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We present a multi-instrument study of the two precursor brightenings priorto the M6.5 flare (SOL2015-06-22T18:23) in the NOAA Active Region 12371, with afocus on the temperature (T), electron number density (n), and emission measure(EM). The data used in this study were obtained from four instruments with avariety of wavelengths, i.e., the Solar Dynamics Observatory's AtmosphericImaging Assembly (AIA), in six extreme ultraviolet (EUV) passbands; theExpanded Owens Valley Solar Array (EOVSA) in microwave (MW); the Reuven RamatyHigh Energy Solar Spectroscopic Imager (RHESSI) in hard X-rays (HXR); and theGeostationary Operational Environmental Satellite (GOES) in soft X-rays (SXR).We compare the temporal variations of T, n, and EM derived from the differentdata sets. Here are the key results. (1) GOES SXR and AIA EUV have almostidentical EM variations (1.5-3x10^48 per cm^3) and very similar T variations,from 8 to 15 million Kelvin (MK). (2) Listed from highest to lowest, EOVSA MWprovides the highest temperature variations (15-60 MK), followed by RHESSI HXR(10-24 MK), then GOES SXR and AIA EUV (8-15 MK). (3) The EM variation from theRHESSI HXR measurements is always less than the values from AIA EUV and GOESSXR by at most 20 times. The number density variation from EOVSA MW is greaterthan the value from AIA EUV by at most 100 times. The results quantitativelydescribe the differences in the thermal parameters at the precursor phase, asmeasured by different instruments operating at different wavelength regimes andfor different emission mechanisms.

Multi-instrument Comparative Study of Temperature, Number Density, and Emission Measure during the Precursor Phase of a Solar Flare