{
  "bibcode": "2007GCN..6614....1B",
  "body": "A. Breeveld (MSSL/UCL) reports on behalf of the Swift/UVOT team:\n\nA new, improved calibration for all the UVOT broadband filters (u, b, v, \nuvw1, uvm2, uvw2 and white) has been released by the HEASARC. The new \ncalibration includes updated zero points, coincidence loss formula, \nfilter effective areas, colour transformations and count rate to flux \ntransformations. The latest CALDB files and documentation can be \ndownloaded from:\nhttp://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/swift/\n\nFor filters u, b and v the zero points are consistent with the previous \nzero points within the previous quoted error, but the uv and white zero \npoints have changed more significantly, by up to 0.5 mag (white). Please \nbe aware that from now on the UVOT magnitudes given in GCNs sent out by \nthe Swift UVOT team will be calculated using these zero points. The \nquoted magnitudes are in the UVOT instrumental system (lower case u, b, \nv) and can be converted to Johnson U, B, V magnitudes using the colour \ntransformations. The differences between UVOT magnitudes and Johnson are \nmost significant in the u filter but are generally small.",
  "circularId": 6614,
  "createdOn": 1183984476000,
  "email": "aad@mssl.ucl.ac.uk",
  "subject": "Updated Swift/UVOT calibration",
  "submitter": "Alice Breeveld at MSSL-UCL  <aad@mssl.ucl.ac.uk>"
}