GCN Circular 43622

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 GRB
260204A, collecting 1.7 ks of Photon Counting (PC) mode data between T0+23 ks and
T0+25 ks after the trigger. We have detected 4 sources.  These have been
automatically classified as follows:
  * 0 likely counterparts
  * 0 candidate counterparts
  * 3 uncatalogued X-ray sources
  * 1 known X-ray source

As already reported source 1 is consistent with an optical source (Li et al., GCN
Circ. 43620
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 ; Malesani et al., GCN Circ. 43621
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 ). We note that, in the X-rays, this
source is not well separated from source 3 and cannot rule out that these arise not
from point sources but from a patch of diffuse emission. 

We note also the presence of a source in the XMM Slew survey XMMSL3 catalogue,
XMMSL3 J134023.8+015613 at RA,Dec = 205.0888, +1.9370 degrees (J2000), with a
1-sigma error of 4.3" (statistical) and an estimated systematic error of ~8" (see
http://xmmssc.irap.omp.eu/Catalogue/XMMSL3/XMMSL3_Catalogue_User_Guide.html#Astromet
ry). This source is 33" from the position of source 1.

Source 2 is consistent with the position of HD 118981, a high proper motion star,
while source 4 is a known quasar.

Further observations are planned.

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

  Source 1 (SWIFT J134025.4+015552):
  ==================================
    RA (J2000.0):   205.1060  =  13 40 25.44
    Dec (J2000.0):  +1.9313  =	+01 55 52.7
    Error:	    5.0 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    5.4 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    0.0235 +/- 0.0046 ct s^-1
    Mean flux:	    (8.7 +/- 1.7)e-13 erg cm^-2 s^-1
    Peak rate:	    0.0235 +/- 0.0046 ct s^-1
    Peak flux:	    (8.7 +/- 1.7)e-13 erg cm^-2 s^-1
    ECF:	    3.71e-11 erg cm^-2 ct^-1
		      assuming NH=1.90e+20 cm^-2, gamma=1.76
		      determined from a spectral fit.
    RASS UL:	    4.1e-02 ct s^-1 (converted to XRT; 0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.

  Source 2 (SWIFT J134026.9+020905):
  ==================================
    RA (J2000.0):   205.1125  =  13 40 27.00
    Dec (J2000.0):  +2.1515  =	+02 09 05.4
    Error:	    5.0 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    7.9 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    0.0136 +/- 0.0036 ct s^-1
    Mean flux:	    (2.28 +/- 0.61)e-13 erg cm^-2 s^-1
    Peak rate:	    0.0136 +/- 0.0036 ct s^-1
    Peak flux:	    (2.28 +/- 0.61)e-13 erg cm^-2 s^-1
    ECF:	    1.67e-11 erg cm^-2 ct^-1
		      assuming NH=1.30e+22 cm^-2, gamma=9.94
		      determined from a spectral fit.
    RASS UL:	    3.3e-02 ct s^-1 (converted to XRT; 0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.
    A SIMBAD object `HD 118981' is 0.7" away.
    There is 1 2MASS object within the source's 3-sigma error radius.

  Source 4 (SWIFT J134043.1+020310):
  ==================================
    RA (J2000.0):   205.1796  =  13 40 43.10
    Dec (J2000.0):  +2.0530  =	+02 03 10.8
    Error:	    6.6 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    4.2 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    (7.2 [+2.9, -2.3])e-3 ct s^-1
    Mean flux:	    (1.49 [+0.60, -0.48])e-13 erg cm^-2 s^-1
    Peak rate:	    (7.2 [+2.9, -2.3])e-3 ct s^-1
    Peak flux:	    (1.49 [+0.60, -0.48])e-13 erg cm^-2 s^-1
    ECF:	    2.07e-11 erg cm^-2 ct^-1
		      assuming NH=6.90e+21 cm^-2, gamma=9.20
		      determined from a spectral fit.
    RASS UL:	    2.1e-02 ct s^-1 (converted to XRT; 0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.
    A SIMBAD object `[VV2006] J134042.9+020307' is 4.5" away.


Known X-ray sources
-------------------

  Source 3 (SWIFT J134023.6+015612):
  ==================================
    RA (J2000.0):   205.0984  =  13 40 23.62
    Dec (J2000.0):  +1.9369  =	+01 56 12.8
    Error:	    6.1 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    5.1 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	    0.0225 +/- 0.0058 ct s^-1
    Mean flux:	    (2.54 +/- 0.65)e-12 erg cm^-2 s^-1
    Peak rate:	    0.0225 +/- 0.0058 ct s^-1
    Peak flux:	    (2.54 +/- 0.65)e-12 erg cm^-2 s^-1
    ECF:	    1.13e-10 erg cm^-2 ct^-1
		      assuming NH=1.89e+20 cm^-2, gamma=1.04
		      determined from a spectral fit.
    This matches a catalogued X-ray source XMMSL3 J134023.8+015613
    in the XMM-NEWTON/XMMSLEWCLN catalogue. Details:
    Separation:     1.6" from the XRT source
    Cat Rate:	    4.8e-01 +/- 2.6e-01 ct s^-1 
    Cat Flux:	    7.7e-12 +/- 4.1e-12 erg cm^-2 s^-1 (0.3-10 keV)
		      so the source is not above the catalogued flux.
    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_FIELD00057.

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