{
  "bibcode": "2014GCN.16414....1E",
  "body": "P. A. Evans (U. Leicester), A.P. Beardmore (U. Leicester), H. A. Krimm\n(CRESST/GSFC/USRA) and A. Y. Lien (GSFC/CRESST/UMBC) report on behalf of \nthe Swift team:\n\nAt 06:37:31 UT on 2014 June 17 Swift-BAT triggered on a source \nconsistent with the location of V490 Cep (= Cep X-4 = Ginga 2138+56)\nwhich the MAXI team reported to be in outburst in ATEL #6212.\nThis trigger was reported in GCN Circ. 16413. The refined BAT position \nis RA, Dec = 324.784, 56.949 deg which is equivalent to:\n    RA(J2000)  =  21h 39m 08.2s\n    Dec(J2000) = +56d 56' 56.9\"\nwith an uncertainty of 4.1 arcmin, (radius, 90% confidence).\nThe partial coding was 89%.\n\nXRT finds a single X-ray source in the BAT error circle, with an \nenhanced XRT position of RA,Dec= 324.87743, 56.98608 which is equivalent to:\n\n   RA (J2000)  = 21h 39m 30.58s\n   Dec (J2000) = +56d 59' 09.9\"\n\nwith an uncertainty of 1.7 arcsec (radius, 90% confidence). This is 1 \narcsec away from the catalogued position of V490 Cep in SIMBAD.\n\nThis source has been regularly monitored by the BAT Transient Monitor\n(Krimm et al., 2013, ApJSS 209,14) and has been seen to be steadily \nrising, with an average flux at present of 80 mCrab. The observation\nwhich triggered BAT was that with the highest significance detection of\nthis source by the BAT during the current outburst.\n\nThe time-averaged BAT spectrum from T+0.00 to T+303.04 sec is best fit \nby a simple power-law model.  The power law index of the time-averaged \nspectrum is 3.52 +/- 0.63.  The fluence in the 15-150 keV band is\n3.9 (+/- 1.1) e-7 erg cm^-2\n\nThe Windowed Timing mode XRT spectrum can be modelled with an absorbed\npower-law, with a photon index of 1.01 (+/- 0.05) and an absorption \ncolumn of 1.32 (+0.10, -0.09) e22 cm^-2. The mean 0.3-10 keV count-rate \nis ~15 ct/sec, which is consistent with the MAXI-GSC count-rate of 0.11\nct/sec reported in ATEL #6212, assuming the WT mode spectrum.\n\nThe X-ray data show clear signs of modulation, with a period of 66.58 \n+/- 0.22 s (90% confidence). Compared to the measurements reported in \nWilson, Finger & Scott (1999, ApJ, 511, 367), this implies a spin-down \nrate of 1.3e-13 Hz/s; a factor of 3 higher than measured in that paper \nbetween 1993 and 1997.\n\nThis circular is an official product of the Swift team.",
  "circularId": 16414,
  "createdOn": 1403020738000,
  "email": "pae9@leicester.ac.uk",
  "subject": "Swift trigger 601928 is V490 Cep: BAT+XRT refined analysis.",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>"
}