Comparison to instability mechanisms. From left to right: temperature anisotropy versus parallel electron beta for wave events. The upper red line is the whistler temperature anisotropy threshold,, and the lower red line is an arbitrary firehose instability (both from Lacombe et al. 2014, based on Gary et al. 1999). Normalized electron heat flux versus β_e∥. The yellow and red lines plot the linear instability thresholds for the whistler heat flux fan instability from Eq. (5) of Vasko et al. (2019) for the parameters of 0.5 and 1 in their Table 1). The electron Alfvén energy to compare to the threshold for the beam mechanism of Sauer & Sydora (2010) which requires electron beams with energies greater than four times the Alfvén energy.