Diapositive 1

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AGN Accretion and Gravitational Wave Background
for LISA
Sigl, Schnittman, Buonanno, to be finished
Günter Sigl GReCO, Institut dAstrophysique de
Paris, CNRS et Fédération de Recherche
Astroparticule et Cosmologie, Université Paris
7 http//www2.iap.fr/users/sigl/homepage.html
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Active Galactic Nuclei as Photon
and Gravitational Wave Sources
The bolometric luminosity Lbol of an AGN is
related to the accretion rate Lacc and the
Eddington rate LEdd by
of which a fraction fX is in X-rays between 2 and
10 keV, LX fX Lbol. Assume that a fraction ?c
of accretion is in the form of compact objects of
typical mass m 100 Msun. These objects release
a fraction a 1/12 of their mass m in
gravitational waves during inspiral to the last
stable orbit
Thus, from the observed X-ray luminosity function
dn/dLX for AGNs, we can compute the cosmological
gravitational wave background.
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For OSMBH fraction of critical density in
SMBHs, Oacc fraction of critical density in
accreted gas, OX fraction of critical density
of X-rays in the 2-10 keV band, facc fraction
of SMBH mass due to accreted gas, fobsc
fraction of obscured emission 0.3, one has
facc OSMBH (1 ?em) Oacc
OX lt(1z)-1gt fobsc fX ?em Oacc Since OX/OSMBH
1.3x10-3, lt(1z)-1gt 0.4 from AGN evolution
data, one obtains the condition fobsc facc
fX ?em 3x10-3 Observations then imply that
facc 1 and , thus, that SMBH growth
is accretion dominated, which will be our
standard case.
Observations suggest that ?em is not much smaller
than 0.1, and that SMBH build-up is dominated by
accretion facc 1 and NOT by mergers gt fX
0.1 bolometric emission dominated by infrared.
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The universal photon spectrum
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Diffuse X-ray background
AGNgalaxy clusters
Compton thin
Compton thick
unobscured
Comastri, Gilli, Hasinger. astro-ph/0604523
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The X-ray background between 1 and 100 keV is
explained by AGNs.
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compare fX 0.1, ?em 0.1, (infrared emission
dominated, solid line) with fX 0.3, ?em 0.03
(X-ray emission dominated, dashed line), facc
0.5, fco 0.01, a 1/12 in both cases
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The duty factor is the event rate times the time
tcoh f/(df/dt) f -8/3 spent emitting at
frequency f.
Below a few milli-Hertz gt 1 event contributes at
any given time and the signal is gaussian. At
higher frequencies one would see individual
events at final stages of inspiral.
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The observable inspiral rate as function of
frequency f.
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compare fX 0.1, ?em 0.1, (infrared emission
dominated), facc 0.5, fco 0.01, a 1/12,
m105 Msun This could, e.g., be recently much
discussed intermediate mass black holes
Individual events
stochastic
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Compare this with upper limits, sensitivities,
and cosmological predictions
BBO
BBO correlated
Giovannini
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Conclusions
1.) The accretion powering Active Galactic Nuclei
give rise to electromagnetic emission from
the infrared to ?-rays and at the same time
to gravitational waves from inspiral of compact
objects. This gravitational wave background
may be observable by LISA.