GRB 250103B

M. Ferro, R. Brivio, P. D’Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:

We observed the field of GRB 250103B detected by Swift (Eyles-Ferris et al., GCN 38796
Loading...
 
 ), also detected by SVOM (Bouchet et al., GCN 38797
Loading...
 
 ) with the REM 60cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, K bands, starting on 2025 January 04 at 00:47:49 UT (i.e. 9.1 hours after the Swift trigger), and lasting for about 1 hour.
From preliminary photometry we do not detect any optical or NIR counterpart at the optical afterglow position (Qiu et al., GCN 38813
Loading...
 
 ; Habeeb et al., GCN 38820
Loading...
 
 ; Turpin et al., GCN 38822
Loading...
 
 ) down to the following 3sigma magnitude upper limits:

r > 20.4 (AB; calibrated against the SkyMapper catalogue)
at a mid-time of t - t0 = 9.5 hr after the trigger,

H > 17.3 (Vega; calibrated against the 2MASS catalogue) 
at a mid-time of t - t0 = 9.4 hr after the trigger.

J.P. Osborne (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo
(INAF-OAB), M.G. Bernardini (INAF-OAB), D.N. Burrows (PSU), M. A.
Williams (PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A.
Evans report on behalf of the Swift-XRT team:

We have analysed 3.5 ks of XRT data for GRB 250103B, from 144 s to 44.7
ks after the  BAT trigger. The data comprise 31 s in Windowed Timing
(WT) mode with the remainder in Photon Counting (PC) mode. The best
available XRT position	(using the promptly downlinked event data, the
XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue) is RA, Dec = 54.66413, -33.74945 which is equivalent to:

RA (J2000): 03 38 39.39
Dec(J2000): -33 44 58.0

with an uncertainty of 1.9 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=3.9 (+/-0.4).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 4.2 (+0.7, -0.5). The
best-fitting absorption column is  6.3 (+6.6, -4.5) x 10^20 cm^-2, in
excess of the Galactic value of 1.0 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 2.5 x 10^-11 (4.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     6.3 (+6.6, -4.5) x 10^20 cm^-2
Galactic foreground: 1.0 x 10^20 cm^-2
Excess significance: 2.0 sigma
Photon index:	     4.2 (+0.7, -0.5)

If the light curve continues to decay with a power-law decay index of
3.9, the count rate at T+24 hours will be 2.5 x 10^-10 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.3 x
10^-21 (1.2 x 10^-20) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01278865.

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

D. Turpin (CEA/Irfu), A. Saccardi (GEPI/Obs. de Paris, CEA/Irfu), S. Basa (UAR Pytheas, OHP, LAM), D. B. Malesani (DAWN/NBI and Radboud Univ.), J. T. Palmerio (CEA/Irfu, GEPI/Obs. de Paris), S. Vergani (GEPI/Obs. de Paris), E. Le Floc'h (CEA Paris-Saclay, DAp/AIM) on behalf of a larger collaboration.

We observed the field of GRB 250103B detected by Swift (Eyles-Ferris et al. GCN 38796
Loading...
 
 ) and SVOM (Bouchet et al., GCN 38797
Loading...
 
 ) with the LCO 1.0m telescope at the Sutherland Observatory (SAAO) equipped with the Sinistro instrument. Our observation started at 2025-01-03T20:25:20.617 (T - TGRB ~ 4.68 hr) with 5 x 120s exposure using the sdss-r filter.

We marginally detect the optical afterglow candidate seen by SVOM/VT (Qiu et al., GCN 38813
Loading...
 
 ) and VLT (Habeeb et al., GCN 38820
Loading...
 
 ) from the difference image analysis between our stacked image and the Legacy Survey DR10 template image. At the position reported by VLT, we derived the following magnitude r = 22.32 +/- 0.26 (at Tmid - T0 = 4.78 hr) calibrated with the SkyMapper DR4 catalog and not corrected from the galactic extinction E(B-V): 0.01.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101004719.

