GCN Circular 41699

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 250903A, collecting 2.4 ks of Photon Counting (PC) mode data between T0+12 ks
and T0+24 ks after the trigger. We have detected 2 sources inside the ECLAIRs error
region.  
These have been automatically classified as follows:
  * 0 likely counterparts
  * 0 candidate counterparts
  * 2 uncatalogued X-ray sources
  * 0 known X-ray sources


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

  Source 1 (SWIFT J234712.1-755757):
  ==================================
    RA (J2000.0):   356.8008  =  23 47 12.19
    Dec (J2000.0):  -75.9660  =  -75 57 57.6
    Error:	    4.3 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    2.7 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    0.0387 [+0.0049, -0.0047] ct s^-1
    Mean flux:	    (1.33 [+0.17, -0.16])e-12 erg cm^-2 s^-1
    Peak rate:	    0.052 +/- 0.014 ct s^-1
    Peak flux:	    (1.80 +/- 0.47)e-12 erg cm^-2 s^-1
    ECF:	    3.42e-11 erg cm^-2 ct^-1
		      assuming NH=4.68e+20 cm^-2, gamma=1.95
		      determined from a spectral fit.
    XMM UL:	    2.0e-12 erg cm^-2 s^-1, (0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    The source may be fading, at the 0.8-sigma level.

  Source 2 (SWIFT J234819.4-755214):
  ==================================
    RA (J2000.0):   357.0812  =  23 48 19.49
    Dec (J2000.0):  -75.8707  =  -75 52 14.5
    Error:	    6.4 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    4.8 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    (8.6 [+2.9, -2.4])e-3 ct s^-1
    Mean flux:	    (1.06 [+0.36, -0.30])e-11 erg cm^-2 s^-1
    Peak rate:	    (8.6 [+2.9, -2.4])e-3 ct s^-1
    Peak flux:	    (1.06 [+0.36, -0.30])e-11 erg cm^-2 s^-1
    ECF:	    1.23e-09 erg cm^-2 ct^-1
		      assuming NH=4.41e+20 cm^-2, gamma=-2.35
		      determined from a spectral fit.
    XMM UL:	    1.9e-12 erg cm^-2 s^-1, (0.3-10 keV)
		      so the source is 2.7-sigma above this 3-sigma upper limit.
    There is no evidence for fading.
    A SIMBAD object `LEDA  242511' is 4.1" away.
    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.

Source 1 position is consistent with the optical counterpart discovered by TRT (GCN
41679
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 ).

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_FIELD00034.

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