GRB 251106A
GCN Circular 42635
Subject
GRB 251106A: Swift/UVOT Upper Limits
Date
2025-11-10T15:56:36Z (20 hours ago)
From
Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>
Via
Web form
M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 251106A 4.1 ks after the SVOM/ECLAIRs trigger (Antier et al., GCN Circ. 42605). We do not detect any afterglow consistent with the XRT position (D'Ai et al., GCN Circ. 42611) or optical position (Angulo et al., GCN Circ. 42607).
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
u 4066 9896 1987 >20.56
u 199146 273340 4837 >21.08
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.016 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 42613
Subject
GRB 251106A: SVOM/COLIBRÍ (FM-GFT) fading of the optical counterpart
Date
2025-11-07T14:32:43Z (4 days ago)
From
F. Fortin at IRAP <ffortin.sci.edu@gmail.com>
Via
Web form
Francis Fortin (IRAP), Camila Angulo (UNAM), Jean-Luc Atteia (IRAP), Benjamin Schneider (LAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), 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), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of the SVOM GRB 251106A (Antier et al., GCN Circ. 42605) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed a second epoch from 2025-11-07 12:34 to 12:50 UTC (from 16.63 to 16.89 hours after the trigger) and obtained an additional 16 minutes of exposure in the r filter at high airmass (3 to 3.5).
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 detect the optical counterpart we previously reported (Angulo et al, GCN Circ. 42607) at the following preliminary magnitude:
r = 21.85 +/- 0.13
Our photometry shows clear fading with respect to our earlier epoch, confirming that this is the optical counterpart of the GRB.
We note that the position of the afterglow optical counterpart is coincident with a faint source in the Legacy Survey (Dey et al. 2019) at r = 22.56 +/- 0.17, which could be the host galaxy of the GRB.
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.
GCN Circular 42611
Subject
GRB 251106A: Swift-XRT afterglow detection
Date
2025-11-07T10:12:12Z (4 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), J.A. Kennea (PSU), D.N.
Burrows (PSU), S. Lanava (PSU), A.P. Beardmore (U. Leicester), J.P.
Osborne (U. Leicester), A. Melandri (INAF-OAR) and P.A. Evans (U.
Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of GRB 251106A. We
searched for X-ray sources in 2.0 ks of Photon Counting (PC) mode
data. The total exposure at the position of the afterglow (see below)
is 2.0 ks, obtained between T0+4.0 ks and T0+9.9 ks.
Three uncatalogued X-ray sources are detected, of which one ("Source
1") is above the RASS 3-sigma upper limit at this position, and is
therefore likely the GRB afterglow. Using 2020 s of PC mode data and 2
UVOT images, we find an enhanced XRT position (using the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue):
RA, Dec = 234.46260, +63.36779 which is equivalent to:
RA (J2000): 15h 37m 51.02s
Dec(J2000): +63d 22' 04.0"
with an uncertainty of 2.6 arcsec (radius, 90% confidence). This
position is consistent with the optical afterglow candidate identified
by Angulo et al. (GCN 42607).
The light curve can be modelled with a power-law decay with a decay
index of alpha=0.87 (+0.33, -0.29).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.96 (+0.23, -0.22). The
best-fitting absorption column is 1.1 (+0.6, -0.5) x 10^21 cm^-2, in
excess of the Galactic value of 1.7 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 3.2 x 10^-11 (3.9 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.1 (+0.6, -0.5) x 10^21 cm^-2
Galactic foreground: 1.7 x 10^20 cm^-2
Excess significance: 2.8 sigma
Photon index: 1.96 (+0.23, -0.22)
If the light curve continues to decay with a power-law decay index of
0.87, the count rate at T+24 hours will be 0.038 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-12 (1.5 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/03000182.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/SVOM/SVOM_FIELD00048.
This circular is an official product of the Swift-XRT team.
GCN Circular 42610
Subject
GRB 251106A: Kilonova-Catcher optical upper limit
Date
2025-11-07T08:48:49Z (4 days ago)
Edited On
2025-11-07T18:15:45Z (4 days ago)
From
Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Via
Web form
M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration:
We observed the field of GRB 251106A detected by SVOM (Antier et al., GCN 42605), Swift/BAT-GUANO (Delaunay et al., GCN 42608) and Fermi/GBM subthreshold (Godwin et al., GCN 42608