Nessun titolo diapositiva

1
Cosmology with Gamma-Ray Bursts
Lorenzo Amati INAF, Istituto di
Astrofisica Spaziale e Fisica Cosmica, Bologna
XLIV Rencontres de Moriond La Thuile, February
1 - 8, 2009
2

• Outline
• Gamma-Ray Bursts promising powerful
  cosmological probes
• Cosmological parameters estimates with GRB
• GRB as cosmological tracers and beacons
• Future perspectives

• using GRB spectrum-energy correlations
• including other GRB correlations
• calibrating low-z GRBs with SN Ia

3

• Outline
• Gamma-Ray Bursts promising powerful
  cosmological probes
• Cosmological parameters estimates with GRB
• GRB as cosmological tracers and beacons
• Conclusions and future perspectives

• using GRB spectrum-energy correlations
• including other GRB correlations
• calibrating low-z GRBs with SN Ia

4
Early evidences for a cosmological origin of GRBs

• isotropic distribution of GRBs directions
• paucity of weak events with respect to
  homogeneous distribution in euclidean space
• given the high fluences (up to more than 10-4
  erg/cm2 in 20-1000 keV) a cosmological origin
  would imply huge luminosity
• thus, a local origin was not excluded until
  1997 !

5
Establishing the GRB cosmological distance scale

• in 1997 discovery of afterglow emission by
  BeppoSAX
• first X, optical, radio counterparts, host
  galaxies

6

• optical spectroscopy of afterglow and/or host
  galaxy gt first measurements of GRB redshift
• redshifts higher than 0.1 and up to gt6 -gt GRB
  are cosmological
• their isotropic equivalent radiated energy is
  huge (up to more than 1054 erg in a few tens of s
  !)
• fundamental input for origin of long / short

GRB COSMOLOGY ?
7
Are GRB standard candles ?

• all GRBs with measured redshift (170, including
  a few short GRB) lie at cosmological distances (z
  0.033 6.7) (except for the peculiar
  GRB980425, z0.0085)
• isotropic luminosities and radiated energy are
  huge and span several orders of magnitude GRB
  are not standard candles (unfortunately)

Jakobsson, 2009
Amati, 2006
8

• jet angles derived from break time of optical
  afterglow light curve by assuming standard
  scenario, are of the order of few degrees
• the collimation-corrected radiated energy spans
  the range 5x1040 1052 erg-gt more clustered
  but still not standard

Ghirlanda et al., 2004
9

• GRB have huge luminosity, a redshift
  distribution extending far beyond SN Ia
• high energy emission -gt no extinction problems
• potentially powerful cosmological sources but
  need to investigate their properties to find ways
  to standardize them (if possible)

Ghirlanda et al, 2006
10
Standardizing GRB with spectrum-energy
correlations

• GRB nFn 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(Eiso) 1.0 , s 0.9
Amati, 2006
11

• Amati et al. (2002) analyzed a sample of
  BeppoSAX events with known redshift finding
  evidence for a strong correlation between Ep,i
  and Eiso
• Further analysis with updated samples (BATSE,
  HETE-2, KW, Swift) confirmed the correlation and
  extended it to the weakest and softest events
• Significant extra-Poissonian scatter of the data
  around the best fit power-law sext log(Ep,i)
  0.17
• Correlation not followed by short GRBs and
  peculiar sub-energetic GRBs

Amati et al., 2008 Amati 2008
12

• A first step using Ep,i Eiso correlation for
  z estimates

• redshift estimates available only for a small
  fraction of GRBs occurred in the last 10 years
  based on optical spectroscopy
• pseudo-redshift estimates for the large amount
  of GRB without measured redshift -gt GRB
  luminosity function, star formation rate
  evolution up to z gt 6, etc.
• use of the Ep,i Eiso correlation for
  pseudo-redshift most simple method is to study
  the track in the Ep,i - Eiso plane ad a function
  of z
• not precise z estimates and possible degeneracy
  for z gt 1.4
• anyway useful for low z GRB and in general when
  combined with optical

13

• more refined combine the Ep,i Eiso
  correlation with other observables to construct
  GRB redshift estimators (es. Atteia, 2003,
  Pelangeon et al. 2006) pseudo-redshift of HETE-2
  bursts published in GCN

