Probing AGN jet precession with LISA

TL;DR

Jet precession in AGN likely traces the coupled dynamics of accretion disks around SMBHs, but EM observations alone struggle to constrain long precession timescales. The authors develop a self-consistent semi-analytic model linking warped minidisks, BH-spin alignment, and disk migration (including disk breaking) to two jet-precession timescales, $t_{ m LT}$ and $t_{ m tid}$, and connect these to the LISA detectability of SMBH mergers using post-Newtonian evolution and IMRPhenomXPHM waveforms with Monte Carlo marginalization. They find $t_{ m LT}$ is typically $ ext{a few Myr}$ and $t_{ m tid}$ spans $ ext{1 yr}$ to $ ext{10^7 yr}$, with disk breaking yielding the longest values and spin alignment the shortest; LISA SNRs exhibit structure tied to spin configurations, suggesting a selection effect toward progenitors with shorter jet-precession times. This framework enables GW observations to probe AGN jet precession histories, offering a path to study the population of precessing-jet AGN and guiding future multi-messenger investigations.

Abstract

The precession of astrophysical jets produced by active-galactic nuclei is likely related to the dynamics of the accretion disks surrounding the central supermassive black holes (BHs) from which jets are launched. The two main mechanisms that can drive jet precession arise from Lense-Thirring precession and tidal torquing. These can explain direct and indirect observations of precessing jets; however, such explanations often utilize crude approximations of the disk evolution and observing jet precession can be challenging with electromagnetic facilities. Simultaneously, the Laser Interferometer Space Antenna (LISA) is expected to measure gravitational waves from the mergers of massive binary BHs with high accuracy and probe their progenitor evolution. In this paper, we connect the LISA detectability of binary BH mergers to the possible jet precession during their progenitor evolution. We make use of a semi-analytic model that self-consistently treats disk-driven BH alignment and binary inspiral and includes the possibility of disk breaking. We find that tidal torquing of the accretion disk provides a wide range of jet precession timescales depending on the binary separation and the spin direction of the BH from which the jet is launched. Efficient disk-driven BH alignment results in shorter timescales of $\sim 1$ yr which are correlated with higher LISA signal-to-noise ratios. Disk breaking results in the longest possible times of $\sim 10^7$ yrs, suggesting a deep interplay between the disk critical obliquity (i.e. where the disk breaks) and jet precession. Studies such as ours will help to reveal the cosmic population of precessing jets that are detectable with gravitational waves.

Figures (5)

• Figure 1: The dependence of various timescales on the binary BH total mass, $M$. The dashed red and dot-dashed blue lines are the tidal disk precession timescale [Eq. (\ref{['E:Ttid2']})] for in-plane and aligned primary BH spin, respectively, which define the allowed range of values shown by the light-pink shaded patch. The dotted black line is the Lense-Thirring precession timescale $t_{\rm LT}$ [Eq. (\ref{['E:Tlt']})], and the black solid line is the GW-driven binary merger timescale $t_{\rm merge}$ [Eq. (\ref{['E:Tmerge']})]. We use our fiducial values for the remaining parameters as listed in Sec. \ref{['sec:Results']}.
• Figure 2: The Lense-Thirring jet precession timescale $t_{\rm LT}$ of the jet of the primary BH during the phase of disk migration and the LISA signal-to-noise ratio $\rho$ of the binary BH merger after the PN inspiral as we vary the dimensionless spin magnitude of the primary BH $\chi_1$ from 0.01 to 0.9 which translates to the Lense-Thirring period via Eq. (\ref{['E:Tlt']}). Three initial binary BH spin orientations are indicated by the red (solid), blue (dashed), and green (dash-dot) lines. Note that each value of $\chi_1$ corresponds to a different system, as $\chi_1$ is constant in our model of binary disk migration (see Sec. \ref{['subsec:DiskMig']}).
• Figure 3: The evolution of the tidal jet precession timescale $t_{\rm tid}$ during the phase of disk migration, which depends on both the binary separation $r$ (or equivalently $\kappa_1$) and the spin-orbit misalignment of the primary BH $\theta_1$. This distribution of binaries are initialized with our fiducial parameters (Sec. \ref{['sec:Results']}) and differ only by their initial spin orientations which are isotropic. Here we terminate the evolution of the binary when the spin of the primary BH becomes aligned, shown by the blue dotted lines and open circles, or ceases to align further due to encountering a broken accretion disk, as shown by the red dashed lines and stars. Note that $t_{\rm tid} \approx 3.6$ yrs at the decoupling separation, $r_{\rm decoup} \approx 0.006$ pc, for an aligned primary BH spin ($\cos\theta_1 = 1$).
• Figure 4: Distributions of the tidal jet precession timescale $t_{\rm tid}$ (at $r_{\rm decoup}$), the binary BH spin orientations $\theta_1$ and $\theta_2$ (at $r_{\rm f}$), and the signal-to-noise ratio $\rho$ of the binary BH merger as seen by LISA for the set of binaries from Fig. \ref{['F:jet_disk']}. The two peaks in $t_{\rm tid}$ correspond to the aligned and misaligned cases of $\theta_1$, and the four peaks in $\rho$ correspond to the four combinations of aligned and misaligned primary and secondary BH spins. Contours enclose 50% and 90% of the distributions.
• Figure 5: The dependence of the tidal jet-precession timescale $t_{\rm tid}$ (colored regions) and of the LISA signal-to-noise $\rho$ (solid black lines) on the source-frame total binary mass $M$ and the redshift $z$. All other parameters are fixed to their fiducial values; the binary BH spins are aligned during disk migration.