2020MNRAS.496L..28L

Five fast radio bursts (FRBs), including three apparently non-repeating ones, FRB 180924, FRB 181112, and FRB 190523, and two repeaters, FRB 121102 and FRB 180916.J0158+65, have already been localized so far. We apply a method developed recently by us to these five localized FRBs to give a cosmology-insensitive estimate of the fraction of baryon mass in the intergalactic medium, f_IGM. Using the measured dispersion measure (DM) and luminosity distance d_L data (inferred from the FRB redshifts and d_L of Type Ia supernovae at the same redshifts) of the five FRBs, we constrain the local f_IGM = 0.84^+0.16_–0.22 with no evidence of redshift dependence. This cosmology-insensitive estimate of f_IGM from FRB observations is in excellent agreement with previous constraints using other probes. Moreover, using the three apparently non-repeating FRBs only we get a little looser but consistent result: f_IGM = 0.74^+0.24_–0.18. In these two cases, reasonable estimations for the host galaxy DM contribution (DM_host) can be achieved by modelling it as a function of star formation rate. The constraints on both f_IGM and DM_host are expected to be significantly improved with the rapid progress in localizing FRBs.