GRB 260104A

M. J. Moss (GSFC), S. D. Barthelmy (GSFC),
R. Caputo (GSFC), R. Gupta (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), C. B. Markwardt (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-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 260104A (trigger #1430212)
(Caputo, et al., GCN Circ. 43315
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 ).  The BAT ground-calculated position is
RA, Dec = 337.395, -21.291 deg which is
   RA(J2000)  =  22h 29m 34.8s
   Dec(J2000) = -21d 17' 27.5"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 99%.

The mask-weighted light curve shows two pulses. T90 (15-350 keV) is 13.26 +- 2.65 sec (estimated error including systematics).

The time-averaged spectrum from T-10.09 to T+5.22 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.32 +- 1.08,
and Epeak of 42.5 +- 8.8 keV (chi squared 67.04 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 3.5 +- 0.5 x 10^-07 erg/cm2
and the 1-sec peak flux measured from T-0.23 sec in the 15-150 keV band is
1.3 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.85 +- 0.16 (chi squared 76.81 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/1430212

Noémie Globus (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Dalya Akl (NYUAD), Camila Angulo (UNAM), 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), Nikos Mandarakas (LAM), Kin Ocelotl López (UNAM), 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 imaged the field of GRB 260104A (Caputo et al., GCN Circ. 43315
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 ; Evans et al., GCN Circ. 43319
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 ; Kennea et al., GCN Circ. 43320
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 ), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-01-05 at 01:46 to 02:44 UTC (from 20.16 to 21.12 hr after the trigger) and obtained 41 minutes of simultaneous exposure in the r and z filters.

The data were reduced and coadded with the COLIBRÍ ASU pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and was not corrected for Galactic extinction.

In the stacked image, we do not detect any new source at the XRT uncertainty region (Caputo et al., GCN Circ. 43315
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 ) down to the following 5-sigma limit:
r > 21.90,
z > 20.96.

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.

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 GRB 260104A ( R. Caputo et al., GCN 43315
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 ) errorbox  39152 sec after notice time and 39173 sec after trigger time at 2026-01-04 16:29:55 UT, with upper limit up to  15.0 mag. The observations began at zenith distance = 82 deg. The sun  altitude  is -28.6 deg. 

The galactic latitude b = -58 deg., longitude l = 36 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3095622

We obtain a following upper limits.  

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

   39263 |   MASTER-Kislovodsk |   C |   180 | 13.5 |        
   39263 |   MASTER-Kislovodsk |   C |   180 | 14.3 |        
   39471 |   MASTER-Kislovodsk |   C |   180 | 13.5 |        
   39471 |   MASTER-Kislovodsk |   C |   180 | 14.1 |        
   39687 |   MASTER-Kislovodsk |   C |   180 | 14.2 |        
   39687 |   MASTER-Kislovodsk |   C |   180 | 15.0 |        
   39903 |   MASTER-Kislovodsk |   C |   180 | 14.7 |        
   39903 |   MASTER-Kislovodsk |   C |   180 | 15.0 |        
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

J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU), A.P. Beardmore
(U. Leicester), J.P. Osborne (U. Leicester), E. Ambrosi  (INAF-IASFPA)
, M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR) and P.A. Evans
report on behalf of the Swift-XRT team:

We have analysed 6.3 ks of XRT data for GRB 260104A, from 101 s to 28.3
ks after the   trigger. The data comprise 10 s in Windowed Timing (WT)
mode (taken while Swift was slewing), with the remainder in Photon
Counting (PC) mode. 

The late-time light curve (from T0+5.1 ks) can be modelled with a
power-law decay with a decay index of alpha=1.22 (+0.26, -0.23).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.78 (+0.16, -0.10). The
best-fitting absorption column is  3.55 (+3.69, -0.15) x 10^20 cm^-2,
consistent with the Galactic value of 3.4 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 (4.0 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.55 (+3.69, -0.15) x 10^20 cm^-2
Galactic foreground: 3.4 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.78 (+0.16, -0.10)

If the light curve continues to decay with a power-law decay index of
1.22, the count rate at T+24 hours will be 4.6 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x
10^-13 (1.8 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01430212.

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

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

Using 3264 s of XRT Photon Counting mode data and 6 UVOT
images for GRB 260104A, 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 = 337.39920, -21.29552 which is equivalent
to:

RA (J2000): 22h 29m 35.81s
Dec (J2000): -21d 17' 43.9"

with an uncertainty of 2.0 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.

R. Caputo (GSFC), J. J. DeLaunay (PSU), K. L. Page (U Leicester) and
M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 05:37:02 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 260104A (trigger=1430212).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 337.415, -21.280 which is 
   RA(J2000) = 22h 29m 40s
   Dec(J2000) = -21d 16' 48"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 20 sec.  The peak count rate
was ~2400 counts/sec (15-350 keV), at ~0 sec after the trigger.

The XRT began observing the field at 05:38:28.9 UT, 86.1 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 337.39898, -21.29547
which is equivalent to:
   RA(J2000)  = 22h 29m 35.76s
   Dec(J2000) = -21d 17' 43.7"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 77 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 (3.40 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.8
(+2.48/-2.16) x 10^21 cm^-2 (90% confidence).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 90 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 0.033.

Burst Advocate for this burst is R. Caputo (regina.caputo AT nasa.gov).
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/)