Atteia, AA, 2003
Pelangeon et al., 2006
14

• A step forward standardizing GRBs with
  3-parameters spectrum-energy correlations

• the Ep,i-Eiso correlation becomes tighter when
  adding a third observable the optical afterglow
  break time tb (Liang ZHang 2004), the jet
  opening angle derived from tb (qjet -gt Eg
  1-cos(qjet)Eiso (Ghirlanda et al. 2004) or the
  high signal time T0.45 (Firmani et al. 2006)
• the logarithmic dispersion of these correlations
  seems low enough to allow their use to
  standardize GRB (Ghirlanda et al., Dai et al.,
  Firmani et al., and many)

15

• Methods (e.g., Ghirlanda et al, Firmani et al.,
  Dai et al., Zhang et al.)

Ep,i Ep,obs x (1 z)
Dl Dl (z, H0, WM, WL, )

• general purpouse estimate c.l. contours in
  2-param surface (e.g. WM-WL)
• general method construct a chi-square
  statistics for a given correlation as a function
  of a couple cosmological parameters
• method 1 luminosity distance fit the
  correlation and construct an Hubble diagram for
  each couple of cosmological parameters -gt derive
  c.l. contours based on chi-square

16

• method 2 minimum correlation scatter for each
  couple of cosm.parameters compute Ep,i and Eiso
  (or Eg), fit the points with a pl and compute the
  chi-square -gt derive c.l. contours based on
  chi-square surface
• method 3 bayesian method assuming that the
  correlation exists and is unique

Ghirlanda et al., 2004
Firmani et al. 2007
17

• What can be obtained with 150 GRB with known z
  and Ep and complementarity with other probes (SN
  Ia, CMB)
• complementary to SN Ia extension to much higher
  z even when considering the future sample of SNAP
  (z lt 1.7), cross check of results with different
  probes

Ghirlanda, Ghisellini et al. 2005, 2006,2007
18

• Crisis of 3-parameters spectrum-energy
  correlations ?
• Recent debate on Swift outliers to the Ep-Eg
  correlation (including both GRB with no break and
  a few GRB with chromatic break)
• lack of jet breaks in several Swift X-ray
  afterglow light curves, in some cases, evidence
  of chromatic break challenging jet and afterglow
  models
• which break, which afterglow (X, opt), which
  GRBs can be used for Ep-Eg ?

Campana et al. 2007
Ghirlanda et al. 2007
19

• recent analysis (Rossi et al. 2008, Schaefer et
  al. 2008) , based on BeppoSAX and Swift GRBs that
  the dispersion of the Lp-Ep-T0.45 correlation is
  significantly higher than thought before and that
  the Ep,i-Lp,iso-T0.45 correlation my be
  equivalent to the Ep,i-Eiso correlation

Rossi et al. 2008
20
The genealogy and nomenclature of spectrum-energy
correlations
21
The genealogy and nomenclature of spectrum-energy
correlations
22

• Using the simple Ep,i-Eiso correlation for
  cosmology
• Based on only 2 observables
• a) much higher number of GRB that can be
  used
• b) reduction of systematics
• Evidence that a fraction of the extrinsic scatter
  of the Ep,i-Eiso correlation is due to choice of
  cosmological parameters used to compute Eiso

70 GRB
Simple PL fit
Amati et al. 2008
23

• By using a maximum likelihood method the
  extrinsic scatter can be parametrized and
  quantified (e.g., DAgostini 2005)
• WM can be constrained to 0.04-0.40 (68) and
  0.02-0.68 (90) for a flat LCDM universe (WM 1
  excluded at 99.9 c.l.)

