Observational signatures and polarized images of rotating charged black holes in Kalb–Ramond gravity

Abstract This paper investigates the shadow images of rotating charged black holes in Kalb–Ramond (KR) gravity, using an accretion disk that is both optically and geometrically thin and located on the equatorial plane as the light source model. The results show that, compared to Sgr A*, the observational data of M87* impose stronger constraints on the charge parameter Q and the Lorentz-violating parameter $$\mathcal {G}$$ G . Under the thin accretion disk model, a larger observer inclination $$\theta _o$$ θ o deforms the central brightness depression into a hat-like structure. The parameters $$(a, Q, \mathcal {G})$$ ( a , Q , G ) mainly affect the size of the central brightness depression and the brightness of the critical curve, where increasing these parameters reduces the shadow size and enhances the distinguishability of the critical curve. In the retrograde accretion disk case, the crescent-shaped bright area appears on the side opposite to that in the prograde case. In addition, we compute the distribution of the redshift factor on the projection screen. The results indicate that the Doppler effect induced by large $$\theta _o$$ θ o enhances the blueshift in the image, while the light emitted by particles plunging into the black hole leads to strong redshift near the central brightness depression. Finally, we study the polarization images under synchrotron radiation and find that the polarization intensity $$\mathcal {P}_o$$ P o reaches its maximum around the lensed image and higher-order images, whereas no polarization vectors appear within the central brightness depression. This stands in sharp contrast to horizonless compact objects. These findings contribute to a deeper understanding of the shadow properties of charged black holes within Lorentz-violating gravity.