1. Searching for supermassive black hole binaries with CRTS Matthew J. Graham Center for Data-Driven Discovery, Caltech and NOAO May 12, 2015 Hotwiring The Transient Universe IV

2. May 12, 2015Matthew J. Graham 2 Our future

3. May 12, 2015Matthew J. Graham 3 The physics of a SMBH binary merger Stage I (> 1pc) SMBHs dissipate angular momentum through dynamical friction with surrounding stars Stage II (0.01 – 1pc) Stalled phase due to stellar depletion (~10 6 – 10 7 yrs) Stage III ( < 0.01pc) Orbital angular momentum lost by gravitational radiation Stage IV Coalescence and recoil ---- The “final parsec” problem Subparsec systems are not resolvable

4. May 12, 2015Matthew J. Graham 4 Structure of a close SMBH binary Circumbinary disk Primary black hole Secondary black hole Minidisk BLR

5. May 12, 2015Matthew J. Graham 5 Spectroscopic searches A fraction of all quasar spectra exhibit double-peaked broad emission lines (attributable to a number of causes) If two BLRs bound to two SMBHs coorbiting, we should see characteristic Doppler-shifts reflecting orbital motion Monitor samples of broad-line double peakers or systems with single, kinematically-shifted broad lines Limited to > 0.1 pc separation systems

6. May 12, 2015Matthew J. Graham 6 Catalina Real-time Transient Survey (2005-) Collaborative survey with Catalina Sky Survey (LPL, UA) Unfiltered observations 21 nights/lunation covering up to 2000 deg 2 /night Covers 33000 sq. deg. (0 < RA < 360, -75 < Dec < 70). Calibrated photometry for 500 million objects (> 100 billion data points) Depth V = 19 to 21.5 100 – 600 observations in most regions (median ~ 250) More published SNe and CVs than any other survey (public instantly) Open data policy (http://catalinadata.org) ~3% LSST

7. May 12, 2015Matthew J. Graham 7 Quasar variability First quasar identified 3C 48 – most striking feature was that the optical radiation varied Physical origin of photometric variability in optical/UV is unclear Many studies based on small sample size or (very) sparse time sampling The current best statistical description is damped random walk (CAR(1)): characterized by σ 2 and τ 335000 spectroscopically-confirmed quasars in CRTS archive: 250000 have sufficient coverage (npts > 50)

8. May 12, 2015Matthew J. Graham 8 The best binary candidate to date OJ 287 shows a pair of outburst peaks every 12.2 years for at least the last century

9. May 12, 2015Matthew J. Graham 9 Periodicity search criteria Wavelets Peak value Period Slepian wavelet characteristic timescale Autocorrelation function Period Amplitude of exponentially damped cosine Decay constant of exponentially damped cosine Shape and coverage Scatter around best-fit Fourier series At least 1.5 cycles Train SVM to better describe discriminating hyperplane

10. May 12, 2015Matthew J. Graham 10 How many SMBH binaries detected? From merger tree assembly models and hydro simulations with  period from 20 – 300 weeks  sky coverage of 2π ster.  V < 20  0.0 < z < 4.5 => 450 binaries are predicted 111 candidates identified out of 250000 quasars Simulated data set of objects following a CAR(1) model gives no candidates

11. May 12, 2015Matthew J. Graham 11 SMBH binary candidates

12. May 12, 2015Matthew J. Graham 12 PG 1302-102 z = 0.28, core-dominated flat-spectrum radio source Luminous elliptical host with nearby companions Coincident radio and optical structural features (Graham et al. 2015, Nature, 518, 74)

13. May 12, 2015Matthew J. Graham 13 Quasi-periodicity in CARMA models 5 candidates show a periodicity consistent with best-fit CARMA but bandwidth of these covers full temporal baseline 100 mock CARMA light curves for each candidate give statistically different selection parameters

14. May 12, 2015Matthew J. Graham 14 Possible interpretations Superposition of thermal emission from accretion disk and non- thermal contribution from a precessing jet driven by SMBH binary Warped accretion disk caused by SMBH binary Periodic accretion rates from a SMBH binary can lead to an overdense hump in the inner circumbinary accretion disk Hydrodynamical simulations suggest that strongest periodicity associated with cavity in circumbinary disk => true binary period 3-8 times shorter Relativistic boosting for line-of-sight motion of minidisk around secondary orbiting around system barycenter Scaled version of QPOs seen in stellar black hole binaries (D’Orazio et al. 2015)

15. May 12, 2015Matthew J. Graham 15 What about other SMBH binary candidates? No spectroscopic binary candidates in the literature show any sign of significant periodicity in their CRTS photometry Some suggestion of differences in light curve morphology for specific spectroscopic samples The quiescent milliparsec binary J120136.02+300305.5 shows no optical variation in CRTS data Blazars with reported (quasi-)periodicity do not show consistent periodicity in CRTS data FBQS J221648.7+012427 does not pass our selection criteria

16. May 12, 2015Matthew J. Graham 16 Testing the binary hypothesis Further monitoring looking for amplitude/phase trends with wavelength Spectroscopic monitoring Multiple periods with cavity and broad line widths X-ray imaging to detect relativistic effects in Fe Kα SED effects Reverberation mapping to distinguish between different scenarios

17. May 12, 2015Matthew J. Graham 17 The GW-driven population Haiman, Kocsis & Menou (2009) predict: The power law at longer timescales depends on accretion physics Circumbinary gas is present at small orbital radii and is being perturbed by the black holes

18. May 12, 2015Matthew J. Graham 18 Detecting gravitational waves Are any of the candidates resolvable by PTAs as continuous GW sources and not just part of the stochastic background?

19. May 12, 2015Matthew J. Graham 19 Summary Supermassive black holes are an expected consequence of galaxy mergers To date, they have been very difficult to detect CRTS presents an unprecedented data set for exploring all types of variable astronomical phenomena Using a robust selection technique, we have identified 111 periodic candidates out of 250000 with CRTS coverage The best is PG 1302-105 showing strong periodicity over 20 yrs Several physical mechanisms can explain the variability but all involve a supermassive black hole binary Various followup tests can distinguish between different mechanisms Potentially resolvable by PTAs in the next decade or so

20. THIRD ANNUAL SCHOOL DATES: 16-23 AUGUST 2015 Training the next generation of scientists (in fields of astronomy, mathematics, computer science, and others) in the tools and techniques of massive data in Astronomy International program: funding for students from Chile and the U.S. Target students: senior undergraduate and beginning graduate students For further information, visit our website: http://www.aura-o.aura-astronomy.org/winter_school/