Diagnosing Loops with Varying Cross-sectional Area using Emission Measure

The magnetic field in the photosphere appears to be concentrated in tight bundles, while it becomes volume filling in the corona. However, observations of active region loops show neither significant expansion along the loop nor where this transition occurs. Therefore, the location and extent of expansion in a loop are largely unknown. To investigate whether these properties show observationally unique signatures, we study the emission measure (EM) from impulsively heated loops. We use the recently upgraded EBTEL2.0 for this purpose. We have run a series of simulations over a range of loop lengths and expansion factors, with three different expansion profiles, to examine the impact of expansion on the EM. We find that the EM slopes decrease with increasing expansion factors, but the range of slope values are within the uncertainties of observational measurements.