SOME LIKE IT HOT: CORONAL HEATING OBSERVATIONS FROM HINODE X-RAY TELESCOPE AND RHESSI

We have used Hinode X-Ray Telescope observations and RHESSI upper limits together to characterize the differential emission measure (DEM) from a quiescent active region. We find a relatively smooth DEM curve with the expected active region peak at log T = 6.4. We also find a high-temperature component with significant emission measure at log T greater than or similar to 7. This curve is consistent with previous observations of quiescent active regions in that it does not produce observable Fe XIX lines. It is different from that generated with X-Ray Telescope (XRT) data alone-RHESSI rules out the possibility of a separate high-temperature component with a peak of approximately log T = 7.4. The strength and position of the high-temperature peak in this XRT-only analysis was, however, poorly determined; adding RHESSI flux upper limits in the 4-13 keV energy range provide a strong high-temperature constraint which greatly improves the multi-thermal findings. The results of the present work as well as those from a growing number of papers on this subject imply that our previous understanding of the temperature distribution in active regions has been limited. Hot plasma (log T approximate to 7) appears to be prevalent, although in relatively small quantities as predicted by nanoflare models. Other models may need to be adjusted or updated to account for these new results.