TITLE: GCN CIRCULAR NUMBER: 41330 SUBJECT: EP250812a: Swift-XRT counterpart detection DATE: 25/08/12 17:22:44 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 EP250812a, collecting 1.7 ks of Photon Counting (PC) mode data between T0+1.5 ks and T0+3.4 ks after the trigger. A likely counterpart has been found. The position is consistent with the uncatalogued X-ray source detected by EP-FXT (Zhang et al., GCN 41327). The details of this source are: Source 1 (SWIFT J020358.1-091907): ================================== RA (J2000.0): 30.9921 = 02h 03m 58.10s Dec (J2000.0): -9.3187 = -09d 19' 07.3" Error: 3.7 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 67 arcsec from the Einstein Probe/WXT position. Mean rate: 0.1069 +/- 0.0091 ct s^-1 Mean flux: (4.00 +/- 0.34)e-12 erg cm^-2 s^-1 Peak rate: 0.203 +/- 0.046 ct s^-1 Peak flux: (7.6 +/- 1.7)e-12 erg cm^-2 s^-1 ECF: 3.75e-11 erg cm^-2 ct^-1 assuming NH=4.71e+20 cm^-2, gamma=1.83 determined from a spectral fit. LSXPS UL: 1.5e-03 ct/sec, (0.3-10 keV) so the source is 4.4-sigma above this 3-sigma upper limit. The source may be fading, at the 2.6-sigma level. We have detected a total of 3 sources. These have been automatically classified as follows: * 1 likely counterpart * 0 candidate counterparts * 0 uncatalogued X-ray sources * 2 known X-ray sources Known X-ray sources ------------------- Source 2 (SWIFT J020340.7-092134): ================================== RA (J2000.0): 30.9196 = 02h 03m 40.70s Dec (J2000.0): -9.3596 = -09d 21' 34.6" Error: 5.8 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.8 arcmin from the Einstein Probe/WXT position. Mean rate: (8.5 [+3.0, -2.5])e-3 ct s^-1 Mean flux: (2.42 [+0.87, -0.71])e-13 erg cm^-2 s^-1 Peak rate: (8.5 [+3.0, -2.5])e-3 ct s^-1 Peak flux: (2.42 [+0.87, -0.71])e-13 erg cm^-2 s^-1 ECF: 2.86e-11 erg cm^-2 ct^-1 assuming NH=4.16e+20 cm^-2, gamma=2.23 determined from a spectral fit. This matches a catalogued X-ray source LSXPS J020340.7-092134 in the LSXPS catalogue. Details: Separation: 1.0" from the XRT source Cat Rate: 4.6e-03 +/- 8.6e-04 ct s^-1 Cat Flux: 1.3e-13 +/- 2.5e-14 erg cm^-2 s^-1 (0.3-10 keV) so the source is 1.3-sigma above the catalogued flux. There is no evidence for fading. A SIMBAD object `[VV2006] J020341.0-092134' is 3.4" away. Source 4 (SWIFT J020404.7-091504): ================================== RA (J2000.0): 31.0199 = 02h 04m 04.78s Dec (J2000.0): -9.2513 = -09d 15' 04.7" Error: 5.8 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.0 arcmin from the Einstein Probe/WXT position. Mean rate: (6.6 [+2.8, -2.2])e-3 ct s^-1 Mean flux: (2.14 [+0.92, -0.72])e-13 erg cm^-2 s^-1 Peak rate: (6.6 [+2.8, -2.2])e-3 ct s^-1 Peak flux: (2.14 [+0.92, -0.72])e-13 erg cm^-2 s^-1 ECF: 3.25e-11 erg cm^-2 ct^-1 assuming NH=2.48e+20 cm^-2, gamma=1.94 determined from a spectral fit. This matches a catalogued X-ray source LSXPS J020405.1-091509 in the LSXPS catalogue. Details: Separation: 7.3" from the XRT source Cat Rate: 5.6e-03 +/- 1.5e-03 ct s^-1 Cat Flux: 1.8e-13 +/- 4.9e-14 erg cm^-2 s^-1 (0.3-10 keV) so the source is 0.3-sigma above the catalogued flux. 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_FIELD00058. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41330. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...