J band selected magnitude in the 2MASS survey, or if the source is not detected in the J-band, the 95% confidence upper limit derived from a 4 arcsec radius aperture measurement taken at the position of the source on the Atlas Image. (The Atlas Images are quick-look images suitable for deriving positional information but not accurate photometry.) The origin of the magnitude is given by the first character of the rd_flg value.
