The NANOGrav Nine-year Data Set: Monitoring Interstellar Scattering Delays

Levin, L. and McLaughlin, M. A. and Jones, G. and Cordes, J. M. and Stinebring, D. R. and Chatterjee, S. and Dolch, T. and Lam, M. T. and Lazio, T. J. W. and Palliyaguru, N. and Arzoumanian, Z. and Crowter, K. and Demorest, P. B. and Ellis, J. A. and Ferdman, R. D. and Fonseca, E. and Gonzalez, M. E. and Jones, M. L. and Nice, D. J. and Pennucci, Timothy Thomas and Ransom, S. M. and Stairs, I. H. and Stovall, K. and Swiggum, J. K. and Zhu, W. W. (2016) The NANOGrav Nine-year Data Set: Monitoring Interstellar Scattering Delays. ASTROPHYSICAL JOURNAL, 818 (2). ISSN 1538-4357

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Abstract

We report on an effort to extract and monitor interstellar scintillation parameters in regular timing observations collected for the North American Nanohertz Observatory for Gravitational Waves pulsar timing array. Scattering delays are measured by creating dynamic spectra for each pulsar and observing epoch of wide-band observations centered near 1500 MHz and carried out at the Green Bank Telescope and the Arecibo Observatory. The similar to 800 MHz wide frequency bands imply dramatic changes in scintillation bandwidth across the bandpass, and a stretching routine has been included to account for this scaling. For most of the 10 pulsars for which the scaling has been measured, the bandwidths scale with frequency less steeply than expected for a Kolmogorov medium. We find estimated scattering delay values that vary with time by up to an order of magnitude. The mean measured scattering delays are similar to previously published values and are slightly higher than predicted by interstellar medium models. We investigate the possibility of increasing the timing precision by mitigating timing errors introduced by the scattering delays. For most of the pulsars, the uncertainty in the time of arrival of a single timing point is much larger than the maximum variation of the scattering delay, suggesting that diffractive scintillation remains as only a negligible part of their noise budget.

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