GCN Circular 42827

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 EP251124a, collecting 2.5 ks of Photon Counting (PC) mode data between T0+5.1
ks and T0+11 ks after the trigger. The field is full of extended emission due to a
cluster of galaxies. We have detected 3 sources.  These have been automatically
classified as follows:
  * 0 likely counterparts
  * 0 candidate counterparts
  * 3 uncatalogued X-ray sources
  * 0 known X-ray sources

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

  Source 2 (SWIFT J025449.9+413724):
  ==================================
    RA (J2000.0):   43.7081  =	02 54 49.94
    Dec (J2000.0):  +41.6234  =  +41 37 24.2
    Error:	    5.4 (arcsec, radius, 90% confidence).
    Detect flag:    GOOD
    Distance:	    3.0 arcmin from the Einstein Probe/WXT position.
    Mean rate:	    (-1.0 +/- -1.0)e0 ct s^-1
    Mean flux:	    (-2.1 +/- -2.1)e-11 erg cm^-2 s^-1
    Peak rate:	    (8.5 [+3.4, -3.0])e-3 ct s^-1
    Peak flux:	    (1.80 [+0.71, -0.63])e-13 erg cm^-2 s^-1
    ECF:	    2.12e-11 erg cm^-2 ct^-1
		      assuming NH=2.22e+22 cm^-2, gamma=5.93
		      determined from a spectral fit.
    LSXPS UL:	    1.0e-02 ct/sec, (0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.
    A SIMBAD object `2MASX J02544959+4137278' is 5.1" away.
    There is 1 2MASS object within the source's 3-sigma error radius.

  Source 3 (SWIFT J025510.5+413444):
  ==================================
    RA (J2000.0):   43.7940  =	02 55 10.56
    Dec (J2000.0):  +41.5789  =  +41 34 44.0
    Error:	    5.7 (arcsec, radius, 90% confidence).
    Detect flag:    POOR
    Distance:	    2.8 arcmin from the Einstein Probe/WXT position.
    Mean rate:	    (-1.0 +/- -1.0)e0 ct s^-1
    Mean flux:	    (-1.6 +/- -1.6)e-10 erg cm^-2 s^-1
    Peak rate:	    (3.8 [+2.5, -2.2])e-3 ct s^-1
    Peak flux:	    (6.0 [+4.0, -3.4])e-13 erg cm^-2 s^-1
    ECF:	    1.57e-10 erg cm^-2 ct^-1
		      assuming NH=2.84e+21 cm^-2, gamma=0.31
		      determined from a spectral fit.
    LSXPS UL:	    1.6e-02 ct/sec, (0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.

  Source 6 (SWIFT J025445.0+413429):
  ==================================
    RA (J2000.0):   43.6876  =	02 54 45.02
    Dec (J2000.0):  +41.5749  =  +41 34 29.6
    Error:	    5.4 (arcsec, radius, 90% confidence).
    Detect flag:    POOR
    Distance:	    2.0 arcmin from the Einstein Probe/WXT position.
    Mean rate:	    0.0245 [+0.0084, -0.0071] ct s^-1
    Mean flux:	    (8.9 [+3.1, -2.6])e-13 erg cm^-2 s^-1
    Peak rate:	    0.043 [+0.022, -0.018] ct s^-1
    Peak flux:	    (1.56 [+0.81, -0.66])e-12 erg cm^-2 s^-1
    ECF:	    3.63e-11 erg cm^-2 ct^-1
		      assuming NH=1.20e+21 cm^-2, gamma=1.87
		      determined from a spectral fit.
    LSXPS UL:	    3.2e-02 ct/sec, (0.3-10 keV)
		      so the source is not above this 3-sigma upper limit.
    There is no evidence for fading.

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/EP/EP_FIELD00083.

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