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Effect of small interpulsar distances in stochastic gravitational wave background searches with pulsar timing arrays

Mingarelli, Chiara M. F. and Sidery, Trevor (2014) Effect of small interpulsar distances in stochastic gravitational wave background searches with pulsar timing arrays. Physical Review D, 90 (6). Art. No. 062011. ISSN 2470-0010. doi:10.1103/PhysRevD.90.062011.

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One of the primary objectives for pulsar timing arrays (PTAs) is to detect a stochastic background generated by the incoherent superposition of gravitational waves (GWs), in particular from the cosmic population of supermassive black hole binaries. Current stochastic background searches assume that pulsars in a PTA are separated from each other and the Earth by many GW wavelengths. As more millisecond pulsars are discovered and added to PTAs, some may be separated by only a few radiation wavelengths or less, resulting in correlated GW phase changes between close pulsars in the array. Here we investigate how PTA overlap reduction functions (ORFs), up to quadrupole order, are affected by these additional correlated phase changes, and how they are in turn affected by relaxing the assumption that all pulsars are equidistant from the solar system barycenter. We find that in the low-frequency GW background limit of f ∼ 10^(−9) Hz, and for pulsars at varying distances from the Earth, these additional correlations only affect the ORFs by a few percent for pulsar pairs at large angular separations, as expected. However, when nearby (order 100 pc) pulsars are separated by less than a few degrees, the correlated phase changes can introduce variations of a few tens of percent in the magnitude of the isotropic ORF, and much larger fractional differences in the anisotropic ORFs—up to 188 in the m = 0, l = 2 ORF for equidistant pulsars separated by 3°. In fact, the magnitude of most of the anisotropic ORFs is largest at small, but nonzero, pulsar separations. Finally, we write down a small angle approximation for the correlated phase changes which can easily be implemented in search pipelines, and for completeness, examine the behavior of the ORFs for pulsars which lie at a radiation wavelength from the Earth.

Item Type:Article
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URLURL TypeDescription Paper
Mingarelli, Chiara M. F.0000-0002-4307-1322
Additional Information:© 2014 American Physical Society. Received 13 June 2014; published 26 September 2014. The authors would like to thank Alberto Vecchio, Will Farr, Ilya Mandel, Cees Bassa, Rutger van Haasteren, and colleagues from the European Pulsar Timing Array. This research made use of Python and its standard libraries, numpy and matplotlib. This research was supported by a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme.
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Marie Curie International Outgoing FellowshipUNSPECIFIED
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Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2015-35
Issue or Number:6
Classification Code:PACS numbers: 04.80.Nn, 04.25.dg, 97.60.Gb, 04.30.-w
Record Number:CaltechAUTHORS:20141030-091935281
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51050
Deposited By: Jason Perez
Deposited On:30 Oct 2014 18:56
Last Modified:10 Nov 2021 19:05

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