Amati et al. 2008
24

• releasing assumption of flat universe still
  provides evidence of low WM, with a low
  sensitivity to WL
• significant constraints on both WM and WL
  expected from sample enrichment and z extension
  by present and next GRB experiments (e.g., Swift,
  Konus_WIND, Fermi, SVOM)
• completely independent on other cosmological
  probes (e.g., CMB, type Ia SN, BAO clusters)
  and free of circularity problems

70 REAL
70 REAL 150 SIMUL
Amati et al. 2008
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• Drawbacks lack of settled physical explanation

• physics of prompt emission still not settled,
  various scenarios SSM internal shocks,
  IC-dominated internal shocks, external shocks,
  photospheric emission dominated models, kinetic
  energy dominated fireball , poynting flux
  dominated fireball)
• e.g., Ep,i ? G-2 L1/2 tn-1 for syncrotron
  emission from a power-law distribution of
  electrons generated in an internal shock (Zhang
  Meszaros 2002, Ryde 2005)
  
  
• for
  Comptonized thermal emission
• geometry of the jet (if assuming collimated
  emission) and viewing angle effects also may play
  a relevant role

26

• physical explanations of the Ep,i Eiso
  correlation in alternative GRB scenarios

Cannonball model (Dar et al.)
Fireshell model (Ruffini et al.)
27

• Drawbacks lack of calibration
• differently to SN Ia, there are no low-redshift
  GRB (only 1 at z lt 0.1) -gt correlations cannot be
  calibrated in a cosmology independent way
• would need calibration with a good number of
  events at z lt 0.01 or within a small range of
  redshift -gt neeed to substantial increase the
  number of GRB with estimates of redshift and Ep
• Bayesian methods have been proposed to cure
  the circularity problem (e.g., Firmani et al.,
  2006, Li et al. 2008), resulting in slightly
  reduced contours w/r to simple (and circularity
  free) scatter method (using Lp,iso-Ep,i-T0.45
  corr.)

28

• possible further improvements on cosmological
  parameter estimates by exploiting
  self-calibration with GRB at similar redshift or
  solid phyisical model for the correlation

70 REAL 150 SIMUL
70 REAL
70 REAL
70 REAL 150 SIMUL
Amati et al. 2008
29
Combining spectrum-energy correlations with other
(less tight) GRB correlations (e.g., Schaefer
2007, Mosquera Cuesta et al. 2008)
Luminosity-Variability correlation (Reichart et
al., Guidorzi et al., Rizzuto et al.)
Luminosity-time lag correlation (Norris et al.)
30

• pseudo redshift estimates and GRB Hubble diagram
• cosmological parameters consistent with
  standard cosmology with no dark energy evolution
• drawbacks no substantial improvements in
  estimation accuracy with respect to
  spectrum-energy correlations alone adding other
  more dispersed correlations and new observables
  adds more systematics and uncertainties (and some
  correlations are not independent)

31
Calibrating spectrum-energy correlations with SN
Ia

• Very recently, several authors (e.g., Kodama et
  al., 2008 Liang et al., 2008, Li et al. 2008)
  calibrated GRB spectrumenergy correlation at z lt
  1.7 by using the luminosity distance redshift
  relation derived for SN Ia (e.g., Riess et al,
  2007)
• The aim is to extend the SN Ia Hubble diagram up
  to redshift where the luminosity distance is more
  sensitive to dark energy properties and evolution
• Obtained significant constraints on both WM and
  WL but with this method GRB are no more an
  indipendent cosmological probe

32
GRB as tracers of star formation rate and cosmic
beacons

• Because of the association with the death of
  massive stars GRB allow the study the evolution
  of massive star formation rate back to the early
  epochs of the Universe (z gt 6)
• several attempts to reconstruct the GRB
  luminosity function, and thus the massive SFR
  evolution have been done by using pseudo-z
  derived with GRB luminosity correlations (e.g.,
  Yonetoku et al. 2004)

33

• GRB can be used as cosmological beacons for
  study of the IGM up to z gt 6 and the evolution of
  their host galaxy ISM back to the early epochs of
  the Universe (z gt 6)

EDGE Team
34
The future what is needed ?

