Snapshots of the flare region around the peak time of the flare at |${00^{\rm h}01^{\rm m}}$| UT. (a)–(b) SDO/AIA 94 Å. (c) IRIS SJI 1400 Å. (d) IRIS SJI 2796 Å. (e) SDO/HMI continuum. (f) SDO/HMI line-of-sight magnetogram. Characteristic temperatures are shown in (a)–(d). In panel (a), we overlaid contour images of NoRH 17 GHz: orange dash-dotted contours show 40% and 80% levels of the peak intensity at 23:57:57 UT and yellow solid contours show 40%, 80%, and 94% levels of the peak intensity at 00:01:14 UT. In panel (f), two sets of two conjugate flare ribbons are shown by the overlaid contour image (10% level of the peak intensity of the IRIS SJI 2796 Å): the northern flare ribbons with positive and negative polarity (FR|$_{\rm N}^+$| and FR|$_{\rm N}^-$|⁠) are indicated by magenta and cyan lines, and the southern flare ribbons with positive and negative polarity (FR|$_{\rm S}^+$| and FR|$_{\rm S}^-$|⁠) by red and blue lines, respectively. The vertical-dashed line is the location of the IRIS slit. The white box is the region shown in figure 4. (Color online)