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Sarah Burke Spolaor

“ The First Spectroscopically Resolved Sup-pc Orbit of a Supermassive Binary Black Hole ” E. Bon et al., accepted (?) to ApJ. Sarah Burke Spolaor. Argh!. Confusing and unscientific language makes it difficult to understand what they did, why, and their results.

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Sarah Burke Spolaor

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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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