{
  "bibcode": "2018GCN.23582....1T",
  "body": "A. Tohuvavohu (PSU), A. D'Ai (INAF-IASFPA), M. Siegel (PSU), J.A.\nKennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester),\nA. Melandri (INAF-OAB), and P.A. Evans (U. Leicester) report on behalf\nof the Swift-XRT and Swift-UVOT teams:\n\nSwift has performed follow-up observations of the MASTER optical\ntransient J204928.79+245744.0  (V. Lipunov et al. GCN Circ. 23588),\nwithin the IPN localization region of Fermi/GBM and Konus detected GRB\n181222B (P. Veres GCN Circ. 23551, D. Svinkin et al. GCN Circ. 23556).\n\nSwift/XRT collected 3.9 ks of Photon Counting (PC) mode data between\nT0+414.9 ks and T0+427.0 ks. No X-ray source was detected at the MASTER\nposition with an upper limit of 2.4 e-3 ct s^-1.\n\nTwo uncatalogued X-ray sources have been detected in the field during\nthis observation.  Both sources are below the RASS limit and show no\ndefinitive signs of fading. Given the large localization region of this\nburst and the amount of time elapsed between the GRB and these\nobservations, we believe it unlikely that these X-ray sources are\nrelated to the GRB.\nDetails of the sources are given below:\n\nSource 1:\n RA (J2000.0): 312.2708 = 20:49:52.88\n Dec (J2000.0): +25.0419= +25:02:30.9\n Error: 2.5 arcsec (radius, 90% conf.)\n Count-rate (9.9 [+2.0, -1.9])e-3 ct s^-1\n Distance: 7.2 arcminutes from MASTER position.\n Flux: (2.3 [+0.5, -0.4])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)\n\nSource 2:\n  RA (J2000.0):  312.3700  =  20:49:28.81\n  Dec (J2000.0): +24.9769  =  +24:58:37.0\n  Error: 7.7 arcsec (radius, 90% conf.)\n  Count-rate: (3.03 [+1.21, -0.97])e-3 ct s^-1\t \n  Distance: 53 arcsec from MASTER position.\n  Flux: (1.22 [+0.49, -0.39])e-13 erg cm^-2 s^-1 (observed, 0.3-10\nkeV).\n\nSwift/UVOT began observing the field in the White filter 414 ks after\nthe GRB trigger. We do not find any optical source at the MASTER\nposition, with an upper limit of 21.48 +/- 0.22 magnitude (AB) in a \n3094 second exposure.  This magnitude is not corrected for the Galactic\nextinction due to the reddening of E(B-V) = 0.24 in the direction of\nthe burst (Schlegel et al. 1998).\n\nThe results of the XRT-team automatic analysis of the XRT observations,\n\nincluding a position-specific upper limit calculator, are available at\nhttp://www.swift.ac.uk/ToO_GRBs/00020850/.\n\nThis circular is an official product of the Swift team.",
  "circularId": 23582,
  "createdOn": 1546018610000,
  "email": "antonino.dai@ifc.inaf.it",
  "subject": "GRB 181222B: Swift follow-up observations of MASTER optical transient J204928.79+245744.0",
  "submitter": "Antonino D'Ai at IASF-PA  <antonino.dai@ifc.inaf.it>",
  "eventId": "GRB 181222B"
}