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NGC 4151 Binary Black Hole Orbit Study in Multi-Wavelength Overview

This study delves into the spectroscopically resolved orbit of a supermassive binary black hole in NGC 4151 over 20 years of data, revealing variability and velocity changes in model components like the Core Broad Component (CBC) and Very Broad Component (VBC). The periodicity found suggests a possible orbital period ranging from 0.5 to 50 years, precession periods, and disk precession. Various interpretations and implications are discussed, including the danger of associated components being too small for bound BLR associations. Possible explanations like disk warping and accretion disk emissions are explored, along with the significance of supersonic shock heating and specific shapes of X-ray spectra. This study raises questions on the stability of BLR associations, the authenticity of periodicities in sparse data, and the general reliability of the LS periodogram.

daniellewilliams
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NGC 4151 Binary Black Hole Orbit Study in Multi-Wavelength Overview

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  1. “The First Spectroscopically Resolved Sup-pc Orbit of a Supermassive Binary Black Hole”E. Bon et al., accepted(?) to ApJ Sarah Burke Spolaor

  2. Argh! • Confusing and unscientific language makes it difficult to understand what they did, why, and their results. • “It is not that obvious, but one can see a peak…” • “We measured the width of the bump on the profiles” • “the pretty large value of eccentricity suggests…” • Entire sentence (putting it in context does not help): “gravitational wave detection campaigns.” • Few statements on statistical significance • (Minor) conflicting reports of numerical results • Etc.

  3. NGC 4151 multi-wavelength overview

  4. NGC 4151 multi-wavelength overview Radio X-ray Optical

  5. AGN Emission Lines Broad-line region clouds (orbiting BH) Narrow-line region clouds (further out from central BH torus-accretion disk system)

  6. Data span: 11 years regularly, 20 years total • Measured variability in Ha • Measured velocity changes in model components CBC:“Core broad component”. (fixed velocity) VBC:“Very broad component” Bump: Rogue component associated with ??? Unlabelled: Narrow emission line template

  7. Periodicity: FOUND! Variability in all components!

  8. Possible interpretations of periodicity • Orbital period  T depends on mass; ~0.5-50 years • Precession period (from BH spin) ~ 105 yr • Accretion disk precession (from second BH’s orbit) ~ 250ish years? • “Self-warping” from radiation force ~ “consistent” r16 = period/16 years; Rd = accretion disk radius, size ???; no explanation of other parameters

  9. Possible interpretations of periodicity ✓ • Orbital period  T depends on mass; ~0.5-50 years • Precession period (from BH spin) ~ 105 yr • Accretion disk precession (from second BH’s orbit) ~ 250ish years? • “Self-warping” from radiation force ~ “consistent” ✗ ✗ ✓ r16 = period/16 years; Rd = accretion disk radius, size ???; no explanation of other parameters

  10. “Actual binary” period VBC Radial velocity • Velocity fit to drifting “bump” and “VBC” components • Solution: • e = 0.42 • P = 5776 d = 15.8 y • a1, a2 sin(i) = 0.002, 0.008 • m1,m2 sin3(i) = 3e7, 8.5e6 Msun • Discussion: variability comes from supersonic shocks (v>vsound when moving towards observer) • Danger: a1,a2 too small for bound BLR associations (Roche lobe overflow)? Bump Continuum flux Model component fluxes

  11. Bogdanovic et al. (2008): Theoretical BLR particle modelling for Ha lines

  12. Other interpretations • Disk warping • (Intrinsically) possible with or without binary • For binary: sinusoidal radial velocityvariations not observed • Accretion disk emission • Explanation for Ha“bumps” • Elliptical, precessing disk episodes • Circular (accretion?) disk with spiral arm • “Tests need to be made to prove or disprove these”

  13. Useful for a PPTA search? • Tgw ~ 108 years • Pgw ~ 8 years • z = 0.003; 13.8 Mpc away! (note: 3C66B @ 88 Mpc, OJ287 @ 1 Gpc) • havg < 1.6e-17 (ignoring eccentricity) • Probably not yet, but maybe with new techniques, ideally-positioned pulsars, a little boost from eccentricity, and a few more years of data!

  14. VLBI follow-up? • Resolved binary • 0.008pc = 0.5 mas (way too small to resolve) • Jet modulation • 15.8 years  possible periodicities at ~0.3 mas if jet flux is modulated by the binary (e.g. periodic accretion), and jet is travelling at c (also probably too small to detect)

  15. Important secondary implications (if true) • BLR structures may remain intact to very small BH orbits. • Possible new method(s) to discover binary systems • Multi-component modelling to discover velocity shifts • Supersonic shock heating: multi-n variability • Specific shapes of hard X-ray spectrum • Seyfert-type switching: broad indication of binary activity? • Are many small-orbit binaries eccentric?

  16. Open questions • Periodicity seems to be genuine, but…. • Reliability of LS periodogram for <= one period/sparse data? • Stability of clear BLR associations in small-orbit binaries? • What does the observed period relate to? • Orbital period: generally consistent. • Other explanations possible; yet to be explored • Are there more systems discoverable by this technique?

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