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ABSTRACT 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 at redshift $z=1$. Gas induces a phase correction to the GW signal with an effective amplitude ($$C_{\rm g}$$) and a semimajor 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 inspiral-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 $$\chi _{1,2}$$ 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 $$M_z=10^5~{\rm M}_{\odot }$$, $q=8$, $$\chi _{1,2}=0.9$$, and $$t_c=4$$ years MBHB, we can confidently measure (with a relative error of $$\lt 50$$ per cent) an Eddington ratio $${\rm f}_{\rm Edd}\sim 0.1$$ for a circular binary and $${\rm f}_{\rm Edd}\sim 1$$ for an eccentric system assuming $$\mathcal {O}(10)$$ stronger gas torque near-merger than at the currently explored much-wider binary separations. The minimum measurable eccentricity is $$e_0\gtrsim 10^{-2.75}$$ in vacuum and $$e_0\gtrsim 10^{-2}$$ in gas. A weak environmental perturbation ($${\rm f}_{\rm Edd}\lesssim 1$$) to a circular binary can be mimicked by an orbital eccentricity during inspiral, implying that an electromagnetic counterpart would be required to confirm the presence of an accretion disc.
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Evolution of gas disc–embedded intermediate mass ratio inspirals in the LISA band
Abstract Among the potential milliHz gravitational wave (GW) sources for the upcoming space-based interferometer LISA are extreme- or intermediate-mass ratio inspirals (EMRI/IMRIs). These events involve the coalescence of supermassive black holes in the mass range 105M⊙ ≲ M ≲ 107M⊙ with companion BHs of much lower masses. A subset of E/IMRIs are expected to occur in the accretion discs of active galactic nuclei (AGN), where torques exerted by the disc can interfere with the inspiral and cause a phase shift in the GW waveform. Here we use a suite of two-dimensional hydrodynamical simulations with the moving-mesh code DISCO to present a systematic study of disc torques. We measure torques on an inspiraling BH and compute the corresponding waveform deviations as a function of the binary mass ratio q ≡ M2/M1, the disc viscosity (α), and gas temperature (or equivalently Mach number; $$\mathcal {M}$$). We find that the absolute value of the gas torques is within an order of magnitude of previously determined planetary migration torques, but their precise value and sign depends non-trivially on the combination of these parameters. The gas imprint is detectable by LISA for binaries embedded in AGN discs with surface densities above $$\Sigma _0\ge 10^{4-6} \rm \, g cm^{-2}$$, depending on q, α and $$\mathcal {M}$$. Deviations are most pronounced in discs with higher viscosities, and for E/IMRIs detected at frequencies where LISA is most sensitive. Torques in colder discs exhibit a noticeable dependence on the GW-driven inspiral rate as well as strong fluctuations at late stages of the inspiral. Our results further suggest that LISA may be able to place constraints on AGN disc parameters and the physics of disc-satellite interaction.
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- Award ID(s):
- 1715661
- PAR ID:
- 10225558
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 501
- Issue:
- 3
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 3540 - 3557
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/staa3976