• increase the number of z estimates, reduce
  selection effects and optimize coverage of the
  fluence-Ep plane in the sample of GRBs with known
  redshift
• more accurate estimates of Ep,i by means of
  sensitive spectroscopy of GRB prompt emission
  from a few keV (or even below) and up to at least
  1 MeV
• Swift is doing greatly the first job but cannot
  provide a high number of firm Ep estimates, due
  to BAT narrow energy band (sensitive spectral
  analysis only from 15 up to 200 keV)
• in last years, Ep estimates for some Swift GRBs
  from Konus (from 15 keV to several MeV) and, to
  minor extent, RHESSI and SUZAKU

NARROW BAND
BROAD BAND
35

• 2008 main contribution expected from joint
  Fermi Swift measurements
• Fermi/GBM (8-30000 keV) -gt increase in number
  and accuracy of Ep measurements Swift -gt z
  estimate for simultaneously detected events
  Fermi/LAT -gt up to GeV for few
• Up to now about 110 GBM GRBs, 90 Ep estimates
  (82), 14 detected and localized by Swift (13),
  4 detected and localized by LAT, 4 with z
  estimates (4), 4 with Ep z (4)
• 2008 pre-Fermi 61 Swift detections, 5 BAT Ep
  (8), 15 BATKONSUZ Ep estimates (25), 20
  redshift (33), 11 Ep z (16)
• Fermi provides a dramatic increase in Ep
  estimates (as expected), but only 14 Fermi GRBs
  have been detected / localized by Swift (13) -gt
  low number of Fermi GRBs with redshift. Will it
  be possible to improve this number ? BAT FOV much
  narrower than Fermi/GBM similar orbits, each
  satellite limited by Earth occultation but at
  different times, )

36

• 2008 main contribution expected from joint
  Fermi Swift measurements
• Fermi/GBM (8-30000 keV) -gt increase in number
  and accuracy of Ep measurements Swift -gt z
  estimate for simultaneously detected events
  Fermi/LAT -gt up to GeV for few
• Up to now about 110 GBM GRBs, 90 Ep estimates
  (82), 14 detected and localized by Swift (13),
  4 detected and localized by LAT, 4 with z
  estimates (4), 4 with Ep z (4)
• 2008 pre-Fermi 61 Swift detections, 5 BAT Ep
  (8), 15 BATKONSUZ Ep estimates (25), 20
  redshift (33), 11 Ep z (16)
• Fermi provides a dramatic increase in Ep
  estimates (as expected), but only 14 Fermi GRBs
  have been detected / localized by Swift (13) -gt
  low number of Fermi GRBs with redshift. Will it
  be possible to improve this number ? BAT FOV much
  narrower than Fermi/GBM similar orbits, each
  satellite limited by Earth occultation but at
  different times, )

37

• 2008 main contribution expected from joint
  Fermi Swift measurements
• Fermi/GBM (8-30000 keV) -gt increase in number
  and accuracy of Ep measurements Swift -gt z
  estimate for simultaneously detected events
  Fermi/LAT -gt up to GeV for few
• Up to now about 110 GBM GRBs, 90 Ep estimates
  (82), 14 detected and localized by Swift (13),
  4 detected and localized by LAT, 4 with z
  estimates (4), 4 with Ep z (4)
• 2008 pre-Fermi 61 Swift detections, 5 BAT Ep
  (8), 15 BATKONSUZ Ep estimates (25), 20
  redshift (33), 11 Ep z (16)
• Fermi provides a dramatic increase in Ep
  estimates (as expected), but only 14 Fermi GRBs
  have been detected / localized by Swift (13) -gt
  low number of Fermi GRBs with redshift. Will it
  be possible to improve this number ? BAT FOV much
  narrower than Fermi/GBM similar orbits, each
  satellite limited by Earth occultation but at
  different times, )

38

• In the gt 2014 time frame a significant step
  forward expected from SVOM
• spectral study of prompt emission in 5-5000 keV
  -gt accurate estimates of Ep and reduction of
  systematics (through optimal continuum shape
  determination and measurement of the spectral
  evolution down to X-rays)
• fast and accurate localization of optical
  counterpart and prompt dissemination to optical
  telescopes -gt increase in number of z estimates
  and reduction of selection effects

• optimized for detection of XRFs, short GRB,
  sub-energetic GRB, high-z GRB
• substantial increase of the number of GRB with
  known z and Ep -gt test of correlations and
  calibration for their cosmological use

39

• Under study GRB as cosmological beacons with
  EDGE/Xenia

• use of GRB as cosmological beacons for
  absorption spectroscopy of the WHIM and galaxies
  ISM GRB redshift and Ep
• proposed to ESA CV as EDGE will be proposed to
  NASA decadal survey as Xenia

