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Gravitational-wave astrophysics with effective-spin measurements: Asymmetries and selection biases

Ng, Ken K. Y. and Vitale, Salvatore and Zimmerman, Aaron and Chatziioannou, Katerina and Gerosa, Davide and Haster, Carl-Johan (2018) Gravitational-wave astrophysics with effective-spin measurements: Asymmetries and selection biases. Physical Review D, 98 (8). Art. No. 083007. ISSN 2470-0010. http://resolver.caltech.edu/CaltechAUTHORS:20181009-092350127

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Abstract

Gravitational waves emitted by coalescing compact objects carry information about the spin of the individual bodies. However, with present detectors only the mass-weighted combination of the components of the spin along the orbital angular momentum can be measured accurately. This quantity, the effective spin χ_(eff), is conserved up to at least the second post-Newtonian order. The measured distribution of χ_(eff) values from a population of detected binaries, and in particular whether this distribution is symmetric about zero, encodes valuable information about the underlying compact-binary formation channels. In this paper we focus on two important complications of using the effective spin to study astrophysical population properties: (i) an astrophysical distribution for χ_(eff) values which is symmetric does not necessarily lead to a symmetric distribution for the detected effective spin values, leading to a selection bias; and (ii) the posterior distribution of χ_(eff) for individual events is asymmetricand it cannot usually be treated as a Gaussian. We find that the posterior distributions for χ_(eff) systematically show fatter tails toward larger positive values, unless the total mass is large or the mass ratio m2/m1 is smaller than ∼1/2. Finally we show that uncertainties in the measurement of χ_(eff) are systematically larger when the true value is negative than when it is positive. All these factors can bias astrophysical inference about the population when we have more than ∼100 events and should be taken into account when using gravitational-wave measurements to characterize astrophysical populations.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1103/PhysRevD.98.083007DOIArticle
https://journals.aps.org/prd/abstract/10.1103/PhysRevD.98.083007PublisherArticle
https://arxiv.org/abs/1805.03046arXivDiscussion Paper
Additional Information:© 2018 American Physical Society. Received 28 June 2018; published 9 October 2018. K. N. and S. V. acknowledge support of the MIT physics department through the Solomon Buchsbaum Research Fund, the National Science Foundation, and the LIGO Laboratory. LIGO was constructed by the California Institute of Technology and Massachusetts Institute of Technology with funding from the National Science Foundation and operates under cooperative Agreement No. PHY-0757058. D. G. is supported by NASA through Einstein Postdoctoral Fellowship Grant No. PF6–170152 by the Chandra X-ray Center, operated by the Smithsonian Astrophysical Observatory for NASA under Contract No. NAS8–03060. The authors acknowledge the LIGO Data Grid clusters. LIGO Document No. P1800103.
Group:TAPIR, LIGO
Funders:
Funding AgencyGrant Number
Massachusetts Institute of Technology (MIT)UNSPECIFIED
NSFPHY-0757058
LIGO LaboratoryUNSPECIFIED
NASA Einstein FellowshipPF6-170152
NASANAS8-03060
Other Numbering System:
Other Numbering System NameOther Numbering System ID
LIGO DocumentP1800103
Record Number:CaltechAUTHORS:20181009-092350127
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20181009-092350127
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90183
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:09 Oct 2018 16:56
Last Modified:09 Oct 2018 16:56

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