@article{articled7c046a0,
title   = {On quasinormal frequencies of black hole perturbations with an external source},
author = {Qian, Wei-Liang and Lin, Kai and Wu, Jian-Pin and Wang, Bin and Yue, Rui-Hong},
year = {2020},
doi = {10.1140/epjc/s10052-020-08539-x},
publisher = {Springer},
journal   = {European Physical Journal C}
}