TITLE:   GCN CIRCULAR
NUMBER:  41698
SUBJECT: EP250903a: Swift-XRT observations
DATE:    25/09/04 13:34:42 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 Einstein Probe/WXT-detected
source EP250903a, collecting 3.7 ks of Photon Counting (PC) mode data between T0+1.3
ks and T0+35 ks after the trigger. We have detected 1 source inside the EP/WXT error
region. This has been automatically classified as follows:
  * 0 likely counterparts
  * 0 candidate counterparts
  * 1 uncatalogued X-ray source
  * 0 known X-ray sources

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

  Source 2 (SWIFT J223627.0-495113):
  ==================================
    RA (J2000.0):   339.1126  =  22 36 27.02
    Dec (J2000.0):  -49.8538  =  -49 51 13.7
    Error:	    7.1 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    37 arcsec from the Einstein Probe/WXT position.
    Mean rate:	    (3.8 [+1.4, -1.2])e-3 ct s^-1
    Mean flux:	    (2.20 [+0.83, -0.67])e-13 erg cm^-2 s^-1
    Peak rate:	    (3.8 [+1.4, -1.2])e-3 ct s^-1
    Peak flux:	    (2.20 [+0.83, -0.67])e-13 erg cm^-2 s^-1
    ECF:	    5.78e-11 erg cm^-2 ct^-1
		      assuming NH=1.17e+20 cm^-2, gamma=1.15
		      determined from a spectral fit.
    XMM UL:	    1.9e-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.
    There are 2 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 position of Source 2 is consistent with the optical counterpart detected by LCO
(GCN 41680) and SVOM/VT (GCN 41683).

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/EP/EP_FIELD00068.

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