{
  "circularId": 35600,
  "bibcode": "2024GCN.35600....1A",
  "createdOn": 1706009105611,
  "eventId": "GRB 240122A",
  "body": "E. Ambrosi  (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC &\nINAF-OAR), D.N. Burrows (PSU), J. D. Gropp (PSU), S. Dichiara (PSU),\nJ.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans\n(U. Leicester) reports on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the MAXI-detected\nburst GRB 240122A in a series of observations tiled on the sky. The\ntotal exposure time is 3.6 ks, distributed over 7 tiles; the maximum\nexposure at a single sky location was 1.3 ks. The data were collected\nbetween T0+29.5 ks and T0+35.6 ks, and are entirely in Photon Counting\n(PC) mode. \n\nFour uncatalogued X-ray sources are detected, of which one (\"Source 3\")\nis above the RASS 3-sigma upper limit at this position, and is\ntherefore likely the GRB afterglow. Using 930 s of PC mode data and 2\nUVOT images, we find an enhanced XRT position (using the XRT-UVOT\nalignment and matching UVOT field sources to the USNO-B1 catalogue):\nRA, Dec = 93.05391, -19.14418 which is equivalent to:\n\nRA (J2000): 06h 12m 12.94s\nDec(J2000): -19d 08' 39.0\"\n\nwith an uncertainty of 2.9 arcsec (radius, 90% confidence). This\nposition is 14.5 arcmin from the MAXI position, and it is consistent\nwith the GOTO optical detection (GCN 35596, Kumar et al. 2024).\n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=2.5 (+0.7, -2.1).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.82 (+0.33, -0.25). The\nbest-fitting absorption column is  consistent with the Galactic value\nof 1.0 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed\n(unabsorbed) 0.3-10 keV flux conversion factor deduced from this\nspectrum  is 3.3 x 10^-11 (3.6 x 10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.0 (+/-0.8) x 10^21 cm^-2\nGalactic foreground: 1.0 x 10^21 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.82 (+0.33, -0.25)\n\nIf the light curve continues to decay with a power-law decay index of\n2.5, the count rate at T+24 hours will be 0.012 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.8 x\n10^-13 (4.2 x 10^-13) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00021645.\nThe results of the full analysis of the tiled XRT observations are\navailable at https://www.swift.ac.uk/xrt_products/TILED_GRB00119.\n\nThis circular is an official product of the Swift-XRT team.\n\n",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "submittedHow": "email",
  "subject": "GRB 240122A: Swift-XRT afterglow detection"
}