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The electron density distribution in the central regions of the Milky Way Galaxy is still poorly known. Kinematic distance estimates from 21-cm emission/ absorption spectra of pulsars, when combined with pulsar dispersion measurements, provide the best technique for the determination of this quantity.
We have used the Very Large Array in phased array mode to measure the neutral hydrogen emission and absorption spectra in the direction of four distant, low-latitude pulsars in the inner Galaxy whose spectra have not previously been recorded. In two cases, we were able to measure simultaneously the absorption spectrum of another "reference" source lying in the same primary beam as the pulsar, which greatly facilitates the interpretation of the pulsar spectrum.
We display the emission and absorption spectra and corresponding distance - velocity plots. We derive kinematic distances and electron densities along the lines of sight where possible, and discuss the relevance of these measurements for the electron density distribution in the Galaxy.
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