{
  "bibcode": "2018GCN.22405....1B",
  "body": "D. N. Burrows (PSU), A. D'Ai (INAF-IASFPA), V. D'Elia (ASDC),\nA. Deich (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU),\nD. M. Palmer (LANL), B. Sbarufatti (PSU) and A. Tohuvavohu (PSU)\nreport on behalf of the Neil Gehrels Swift Observatory Team:\n\nAt 22:58:59 UT, the Swift Burst Alert Telescope (BAT) detected\nthe known RS CVn star HD 8357 (trigger=809217) in a 320s image. \nSwift slewed immediately to the location.  The BAT on-board \ncalculated location is \nRA, Dec 20.786, +7.444 which is \n   RA(J2000) = 01h 23m 09s\n   Dec(J2000) = +07d 26' 38\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  As is usual for an image trigger,\nno obvious variation is detectable in the immediately available\nBAT rates lightcurve. \n\nThe XRT began observing the field at 23:05:26.8 UT, 387.4 seconds after\nthe BAT trigger. XRT found a bright X-ray source located at RA, Dec\n20.7371, 7.4200 which is equivalent to:\n   RA(J2000)  = +01h 22m 56.90s\n   Dec(J2000) = +07d 25' 12.0\"\nwith an uncertainty of 4.8 arcseconds (radius, 90% containment). This\nlocation is 194 arcseconds from the BAT onboard position, outside the\nBAT error circle. This position is 1.9 arcseconds from that of a known\nX-ray source: 3XMM J012256.8+072510 in the XMM-NEWTON XMMSSC catalogue\nand is consistent with the position of HD 8357. \n\nAssuming a typical GRB power-law spectrum (NH=3e21 cm^-2, gamma=2), the\nXMM catalogue entry for this object is equivalent to a 0.2-10 keV flux of\n6.2e-11 erg cm^-2 s^-1; the flux in the 2.5 s XRT image was 7.63e-09\nerg cm^-2 s^-1. No event data are yet available to determine the column\ndensity using X-ray spectroscopy. \n\nBecause HD 8357 is a known bright star (V=7.31) UVOT did not\ntake data. \n\nThis appears to be the first time that this source has triggered\nBAT in the on-board imaging.",
  "circularId": 22405,
  "createdOn": 1518132651000,
  "email": "palmer@lanl.gov",
  "subject": "Trigger 809217: Swift trigger on RS CVn Star HD 8357",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>"
}