TITLE:   GCN CIRCULAR
NUMBER:  40679
SUBJECT: GRB 250610B: Swift-XRT counterpart detection
DATE:    25/06/10 23:55:14 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 SVOM/ECLAIRs-detected source
GRB 250610B, collecting 2.0 ks of Photon Counting (PC) mode data between T0+2.8 ks
and T0+8.9 ks after the trigger. A likely counterpart has been found consistent with
the optical detection (GCN Circ. 40676, 40677 and 40678). The details of this source
are:

  Source 1 (SWIFT J132043.2+310614):
  ==================================
    RA (J2000.0):  200.1802  =	13h 20m 43.25s
    Dec (J2000.0): +31.1040  =	+31d 06' 14.4"
    Error:	   3.7 (arcsec, radius, 90% confidence).
    Detect flag:   GOOD
    Distance:	   4.3 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	   0.1084 +/- 0.0084 ct s^-1
    Mean flux:	   (3.91 +/- 0.30)e-12 erg cm^-2 s^-1
    Peak rate:	   0.134 +/- 0.022 ct s^-1
    Peak flux:	   (4.85 +/- 0.81)e-12 erg cm^-2 s^-1
    ECF:	   3.61e-11 erg cm^-2 ct^-1, assuming NH=1.44e+20 cm^-2,
		   gamma=1.78; determined from a spectral fit.
    XMM UL:	   2.4e-12 erg cm^-2 s^-1, (0.3-10 keV)
	 so the source is 3.0-sigma 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/SVOM.

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