40

• the quest for high-z GRB
• for both cosmological parameters and SFR
  evolution studies it is of fundamental
  importance to increase the detection rate of
  high-z GRBs
• Swift recently changed the BAT trigger threshold
  to this purpouse
• the detection rate can be increased by lowering
  the low energy bound of the GRB detector trigger
  energy band

Qui et al. 2009
adapted from Salvaterra et al. 2007
41

• final remark X-ray redshift measurements are
  possible !
• a transient absorption edge at 3.8 keV was
  detected by BeppoSAX in the firs 13 s of the
  prompt emission of GRB 990705 (Amati et al.
  Science, 2000)
• by interpreting this feature as a redhsifted
  neutral iron edge a redshift of 0.86/-0.17 was
  estimated
• the redshift was later confirmed by optical
  spectroscopy of the host galaxy (z 0.842)

42
END OF THE TALK
43
BACK UP SLIDES
44

• Debate based on BATSE GRBs without known redshift

• Nakar Piran and Band Preece 2005 a
  substantial fraction (50-90) of BATSE GRBs
  without known redshift are potentially
  inconsistent with the Ep,i-Eiso correlation for
  any redshift value
• they suggest that the correlation is an artifact
  of selection effects introduced by the steps
  leading to z estimates we are measuring the
  redshift only of those GRBs which follow the
  correlation
• they predicted that Swift will detect several
  GRBs with Ep,i and Eiso inconsistent with the
  Ep,i-Eiso correlation
  

• Ghirlanda et al. (2005), Bosnjak et al. (2005),
  Pizzichini et al. (2005) most BATSE GRB with
  unknown redshift are consistent with the
  Ep,i-Eiso correlation
• different conclusions mostly due to the
  accounting or not for the dispersion of the
  correlation

45

• Swift GRBs and selection effects

• Swift / BAT sensitivity better than BATSE for
  Ep lt 100 keV, slightly worse than BATSE for Ep gt
  100 keV but better than BeppoSAX/GRBM and
  HETE-2/FREGATE -gt more complete coverage of the
  Ep-Fluence plane

CGRO/BATSE
Swift/BAT
Ghirlanda et al., MNRAS, (2008)
Band, ApJ, (2003, 2006)
46

• fast (1 min) and accurate localization (few
  arcesc) of GRBs -gt prompt optical follow-up with
  large telescopes -gt substantial increase of
  redshift estimates and reduction of selection
  effects in the sample of GRBs with known redshift
• fast slew -gt observation of a part (or most,
  for very long GRBs) of prompt emission down to
  0.2 keV with unprecedented sensitivity gt
  following complete spectra evolution, detection
  and modelization of low-energy absorption/emission
  features -gt better estimate of Ep for soft
  GRBs
• drawback BAT narrow energy band allow to
  estimate Ep only for 15-20 of GRBs (but for
  some of them Ep from HETE-2 and/or Konus

GRB060124, Romano et al., AA, 2006
47

• all long Swift GRBs with known z and published
  estimates or limits to Ep,i are consistent with
  the correlation
• the parameters (index, normalization,dispersion)
  obatined with Swift GRBs only are fully
  consistent with what found before
• Swift allows reduction of selection effects in
  the sample of GRB with known z -gt the Ep,i-Eiso
  correlation is passing the more reliable test
  observations !

Amati 2006, Amati et al. 2008
48

• very recent claim by Butler et al. 50 of Swift
  GRB are inconsistent with the pre-Swift Ep,i-Eiso
  correlation
• but Swift/BAT has a narrow energy band 15-150
  keV, nealy unesuseful for Ep estimates, possible
  only when Ep is in (or close to the bounds of )
  the passband (15-20) and with low accuracy
• comparison of Ep derived by them from BAT
  spectra using Bayesian method and those MEASURED
  by Konus/Wind show they are unreliable
• as shown by the case of GRB 060218, missing the
  soft part of GRB emission leads to overestimate
  of Ep

