Hot core loop in AR 11890 and its association with the cancellation of surface magnetic flux. Panel a: AIA 9.4 nm filter image showing a fully formed coronal loop seen from almost directly above. The black (east) and magenta (west) boxes mark the regions near the footpoints. The field of view is 180″ × 90″. Panel b: AIA 9.4 nm light curves from the footpoint regions. The short vertical bars point to the near-simultaneous peaks in the two light curves. Panels c and d: as in panels a and b: but with the AIA 17.1 nm filter. Panel e: HMI line-of-sight magnetic field map, in which darker shading represents negative polarity and lighter shading positive polarity field. The black box encloses magnetic flux near the eastern footpoint of the loop; it lies at the same position as the black boxes in panels a and c. The blue (positive polarity) and red (negative polarity) contours within this box cover regions with a magnetic flux density of ±75 G or more (see also panels a and c). Panel f Magnetic flux of the negative polarity near the eastern footpoint as a function of time (see arrow). The vertical dashed line in the right panels marks the time-stamp of the corresponding spatial maps displayed on the left. See online movie to follow the evolution of this loop brightening. North is up. See Sect. 3 for details.