Exploring an evidence of supermassive black hole binaries in AGN with MAXI

Naoki Isobe (RIKEN, isobe@crab.riken.jp ) and the MAXI Team§1. Introduction of MAXI

§2. Periodicity in AGN - as an evidence of super massive black hole binaries in AGN-

Historical light curve of a famous BL Lac object OJ 287 in optical V band (Valtaoja et al. 2000).

Search for X-ray flux periodicity with MAXI

A schematic view of ISS

Monitor of All Sky X-ray Image (MAXI)

The structure of MAXI

JEM Gas Slit Camera (GSC)

Solid-state Slit Camera

(GSC)

What to be explored with MAXIContinuous monitoring of variable X-ray sources, such as black holes, and especially, active galactic nuclei (AGNs) Prompt alert of transient X-ray sources, such as X-ray burst, flaring stars, and supernovae. Mapping the distribution of distant AGNs by probing the cosmic X-ray background. Mapping the distribution of hot plasma (and elements such as Si, S and Fe) in the Galactic plane.etc.

MAXI carries two kinds of X-ray instruments, Gas Slit Camera (GSC) and Solid-state Slit Camera (SSC).

CCD Chip

an X-ray source

sensitive detector

slit

collimator

position

Zenithal FoV

Earth

MAXI

Celestial sphere Scanningdirection

Forward FoV

Proportional counter

A4-size window

SSCGSC

Slit and collimator

Periodic variation has been discovered in a few AGNs, in optical, radio or X-ray observations.

Such periodicity is frequently interpreted on the basis of Keplerian motion of supermassive black hole binary in AGNs (and associated helical motion of jets). (e.g. Sillnapaa et 1988, Sudou et al. 2003 ).

OJ287 : 11.65 yr (Sillnapaa et al 1988)AO 0235+16 : 5.7 yr (Raiteri et al. 2001)Mrk501 : 23.6 day (Osone et al 2001)

Examples

P = 2 r2/3 G-1/2 (M+m)-1/2 = 1.7 yr (r / 1016 cm)2/3 (M / 108M◎)-1/2 (1+m/M)-1/2

Kepler’s 3rd law.

P : period, r : separation between two black holes, G : gravitational constantM : mass of primary black hole, m : mass of secondary black hole, M◎ : solar mass( )

Periodic elliptical motion of a radio core in 3C66B (Sudou et al. 2003)

M ～ 5 x109 M◎ , r ～ 3 x 1017 cm

M ～ 4.4x109 M◎ , r ～ 5.5 x 1016 cm

X-ray observation of AGNs is important to probe into the central regions close to the black hole, such as accretion disk.However, previous X-ray observatories are not adequate to systematic search for X-ray periodicity.

MAXI can measure X-ray flux of more than 100 AGNs, weekly or even daily, thanks to its unprecedentedly high sensitivity.

Chandra, Newton, Suzaku etc : low monitoring efficiencyAll Sky Monitors (RXTE ASM etc.) : low detection sensitivity

MAXI is the first ideal observatory to systematically search for X-ray flux periodicity of AGNs,

as an evidence of supermassive binary black hole.

X-ray flux of famous X-ray sources, plotted against the distance to them.

＊ : Galactic sources＋ : AGNs○ : Clusters of Galaxies

Sources, from which periodicity is indicated in other wavelength.Almost all of these source is detected with MAXI.

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Simulated lightcurve of an X-ray source, with a flux of about 1 mCrab. Although periodicity is not introduced

in the simulation, MAXI can explore periodicity in these sources.

(1 mCrab = 2.4 x 10-8 erg s-1 cm-2 in 2 – 10 keV)

X-ray observatory, to be mounted on the Japanese Experimental Module (JEM) of the International Space Station (ISS). MAXI scans all over the sky in every 90 minutes.Operation start : 2008.Mission life time : 2 years (minimum). Sensitivity : 10 mCrab in one orbit, 1 m Crab in a week significantly higher than those of previous X-ray monitors (such as RXTE ASM). Everyone will be able to access the data (lightcurves, images, and spectra) with MAXI, through the internet.

Instrument on MAXI

Detector

EnergyEffective AreaField of View Energy Resolution Position Accuracy

Proportional counter(Xe + CO2 gas)2 – 30 keV5350 cm2

1.5 x 160 degree 18 % at (Mo-K)0.1 degree

X-ray CCD

0.5 – 10 keV200 cm2

1.5 x 90 degree140 eV 0.1 degree

GSC SSC

The concept of GSC and SSC.GSC and SSC consist of a narrow slit, slat collimators and position sensitive detectors.Both instruments have two field of views, toward horizontal and zenithal directions.

Simulated all sky X-ray image, in 5 month observation with MAXI

Gal

actic

pla

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11.65 yr