Extending the cosmic ladder to z~7 and beyond: using SNIa to calibrate GRB standard candels
Speaker:Speaker: Shuang-Nan Zhang
Collaborators: Nan Liang, Pu-Xun Wu
Tsinghua Center for Astrophysics , Tsinghua UniversityTsinghua Center for Astrophysics , Tsinghua University
New Directions of Cosmology
Mar, 18th, 2009, KITPC/ITP - CAS
• Gamma-Ray Bursts (GRBs) are the most intense explosions observed so far.
→ GRBs are likely to occur in high redshift range (z~7).
• GRB luminosity relations are connections between measurable properties of the γ-ray emission with the luminosity or energy.
→ Recent years, several power law GRB relations have been proposed in many works.
→ Many authors have made use of GRB relations as “standard candles” at very high redshift for cosmology research.
GRB luminosity relations
see e.g. Ghirlanda, Ghisellini, & Firmani (2006), Schaefer (2007) for reviews
Five GRB luminosity relations (Schaefer 2007, 69 GRBs)
lag - L relation(Norris, Marani, & Bonnell 2000)
Variability - L relation (Fenimore & Ramirez-Ruiz 2000)
Epeak- L relation (Schaefer 2003; Yonetoku et al. 2004) τRT - L relation (Schaefer, 2007)
E γ - Epeak relation (Ghirlanda, Ghisellini & Lazzati 2004)
• SN Ia cosmology: ---- adequate sample at low-z which can be us
ed to calibrate the Phillips relation essentially independent of any cosmology.
• GRB cosmology : ---- difficult to calibrate the relations using a lo
w-z sample. ---- Calibration of GRB relations so far have be
en derived by assuming a particular cosmology (e.g. ΛCDM model).
Calibration of GRB relations
The circularity problem
• In order to investigate cosmology, the relations of standard candles should be calibrated in a cosmological model independent way.
----Otherwise the circularity problem can not be avoided easily.
• In principle, the circularity problem can be avoided in two ways (Ghirlanda et al. 2006):
(i) A solid physical interpretation of these relations which
would fix their slope independently from cosmology.
(ii) The calibration of these relations by several low redshift GRBs.
Many previous works treated the circularity problem by means of statistical approaches.
→ simultaneous fitting (Schaefer 2003) the parameters in the calibration curves and t
he cosmology should be carried out at the same time.
→ Bayesian method (Firmani et al. 2005) → Markov Chain Monte Carlo global fitting (Li et al. 2008, Wang 2008)
Statistical approaches
• It is obvious that the sources at the same redshift should h
ave the same luminosity distance for any certain cosmology.
• Distance of SN Ia obtained directly from observations are completely cosmological model independent.
• SN Ia cosmology: the distance of nearby SN Ia used to calibrate the Phillips relation can be obtained by measuring Cepheids in the same galaxy.
Thus Cepheids has been regard as the first order standard candle to calibrate SNe Ia as the secondly order standard candle.
• If distance modulus of GRBs can be obtained direct from the SN Ia data, we can calibrate the relations of GRBs in a cosmology independent way.
SN Ia → GRBs
Cosmic distance ladder
Cepheids → SN Ia
• There are so many SN Ia samples that we can obtain the distance modulus at any redshift in the redshift range of SN Ia directly from the Hubble diagram of SN Ia.
→ Interpolation Method (Liang et al, 2008, ApJ) → Iterative Method (Liang & Zhang, 2008, AIPC)
• If regarding the SN Ia as the first order standard candle, we can obtain the distance modulus of GRBs in the redshift range of SN Ia and calibrate the relations of GRBs in a completely cosmology independent way.
• By utilizing the relations to the GRB data at high redshift, we can use the standard Hubble diagram method to constrain the cosmological parameters.
