  We explore the band dependence of the inferred X-ray temperature of the
intracluster medium (ICM) for 192 well-observed galaxy clusters selected from
the Chandra Data Archive. If the hot ICM is nearly isothermal in the projected
region of interest, the X-ray temperature inferred from a broad-band (0.7-7.0
keV) spectrum should be identical to the X-ray temperature inferred from a
hard-band (2.0-7.0 keV) spectrum. However, if unresolved cool lumps of gas are
contributing soft X-ray emission, the temperature of a best-fit
single-component thermal model will be cooler for the broad-band spectrum than
for the hard-band spectrum. Using this difference as a diagnostic, the ratio of
best-fitting hard-band and broad-band temperatures may indicate the presence of
cooler gas even when the X-ray spectrum itself may not have sufficient
signal-to-noise to resolve multiple temperature components. To test this
possible diagnostic, we extract X-ray spectra from core-excised annular regions
for each cluster in our archival sample. We compare the X-ray temperatures
inferred from single-temperature fits when the energy range of the fit is
0.7-7.0 keV (broad) and when the energy range is 2.0/(1+z)-7.0 keV (hard). We
find that the hard-band temperature is significantly higher, on average, than
the broad-band temperature. Upon further exploration, we find this temperature
ratio is enhanced preferentially for clusters which are known merging systems.
In addition, cool-core clusters tend to have best-fit hard-band temperatures
that are in closer agreement with their best-fit broad-band temperatures. We
show, using simulated spectra, that this diagnostic is sensitive to secondary
cool components (TX = 0.5-3.0 keV) with emission measures >10-30% of the
primary hot component.
