Post on 28-Mar-2015
transcript
Gravitational Wave – GRB connections?
Jim HoughInstitute for Gravitational Research
University of Glasgow
Royal Society September 2006
‘Gravitational Waves’ Produced by violent acceleration of mass in:
neutron star binary coalescences black hole formation and interactions cosmic string vibrations in the early universe
and in less violent events: pulsars binary stars
Gravitational waves
‘ripples in the curvature of spacetime’ that carry information about changing gravitational fields – or fluctuating strains in space of amplitude h where L
Lh
~
Sources – the gravitational wave spectrum
Gravity gradient wall
ADVANCED GROUND - BASED DETECTORS
“Indirect”detection
of gravitational waves
PSR 1913+16
Evidence for gravitational waves
One cycle
Fabry-Perot/MichelsonInterferometer
Gravitational waves have very weak effect: Expect movements of less than a trillionth of the wavelength of light (10-18 m) over 4km
Detection of Gravitational waves
Consider the effect of a wave on a ring of particles :
GW detector network
GEO 600
600m
Gravitational wave network sensitivity
Frequency (Hz)
Gra
vit
ati
on
al w
ave a
mp
litu
de h
(/
Hz)
LIGO now at design sensitivity
Science data runs to date
S5: started on 4th Nov. 2005 at Hanford (LLO a few weeks later) - GEO joined initially for overnight data taking, then 24/7
18 months data taking in coincidence
Since Autumn 2001 GEO and LIGO have completed 4 science runs Analysis completed for S1/2 and (most) papers published; For S3/4 analysis – 2 papers published and many more in preparation Some runs done in coincidence with TAMA and bars (Allegro) LIGO now at design sensitivity
‘Upper Limits’ have been set for a range of signals Coalescing binaries Pulsars Bursts (including GRBs) Stochastic background
>15 major papers published or in press since 2004 (work from a collaboration (LSC) of more than 400 scientists)
Gravitational Waves from compact binaries
Estimates give upper bound of 1/3 yr in LIGO S5
Binary Coalescence Sources & Science:
Image: R. Powell
LIGO Range
binary neutron star max. distance
binary black hole max.distance
Burst sources
Burst Sources:
No gravitational wave bursts detected during S1, S2, S3, and S4; upper limits set through injection of trial waveforms
S5 anticipated sensitivity, determined using injected generic waveforms to determine minimum detectable in-band energy in GWs
Current sensitivity:EGW > 1 Msun @ 75 Mpc, EGW > 0.05 Msun @ 15 Mpc (Virgo cluster)
Outline of GRB-GWB search (from Leonor et al, (ExtTrig group), APS April 06)
search for short-duration gravitational-wave bursts (GWBs) coincident with gamma-ray bursts (GRBs)(39 events during the S2to S4 runs) see :“A search for gravitational waves associated with the gamma ray burst GRB030329 using the LIGO detectors", B. Abbott et al. [LIGO Scientific Collaboration], Phys. Rev. D 72, 042002 (2005)
use GRB triggers observed by satellite experiments distributed by the GCN and IPN Networks
Swift, HETE-2, INTEGRAL, IPN, Konus-Wind include both “short” and “long” GRBs, SGRs etc
search the astrophysically motivated time interval of LIGO data (~180s) surrounding each GRB trigger (on-source segment)
waveforms of GWB signals associated with GRBs are not known so use crosscorrelation of two interferometers (IFOs) to search for associated GW signal
use crosscorrelation lengths of 25 ms and 100 ms to target short-duration GW bursts of durations ~1 ms to ~100 ms
use bandwidth of 40 Hz to 2000 Hz
i ii
j kj k
crosscorrx y
x y2 2
correlated signal in two IFOs large crosscorr
no evidence for GW bursts associated with GRBs using this sample
The GRB sample for LIGO S5 run (from Leonor et al, APS April 06)
53 GRB triggers in 5 months of LIGO S5 run (as of April 10,
2006) most from Swift 16 triple-IFO coincidence 31 double-IFO coincidence 6 short-duration GRBs 11 GRBs with redshift
z = 6.6, farthest z = 0.0331, (~120Mpc)
nearest
performed GW burst search on this sample using same pipeline No loud events seen
that are inconsistent with expected probability distribution
SGR hyperflares are also of interest – Clark et al (Poster)
