Gamma-Ray%20Bursts%20%20and%20%20Gravitational%20Waves

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Gamma-Ray Bursts and Gravitational Waves

Shiho Kobayashi (Penn State)
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Gamma-Ray Bursts (GRBs) sudden, intense flashes
of 0.1- 1MeV rays arriving from random
directions in the sky.
luminosity
Timesec
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gt2sec
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Discovery of counterparts of (long) GRBs
in longer wave lengths afterglow
Confirm
(1) Cosmological model
Emission and absorption lines in optical
afterglow
Isotropic gamma-ray energy
(2) Relativistic Fireball model
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External Shocks
Internal Shocks

Outflow and ambient matter
Faster and slower shells

GRB
afterglow
?
Relativistic Outflow Lorentz factor gt 100
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We know HOW GRBs are produced. ----
relativistic shocks and synchrotron process
What produces the relativistic flow?
Catastrophic events involving Neutron Star or a
Stellar-mass Black Hole?
Bulk of energy radiated into ray band
Energy budget comparable to kinetic energy in
Supernovae
Variability in GRBs msec time scale
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The engine must active much longer than
its variablity timescale!
BH - massive Accretion Disk System
Massive stellar collapse Compact mergers
Collapsar, Hypernova, failed SN iron core
collapses to BH
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X
O
R

GRB
GW
Bloom
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In-spiral
merger
Ring-down
Merger begins when orbital evolution is so rapid
that adiabatic evolution is not a good
approximation. Masses violently merger to form a
BH.
BH is initially deformed. Energy associated
with deformation is radiated as GWs
As binary losses energy by GW the masses
gradually spiral in toward each other.
S.K Meszaros, astro-ph/0210211
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Massive stellar collapse leading to a GRB
requires a high core rotation rate, which may be
easier to achieve if the star is in a binary
system, although this is not necessary. Anyway,
In-spiral signal terminates at a frequency well
below seismic cutoff.
Fryer, Woosley Hartmann 99
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Numerical calculations of GW radiation from
collapsars have been done in the Newtonian
approximation in 2D ( e.g. Fryer et al 1999
MacFadyen Woosley 1999 ), relativistic in 2D
(Dimmelmeier et al. 2002). They suggest that GW
emission from collapsars may be much less
important than from compact binaries, even though
these numerical estimates are not conclusive as
a number of effects ( GR, secular evolution,
non-axisymmetry) are neglected.
High rotation rate is required to form
centrifugally supported disk around BH to power
GRB jet. The same high rotation rate could lead
to a bar or fragmentation type instability in the
collapsing core or/and in the massive
disk. (Nakamura Fukugita 1989 Fryer et al
2002 van Putten 2002 Davies et al
2002) Infalling matter perturbs BHs geometry.
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GRBs and GWBs
GRBs and Afterglows can give the occurrence times
and the directions.
Binaries, bars, fragmentations and QNMs (
) emit GWs more strongly along the
polar axis, along which GRB jets are also
launched. Then, GRB souces are stonger than the
average.
(Kochanek Piran 1993 S.K Meszaros in prep)
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msec-sec
EM waves
???Waveform???
GWs
BH formation
The correlated output of two GW detectors
evaluated in the moment just prior to GRB (on)
will differ from that evaluated at other time
(off).
(Finn et al. 1999)
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Output of two detectors (identical locations and
arm orientations)
Cross-correlation
Averaged over source population
Filter function
if we knew
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if
By collecting many sample, we can get some
information on association between GRBs and GWs.
(99 signicance)
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We should select nearby GRBs.
Typical GRB at 3000Mpc
GRO almost full sky coverage but
large error box HETE, Swift smaller coverage
accurate positioning allow
the follow up by optical-telescope
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When we analyze the nearest events in a year
Typical distance
(uniform distribution)
The number of events needed to detect the
association
The number of years it takes to collect sample
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Contamination to estimate on by undetected GRBs
Possibly we do not see a large fraction of GRBs
Sky coverage by gamma-ray detectors
Beaming of GRB jets
If the reduction factor is
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Bloom
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Light curves of afterglow
Distribution of Opening Angles
We can observe
Sample 105 GRBs
(Frail et al. 2001)
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Fast X-ray Transients (FXTs)
BATSE(gt20keV) SAX-WFC(2-26keV)
GRB
FXT???

Kippen et al. 2001
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Binary , QNM(lm2), bar...
The amplitude and polarization of GWs depend on
the viewing angle from the polar axis!
GRB Luminosity also depends on the polar angle!!!
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Correlation
GW Linear Polarization degree
GRB luminosity
LIGO observatories are co-aligned, no information
about P
(S.K. Meszaros in prep)
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Distance to GRB sources might be determined by
GW observation!
Dark GRBs
26 well localized GRBs
Kulkarni et al. 2000
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Detection of counterparts of GRBs in GWs will
revolutionize GRB field.
GRBs and Afterglows provide occurrence time and
sky position. Cross-correlation technique can be
used to get some information of association
between GRBs and GWBs.