Measuring the cosmological parameters with GammaRay Bursts Massimo

Measuring the cosmological parameters with Gamma-Ray Bursts Massimo Della Valle European Southern Observatory (ESO-Munchen) ICRANet (Pescara) INAF-Osservatorio Astronomico di Capodimonte (Napoli)

Outline • The measurements of m and with SNe-Ia • A short discussion of the Supernova systematics: the need of an independent measurement of m and • Our measurements of m obtained via Epeak -Eiso (“Amati”) relationship. Amati, Guidorzi, Frontera, Landi, Finelli and Montanari Ferrara University

Measuring the cosmological parameters means to study the expansion rate of the Universe, and this is a (relatively) easy task All it takes is to measure velocities and distances for a class of cosmological objects and to plot one vs. the other….

The Hubble Diagram in the low red-shift limit(v=Hox. D) i ii i i i Hubble & Humason 1931

The Hubble Diagram at high z For an object of known absolute magnitude M, the measurement of the apparent magnitude m at a given z is sensitive to the universal parameters, through the luminosity distance:

S(x)= sin(x) if k<0 x if k=0 sinh(x)if k>0

Standard Candles A population of unevolving sources, having a fixed intrinsic luminosity at all redshifts

The problem is to find a class of objects as bright as galaxies (to be detected up to cosmological distances) but which does not evolve

Pioneering Hubble diagrams (Sandage et al. 1976) provided formal values of qo=1 0. 5 (cfr. ~ -0. 5). These measurements (based on galaxies luminosity) cannot be trusted because of the stellar population evolution and merging. The evolution destroys the concept of standard candle (which is independent of age)

In the last decade several pieces of observations converged to identify this class of very bright and noevolving objects with Supernovae

Supernova Classification IIp (P-Cygni), IIb IIl, IIn (Balmer emission) H II Core collapse of massive single stars SNe Ic (weak He) High KE=HNe No Ib (strong He) H I Ia (strong Si) Core collapse of massive stars (likely) in binary systems Thermonuclear explosion of white dwarfs

The commonly accepted idea is that SNe-Ia are thermonuclear disruption of C-O WDs (3 -8 M ) in binary systems. Are they standard candles ?

SN Diversity from Observations Barbon, Ciatti & Rosino 1974 (Ia) Filippenko 1997 SNe-Ia have been believed, in the past to form an “homogeneous” class of objetcs. Both photometrically (s~0. 3 mag at max) than spectroscopically (similar SED at the same stages) 13

Cappellaro et al. 1997

Cappellaro et al. 1997

Type Ia Supernovae as Standard Candles After correction for light-curve shape, supernovae become “calibrated” candles with ~0. 15 magnitude dispersion.

Perlmutter et al. 1997 Perlmutter et al. 1998 Riess at al. 1998 (1998) Schmidt et al. 1998 Perlmutter et al. 1999 Riess et al. 2001 Tonry et al. 2003 Knopp et al. 2003 Riess et al. 2004 Astier et al. 2006 ……. . and more

m=0. 6± 0. 2 Perlmutter et al. (1998)

1999 m~ 0. 28; L~ 0. 72 Perlmutter et al. (1999)

m~ 0. 29; L~ 0. 71 Riess 2004

Conclusions from SNe The two teams consistently found that SNIa at redshifts z ~ 0. 5 appear dimmer than expected by ~0. 25 magnitudes. z ~ 0. 5 is the transition epoch between acceleration and deceleration. This suggests (after assuming a flat universe) that the expansion of the Universe is accelerating, propelled by “dark energy”, with ~ 0. 71 and M ~ 0. 29. Once we combine SN data with external flat. Universe constraints (WMAP), we find w= -1. 02 (w <- 0. 76 at the 95% confidence level) and w’=0, both implies DE=cosmological constant. Riess et al. 2004 M

SN Chinks: Systematics The cosmological interpretation rely on the lack of evolutionary effects on progenitors of type Ia SNe.

Two populations: 50% prompt + 50% exp “prompt” “tardy” Della Valle et al. 2005 Mannucci et al. 2006; Sullivan et al. 2006 Aubourg et al. 2007

Phillips’s relationship is calibrated on the “tardy” component luminositydecline rate relation might change with redshift? ? ? Metallicity? (Nomoto et al. 2003 Dominguez et al. 2005)

Two scenarios for type Ia • Double degenarate: where two C-O WDs in a binary systems make coalescence as result of the lost of orbital energy for GWs (Webbink 1984; Iben & Tutukov 1984) • Single Degenerate (Whelan & Iben 1973, Nomoto 1982) Cataclysmic-like systems: RNe (WD+giant, WD+He) Symbiotic systems (WD+Mira or red giant) Supersoft X-ray Sources (WD+MS star) Both explosive channels are at play? maybe at different redshifts?