Using SN Ia calibrate GRB relations
High-z GRBCosmology
Low-z GRBStandard Candle
z SN: 1.7 GRB: ~7
Distinguish cosmological models ？
Nearby SN IaStandard Candle
Low-z SN IaCosmology
Extra-galacticCepheids
GalacticCepheids
1998: Discovery of Dark Energy
1929: Discovery of cosmic
expansion
Cosmic distance ladder: Cepheids → SNe Ia → GRBs
1(1) : log log ( (1 ) / 0.1
(2) : log log ( (1 ) / 0.02
(3) : log log ( (1 ) / 300
(4) : log log ( (1 ) / 300
lag lag
p p
p p
L L a b z s
V L L a b V z
L E L a b E z keV
E E E a b E z k
1(5) : log log ( (1 ) / 0.1
---- the five GRB luminosity relations used in Schaefer (2007)
RT RT
eV
L L a b z s
1
2
(6) : log log ( (1 ) / 300
(7) : log log ( (1 ) / 300
log ( /(1 ) /1
iso p iso p
iso p b iso p
b
E E E a b E z keV
E E t E a b E z keV
b t z day
We calibrate seven GRB relations with the sample at z<1.4 (Liang et al, 2008, ApJ)
(Amati et al. 2002)
(Liang & Zhang 2005)
GRB Luminosity Relations Calibration
→ Results obtained by using the two interpolation methods are almost identical.
→ Results obtained by assuming the two cosmological models (with the same sample) differ
only slightly from those obtained by using interpolation methods.
Calibration results
Table 1. Calibration results for the 7 GRB relations with the sample at z<1.4.
Fig. 1. The Hubble Diagram of SNe Ia and GRBs
→ SNe Ia data (Davis et al. 2007), directly from observations, cosmology independent. These data used to interpolate the distance moduli of GRB low-z “data”,
→ GRB low-z “data”, interpolated from SN Ia data, (thus also cosmology independent). These data are used to calibrate the GRB “standard” candles.
→ GRB high-z “data” , obtained from the calibrated GRB “standard” candles (weighted average over 5 relations used in Schaefer 2007); These data are used to fit cosmological parameters at high-z.
Concordance modelz=1.4
Hubble Diagram of SNe Ia and GRBs
SN1997ff (z = 1.755)
Cosmological results from GRBs (for ΛCDM model)
Fig. 2. ΩM -ΩΛ joint confidence contours from 42 GRBs (z>1.4)
Fig. 3. Confidence region in (ΩM –w0 ) plane
Dark Energy model with a constant EoS (w0)
About double-use of SN Ia data
• After using SN Ia data to calibrate GRB relations, some of the SN Ia events are no-longer independent of GRB relations (Yun Wang 2008)– Problematic for combining SN Ia data with GR
B data
• A possible solution to this problem– Simply throw away those SN Ia events used f
or calibrating GRB relations
Combined GRBs with SNe Ia, WMAP5, BAO
Independent distance modulus data: 357 SNe Ia + 42 GRBs
New SN Ia data• 307 SCP Union data (Kowalski et al. 2008) • 397 CfA SN Ia data (Hicken et al. 2009)
CfA3 sample is added to Union data
69 GRB Data• Using 40 SN Ia points from 397 CfA SN Ia data to inter
polate 27 GRB distance modulus (z<1.4)
→ 42 GRB data (1.4<z<=6.6)
(Liang, Wu & Zhang, 2009)
CMB and BAO Data
(WMAP5)
→ The shift parameter R of CMB
→ The distance parameter A of baryon acoustic oscillation
(SDSS+ WMAP5)
GRB + SN Ia + CMB + BAO
357 SN Ia + 42 GRB
CMB (WMAP5)
BAO(SDSS+WMAP5)
(i) ΛCDM model: ΩM0 -ΩΛ joint confidence
flat universe
ΩM0 = 0.288+0.028−0.026 , ΩΛ = 0.721+0.024
−0.023
ΩM0 = 0.278+0.017−0.015
(ii) wCDM model: ΩM0 - w joint confidence
ΩM0 = 0.275+0.025−0.023 , w = -0.94+0.08
−0.08
(iii) Parameterized w(z) model:
w0 = -0.95+0.19−0.20 , w a = 0.66+0.32
−0.58
Summary and Discussion
• With the basic assumption that objects at the same redshift should have the same luminosity distance, the distance modulus of a GRB can be obtained by interpolating from the Hubble diagram of SNe Ia at z <1.4.
• Thus we construct the GRB Hubble diagram and constrain cosmological parameters for 42 GRBs at 1.4<z<6.6.
• Finally, we fit the cosmological parameters by combining the SN Ia and GRB data with the new WMAP 5-year data and BAO data.
• Further examinations to the possible evolution effects and selection bias, as well as some unknown biases of SN Ia luminosity relations should be required for considering GRBs as standard candles to cosmological use.
• Our method avoids the circularity problem completely, compared to previous cosmology-dependent calibration methods.
