A New Model for the Galactic Distribution of Free Electrons and its Fluctuations

By Jim Cordes, T. Lazio. 2002

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We present a new model for the Galactic distribution of free electrons. It (a) describes the distribution of the free electrons responsible for pulsar dispersion measures and thus can be used for estimating the distances to pulsars; (b) describes large-scale variations in the strength of fluctuations in electron density that underly interstellar scattering; (c) can be used to interpret interstellar scattering and scintillation observations of Galactic objects and of extragalactic objects, such as intrinsically compact AGNs and Gamma-ray burst afterglows; and (d) serves as a preliminary, smooth spatial model of the warm ionized component of the interstellar gas. This work builds upon and supercedes the Taylor & Cordes (1993) model by exploiting new observations and analysis methods. For lines of sight directed out of the Galactic plane, the new model yields substantially larger values for pulsar dispersion measures, except for directions dominated by the local hot bubble. Unlike the TC93 model, the new model provides sufficient electrons to account for the dispersion measures of the vast majority of known, Galactic pulsars. The new model is described and exemplified using plots of astronomically useful quantities on Galactic-coordinate grids. Software available on the Internet is also described. Future observations and analysis techniques that will improve the Galactic model are outlined.

Subfields: Astronomy and Astrophysics, Oceanography

View Paper: https://www.semanticscholar.org/paper/ef3e5fe9c720d7fbbf818fd2d6d4141a07bfe25f

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Citations in the corpus

A fast radio burst associated with a Galactic magnetar (2020, methodology): “According to two models for the Galactic distribution of free electrons, this DM corresponds to distances of 6–13 kpc [36] and 4–16 kpc [37].”
Observing pulsars and fast transients with LOFAR (2011, background): “As the majority of these pulsars will be nearby or out of the Galactic plane, the dispersion and scattering measures of this new sample will improve our model of the distribution of the ionized ISM and its degree of clumpiness (Cordes & Lazio 2002).”
Timing analysis for 20 millisecond pulsars in the Parkes Pulsar Timing Array (2015, methodology): “Measured values L-K bias-corrected values DM distances (kpc) Pulsar name Parallax π (mas) Ṗb distance (kpc) Parallax π (mas) π distance (kpc) TC93 NE2001 J0437−4715 6.37 ± 0.09 0.15679 ± 0.00025 6.37 ± 0.09 0.156.9 ± 0.0022 0.14 0.189 J0613−0200 0.86 ± 0.13 – 0.81 ± 0.13 1.09+0.18−0.14 2.19 1.700 J”
The observed spiral structure of the Milky Way (2014, methodology): “In the best-fitted models, the Scutum Arm is relatedto many bright HII regions in the distant parts of the first Galaxy quadrant aroundx ∼4 kpc, y ∼0 kpc, which is consistent with the spiral arm models of GG76 and Cordes & Lazio (2002).”
EXTENDING THE BIG POWER LAW IN THE SKY WITH TURBULENCE SPECTRA FROM WISCONSIN Hα MAPPER DATA (2009, background): “Other parameters are taken as follows: 〈ne〉 = 0.010 cm−3 (Cordes & Lazio 2002) and R0 = 1800 pc (Gaensler et al. 2008).”
The astrophysics of nanohertz gravitational waves (2018, background): “Many pulsar distances are poorly constrained, since most are estimated via the dispersion measure of the pulse (e. g., Cordes and Lazio 2002; Yao et al. 2017).”
THE REPEATING FAST RADIO BURST FRB 121102: MULTI-WAVELENGTH OBSERVATIONS AND ADDITIONAL BURSTS (2016, methodology): “Here we arbitrarily define a FRB as any few-ms radio burst that has DM at least twice the maximum along the line of sight as predicted by the Cordes & Lazio (2002) NE2001 model, and for which the DM excess cannot be explained by any intervening Galactic structure.”
ON THE NATURE OF THE LOCAL SPIRAL ARM OF THE MILKY WAY (2013, methodology): “From the model of Cordes & Lazio (2002), the interarm spacing between two major arms of the Milky Way is usually more than 2 kpc, even more than 3 kpc in some places.”