GCN Circular 42983

Subject
GRB 251203B: Swift-XRT observations
Event
GRB 251203B
Date
2025-12-03T22:35:55Z (a day ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
S. Lanava (PSU), P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi 
(INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio
(INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A.
D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara
(PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester),
K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T.
Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf
of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source
sb25120304, collecting 972 s of Photon Counting (PC) mode data between T0+4.6 ks and
T0+5.7 ks after the trigger. A candidate counterpart has been found. The details of
this source are:

  Source 1 (SWIFT J011326.9+000111):
  ==================================
    RA (J2000.0):   18.3625  =	01 13 27.00
    Dec (J2000.0):  +0.0198  =	+00 01 11.3
    Error:	    3.5 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    5.9 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    1.785 +/- 0.088 ct s^-1
    Mean flux:	    (5.76 +/- 0.28)e-11 erg cm^-2 s^-1
    Peak rate:	    2.72 +/- 0.62 ct s^-1
    Peak flux:	    (8.8 +/- 2.0)e-11 erg cm^-2 s^-1
    ECF:	    3.23e-11 erg cm^-2 ct^-1
		      assuming NH=1.00e+21 cm^-2, gamma=2.03
		      determined from a spectral fit.
    This matches a catalogued X-ray source 4XMM J011326.8+000107
    in the XMM-NEWTON/XMMSSC catalogue. Details:
    Separation:     3.3" from the XRT source
    Cat Rate:	    2.7e-01 +/- 1.0e-02 ct s^-1 
    Cat Flux:	    2.4e-12 +/- 8.9e-14 erg cm^-2 s^-1 (0.3-10 keV)
		      so the source  is 4.3-sigma above the catalogued flux.
    The source may be fading, at the 0.3-sigma level.
    A SIMBAD object `Gaia DR3 2534635509050352256' is 4.2" away.
    There is 1 2MASS object within the source's 3-sigma error radius.

As pointed out by Malesani et al. (GCNs 42979Loading...
 
 ), Brunet et al. (GCN 42981Loading...
 
 ) and
Perez-Garcia at al. (GCN 42982Loading...
 
 ) this suggest that the transient is due to flaring
activity from this star.


We have detected a total of 4 sources.	These have been automatically classified as
follows:
  * 0 likely counterparts
  * 1 candidate counterpart
  * 3 uncatalogued X-ray sources
  * 0 known X-ray sources

Uncatalogued X-ray sources
--------------------------

  Source 2 (SWIFT J011329.9-000900):
  ==================================
    RA (J2000.0):   18.3746  =	01 13 29.90
    Dec (J2000.0):  -0.1502  =	-00 09 00.7
    Error:	    7.9 (arcsec, radius, 90% confidence).
    Detect flag:    POOR
    Distance:	    10.3 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    (6.9 [+4.4, -3.1])e-3 ct s^-1
    Mean flux:	    (3.0 [+1.9, -1.3])e-13 erg cm^-2 s^-1
    Peak rate:	    (6.9 [+4.4, -3.1])e-3 ct s^-1
    Peak flux:	    (3.0 [+1.9, -1.3])e-13 erg cm^-2 s^-1
    XMM UL:	    1.8e-14 erg cm^-2 s^-1, (0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.

  Source 3 (SWIFT J011422.6+000036):
  ==================================
    RA (J2000.0):   18.5945  =	01 14 22.68
    Dec (J2000.0):  +0.0102  =	+00 00 36.7
    Error:	    8.3 (arcsec, radius, 90% confidence).
    Detect flag:    POOR
    Distance:	    8.1 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    (6.2 [+4.0, -2.8])e-3 ct s^-1
    Mean flux:	    (2.6 [+1.7, -1.2])e-13 erg cm^-2 s^-1
    Peak rate:	    (6.2 [+4.0, -2.8])e-3 ct s^-1
    Peak flux:	    (2.6 [+1.7, -1.2])e-13 erg cm^-2 s^-1
    XMM UL:	    1.1e-14 erg cm^-2 s^-1, (0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.

  Source 4 (SWIFT J011327.9-000300):
  ==================================
    RA (J2000.0):   18.3663  =	01 13 27.91
    Dec (J2000.0):  -0.0501  =	-00 03 00.4
    Error:	    9.4 (arcsec, radius, 90% confidence).
    Detect flag:    POOR
    Distance:	    6.4 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    (-1.0 +/- -1.0)e0 ct s^-1
    Mean flux:	    (-4.3 +/- -4.3)e-11 erg cm^-2 s^-1
    Peak rate:	    (4.0 [+3.3, -2.3])e-3 ct s^-1
    Peak flux:	    (1.7 [+1.4, -1.0])e-13 erg cm^-2 s^-1
    XMM UL:	    3.6e-14 erg cm^-2 s^-1, (0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.
    There is 1 2MASS object within the source's 3-sigma error radius.

All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with
catalogues and upper limits  from other missions, we assumed a power-law spectrum
with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.

The results of the XRT-team automatic analysis of the XRT observations, including a
position-specific upper limit calculator, are available at
https://www.swift.ac.uk/SVOM/SVOM_FIELD00054.

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