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The distortion of the spectrum of synchrotron radiation received by a distant observer due to magnetic field inhomogeneity is discussed. It is shown that for single-particle radiation, a noticeable difference in the integrated spectrum from the case of a uniform magnetic field occurs only for observation times significantly exceeding the observer's departure from the beam pattern, and only for subrelativistic particles, when the radiation arrives from regions with significantly different magnetic fields during the observation time. For shorter observation times, field inhomogeneity leads only to small-scale distortions (smaller or comparable in frequency to the gyrofrequency) and does not manifest itself in the averaged spectrum. For the case of a particle ensemble, which is of interest for astrophysical applications, the difference in the integrated spectrum becomes negligible.

In this paper, we generate a rotating charged black hole (BH) with scalar hair via the Newman--Janis algorithm (NJA) and study its thin accretion disk and shadow. The structure of the event horizon and ergosurface is analyzed in detail, revealing how the charge parameter Q and scalar hair parameter s influence the spacetime geometry. We analyze the energy flux and temperature distribution of the accretion disk, finding that increasing either Q or s leads to higher energy flux and peak temperature. The BH shadow is also examined, showing that its apparent size decreases monotonically with increasing Q or s. Notably, in the near-extremal regime, the shadow develops a distinctive cuspy edge, indicative of strong light bending in the scalarized and charged spacetime. By comparing the theoretically predicted shadow diameter with Event Horizon Telescope (EHT) observations of Sgr A*, we derive observational constraints on the model parameters. For inclination angles of 17<SUP>∘</SUP> and 90<SUP>∘</SUP>, a joint analysis constrains the charge parameter to 0 &lt; Q &lt; 0.522745 (at fixed <mml:math><mml:mrow><mml:mi>s</mml:mi><mml:mo>=</mml:mo><mml:mn>0.1</mml:mn></mml:mrow></mml:math>) and the scalar hair parameter to 0 &lt; s &lt; 0.283373 (at fixed <mml:math><mml:mrow><mml:mi>Q</mml:mi><mml:mo>=</mml:mo><mml:mn>0.3</mml:mn></mml:mrow></mml:math>). Our results demonstrate how scalar hair and electric charge leave imprints on accretion disk emissions and BH shadows, offering new observational signatures for testing gravity theories beyond general relativity.