{ "bibcode": "2026GCN.43622....1E", "submittedHow": "email", "eventId": "GRB 260204A", "subject": "GRB 260204A: Swift-XRT observations", "circularId": 43622, "submitter": "Phil Evans at U of Leicester ", "createdOn": 1770298149700, "body": "P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P.\nBeardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.\nBurrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),\nP. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro\n(INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U.\nLeicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato\n(INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the\nSwift-XRT team:\n\nSwift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected GRB\n260204A, collecting 1.7 ks of Photon Counting (PC) mode data between T0+23 ks and\nT0+25 ks after the trigger. We have detected 4 sources. These have been\nautomatically classified as follows:\n * 0 likely counterparts\n * 0 candidate counterparts\n * 3 uncatalogued X-ray sources\n * 1 known X-ray source\n\nAs already reported source 1 is consistent with an optical source (Li et al., GCN\nCirc. 43620; Malesani et al., GCN Circ. 43621). We note that, in the X-rays, this\nsource is not well separated from source 3 and cannot rule out that these arise not\nfrom point sources but from a patch of diffuse emission. \n\nWe note also the presence of a source in the XMM Slew survey XMMSL3 catalogue,\nXMMSL3 J134023.8+015613 at RA,Dec = 205.0888, +1.9370 degrees (J2000), with a\n1-sigma error of 4.3\" (statistical) and an estimated systematic error of ~8\" (see\nhttp://xmmssc.irap.omp.eu/Catalogue/XMMSL3/XMMSL3_Catalogue_User_Guide.html#Astromet\nry). This source is 33\" from the position of source 1.\n\nSource 2 is consistent with the position of HD 118981, a high proper motion star,\nwhile source 4 is a known quasar.\n\nFurther observations are planned.\n\nUncatalogued X-ray sources\n--------------------------\n\n Source 1 (SWIFT J134025.4+015552):\n ==================================\n RA (J2000.0): 205.1060 = 13 40 25.44\n Dec (J2000.0): +1.9313 =\t+01 55 52.7\n Error:\t 5.0 (arcsec, radius, 90% confidence).\n Detect flag: GOOD\n Distance:\t 5.4 arcmin from the SVOM/ECLAIRs position.\n Mean rate:\t 0.0235 +/- 0.0046 ct s^-1\n Mean flux:\t (8.7 +/- 1.7)e-13 erg cm^-2 s^-1\n Peak rate:\t 0.0235 +/- 0.0046 ct s^-1\n Peak flux:\t (8.7 +/- 1.7)e-13 erg cm^-2 s^-1\n ECF:\t 3.71e-11 erg cm^-2 ct^-1\n\t\t assuming NH=1.90e+20 cm^-2, gamma=1.76\n\t\t determined from a spectral fit.\n RASS UL:\t 4.1e-02 ct s^-1 (converted to XRT; 0.3-10 keV)\n\t\t so the source is not above this 3-sigma upper limit.\n There is no evidence for fading.\n\n Source 2 (SWIFT J134026.9+020905):\n ==================================\n RA (J2000.0): 205.1125 = 13 40 27.00\n Dec (J2000.0): +2.1515 =\t+02 09 05.4\n Error:\t 5.0 (arcsec, radius, 90% confidence).\n Detect flag: GOOD\n Distance:\t 7.9 arcmin from the SVOM/ECLAIRs position.\n Mean rate:\t 0.0136 +/- 0.0036 ct s^-1\n Mean flux:\t (2.28 +/- 0.61)e-13 erg cm^-2 s^-1\n Peak rate:\t 0.0136 +/- 0.0036 ct s^-1\n Peak flux:\t (2.28 +/- 0.61)e-13 erg cm^-2 s^-1\n ECF:\t 1.67e-11 erg cm^-2 ct^-1\n\t\t assuming NH=1.30e+22 cm^-2, gamma=9.94\n\t\t determined from a spectral fit.\n RASS UL:\t 3.3e-02 ct s^-1 (converted to XRT; 0.3-10 keV)\n\t\t so the source is not above this 3-sigma upper limit.\n There is no evidence for fading.\n A SIMBAD object `HD 118981' is 0.7\" away.\n There is 1 2MASS object within the source's 3-sigma error radius.\n\n Source 4 (SWIFT J134043.1+020310):\n ==================================\n RA (J2000.0): 205.1796 = 13 40 43.10\n Dec (J2000.0): +2.0530 =\t+02 03 10.8\n Error:\t 6.6 (arcsec, radius, 90% confidence).\n Detect flag: GOOD\n Distance:\t 4.2 arcmin from the SVOM/ECLAIRs position.\n Mean rate:\t (7.2 [+2.9, -2.3])e-3 ct s^-1\n Mean flux:\t (1.49 [+0.60, -0.48])e-13 erg cm^-2 s^-1\n Peak rate:\t (7.2 [+2.9, -2.3])e-3 ct s^-1\n Peak flux:\t (1.49 [+0.60, -0.48])e-13 erg cm^-2 s^-1\n ECF:\t 2.07e-11 erg cm^-2 ct^-1\n\t\t assuming NH=6.90e+21 cm^-2, gamma=9.20\n\t\t determined from a spectral fit.\n RASS UL:\t 2.1e-02 ct s^-1 (converted to XRT; 0.3-10 keV)\n\t\t so the source is not above this 3-sigma upper limit.\n There is no evidence for fading.\n A SIMBAD object `[VV2006] J134042.9+020307' is 4.5\" away.\n\n\nKnown X-ray sources\n-------------------\n\n Source 3 (SWIFT J134023.6+015612):\n ==================================\n RA (J2000.0): 205.0984 = 13 40 23.62\n Dec (J2000.0): +1.9369 =\t+01 56 12.8\n Error:\t 6.1 (arcsec, radius, 90% confidence).\n Detect flag: GOOD\n Distance:\t 5.1 arcmin from the SVOM/ECLAIRs position.\n Mean rate:\t 0.0225 +/- 0.0058 ct s^-1\n Mean flux:\t (2.54 +/- 0.65)e-12 erg cm^-2 s^-1\n Peak rate:\t 0.0225 +/- 0.0058 ct s^-1\n Peak flux:\t (2.54 +/- 0.65)e-12 erg cm^-2 s^-1\n ECF:\t 1.13e-10 erg cm^-2 ct^-1\n\t\t assuming NH=1.89e+20 cm^-2, gamma=1.04\n\t\t determined from a spectral fit.\n This matches a catalogued X-ray source XMMSL3 J134023.8+015613\n in the XMM-NEWTON/XMMSLEWCLN catalogue. Details:\n Separation: 1.6\" from the XRT source\n Cat Rate:\t 4.8e-01 +/- 2.6e-01 ct s^-1 \n Cat Flux:\t 7.7e-12 +/- 4.1e-12 erg cm^-2 s^-1 (0.3-10 keV)\n\t\t so the source is not above the catalogued flux.\n There is no evidence for fading.\n There is 1 2MASS object within the source's 3-sigma error radius.\n\nAll fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with\ncatalogues and upper limits from other missions, we assumed a power-law spectrum\nwith NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.\n\nThe results of the XRT-team automatic analysis of the XRT observations, including a\nposition-specific upper limit calculator, are available at\nhttps://www.swift.ac.uk/SVOM/SVOM_FIELD00057.\n\nThis circular is an official product of the Swift-XRT team.\n\n\n" }