49

• Full testing and exploitation of spectral-energy
  correlations may be provided by EDGE in the gt
  2015 time frame
• in 3 years of operations, EDGE will detect
  perform sensitive spectral analysis in 8-2500 keV
  for 150-180 GRB
• redshift will be provided by optical follow-up
  and EDGE X-ray absorption spectroscopy (use of
  microcalorimeters, GRB afterglow as bkg source)
• substantial improvement in number and accuracy
  of the estimates of Ep , which are critical for
  ultimately testing the reliability of
  spectral-energy correlations and their use for
  the estimates of cosmological parameters

50

• Evidence of two populations 50 prompt 50
  exp

prompt tardy
Della Valle et al. 2005 Mannucci et al.
2005 Mannucci et al. 2006 Sullivan et al.
2006 Aubourg et al. 2007
51
Phillipss relationship is calibrated on the
tardy component? luminosity-decline rate
relation might change with redshift???
Metallicity? (Nomoto et al. 2003 Dominguez et al.
2005)
52
Two scenarios for type Ia

• Differerent progenitors / explosion mechanisms ?

• 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 (WDgiant, WDHe)
• Symbiotic systems (WDMira or red giant)
• Supersoft X-ray Sources (WDMS star)

Both explosive channels are at play? maybe at
different redshifts?
53

• 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

54
LONG
SHORT

• energy budget up to gt1054 erg
• long duration GRBs
• metal rich (Fe, Ni, Co) circum-burst environment
• GRBs occur in star forming regions
• GRBs are associated with SNe
• naturally explained collimated emission

• energy budget up to 1051 - 1052 erg
• short duration GRBs (lt 5 s)
• clean circum-burst environment
• GRBs in the outer regions of the host galaxy

55

• Very recently (Kodama et al., 2008 Liang et
  al., 2008) calibrated GRB spectrumenergy
  correlation at z lt 1.7 by using the cosmology
  independent luminosity distance redshift
  relation derived for SN Ia (RIess et al, 2007)
• Obtained significant constraints on both WM and
  WL but with this method GRB are no more an
  indipendent cosmological probe

56

• Combining spectrum-energy correlations with
  other (less tight)
• Luminosity correlations in GRB (Schaefer 2007)

57
GRB as cosmological beacons

• GRB can be used as cosmological beacons for
  study of the IGM up to z gt 6
• Because of the association with the death of
  massive stars GRB allow the study the evolution
  of massive star formation and the evolution of
  their host galaxy ISM back to the early epochs of
  the Universe (z gt 6)

EDGE Team
58
Gamma-Ray Bursts the brightest cosmological
sources

• most of the flux detected from 10-20 keV up to
  1-2 MeV
• measured rate (by an all-sky experiment on a LEO
  satellite) 0.8 / day estimated true rate 2 /
  day
• bimodal duration distribution
• fluences ( av.flux duration) typically of
  10-7 10-4 erg/cm2

short
long
59

• possible further improvements on cosmological
  parameter estimates by exploiting
  self-calibration with GRB at similar redshift or
  solid phyisical model for the correlation

70 REAL 150 SIMUL
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60

• given their redshift distribution (0.033 - 6.3
  up to now) , GRB are potentially the best-suited
  probes to study properties and evolution of dark
  energy

(e.g.,Chevalier Polarski, Linder Utherer)
70 REAL 150 SIMUL (flat)
70 REAL (flat, Wm0.27)
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61
Ep,i Eiso correlation vs. the other
spectrum-energy correlations

• Eiso is the GRB brightness indicator with less
  systematic uncertainties
• Liso is affected by the often uncertain GRB
  duration (e.g., long tails of Swift GRB)
• Lp,iso is affected by the lack of or poor
  knowledge of spectral shape of the peak emisison
  (the time average spectrum is often used) and by
  the subjective choice and inhomogeneity in z of
  the peak time scale
• Comparison with three-parameters correlations
  reduced scatter, but
• addition of a third observable introduces
  further uncertainties (difficulties in measuring
  t_break, chromatic breaks, model assumptions,
  subjective choice of the energy band in which
  compute T0.45, inhomogeneity on z of T0.45) and
  substantially reduces the number of GRB that can
  be used (e.g., Ep,i Eg ¼ Ep,i Eiso )
• recent evidences that dispersion of
  Ep,i-Lp,iso-T0.45 correlation is comparable to
  that of Ep,i - Eiso and debates on possible
  outliers / higher dispersion of the Ep-Eg and
  Ep-Eiso-tb correlations (but see talk by
  Ghirlanda)

