TITLE:   GCN CIRCULAR
NUMBER:  42461
SUBJECT: GRB 251026A: Swift-XRT observations
DATE:    25/10/26 21:42:15 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

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 251026A (SVOM burst-id sb25102605), collecting 1.7 ks of Photon Counting (PC)
mode data between T0+5.8 ks and T0+12 ks after the trigger. We have detected 2
sources.  These have been automatically classified as follows:
  * 0 likely counterparts
  * 0 candidate counterparts
  * 2 uncatalogued X-ray sources
  * 0 known X-ray sources

We note that neither source is consistent with the SVOM/MXT position given in GCN
Circ. 42454.

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

  Source 1 (SWIFT J044944.9+514605):
  ==================================
    RA (J2000.0):   72.4374  =	04 49 44.98
    Dec (J2000.0):  +51.7683  =  +51 46 05.9
    Error:	    5.1 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    5.8 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    0.0123 +/- 0.0033 ct s^-1
    Mean flux:	    (4.6 +/- 1.2)e-13 erg cm^-2 s^-1
    Peak rate:	    0.0123 +/- 0.0033 ct s^-1
    Peak flux:	    (4.6 +/- 1.2)e-13 erg cm^-2 s^-1
    ECF:	    3.75e-11 erg cm^-2 ct^-1
		      assuming NH=1.57e+22 cm^-2, gamma=2.98
		      determined from a spectral fit.
    XMM UL:	    3.5e-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.
    A SIMBAD object `NVSS J044945+514603' is 7.5" away.
    There are 2 2MASS objects within the source's 3-sigma error radius.

  Source 2 (SWIFT J045052.5+515630):
  ==================================
    RA (J2000.0):   72.7189  =	04 50 52.54
    Dec (J2000.0):  +51.9418  =  +51 56 30.5
    Error:	    9.7 (arcsec, radius, 90% confidence).
    Detect flag:    REASONABLE
    Distance:	    9.6 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    (4.0 [+2.6, -1.8])e-3 ct s^-1
    Mean flux:	    (1.74 [+1.10, -0.78])e-13 erg cm^-2 s^-1
    Peak rate:	    (4.0 [+2.6, -1.8])e-3 ct s^-1
    Peak flux:	    (1.74 [+1.10, -0.78])e-13 erg cm^-2 s^-1
    XMM UL:	    2.3e-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.
    A SIMBAD object `NVSS J045052+515630' is 3.9" away.
    There are 6 2MASS objects 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_FIELD00045.

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