Diapositive 1

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Astrophysical Gravitational Wave Backgrounds

• Cosmological supernovae as neutrino and
  gravitational wave sources
• mHz gravitational wave background from inspiral
  of compact objects
• embedded in AGN accretion discs.

Günter Sigl APC (Astroparticule et Cosmologie),
Université Paris 7 and GReCO, Institut
dAstrophysique de Paris, CNRS http//www2.iap.fr/
users/sigl/homepage.html
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Individual and Diffuse Signals
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Event rates and Duty Cycles
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Onion structure of a supernova
Janka, Mueller
Convection, turbulence
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Supernovae as Neutrino and Gravitational Wave
Sources
Anisotropic mass motion and neutrino emission in
collapse of massive stars leads to gravitational
wave emission. At low frequencies anisotropic
neutrino emission of luminosity L?(t) and
anisotropy q(t) dominates and leads to
the dimensionless strain at distance D
Individual supernovae (SN) in our Galaxy can give
prominent signals in neutrinos in
Super-Kamiokande, Amanda, ICECUBE, Uno and
in gravitational waves in Virgo/EGO, LIGO, but
are rare events. However, backgrounds from
cosmological SN may soon be detectable by
gadolinium upgrade of Super-K in neutrinos and by
gravitational wave detectors such as the Big Bang
Observatory (BBO).
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Illustration for a particular rotating core
collapse model by Mueller et al., Astrophys. J.
603 (2004) 221.
time dependent q
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However, note dependence on progenitor model
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SN rate
very massive PopIII stars at z15 future input
from SWIFT
s i m u l a t i o n s
100Msun PopIII
ordinary SN
gravitational wave spectra
neutrino spectra
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gt
diffuse neutrino spectra
stochastic gravitational wave background
Ando and Sato, astro-ph/0410061
Buonanno, Sigl, Raffelt, Janka,
Mueller, Phys.Rev.D 72 (2005) 084001
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At low frequency gravitational wave spectrum
always dominated by anisotropic neutrino
emission. At high frequency f gt 100 Hz
convective mass motion dominates.

• Note that simulations stop after 250 msec,
  during which only about 1/6 of the
• total 3x1053 erg in neutrinos radiated during
  cooling phase has been emitted
• Possible enhancement factors in the GW amplitude
  between v6 and 6
• (bands in previous figure)
• Red vs blue band are different type II SN
  redshift evolutions

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For events with rate R and processes that loose
phase coherence after one cycle, at frequencies f
lt R the signal becomes stochastic , or
 gaussian , i.e. more than one event is  on 
at any given time. Individual events are
also unresolvable at such frequencies because SNR
lt 1.
If metals are released, fIII has to be
lt10-5. However, there are speculations that an
observed infrared background exess could be
explained by efficient Pop III formation
correponding to fIII 0.1. Metallicity
constraints in this case must be circumvented by
fall into black hole.
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Dwek et al., astro-ph/0508262
Diffuse infrared background can not be explained
by galaxies alone -gt may need a Pop III
contribution
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Uncertainties in star formation rates at high
redshift
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Fate of a massive star as function of progenitor
mass and metallicity
Heger et al., astro-ph/0211062
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Fate of a massive star as function of progenitor
mass and metallicity
Heger et al., astro-ph/0211062
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By using more optimistic SFR, Sandick et al,
Phys.Rev.D 73 (2006) 104024 obtain more
optimistic estimates
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Compare this with upper limits, sensitivities,
and cosmological predictions
BBO
BBO correlated
By the way Accelerated expansion could decrease
conventional inflation signal by factor 100 !
This makes astrophysical sources more important.
Giovannini
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General Consequence Gravitational Wave
Background from type II supernovae and PopIII
stars could mask inflationary background
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Phase Transitions in Neutron Stars
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Max neutrino asymmetry
Sigl, JCAP 0604 (2006) 002
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Comparison with other Processes
Sigl, JCAP 0604 (2006) 002
NS-NS Regimbau, de Freitas Pacheco,
Astrophys.J.642 (2006) 455 R-modes Owen et al.,
Phys.Rev. D58 (1998) 084020
Ferrari, Matarrese, Schneider, MNRAS 303 (1999)
258 Magnetar Regimbau, de Freitas Pacheco,
astro-ph/0509880.
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Sensitivities of existing and future ground-based
gravitational wave detectors (uncorrelated)
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Duty cycle is lt 1 above 0.1 Hz gt pop-corn type
noise
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Active Galactic Nuclei as Photon
and Gravitational Wave Sources
The bolometric luminosity Lbol of an AGN with
central black hole of mass M 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 fco
of accretion is in the form of compact objects of
typical mass m 100 Msun. These objects release
a fraction a 0.2 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 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
• fX 0.1 bolometric emission dominated by
  infrared.
• This will be our standard case.

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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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Individual events
Sigl, Schnittman, Buonanno, astro-ph/0610680
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fX 0.03, ?em 0.2, (infrared emission
dominated, solid line) facc 1, fco 0.01,
black hole spin a/M 0.95, for which ?gw 0.2
Confusion noise
Noise induced by subtracting resolvable
events with SNR gt 15
Time-averaged total signal
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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.
Sigl, Schnittman, Buonanno, astro-ph/0610680
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. These events
also have sufficient SNR to be resolved.
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The observable total (solid) and resolvable
(dashed) chirp rate as function of frequency f.
Sigl, Schnittman, Buonanno, astro-ph/0610680
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Conclusions1
1.) There is a deep connection between neutrino
and gravitational wave emission by
collapsing massive stars. Both signals have
good chances to be seen by future experiments.
2.) Such astrophysical backgrounds could
partially mask the inflationary background
in the BBO (0.1 Hz) frequency range. In the
ground based frequency range 100 Hz, these
backgrounds would only be detectable by the
most advanced third generation detectors.
3.) The supernova type II background is gaussian
below 1 Hz, however the neutron star phase
transition background would be pop-corn type.
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Conclusions2
4.) 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.
5.) If gt 1 of the accreted matter fueling AGNs
is in form of compact objects, a continuous
background detectable by LISA results below
1 mHz. If the typical compact object masses are gt
10 solar masses, individual inspirals should
be resolvable above a few mHz with a rate of
a few hundred per year.