

Noémie Globus (UNAM), Antonio de Ugarte Postigo (LAM), 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), 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), and Benjamin Schneider (LAM):

We imaged the field of the Swift GRB 260120B (Ferro at al., GCN Circ. 43479
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 ; Goad et al., GCN Circ. 43484
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 ), also detected by Fermi (Fermi GBM team, GCN Circ. 43477
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 ) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-21 02:00 to 02:19 UTC (from 8.01 to 8.31 hours after the trigger) and obtained 16 minutes of simultaneous exposure in the r and z filters during evening twilight.

The data were reduced and coadded 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.

We do not detect any source within the enhanced XRT error circle (Goad et al., GCN Circ 43484
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 ) down to the following 3-sigma limits:

r > 22.87,
z > 22.12.

We do not detect the afterglow candidate reported by Wu et al (GCN Circ. 43483
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 ). This is consistent with the source having faded below our detection limit by the time of our observation, and indicates a temporal index steeper than -1.0.

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.

M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 609 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 260120B, 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 = 284.65977, +61.90497 which is equivalent
to:

RA (J2000): 18h 58m 38.34s
Dec (J2000): +61d 54' 17.9"

with an uncertainty of 2.3 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.

M. Ferro (INAF-OAB), R. Gupta (NASA GSFC), A. Y. Lien (U Tampa),
K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 18:00:26 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 260120B (trigger=1442454).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 284.666, +61.912 which is 
   RA(J2000) = 18h 58m 40s
   Dec(J2000) = +61d 54' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~1700 counts/sec (15-350 keV), at ~1 sec after the trigger.

The XRT began observing the field at 18:02:51.6 UT, 145.5 seconds after
the BAT trigger. No source was detected in the 2.5-s promptly available
image. We are waiting for the full dataset to detect and localise the
XRT counterpart.

No UVOT data are available at this time.

Burst Advocate for this burst is M. Ferro (matteo.ferro AT inaf.it).
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/)

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) was pointed to the Swift GRB260120.75 (trigger No 1442454,18h 58m 39.84s , +61d 54m 43.2s, R=0.05) errorbox  277 sec after notice time and 308 sec after trigger time at 2026-01-20 18:05:34 UT, with upper limit up to  17.0 mag. The observations began at zenith distance = 72 deg. The sun  altitude  is -43.2 deg. 

The galactic latitude b = 23 deg., longitude l = 92 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3109829

We obtain a following upper limits.  

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

     399 |   MASTER-Kislovodsk |   C |   180 | 12.3 |        
     399 |   MASTER-Kislovodsk |   C |   180 | 17.0 |        
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 18:00:26 UT on 20 Jan 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260120B (trigger 790624831.046372 / 260120750).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 282.2, Dec = 64.2 (J2000 degrees, equivalent to J2000 18h 48m, 64d 12'), with a statistical uncertainty of 1.5 degrees.

The angle from the Fermi LAT boresight is 11.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260120750/quicklook/glg_skymap_all_bn260120750.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/bn260120750/quicklook/glg_healpix_all_bn260120750.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260120750/quicklook/glg_lc_medres34_bn260120750.gif