I found this paper which details how a charged particle falling into a black hole radiates. How is this possible when there is no acceleration on the particle?

I found this paper which details how a charged particle falling into a black hole radiates. How is this possible when there is no acceleration on the particle? https://adsabs.harvard.edu/full/1971PASP...83..633R https://adsabs.harvard.edu/full/1971PASP...83..633R Title: Radiation from Particles Falling into Black-Holes Authors: Ross, D. K. Journal: Publications of the Astronomical Society of the Pacific, Vol. 83, No. 495, p.633 Bibliographic Code: 1971PASP...83..633R