TITLE: GCN CIRCULAR NUMBER: 40662 SUBJECT: EP250610a: Swift-XRT counterpart detection DATE: 25/06/10 08:55:22 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 EP250610a, collecting 2.1 ks of Photon Counting (PC) mode data between T0+2.8 ks and T0+9.4 ks after the trigger. A candidate counterpart has been found. The details of this source are:
Source 1 (SWIFT J163325.5+383159): ================================== RA (J2000.0): 248.3564 = 16h 33m 25.54s Dec (J2000.0): +38.5332 = +38d 31' 59.5" Error: 4.6 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 2.2 arcmin from the Einstein Probe/WXT position. Mean rate: 0.0111 +/- 0.0027 ct s^-1 Mean flux: (4.4 +/- 1.1)e-13 erg cm^-2 s^-1 Peak rate: 0.0111 +/- 0.0027 ct s^-1 Peak flux: (4.4 +/- 1.1)e-13 erg cm^-2 s^-1 ECF: 3.96e-11 erg cm^-2 ct^-1, assuming NH=1.07e+20 cm^-2, gamma=1.73; determined from a spectral fit. LSXPS UL: 2.4e-03 ct/sec, (0.3-10 keV) so the source is 3.1-sigma above this 3-sigma upper limit. There is no evidence for fading.
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 J163309.1+383226): ================================== RA (J2000.0): 248.2883 = 16h 33m 09.19s Dec (J2000.0): +38.5406 = +38d 32' 26.2" Error: 7.1 (arcsec, radius, 90% confidence). Detect flag: REASONABLE Distance: 78 arcsec from the Einstein Probe/WXT position. Mean rate: (2.4 [+1.6, -1.1])e-3 ct s^-1 Mean flux: (1.02 [+0.70, -0.49])e-13 erg cm^-2 s^-1 Peak rate: (2.4 [+1.6, -1.1])e-3 ct s^-1 Peak flux: (1.02 [+0.70, -0.49])e-13 erg cm^-2 s^-1 LSXPS UL: 3.1e-03 ct/sec, (0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. There is 1 2MASS object 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.
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