GRB 251007B

Francesco Magnani (CPPM), Camila Angulo (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), , Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):

We imaged the field of the Swift/SVOM GRB 251007B (Melandri et al., GCN Circ. 42147
Loading...
 
 , Webb et al., GCN Circ. 42148
Loading...
 
 ) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-08 10:34 to 12:32 UTC (from 14.9 to 16.8 hours after the trigger) and obtained 80 minutes of simultaneous exposure in the i and z filters.

The data were reduced and coadded with the COLIBRÍ pipeline and the tenue software, 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.

In the stacked image, we do not detect a source at the SVOM/VT source position (Li et al., GCN Circ. 42163
Loading...
 
 ) down to the following 3-sigma limits:

i > 23.3
z > 22.7

These upper limits are consistent with the ones reported by Wu et al. (GCN Circ. 42150
Loading...
 
 ). Our image is not deep enough to confirm fading of the source reported by Li et al. (GCN Circ. 42163
Loading...
 
 ).

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.

H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu,  Z. H. Yao, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), N. A. Webb, O. Godet  report on behalf of the SVOM/VT Instrument Center: 

SVOM/VT conducted ToO follow-up observations of GRB 251007B (sb25100703) (Melandri et al., GCN 42147
Loading...
 
 ; Webb et al., GCN 42148
Loading...
 
 ). The observation started on 2025-10-07T21:41:47 UT, 1.98 hours after the burst, in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.

Within the error box of enhanced XRT position (Osborne et al., GCN 42159
Loading...
 
 ), an uncatalogued source was detected in both channels of VT, compared to the PanSTARRS catalogue. The position is at R.A., Dec. = 102.1329813, -10.3040289 degrees, equivalent to:
R.A. (J2000) =  6:48:31.92
Dec. (J2000) =  -10:18:14.50
with an uncertainty of 0.5 arcsec.

The magnitudes are as follows:

Mid_time     |  Band   | Exposure Time  |  Magnitude (AB)
4.82 hour       VT_R       43*70 sec      23.00+/-0.20  mag                      
4.82 hour       VT_B       43*70 sec      23.53+/-0.24  mag

Our photometry is in AB magnitude and not corrected for Galactic extinction.

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.

A.P. Beardmore (U. Leicester), M. Perri (SSDC & INAF-OAR), V. D'Elia
(SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), J.A. Kennea (PSU), D.N.
Burrows (PSU), S. Lanava (PSU), J.P. Osborne (U. Leicester) and P.A.
Evans report on behalf of the Swift-XRT team:

We have analysed 6.4 ks of XRT data for GRB 251007B, from 134 s to 33.2
ks after the   trigger. The data comprise 6 s in Windowed Timing (WT)
mode (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=1.68 (+0.24, -0.26).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.79 (+0.39, -0.25). The
best-fitting absorption column is  6.5 (+3.1, -0.5) x 10^21 cm^-2,
consistent with the Galactic value of 6.0 x 10^21 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 5.0 x 10^-11 (7.5 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.5 (+3.1, -0.5) x 10^21 cm^-2
Galactic foreground: 6.0 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.79 (+0.39, -0.25)

If the light curve continues to decay with a power-law decay index of
1.68, the count rate at T+24 hours will be 3.9 x 10^-5 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.9 x
10^-15 (2.9 x 10^-15) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01402467.

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

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

Using 1164 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 251007B, 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 = 102.13270, -10.30374 which is equivalent
to:

RA (J2000): 06h 48m 31.85s
Dec (J2000): -10d 18' 13.4"

with an uncertainty of 2.5 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at http://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.

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-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 251007B ( A. Melandri et al., GCN 42147
Loading...
 
 ) errorbox  9413 sec after notice time and 9658 sec after trigger time at 2025-10-07 22:24:05 UT, with upper limit up to  17.1 mag. The observations began at zenith distance = 83 deg. The sun  altitude  is -52.3 deg. 

The galactic latitude b = -5 deg., longitude l = 222 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3009588

We obtain a following upper limits.  

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

    9688 |         MASTER-SAAO |   C |    60 | 17.1 |        
Filter C is a clear (unfiltred) band. 


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

N. A. Webb, O. Godet, S. Guillot (IRAP), F. Lacreu (IAP) report on behalf of the SVOM mission team


At 2025-10-07T19:43:23 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251007B (SVOM burst-id sb25100703), also detected by Swift/BAT (GCN #42147
Loading...
 
 , Melandri et al. 2025).


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


The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 7 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.53 in the [8-50] keV energy band over a time window of 20.40 seconds starting at 2025-10-07T19:42:57.


The localization of the best alert is R.A., Dec. 101.997, -10.279 degrees:

R.A. (J2000) = 6h47m59.29s

Dec. (J2000) = -10d16m42.81s

with a 90% confidence level (C.L.) radius of 8.33 arcmin (including systematic error of 2 arcmin added in quadrature).


The SVOM/ECLAIRs light curve showed a single peak structure with a T90 duration of about 23.26 (-8.032 +4.41) s.


The platform did not slew to the source. No observations could be performed in the X-rays by SVOM/MXT nor in the optical with SVOM/VT for the time being.


The Space-based multi-band astronomical 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.


The Burst Advocate (BA) on shift for this alert is Natalie Webb: natalie.webb@irap.omp.eu.

Please contact the BA by email if you require additional information.

A. Melandri (INAF-OAR), E. Ambrosi (INAF-IASFPA),
A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU),
R. Gupta (NASA GSFC), N. J. Klingler (GSFC/UMBC/CRESSTII),
N. P. M. Kuin (UCL-MSSL) and M. H. Siegel (PSU) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 19:43:06 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 251007B (trigger=1402467).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 102.117, -10.303 which is 
   RA(J2000) = 06h 48m 28s
   Dec(J2000) = -10d 18' 11"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Due to the continued on-board processing of the
previous burst (GRB 251007A) the BAT lightcurve is not immediately available.

The XRT began observing the field at 19:45:35.0 UT, 148.2 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 102.13232, -10.30328 which is
equivalent to:
   RA(J2000)  = 06h 48m 31.76s
   Dec(J2000) = -10d 18' 11.8"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 54 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.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 5.99
x 10^21 cm^-2 (Willingale et al. 2013).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 151 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image processing
FAILED because of no aspect solution. Results from the list of sources
generated on-board are not available at this time. No correction has been made
for the expected extinction corresponding to E(B-V) of 0.785.

Burst Advocate for this burst is A. Melandri (andrea.melandri 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/)