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

Searching for supermassive black hole binaries with CRTS

Matthew J. GrahamCenter for Data-Driven Discovery, Caltech

and NOAO

May 12, 2015

Hotwiring The Transient Universe IV

May 12, 2015Matthew J. Graham

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Our future


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The physics of a SMBH binary merger

Stage I (> 1pc) SMBHs dissipate angular momentum through dynamical

friction with surrounding starsStage II (0.01 – 1pc) Stalled phase due to stellar depletion (~106 – 107 yrs)Stage III ( < 0.01pc) Orbital angular momentum lost by gravitational radiationStage IV Coalescence and recoil----

The “final parsec” problem Subparsec systems are not resolvable


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Structure of a close SMBH binary

Circumbinary disk

Primary black hole

Secondary black hole

Minidisk

BLR


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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


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Catalina Real-time Transient Survey (2005-) Collaborative survey with Catalina Sky Survey (LPL, UA) Unfiltered observations 21 nights/lunation covering up to 2000 deg2/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


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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 σ2 and τ 335000 spectroscopically-confirmed quasars in CRTS archive:

250000 have sufficient coverage (npts > 50)


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The best binary candidate to date

OJ 287 shows a pair of outburst peaks every 12.2 years for at least the last century


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Periodicity search criteriaWavelets Peak value Period Slepian wavelet characteristic timescaleAutocorrelation function Period Amplitude of exponentially damped cosine Decay constant of exponentially damped cosineShape and coverage Scatter around best-fit Fourier series At least 1.5 cycles

Train SVM to better describe discriminating hyperplane


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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


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SMBH binary candidates


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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)


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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


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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 associatedwith cavity in circumbinary disk => true binary period 3-8 times shorter

Relativistic boosting for line-of-sightmotion of minidisk around secondaryorbiting around system barycenter

Scaled version of QPOs seen in stellar blackhole binaries (D’Orazio et al. 2015)


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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


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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


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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


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Detecting gravitational waves

Are any of the candidates resolvable by PTAs as continuous GW sources and not just part of the stochastic background?


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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

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/

Documents

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