GCN Circular 42645

Subject
GRB 251111A: Swift-XRT observations
Event
GRB 251111A
Date
2025-11-11T14:02:01Z (2 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
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
GRB 251111A, collecting 288 s of Photon Counting (PC) mode data between T0+7.4 ks
and T0+7.8 ks after the trigger. We have detected 1 source.  This has been
automatically classified as an uncatalogued X-ray source.

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

  Source 1 (SWIFT J020926.8+051342):
  ==================================
    RA (J2000.0):   32.3618  =	02 09 26.83
    Dec (J2000.0):  +5.2284  =	+05 13 42.2
    Error:	    5.7 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    2.0 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    0.0264 [+0.0127, -0.0096] ct s^-1
    Mean flux:	    (7.2 [+3.5, -2.6])e-13 erg cm^-2 s^-1
    Peak rate:	    0.0264 [+0.0127, -0.0096] ct s^-1
    Peak flux:	    (7.2 [+3.5, -2.6])e-13 erg cm^-2 s^-1
    ECF:	    2.73e-11 erg cm^-2 ct^-1
		      assuming NH=5.07e+20 cm^-2, gamma=2.63
		      determined from a spectral fit.
    XMM UL:	    2.6e-12 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.

The XRT position is consistent the optical counterpart reported by the SVOM/COLIBRÍ
(FM-GFT; López-Cámara et al., GCN Circ. 42638Loading...
 
 ), LCO 1m (Wu et al., GCN Circ.
42639Loading...
 
 ) and SVOM/VT (Wu et al., GCN 42641Loading...
 
 ) telescopes, as well as the Einstein Probe
FXT X-ray detection (Cheng et al. 42643).

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_FIELD00049.

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