constraining the properties of dark energy using grbs d. q. lamb (u. chicago) high-energy transient...
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Constraining the Properties of Dark Energy Using GRBs
D. Q. Lamb (U. Chicago)
High-Energy Transient Explorer Swift
Department of Astronomy, Nanjing University Nanjing, China, 27 July 2006
The Long and Short of It
Hurley (1991); Lamb, Graziani, and Smith (2003); Kouveliotou et al. (1993)
Short GRBs
Long GRBs
GRB 050709: Accurate LocalizationGRB 050709: Accurate Localization
HETE-2 IPC error circle on Chandra image, showing X-ray afterglow
HST image showing optical afterglow and host galaxy w. Chandra X-ray error circle
Images courtesy of D. Fox
GRB 050709: “Solid Gold” EventGRB 050709: “Solid Gold” Event
Some observational “firsts”: First observation of optical afterglow of short GRB First secure identification of host galaxy First secure measurement of distance to short GRB First determination of where in host galaxy burst occurred
Implications Burst occurred in dwarf irregular galaxy undergoing some
star formation Energy and luminosity of this short GRB is ~ 103 times smaller than for long GRBs No supernova down to very faint limits (R > 27) Properties of long, soft bump imply burst occurred in low-
density environment Prompt emission is jet-like
GRB 050724: Also a “Gold Plated” BurstGRB 050724: Also a “Gold Plated” Burst
Berger et al. (2005)
Swift XRT detection of X-ray afterglow led to discovery of optical afterglow and host galaxy
Kulkarni & Cameron
Red elliptical galaxyz = 0.258L =1.6 L*
SFR < 0.03 M yr-1
GRB 050724: Host GalaxyGRB 050724: Host Galaxy
Evidence That Short GRBs Come Evidence That Short GRBs Come from Mergers of Compact Objectsfrom Mergers of Compact Objects
Short GRBs come from outskirts of star-forming galaxies or from elliptical galaxies – unlike long GRBs which all come from brightest star-forming regions in their host galaxies
No supernova component seen in optical afterglow down to very faint limits – unlike long GRBs for which such components are seen for all bursts with z < 0.5
Luminosity L and isotropic-equivalent energy Eiso
factor 100-1000 smaller than for long GRBs Ambient densities of some short GRBs very low, as
expected if they lie in outskirts of their host galaxy
– these properties are exactly those expected if short GRBs come from mergers of compact objects
Binary Coalescence
1
Collapsar
Magnetar
1
1 1 1
Energy Density Host Offset No SNe
1
1 0 00
0
1
0 0
1
Progenitor ScorecardProgenitor Scorecard
Slide courtesy of D. Frail
Short GRBs Emit Short GRBs Emit Strong Gravitational WavesStrong Gravitational Waves
Slide courtesy of D. Frail
Short GRBs as Standard SirensShort GRBs as Standard Sirens
Detection of gravitational waves gives absolute luminosity distance dGRB to short GRB
This plus distance dCMB to surface of last scattering of CMB means that accurate determination of H0 = cz/dGRB provides strong constraint on dark energy
To see this, consider a flat univers (i.e., a CMB prior) and a constant w; then ΩDE = 1 – ΩM, and only parameters are h, ΩM, and w
CMB provides 2 (dCMB, ΩMh2); short GRBs provide h
Constraints are not degraded by gravitational lensing, as those from Type Ia SNe and long GRBs
K.Thorne / NSF Review Figure courtesy of D. Fox
Detectability of Gravitational Waves Detectability of Gravitational Waves from Short GRBsfrom Short GRBs
Detection of Short GRB gives tmerger, (RA,Dec), andinclination angle i of binary relative to plane of the sky, which increases sensitivity of LIGO y factor ~ 3
Uncertainties in Uncertainties in ww and and hh
Dalal, Holz, Hughes, and Jain (2006); DQL et al. (2006)
Only 200 short GRBs can give accuracy of 0.006 in hand 0.03 in w!
Constraints on Constraints on ww for Different Jet Opening Anglesfor Different Jet Opening Angles
Dalal, Holz, Hughes, and Jain (2006); DQL et al. (2006)
θjet < 20o Isotropic emission
The Long and Short of It
Hurley (1991); Lamb, Graziani, and Smith (2003); Kouveliotou et al. (1993)
Short GRBs
Long GRBs
GRBs Come From Narrow Jets
Frail et al. (1999)
Bulk motion of jet is v = 0.999 c, so special relativistic beaming is dramatic Optical light decreases when jet slows down and we begin to see beyond edge of jet
Type Ia-SN—Like Relation Type Ia-SN—Like Relation Exists Between E Exists Between Eγγ and and
EEpeakpeak
Epeak
Eγ
Ghirlanda et al. (2004)
Empirical Relation Exists Empirical Relation Exists Between Between EEpeakpeak--EEisoiso--ttbreakbreak
Liang and Zhang (2005); Ghirlanda et al. (2006)
Hubble Diagram for Type Ia SNe and GRBsHubble Diagram for Type Ia SNe and GRBs
Before “standard candle” calibration
After “standard candle” calibration
Definition of Emission Duration TDefinition of Emission Duration Temem
Reichart, Lamb, Fenimore, Ramirez-Ruiz, Cline, and Hurley (2001)
Comparison of TComparison of Temem and T and T9090
Donaghy, Graziani, and DQL (2006)
Tem,50 (Tem,90) values are similar to T50 (T90) values Tem is robust to energy range and choice of f Tem can more easily be transformed to burst rest frame
Constraints on Dark Energy Constraints on Dark Energy EOS Parameters EOS Parameters ww00 and and ww11
Firmani et al. (2006)
SNe Ia
SNe Ia
SNe Ia + GRBs
SNe Ia + GRBs
Spectra of Gamma-Ray BurstsSpectra of Gamma-Ray Bursts
GRB SpectrumPeaks in Gamma - Rays
XRF Spectrum Peaks in X-Rays
Epeak
Epeak
XRFs Satisfy Firmani et al. (2006) RelationXRFs Satisfy Firmani et al. (2006) Relation
DQL et al. (2006)
Low-z GRBs Are Vital to Constraining Low-z GRBs Are Vital to Constraining Properties of Dark EnergyProperties of Dark Energy
Ghirlanda et al. (2005)Ghirlanda et al. (2005)
Mostly GRBs w. z > 1 GRBs w. z > 1 + XRFs w. z < 0.5
ConclusionsConclusions
Short GRBs can be used as “standard sirens” to constrain properties of dark energy
Long GRBs can be used as “standard candles” to constrain properties of dark energy
With Firmani et al. (2006) relation, need only satellite that can detect prompt emission
In former case, need efficient detection and accurate localization of short GRBs
In latter case, need efficient detection and accurate localization of long GRBs, plus broad energy response in order to determine Eobs
peak and Liso
Important open question is “What is the size of systematic errors?”