GCN Circular 40756

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 EP#01709178975, collecting 594 s of Photon Counting (PC) mode data between
T0+2.1 ks and T0+2.8 ks after the trigger. A candidate counterpart has been found.
The details of this source are:

  Source 1 (SWIFT J154403.9-331113):
  ==================================
    RA (J2000.0):  236.0166  =	15h 44m 03.98s
    Dec (J2000.0): -33.1871  =	-33d 11' 13.6"
    Error:	   3.6 (arcsec, radius, 90% confidence).
    Detect flag:   GOOD
    Distance:	   52 arcsec from the Einstein Probe/WXT position.
    Mean rate:	   1.079 +/- 0.065 ct s^-1
    Mean flux:	   (3.14 +/- 0.19)e-11 erg cm^-2 s^-1
    Peak rate:	   1.49 +/- 0.24 ct s^-1
    Peak flux:	   (4.32 +/- 0.70)e-11 erg cm^-2 s^-1
    ECF:	   2.91e-11 erg cm^-2 ct^-1, assuming NH=1.85e+21 cm^-2,
		   gamma=2.42; determined from a spectral fit.
    This matches a catalogued X-ray source XMMSL3 J154404.2-331108
    in the XMM-NEWTON/XMMSLEWCLN catalogue. Details:
      Separation:  3.0" from the XRT source
      Cat Rate:    5.9e-01 +/- 2.8e-01 ct s^-1 
      Cat Flux:    4.6e-12 +/- 2.2e-12 erg cm^-2 s^-1 (0.3-10 keV)
	     so the source  is 5.2-sigma above the catalogued flux.
    There is no evidence for fading.
    A SIMBAD object `CD-32 11039B' is 3.3" away.
    There is 1 2MASS object within the source's 3-sigma error radius.


We have detected a total of 2 sources. These have been automatically classified as
follows:
  * 0 likely counterparts
  * 1 candidate counterpart
  * 1 uncatalogued X-ray source
  * 0 known X-ray sources

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

  Source 2 (SWIFT J154417.0-331013):
  ==================================
    RA (J2000.0):  236.0710  =	15h 44m 17.04s
    Dec (J2000.0): -33.1705  =	-33d 10' 13.8"
    Error:	   10.3 (arcsec, radius, 90% confidence).
    Detect flag:   POOR
    Distance:	   2.5 arcmin from the Einstein Probe/WXT position.
    Mean rate:	   0.0122 [+0.0068, -0.0053] ct s^-1
    Mean flux:	   (1.56 [+0.87, -0.67])e-11 erg cm^-2 s^-1
    Peak rate:	   0.0122 [+0.0068, -0.0053] ct s^-1
    Peak flux:	   (1.56 [+0.87, -0.67])e-11 erg cm^-2 s^-1
    ECF:	   1.28e-09 erg cm^-2 ct^-1, assuming NH=3.49e+23 cm^-2,
		   gamma=9.92; determined from a spectral fit.
    XMM UL:	   1.8e-12 erg cm^-2 s^-1, (0.3-10 keV)
	 so the source is 1.8-sigma above this 3-sigma upper limit.
    There is no evidence for fading.
    A SIMBAD object `UCAC4 285-083088' is 1.7" away.
    There are 10 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/EP.

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