Measuring eccentricity and gas-induced perturbation from gravitational waves of LISA massive black hole binaries

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Main Authors: Garg, Mudit, Derdzinski, Andrea, Tiwari, Shubhanshu, Gair, Jonathan, Mayer, Lucio
Format: Preprint
Published: 2024
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author Garg, Mudit
Derdzinski, Andrea
Tiwari, Shubhanshu
Gair, Jonathan
Mayer, Lucio
author_facet Garg, Mudit
Derdzinski, Andrea
Tiwari, Shubhanshu
Gair, Jonathan
Mayer, Lucio
contents We assess the possibility of detecting both eccentricity and gas effects (migration and accretion) in the gravitational wave (GW) signal from LISA massive black hole binaries (MBHBs) at redshift $z=1$. Gas induces a phase correction to the GW signal with an effective amplitude ($C_{\rm g}$) and a semi-major axis dependence (assumed to follow a power-law with slope $n_{\rm g}$). We use a complete model of the LISA response, and employ a gas-corrected post-Newtonian in-spiral-only waveform model TaylorF2Ecc By using the Fisher formalism and Bayesian inference, we constrain $C_{\rm g}$ together with the initial eccentricity $e_0$, the total redshifted mass $M_z$, the primary-to-secondary mass ratio $q$, the dimensionless spins $χ_{1,2}$ of both component BHs, and the time of coalescence $t_c$. We find that simultaneously constraining $C_{\rm g}$ and $e_0$ leads to worse constraints on both parameters with respect to when considered individually. For a standard thin viscous accretion disc around $M_z=10^5~{\rm M}_\odot$, $q=8$, $χ_{1,2}=0.9$, and $t_c=4$ years MBHB, we can confidently measure (with a relative error of $<50 $ per cent) an Eddington ratio ${\rm f}_{\rm Edd}\sim0.1$ for a circular binary and ${\rm f}_{\rm Edd}\sim1$ for an eccentric system assuming ${O}(10)$ stronger gas torque near-merger than at the currently explored much-wider binary separations. The minimum measurable eccentricity is $e_0\gtrsim10^{-2.75}$ in vacuum and $e_0\gtrsim10^{-2}$ in gas. A weak environmental perturbation (${\rm f}_{\rm Edd}\lesssim1$) to a circular binary can be mimicked by an orbital eccentricity during in-spiral, implying that an electromagnetic counterpart would be required to confirm the presence of an accretion disc.
format Preprint
id arxiv_https___arxiv_org_abs_2402_14058
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle Measuring eccentricity and gas-induced perturbation from gravitational waves of LISA massive black hole binaries
Garg, Mudit
Derdzinski, Andrea
Tiwari, Shubhanshu
Gair, Jonathan
Mayer, Lucio
Astrophysics of Galaxies
Cosmology and Nongalactic Astrophysics
High Energy Astrophysical Phenomena
General Relativity and Quantum Cosmology
We assess the possibility of detecting both eccentricity and gas effects (migration and accretion) in the gravitational wave (GW) signal from LISA massive black hole binaries (MBHBs) at redshift $z=1$. Gas induces a phase correction to the GW signal with an effective amplitude ($C_{\rm g}$) and a semi-major axis dependence (assumed to follow a power-law with slope $n_{\rm g}$). We use a complete model of the LISA response, and employ a gas-corrected post-Newtonian in-spiral-only waveform model TaylorF2Ecc By using the Fisher formalism and Bayesian inference, we constrain $C_{\rm g}$ together with the initial eccentricity $e_0$, the total redshifted mass $M_z$, the primary-to-secondary mass ratio $q$, the dimensionless spins $χ_{1,2}$ of both component BHs, and the time of coalescence $t_c$. We find that simultaneously constraining $C_{\rm g}$ and $e_0$ leads to worse constraints on both parameters with respect to when considered individually. For a standard thin viscous accretion disc around $M_z=10^5~{\rm M}_\odot$, $q=8$, $χ_{1,2}=0.9$, and $t_c=4$ years MBHB, we can confidently measure (with a relative error of $<50 $ per cent) an Eddington ratio ${\rm f}_{\rm Edd}\sim0.1$ for a circular binary and ${\rm f}_{\rm Edd}\sim1$ for an eccentric system assuming ${O}(10)$ stronger gas torque near-merger than at the currently explored much-wider binary separations. The minimum measurable eccentricity is $e_0\gtrsim10^{-2.75}$ in vacuum and $e_0\gtrsim10^{-2}$ in gas. A weak environmental perturbation (${\rm f}_{\rm Edd}\lesssim1$) to a circular binary can be mimicked by an orbital eccentricity during in-spiral, implying that an electromagnetic counterpart would be required to confirm the presence of an accretion disc.
title Measuring eccentricity and gas-induced perturbation from gravitational waves of LISA massive black hole binaries
topic Astrophysics of Galaxies
Cosmology and Nongalactic Astrophysics
High Energy Astrophysical Phenomena
General Relativity and Quantum Cosmology
url https://arxiv.org/abs/2402.14058