Analysis of the photospheric LoS magnetic flux density of the flare footpoint located within or at the edge of the sunspot. Left: Absolute value of the mean LoS magnetic flux density as a function of the electron spectral index. Black dots represent events with the footpoint within the sunspot, while blue triangles represent those at the edge of the sunspot. Vertical lines indicate the mean electron spectral indices, with the shaded areas representing its standard deviation. Right: Absolute value of the mean LoS magnetic flux density against the background-subtracted GOES 1−8° SXR flux. The gray crosses and the dashed gray correlation curve are derived from Tschernitz et al. (2018, Figure 9). To be consistent with Tschernitz et al. (2018), in this plot we multiplied the mean LoS magnetic flux density by 1/cos(u), with u the angular distance from disk center of the flare location.