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We studied the properties and occurrence of narrow band whistler waves andtheir interaction with strahl electrons observed between 0.17 and 0.26 auduring the first encounter of Parker Solar Probe. We observe that occurrence ofwhistler waves is low, nearly 1.5% and less than 0.5% in the analyzed peak andaverage BPF data respectively. Whistlers occur highly intermittently and 80% ofthe whistlers appear continuously for less than 3 s. Occurrence rate ofwhistler waves was found to be anti-correlated with the solar wind bulkvelocity. The study of the duration of the whistler intervals revealed ananti-correlation between the duration and the solar wind velocity, as well asbetween the duration and the normalized amplitude of magnetic field variations.The pitch-angle widths (PAWs) of the field-aligned electron population referredto as the strahl are broader by at least 12 degrees during the presence oflarge amplitude narrow band whistler waves. This observation points towards aEM wave electron interaction, resulting in pitch-angle scattering. PAW ofstrahl electrons corresponding to the short duration whistlers are highercompared to the long duration whistlers. Parallel cuts through the strahlelectron velocity distribution function (VDF) observed during the whistlerintervals appear to depart from the Maxwellian shape typically found in thenear-Sun strahl VDFs (Bercic et al. 2020). The relative decrease of parallelelectron temperature and the increase of PAW for the electrons in strahl energyrange suggests that the interaction with whistler waves results in a transferof electron momentum from the parallel to the perpendicular direction.

Whistler wave occurrence and the interaction with strahl electrons during the first encounter of Parker Solar Probe