We thank A. Celotti, G. Ghisellini, A. Segreto, E. Ambrosi and M. Grazia Bernardini for discussions. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. P.D. and S.C. thank N. Schartel for granting XMM-Newton DDT observations. M.B. acknowledges financial support from the Italian Ministry of University and Research . M.B. and G.O. acknowledge financial support from the AHEAD2020 project .
and S.C. acknowledge support from ASI grant I/004/11/5. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.