GCN Circular 41180

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 250727A, collecting 1.6 ks of Photon Counting (PC) mode data between T0+2.2 ks
and T0+8.3 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

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

  Source 1 (SWIFT J234539.1-811248):
  ==================================
    RA (J2000.0):  356.4132  =	23h 45m 39.17s
    Dec (J2000.0): -81.2136  =	-81d 12' 49.0"
    Error:	   4.9 (arcsec, radius, 90% confidence).
    Detect flag:   GOOD
    Distance:	   7.7 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	   0.0155 +/- 0.0041 ct s^-1
    Mean flux:	   (5.2 +/- 1.4)e-13 erg cm^-2 s^-1
    Peak rate:	   0.0155 +/- 0.0041 ct s^-1
    Peak flux:	   (5.2 +/- 1.4)e-13 erg cm^-2 s^-1
    ECF:	   3.37e-11 erg cm^-2 ct^-1, assuming NH=9.71e+20 cm^-2,
		   gamma=1.97; determined from a spectral fit.
    XMM UL:	   4.6e-12 erg cm^-2 s^-1, (0.3-10 keV)
	 so the source is 29.9-sigma below this 3-sigma upper limit.
    There is no evidence for fading.

  Source 2 (SWIFT J234406.8-810315):
  ==================================
    RA (J2000.0):  356.0284  =	23h 44m 06.82s
    Dec (J2000.0): -81.0543  =	-81d 03' 15.5"
    Error:	   8.5 (arcsec, radius, 90% confidence).
    Detect flag:   GOOD
    Distance:	   4.9 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	   (5.2 [+2.6, -2.0])e-3 ct s^-1
    Mean flux:	   (1.52 [+0.77, -0.59])e-13 erg cm^-2 s^-1
    Peak rate:	   (5.2 [+2.6, -2.0])e-3 ct s^-1
    Peak flux:	   (1.52 [+0.77, -0.59])e-13 erg cm^-2 s^-1
    ECF:	   2.93e-11 erg cm^-2 ct^-1, assuming NH=3.26e+22 cm^-2,
		   gamma=4.66; determined from a spectral fit.
    XMM UL:	   1.9e-12 erg cm^-2 s^-1, (0.3-10 keV)
	 so the source is 25.1-sigma below 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/SVOM/SVOM_FIELD00025.

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