wavelengths will provide the necessary context.

Figure \[fig:goes\_intensity\] shows the GOES SXR 1–8 Å flux over most of the event’s evolution. A modest increase in the SXR is visible already from about 16:50 UT, but the main impulsive phase starts only after 17:20 UT. The event then develops very rapidly, with the SXR flux peaking already at 17:45 UT. The Fermi GBM count rates profiles, integrated in the energy bands 6-12, 20-50, 50-100, 100-300 keV, are shown in Figure \[fig:hxr\_intensity\]. While RHESSI was in night-time during most of the flare, Fermi completely covered the impulsive phase, revealing a strong and rapid increase in the 20 – 300 keV flux, starting from $\sim$ 17:22 UT and reaching its maximum around 17:36 UT. A second episode of enhanced HXR flux is also observed, between 17:43 UT and 17:50 UT. Further analysis on Fermi data is provided in Sect. \[sec:fermi\], in particular for the short time interval framed by the dashed lines in Figure \[fig:hxr\_intensity\].

![GOES 1–8 Å flux over several hours around the event. The data utilized in this paper pertains to the very rapid impulsive phase, as framed by the dashed lines.[]{data-label="fig:goes_intensity"}](goes.eps){width="8cm"}

![HXR detector count flux of the SOL2014-09-10T17:45 impulsive phase 