62
Complementarity to other probes the case of SN Ia

• Several possible systematics may affect the
  estimate of cosmological parameters with SN Ia,
  e.g.
• different explosion mechanism and progenitor
  systems ? May depend on z ?
• light curve shape correction for the luminosity
  normalisation may depend on z
• signatures of evolution in the colours
• correction for dust extinction
• anomalous luminosity-color relation
• contaminations of the Hubble Diagram by
  no-standard SNe-Ia and/or bright SNe-Ibc (e.g.
  HNe)

Kowalski et al. 2008
63

• The Hubble diagram for type Ia SNe may be
  significantly affected by systematics -gt need
  to carry out independent measurement of WM and WL
  
• GRBs allow us today to change the experimental
  methodology and provide an independent
  measurement of the cosmological parameters

• GRBs are extremely bright and detectable out of
  cosmological distances (z6.3 Kuwai et al. 2005,
  Tagliaferri et al. 2005) -gt interesting objects
  for cosmology
• SNe-Ia are currently observed at zlt1.7 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 z7-8)
• No need of correction for reddening
• Different orientation of the contours

64
Conclusions

• Given their huge luminosities and redshift
  distribution extending up to at least 6.3, GRB
  are a powerful tool for cosmology and
  complementary to other probes (CMB, SN Ia, BAO,
  clusters, etc.)
• The use of Ep,i Eiso correlation to this
  purpouse is promising (already significant
  constraints on Wm, in agreement with concordance
  cosmology), but
• need to substantial increase of the of GRB
  with known z and Ep (which will be realistically
  allowed by next GRB experiments SwiftGLAST/GBM,
  SVOM,)
• auspicable solid physical interpretation
• identification and understanding of possible
  sub-classes of GRB not following correlations

65
Complementarity to other probes the case of SN Ia

• Several possible systematics may affect the
  estimate of cosmological parameters with SN Ia,
  e.g.
• different explosion mechanism and progenitor
  systems ? May depend on z ?
• light curve shape correction for the luminosity
  normalisation may depend on z
• signatures of evolution in the colours
• correction for dust extinction
• anomalous luminosity-color relation
• contaminations of the Hubble Diagram by
  no-standard SNe-Ia and/or bright SNe-Ibc (e.g.
  HNe)

Kowalski et al. 2008
66

• The Hubble diagram for type Ia SNe may be
  significantly affected by systematics -gt need
  to carry out independent measurement of WM and WL
  
• GRBs allow us today to change the experimental
  methodology and provide an independent
  measurement of the cosmological parameters

• GRBs are extremely bright and detectable out of
  cosmological distances (z6.3 Kuwai et al. 2005,
  Tagliaferri et al. 2005) -gt interesting objects
  for cosmology
• SNe-Ia are currently observed at zlt1.7 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 z7-8)
• No need of correction for reddening
• Different orientation of the contours

67

• The Hubble diagram for type Ia SNe may be
  significantly affected by systematics -gt need
  to carry out independent measurement of WM and WL
  
• GRBs allow us today to change the experimental
  methodology and provide an independent
  measurement of the cosmological parameters

• GRBs are extremely bright and detectable out of
  cosmological distances (z6.3 Kuwai et al. 2005,
  Tagliaferri et al. 2005) -gt interesting objects
  for cosmology
• SNe-Ia are currently observed at zlt1.7 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 z7-8)
• No need of correction for reddening
• Different orientation of the contours

68
Complementarity to other probes the case of SN Ia

• Several possible systematics may affect the
  estimate of cosmological parameters with SN Ia,
  e.g.
• different explosion mechanism and progenitor
  systems ? May depend on z ?
• light curve shape correction for the luminosity
  normalisation may depend on z
• signatures of evolution in the colours
• correction for dust extinction
• anomalous luminosity-color relation
• contaminations of the Hubble Diagram by
  no-standard SNe-Ia and/or bright SNe-Ibc (e.g.
  HNe)