Constraining the Properties of Dark Energy Using GRBs D. Q. Lamb (U. Chicago) High-Energy Transient ExplorerSwift 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 : 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

Movie of HST Images Movie courtesy of D. Fox

GRB : “Solid Gold” Event qSome observational “firsts”: q First observation of optical afterglow of short GRB q First secure identification of host galaxy q First secure measurement of distance to short GRB q First determination of where in host galaxy burst occurred qImplications q Burst occurred in dwarf irregular galaxy undergoing some star formation  Energy and luminosity of this short GRB is ~ 10 3 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 : 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 galaxy z = L =1.6 L * SFR < 0.03 M  yr -1 GRB : Host Galaxy

Evidence That Short GRBs Come from Mergers of Compact Objects qShort 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 qNo 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 qLuminosity L and isotropic-equivalent energy E iso factor smaller than for long GRBs qAmbient 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 Energy Density Host Offset No SNe Progenitor Scorecard Slide courtesy of D. Frail

Short GRBs Emit Strong Gravitational Waves Slide courtesy of D. Frail

Short GRBs as Standard Sirens qDetection of gravitational waves gives absolute luminosity distance d GRB to short GRB qThis plus distance d CMB to surface of last scattering of CMB means that accurate determination of H 0 = cz/d GRB provides strong constraint on dark energy qTo see this, consider a flat univers (i.e., a CMB prior) and a constant w; then Ω DE = 1 – Ω M, and only parameters are h, Ω M, and w qCMB provides 2 (d CMB, Ω M h 2) ; short GRBs provide h qConstraints are not degraded by gravitational lensing, as those from Type Ia SNe and long GRBs

K.Thorne / NSF ReviewFigure courtesy of D. Fox Detectability of Gravitational Waves from Short GRBs Detection of Short GRB gives t merger, (RA,Dec), and inclination angle i of binary relative to plane of the sky, which increases sensitivity of LIGO y factor ~ 3

Determination of D Dalal, Holz, Hughes, and Jain (2006); DQL et al. (2006)

Uncertainties in w and h Dalal, Holz, Hughes, and Jain (2006); DQL et al. (2006) Only 200 short GRBs can give accuracy of in h and 0.03 in w!

Constraints on w for Different Jet Opening Angles Dalal, Holz, Hughes, and Jain (2006); DQL et al. (2006) θ jet < 20 o Isotropic emission

The Long and Short of It Hurley (1991); Lamb, Graziani, and Smith (2003); Kouveliotou et al. (1993) Short GRBs Long GRBs

Schematic Picture of GRB Jets Peter Meszaros

GRBs Come From Narrow Jets Frail et al. (1999)  Bulk motion of jet is v = 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 Exists Between E γ and E peak E peak EγEγ Ghirlanda et al. (2004)

Empirical Relation Exists Between E peak -E iso -t break Liang and Zhang (2005); Ghirlanda et al. (2006)

Hubble Diagram for Type Ia SNe and GRBs  Before “standard candle” calibration  After “standard candle” calibration

GRB Hubble Diagram Xu, Dai, and Liang (2005)

GRB Constraints on Dark Energy Xu, Dai, and Liang (2005)

Definition of Emission Duration T em Reichart, Lamb, Fenimore, Ramirez-Ruiz, Cline, and Hurley (2001)

Comparison of T em and T 90 Donaghy, Graziani, and DQL (2006)  T em,50 ( T em,90 ) values are similar to T 50 (T 90 ) values  T em is robust to energy range and choice of f  T em can more easily be transformed to burst rest frame

Comparison of Ghirlanda et al. (2004) and Firmani et al. (2006) Relations Firmani et al. (2006)

Constraints on Ω M and Ω DE Firmani et al. (2006) SNe Ia SNe Ia + GRBs

Constraints on Dark Energy EOS Parameters w 0 and w 1 Firmani et al. (2006) SNe Ia SNe Ia + GRBs

Spectra of Gamma-Ray Bursts GRB Spectrum Peaks in Gamma - Rays XRF Spectrum Peaks in X-Rays E peak

XRFs Satisfy Firmani et al. (2006) Relation DQL et al. (2006)

Low-z GRBs Are Vital to Constraining Properties of Dark Energy Ghirlanda et al. (2005) Mostly GRBs w. z > 1 GRBs w. z > 1 + XRFs w. z < 0.5

GRB Dark Energy GRB Dark Energy Mission Concept Study

Conclusions qShort GRBs can be used as “standard sirens” to constrain properties of dark energy qLong GRBs can be used as “standard candles” to constrain properties of dark energy qWith Firmani et al. (2006) relation, need only satellite that can detect prompt emission qIn former case, need efficient detection and accurate localization of short GRBs qIn latter case, need efficient detection and accurate localization of long GRBs, plus broad energy response in order to determine E obs peak and L iso qImportant open question is “What is the size of systematic errors?”