  We present a multi-instrument study of the two precursor brightenings prior
to the M6.5 flare (SOL2015-06-22T18:23) in the NOAA Active Region 12371, with a
focus on the temperature (T), electron number density (n), and emission measure
(EM). The data used in this study were obtained from four instruments with a
variety of wavelengths, i.e., the Solar Dynamics Observatory's Atmospheric
Imaging Assembly (AIA), in six extreme ultraviolet (EUV) passbands; the
Expanded Owens Valley Solar Array (EOVSA) in microwave (MW); the Reuven Ramaty
High Energy Solar Spectroscopic Imager (RHESSI) in hard X-rays (HXR); and the
Geostationary Operational Environmental Satellite (GOES) in soft X-rays (SXR).
We compare the temporal variations of T, n, and EM derived from the different
data sets. Here are the key results. (1) GOES SXR and AIA EUV have almost
identical 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 MW
provides 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 the
RHESSI HXR measurements is always less than the values from AIA EUV and GOES
SXR by at most 20 times. The number density variation from EOVSA MW is greater
than the value from AIA EUV by at most 100 times. The results quantitatively
describe the differences in the thermal parameters at the precursor phase, as
measured by different instruments operating at different wavelength regimes and
for different emission mechanisms.
