{
  "circularId": 36558,
  "createdOn": 1716962024142,
  "submittedHow": "email",
  "body": "J. D. Gropp (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne\n(U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U.\nLeicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR), T. Sbarrato\n(INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the\nSwift-XRT team:\n\nSwift-XRT has performed follow-up observations of the\nFermi/LAT-detected burst GRB 240527B, collecting 5.2 ks of Photon\nCounting (PC) mode data between T0+27.3 ks and T0+135.5 ks. \n\nEight uncatalogued X-ray sources are detected, of which one (\"Source\n7\") is above the RASS 3-sigma upper limit at this position and fading\nwith >3-sigma significance, and is therefore likely the GRB afterglow.\nUsing 1624 s of PC mode data and 3 UVOT images, we find an enhanced XRT\nposition (using the XRT-UVOT alignment and matching UVOT field sources\nto the USNO-B1 catalogue): RA, Dec = 128.15387, -14.43738 which is\nequivalent to:\n\nRA (J2000): 08h 32m 36.93s\nDec(J2000): -14d 26' 14.6\"\n\nwith an uncertainty of 2.0 arcsec (radius, 90% confidence). This\nposition is 4.0 arcmin from the Fermi/LAT position. \n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=1.23 (+0.16, -0.14).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.70 (+0.08, -0.06). The\nbest-fitting absorption column is  consistent with the Galactic value\nof 5.7 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed\n(unabsorbed) 0.3-10 keV flux conversion factor deduced from this\nspectrum  is 3.8 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     5.7 (+/-1.9) x 10^20 cm^-2\nGalactic foreground: 5.7 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.70 (+0.08, -0.06)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00021694.\nThe results of the full analysis of the XRT observations are available\nat https://www.swift.ac.uk/ToO_GRBs/00021694.\n\nThis circular is an official product of the Swift-XRT team.\n\n",
  "subject": "GRB 240527B: Swift-XRT afterglow detection",
  "eventId": "GRB 240527B",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "bibcode": "2024GCN.36558....1G"
}