tokens: again. The velocity is calculated by dividing the distance that the center of the BD moved by the time between recordings. The image was then advanced again and this process is repeated until the BD disappears or merges with another BD. Because the lifetime of the BDs is variable, the time between recordings varies, but as a general rule the number of recordings is maximized (minimizing the time between each recording) but there are at least 11 s between each recording. The average velocity of a BD is the average of these multiple velocity measurements. The speed was measured for only 25 BDs because there were not enough data points for five of the BDs. Figure 3 (i) is a scatterplot between the speed and the ratio of length-to-width of the BDs. We plot this figure in an attempt to find a correlation between how long a BD is relative to how fast it is moving (the thought being that faster BDs might be elongated in the radial direction), but evidently there is no clear relationship; there is perhaps a slight tendency for faster BDs to have less elongation. To investigate the formation mechanism and temperature of these BDs, we obtained their light curves from five AIA channels. Figure 4 shows the light curves of four of our BDs. These light curves are made by tracking the BD from when it first begins to brighten, through peak intensity, and ending when it fades from view or gets dim enough. To measure the intensity, we first find the target BD using the Hi-C 193 Å images and then match the location to the AIA 193 Å images. We center a circle on the BD's brightest part and measure the intensity inside. The frame is advanced and the intensity is measured for the new time, again with the circle centered on the brightest part of the BD. In this way, we track the BD's peak brightness over its lifetime or over its brightest peak during its lifetime. This intensity is then normalized to the highest intensity over the period. Figure 4. Normalized light curves for four example BDs from a set of five AIA bands. Each set of light curves is from tracking the brightest part of the BD as it drifts laterally during its peak brightening. As denoted in each panel by different colored lines, orange is for 193 Å, pink is for 211 Å, yellow is for 171 Å, green is for 1600 Å, and red is for 304 Å. Please note that the time on the x -axis is based on the AIA 193 Å channel; the closest available data in time for other channels is taken at each time step. Therefore, a few seconds’ difference in the observation of different channels is not seen. Asterisks on the 193 Å light curves mark data points. We use four AIA wavelengths in addition to the 193 Å: 211, 171, 1600, and 304 Å. The AIA 171, 193, and 211 Å channels are typically coronal, as their response functions peak at temperatures of roughly 1, 1.5, and 2.5 MK, respectively (Lemen et al. 2012 ). However, all of these channels have cooler-TR lines in the passband and hence have some response in the cooler-TR
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