N. Habeeb (Leicester), A. Saccardi (CEA/Irfu), L. Izzo (INAF/OACn and DARK/NBI), B. Schneider (LAM), D. B. Malesani (DAWN/NBI and Radboud Univ.), G. Pugliese (UvA), A. L. Thakur (INAF-IAPS), A. de Ugarte Postigo (CNRS, OCA and LAM), Z.P. Zhu, J. An, D. Xu (NAOC) report on behalf of the Stargate collaboration:

We observed the optical afterglow (Qiu et al., GCN 38813
Loading...
 
 ) of GRB 250103B (Eyles-Ferris et al., GCN 38796
Loading...
 
 ; Bouchet et al., GCN 38797
Loading...
 
 ) using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra cover the wavelength range 3000-25000 AA, and consist of 4 exposures by 1200 s each. The observation mid time was 2025 Jan 4.1283 UT (11.341 hr after the GRB).

In a 60-s acquisition image taken with the z filter (mid time Jan 4.104 UT), we clearly detect the afterglow (Qiu et al., GCN 38813
Loading...
 
 ). We measure the following coordinates (J2000):

RA = 03:38:39.335
Dec = -33:44:56.80

with an uncertainty of ~0.4". We measure a magnitude z = 22.5 +- 0.2 AB, calibrated against a single star in common with the Legacy Survey.

In a preliminary reduction of the spectra, we detect a continuum over the entire wavelength range. From the detection of multiple absorption features, which we interpret as due to Mg II and Fe II, we infer a common redshift of z = 1.416. At a consistent redshift, we also detect emission lines due to Halpha, [O III] 5007 AA and the [O II] 3726, 3729 AA doublet. We conclude that this is the redshift of GRB 250103B.

We note that, at the afterglow position, a faint object is seen in the Legacy survey, only confidently detected in the g band, which is likely the GRB host galaxy.

We acknowledge the expert support from the ESO observing staff at Paranal.

SVOM/VT commissioning team: Y. L. Qiu, H. L. Li, L. P. Xin, C. Wu, X. H. Han, J. Wang, W. J. Xie, H. B. Cai, Y. Xu, Y. J. Xiao, P. P. Zhang, J. S. Deng, L. Lan, X. M. Lu, R. S. Zhang, Z. H. Yao (NAOC), J. Zhang, L. J. Dan, G. Y. Zou, C. J. Wang, Y. F. Du, C. Huang (XIOPM),T. Bouchet, D. Turpin (CEA)

SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Olivier Godet (IRAP), Andrea Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Shao-Lin Xiong (IHEP), Bing Zhang (UNLV)

report on behalf of the SVOM team:

The SVOM/VT conducted a ToO follow-up observations for GRB 250103B triggered by both Swift(R. A. J. Eyles-Ferris, GCN 38796
Loading...
 
 ) and SVOM (T. Bouchet, GCN 38797
Loading...
 
 ) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously, from 2.467 hours to 7.573 hours after the burst. 

An uncatalogued fading source was clearly detected within the errorbox of XRT (R. A. J. Eyles-Ferris, GCN 38796
Loading...
 
 ) in both VT_B and VT_R stacked images, compared to  DESI DR10 catalog. The brightness of the source was estimated to be VT_B=22.1+/-0.1 mag and VT_R=21.8+/-0.1 mag in AB magnitude at the mid time of 2.79 hours post the burst, with a total exposure time of 23*100 seconds. 

The source is located at RA, Dec =  54.66373, -33.74927 deg, which is equivalent to:
RA (J2000) : 03:38:39.30
Dec (J2000): -33:44:57.4
with an uncertainty of 0.2 arcsec.

We proposed that the source is the counterpart for the gamma-ray burst. 

More deep follow-ups are encouraged.

The magnitudes give above are not corrected for the expected Galactic foreground extinction, corresponding to a reddening of E(B-V) = 0.0067 mag in the direction of the optical counterpart (Schlafly & Finkbeiner 2011).

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. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS.

