A New Electron-Density Model for Estimation of Pulsar and FRB Distances

Abstract

We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds, and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic H II regions, a Galactic Center disk, and seven local features including the Gum Nebula, Galactic Loop I, and the Local Bubble. An offset of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.

Pulsar Rotation Measures and Large-scale Magnetic Field Reversals in the Galactic Disk

“…Columns 1 -6 list the pulsar J2000 name, period, dispersion measure, Galactic longitude, Galactic latitude and the estimated pulsar distance. Unless independent distance estimates are available, distances are based on the YMW16 electron-density model (Yao et al 2017). The next two columns list the measured RM and its uncertainty, and the final two columns give the telescope and date of the observations.…”

“…To compare how well these two models "predict" the EGRS RMs, we compute the RM of each EGRS source in Figure 1 using both the NE2001 electron density model (Cordes & Lazio 2002), as used by JF12, and the more recent YMW16 model (Yao et al 2017). In Figure 8 we show the distribution of observed EGRS RMs in Galactic latitude and longitude, along with the RMs computed using our model for the disk field, which is based on both pulsar and EGRS RMs, and from the JF12 model which is based on just the EGRS RMs.…”

“…In this paper, we use the new YMW16 Galactic electron density model (Yao et al 2017) to estimate pulsar distances from DMs because this model is believed to give more reliable estimates in general (see Table 6 of Yao et al 2017). Even so, estimated distances to some pulsars can be in error by a factor of two or even more.…”

R modes and neutron star recycling scenario

“…Thus, MSPs with DM < 70 pc cm −3 should have N H 2.1 × 10 21 cm −2 , a requirement, which is satisfied for more than 67% of currently known fast MSPs (ν > 250 Hz), according to ATNF pulsar catalogue (Manchester et al 2005, catalogue version 1.55 was applied). This catalogue also gives an information on the pulsar distances, and it turns out that 70% of known fast MSPs (ν > 250 Hz) are located closer than HETE J1900.1-2455, but this statistic is not independent because the pulsar distances are estimated using the Yao et al (2017) DM-based distance model as default.…”

The Green Bank North Celestial Cap Pulsar Survey. III. 45 New Pulsar Timing Solutions

“…Table 6 lists the measured proper motions, estimated transverse velocity, v t calculated using the DMinferred distances in both the NE2001 Cordes & Lazio (2002) and YMW16 (Yao et al 2017) models, and kinematic corrections. The observed pulsar spin down is a contribution of several effects,…”