Soft -ray Repeaters – quiescent X-ray sources with active periods of high luminosity soft -ray bursts
though to be magnetars - extremely magnetic neutron stars
Occasionally emit hyperflares – 1000s of time as luminous as ordinary bursts and with a harder spectrum
Catastrophic global reconfiguration of the neutron star crust and magnetic field
Set up oscillations in the neutron star (e.g. possible torsional modes seen – Strohmayer and Watts, 2006)
Vibrational modes, like the fundamental mode, could be seen via gravitational waves as short duration ring-downs
Asteroseismology – study the equation of state of the star via modes, determine mass and radiius (Andersson and Kokkotas, 1998)
• The Soft Gamma-Ray Repeater SGR1806-20 emits a record flare ( d = [7.5 : 15 ] kpc, ~1046ergs )
• Magnetar model: energy release corresponds to the neutron star crust and magnetic field catastrophic re -arrangement
• Quasi-periodic oscillations observed in lightcurve's tail of SGR1806-20 (Israel et al. (2005), Watts & Strohmayer (2006), Strohmayer & Watts (2006)) and SGR1900+14 (Strohmayer & Watts (2005))
• Excitation of neutron star's seismic modes is plausible
• Subset of QPOs fall in LIGO's band
Search for QPOs after the SGR 1806-20 hyperflare (S. Marka)
dth(t)h2
rss
Characteristic search sensitivity
h rss
[str
ain
/rH
z]
Gravitational wave sensitivity illustrated through energetics (S. Marka)
• Assuming
» isotropic emission
» equal amount of power in both polarizations (circular polarization)
• Egw
iso is a characteristic energy radiated in the duration and frequency band we
searched from a source at a distance of 10kpc
» Egw
iso = 2.6 x 10-8 Msun
c2 (~4.6 x 1046 erg) for the best sensitivity of hrss
= 3.5
x 10-22 strain/rHz (92.5Hz, BW=1.6Hz)
• Repeat the analysis for recent flares (SGR1900+14 and SGR1806-20)
Plans for Advanced detectors : 2008-
To move from detection to astronomy the current detector network will upgrade to a series of ‘Advanced’ instruments
Advanced LIGO will comprise a set of significant hardware upgrades to the US LIGO detectors
Advanced Virgo will be built on the same time scale as Advanced LIGO, and will achieve comparable sensitivity
Japan’s Large Cryogenic Gravitational Telescope (LCGT) will pioneer cryogenics and underground installation
GEO HF will improve the sensitivity beyond GEO600’s, mainly at high frequency
What is Advanced LIGO
Project to increase sensitivity (range) of LIGO by factor of ten
Uses existing sites, infrastructure Implements higher power laser, new optics and
monolithic suspensions, improved seismic isolation and other improvements
Increases number of GW emitting sources in range by factor of 1000
Will enable study of significant number of astrophysical sources of gravity waves
Advanced LIGO will pioneer the new field of GW astronomy and astrophysics
Range of Advanced LIGO for 1.4 Mo binary neutron star inspirals
. .
Astronomy & astrophysics with Advanced LIGO
Neutron Star Binaries:
Initial LIGO: ~10-20 Mpc
Advanced LIGO: ~200-350 Mpc
Most likely rate: 1 every 2 days Black hole Binaries:
Up to 10 Mo, at ~ 100 Mpc
up to 50 Mo, in most of
the observable Universe Stochastic Background:
Initial LIGO: ~3e-6 Adv LIGO ~3e-9
x10 better amplitude sensitivity x1000 rate=(reach)3
1 year of Initial LIGO < 1 day of Advanced LIGO
Advance
d LIGO
Status of Advanced LIGO
Fully peer reviewed
Approved by National Science Board
Expect start of US construction funds
in 2008 UK (PPARC), Germany (MPG)
contributions already funded
6 year construction schedule; ~$200M
cost Funded from NSF account for big
projects (MREFC) with operations to be supported by NSF Gravity Program (not from NSF Astronomy Program)
Initial operations expected in 2014
Fused silicafibres or ribbons
Cantileverblades
Advanced detector network
Frequency (Hz)
h (Hz -1/2)
F
Gravitational Wave Astronomy
GW detector systems now reaching levels where they may see signals associated with gamma ray bursts within the next few years.
The essentially guaranteed detection of compact binary systems by the advanced detectors early in the next decade is likely lead to further understanding of the nature of the gamma ray bursts.
A new way to observe the
Universe