x-ray flare class

Rank of a flare based on its x-ray energy output. Flares are classified by the NOAA according to the order of magnitude of the peak burst intensity (I) measured at the Earth by satellites in the 0.1 to 0.8 nm band as follows:
                    Peak, 0.1 to 0.8 nm flux
                                (W m-2)
                                        B      I < 10-6
                                        C      10-6 <= I < 10-5
                                        M     10-5 <= I < 10-4
                                        X     I>=  10-4
                A multiplicative factor is appended to the end of the class (e.g. M8 = 8 x 10-5 W m-2)