The NANOGrav nine-year data set: Monitoring interstellar scattering delays

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.

Title	The NANOGrav nine-year data set: Monitoring interstellar scattering delays
Creator	Levin, L.
	Demorest, P. B.
	Zhu, W. W.
	McLaughlin, M. A.
	Jones, M. L.
	Arzoumanian, Z.
	Lam, M. T.
	Cordes, J. M.
	Crowter, K.
	Jones, G.
	Palliyaguru, N.
	Chatterjee, S.
	Lazio, T. J. W.
	Dolch, T.
	Stairs, I. H.
	Pennucci, T. T.
	Fonseca, E.
	Ransom, S. M.
	Ellis, J. A.
	Ferdman, R. D.
	Nice, David J.
	Stovall, K.
	Gonzalez, M. E.
	Swiggum, J. K.
	Stinebring, D. R.
Publisher	Astrophysical Journal
Academic Department	Physics
Division	Natural Sciences
Organization	Lafayette College
Date Issued	February 20, 2016
Date Available	2016-04-15T14:29:31Z
Type	Article
Language	English
Keyword	methods: data analysis
	pulsars: general
	ISM: general
	gravitational waves
Bibliographic Citation	Levin, L., et al. (2016 Feb 20) "The NANOGrav nine-year data set: Monitoring interstellar scattering delays." Astrophysical Journal 818 (2): Article 166.
Standard Identifier	DOI 10.3847/0004-637X/818/2/166
Standard Identifier	Handle 10385/2109
Permalink	http://hdl.handle.net/10385/2109
Rights Statement	In Copyright
Rights Holders	The American Astronomical Society