• Extinction factor: AB =RB x E(B-V) for SNe-Ia in many cases RB 2 -3 (Capaccioli et al. 1990, Della Valle & Panagia 1992, Phillips et al. 1999, Altavilla et al. 2004, Elias-Rosa et al. 2006, Wang et al. 2006) more important at high-z

Is evolution or dust problem? Leibundgut 2001

Origin of (possible) Supernova systematics 1. unknown explosion mechanism (z? ) 2. unknown progenitor systems (z? ) 3. light curve shape correction methods for the luminosity normalisation may depend on z 4. signatures of evolution in the colours? (z? ) 5. anomalous reddening law 6. contaminations of the Hubble Diagram by no-standard SNe-Ia and/or bright SNe-Ibc (e. g. HNe)

Supernova cosmology Wood-vasey 2006 Tonry et al. 2003

If the “offset from the truth” is just 0. 1 mag….

We need to carry out an independent measurement of m and the Hubble diagram for type Ia SNe is significantly affected by systematics GRBs allow us today to change the “experimental methodology” and provide an independent measurement of the cosmological parameters

S c i en c e wi t h E L T s

GRBs Strengths • GRBs are extremely bright detectable out of cosmological distances (z=6. 3 Kuwai et al. 2005, Tagliaferri et al. 2005) interesting objects for cosmology • SNe-Ia are currently observed at z<1. 7. Then GRBs appear to be (in principle) the only class of objects capable to study the evolution of the dark energy from the beginning (say from z~7 -8) • No correction for reddening

GRBs Chinks • GRBs are not “genuine” standard candles E=1048 -54 erg (however also SNe-Ia need to be standardize) • GRBs cannot be calibrated in the local universe (too few and the only ones observed are peculiar/sub-energetic)

In spite of these “drawbacks”, several attempts for standardizing GRBs with 3 or multi-parameters spectrum-energy correlations have been carried out Ghirlanda et al. (2004), Firmani et al. (2006), Schaefer (2007) They are (at least partially) model dependent. in the Ghirlanda relationship the third parameter, tbreak is assumed to be the signature of beaming for the GRB ejecta. This should be a common feature observable in all GRBs, but this is not true….

Ep, i-E correlation need to clarify and understand the problem lack of chromatic breaks and possible outliers lack of jet breaks in several Swift X-ray afterglow light curves, in some cases, evidence of achromatic break challenging evidences for Jet interpretation of break in afterglow light curves or due to present inadequate sampling of optical light curves w/r to X-ray ones and to lack of satisfactory modeling of jets ? GRB 061007, Mundell et al. Schady et al. GRB 050416 a

Very recently (Kodama et al. , 2008; Liang et al. , 2008) have calibrated the GRB spectrum—energy correlation at z < 1. 7 by using SNe-Ia and they have obtained significant constraints on both M and (very similar to those obtained via SNe-Ia). With this method GRBs are not indipendent cosmological rulers! In these works the basic assumption is that SNe-Ia are all the same at all z (which is just the point that one needs to verify!!! ).

“Crisis” of 3 -parameters spectrum-energy correlations Recent debate on Swift outliers to the Ep-E correlation (including both GRB with no break and a few GRB with chromatic break) Recent evidence that the dispersion of the Lp-Ep-T 0. 45 correlation is significantly higher than thought before and comparable to the Ep, i-Eiso corr. Campana et al. 2007 Rossi et al. 2008

Using the Ep, i-Eiso (Amati) correlation for cosmology It is based on only 2 observables much higher number of GRB that can be used 70 GRB Amati et al. 2008

“Standardizing” GRB with spectrum-energy correlations GRB F spectra typically show a peak at photon energy Ep for GRB with known redshift it is possible to estimate the cosmological rest frame peak energy Ep, i and the radiated energy assuming isotropic emission, Eiso log(Ep, i )= 2. 52 , = 0. 43 GRB Peak Energy Characteristic energy of most emitted photons log(Eiso)= 1. 0 , = 0. 9

Using the Ep, i-Eiso correlation for cosmology We find clear evidence that the observed scatter of the Ep, i-Eiso correlation depends on the choice of cosmological parameters used to compute E iso In other words the observed dispersion is sensitive at varying the values of the cosmological parameters Simple PL fit 70 GRB Maximum likelihood Best fit M ~ 0. 25 0. 15 Amati et al. 2008

Conclusions I i) Our analysis constrains M to 0. 02 -0. 68 (90%). ii) The current GRB sample provides weaker constraints on m than SNe-Ia. Nevertheless present and future GRB experiments (e. g. , Swift, Konus_WIND, AGILE, GLAST, SVOM) are expected to make GRBs capable to measure (independently) m with an uncertainty similar to that provided by the current samples of SNe-Ia 70 REAL Amati et al. 2008 70 REAL + 150 SIM.

Conclusions II iii) for a flat universe ( M = 1 excluded at 99. 9% c. l. ) iv) Our approach does not make any assumption on the Ep-Eiso correlation and does not use any other calibrators to set the zero point of the relation, so it is free from “circular” arguments, our finding provides an independent evidence for the existence of a repulsive energy component (dark energy) which accounts for a large fraction of the energy density of the universe (see Amati et al. 2008 for more) v) Releasing the assumption of a flat universe, we still find evidence for a low value of M (<0. 50 at 68%) and ~ 1. 05 vi) Significant constraints on the evolution of the dark energy with z are expected from both sample enrichment and z extension due to present and future GRB experiments