R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration:

We observed the Swift GRB 250103B field (Eyles-Ferris et al., GCN 38796
Loading...
 
 )  with the LCOGT 1-meter Sinistro instrument at the South African Astronomical Observatory site, on January 3, from 18:51 to 19:23 UT (corresponding to 4.12 to 4.65 hours after the GRB trigger time) with the Bessel I and R filters.

We performed a series of 3x300s exposures in I-band and R-band.  We do not detect a source within the  XRT error region in either band.

The following 5-sigma upper limits are calculated using the USNO-B1.0 catalog as reference:

R > 23.0
I > 22.1

These magnitudes are not corrected for galactic extinction.

V.Lipunov, E.Gorbovskoy, N.Tiurina,  P.Balanutsa, , D.Vlasenko, I.Panchenko,
A.Kuznetsov,  G.Antipov,  A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, 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. 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-SAAO robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 250103B ( R. A. J. Eyles-Ferris et al., GCN 38796
Loading...
 
 ) errorbox  10372 sec after notice time and 10451 sec after trigger time at 2025-01-03 18:38:29 UT, with upper limit up to  18.0 mag. Observations started at twilight.  The observations began at zenith distance = 10 deg. The sun  altitude  is -9.9 deg. 

The galactic latitude b = -53 deg., longitude l = 234 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2732251

We obtain a following upper limits.  

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

   10542 |         MASTER-SAAO |   C |   180 | 18.0 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

T. Bouchet, D. Turpin (CEA), S. Guillot (IRAP), H. Goto (CEA), F. Daigne (IAP),  L. Zhang (IHEP) report on behalf of the SVOM team:

The SVOM/ECLAIRs telescope triggered (sb25010303) at 2025-01-03T15:44:04.223 UTC (Tb) and located the long duration GRB 250103B also detected by Swift (Eyles-Ferris et al. GCN 38796
Loading...
 
 ).

The following trigger information was received on the ground with low-latency by the SVOM VHF Alert Network.

The burst was detected by both the on-board Count-Rate Trigger (CRT) and Image Trigger (IMT) and 7 alerts were received. The best detection is obtained by IMT with a signal-to-noise ratio of 10.6 in the 5-8 keV energy band over a time window of 41 s starting at Tb.
 
The localization of the best Alert is RA, Dec =  54.660, -33.769 (J2000). 
R.A. = 03:38:38.46
Dec = -33:46:09.67
The uncertainty on this position is 7.6 arcminutes at 90% C.L., which includes a systematic uncertainty of 2 arcminutes in quadrature.

The light curve shows a main single episode in the GRM data with a preliminary T90 duration of about 25 s below 550 keV. Further analysis will be conducted once the X-band telemetry data of ECLAIRs and GRM are received.

SVOM did not slew on this burst.

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. 

The SVOM point of contact for this burst is: Tristan Bouchet (tristan.bouchet@cea.fr)

R. A. J. Eyles-Ferris (U Leicester), S. Dichiara (PSU),
P. A. Evans (U Leicester), R. Gupta (NASA GSFC),
N. P. M. Kuin (UCL-MSSL), M. J. Moss (GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL) and M. A. Williams (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 15:44:17 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250103B (trigger=1278865).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 54.651, -33.772 which is 
   RA(J2000) = 03h 38m 36s
   Dec(J2000) = -33d 46' 18"
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 30 sec.  The peak count rate
was ~600 counts/sec (15-350 keV), at ~3 sec after the trigger.

The XRT began observing the field at 15:46:48.8 UT, 151.2 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 54.66403,
-33.74965 which is equivalent to:
   RA(J2000)  = 03h 38m 39.37s
   Dec(J2000) = -33d 44' 58.7"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 89 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 (9.99 x
10^19 cm^-2, Willingale et al. 2013), with an excess column of 4.1
(+3.96/-3.24) x 10^21 cm^-2 (90% confidence).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 155 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 0.008.

Burst Advocate for this burst is R. A. J. Eyles-Ferris (raje1 AT leicester.ac.uk).
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/)