lorenzo amati inaf, istituto di astrofisica spaziale e fisica cosmica, bologna
DESCRIPTION
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. Outline Gamma-Ray Bursts: promising powerful cosmological probes Cosmological parameters estimates with GRB: - PowerPoint PPT PresentationTRANSCRIPT
Lorenzo AmatiLorenzo Amati
INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, BolognaINAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Bologna
Cosmology with Gamma-Ray BurstsCosmology with Gamma-Ray Bursts
XLIV Rencontres de Moriond La Thuile, February 1 - 8, 2009
OutlineOutline
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
OutlineOutline
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
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 !
Early evidences for a cosmological origin of GRBsEarly evidences for a cosmological origin of GRBs
in 1997 discovery of afterglow emission by BeppoSAX
first X, optical, radio counterparts, host galaxies
Establishing the GRB cosmological distance scaleEstablishing the GRB cosmological distance scale
optical spectroscopy of afterglow and/or host galaxy –> first measurements of GRB redshift
redshifts higher than 0.1 and up to >6 -> 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 / shortGRB COSMOLOGY ?
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, z=0.0085)
isotropic luminosities and radiated energy are huge and span several orders of magnitude: GRB are not standard candles (unfortunately)
Are GRB standard candles ?Are GRB standard candles ?
Jakobsson, 2009 Amati, 2006
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-> more clustered but still not standard
Ghirlanda et al., 2004
GRB have huge luminosity, a redshift distribution extending far beyond SN Ia
high energy emission -> 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
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
““Standardizing” GRB with spectrum-energy correlationsStandardizing” GRB with spectrum-energy correlations
log(Ep,i )= 2.52
= 0.43log(Eiso)= 1.0 ,
= 0.9
Amati, 2006
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: ext [log(Ep,i)] ~ 0.17
Correlation not followed by short GRBs and peculiar sub-energetic GRBs
Amati et al., 2008; Amati 2008
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 -> GRB luminosity function, star formation rate evolution up to z > 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 > 1.4
anyway useful for low z GRB and in general when combined with optical
A first step: using Ep,i – Eiso correlation for z estimates
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, A&A, 2003 Pelangeon et al., 2006
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 (jet -> E = [1-cos(jet)]*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)
A step forward: standardizing GRBs with 3-parameters spectrum-energy correlations
general purpouse: estimate c.l. contours in 2-param surface (e.g. M-)
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 -> derive c.l. contours based on chi-square
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, M, , …)
Ghirlanda et al., 2004
method 2 – minimum correlation scatter: for each couple of cosm.parameters compute Ep,i and Eiso (or E), fit the points with a pl and compute the chi-square -> derive c.l. contours based on chi-square surface
method 3: bayesian method assuming that the correlation exists and is unique
Firmani et al. 2007
Ghirlanda, Ghisellini et al. 2005, 2006,2007
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 < 1.7), cross check of results with different probes
“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)
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-E ?
Campana et al. 2007 Ghirlanda et al. 2007
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
The genealogy and nomenclature of spectrum-energy correlations
Ep,i – Eiso“Amati” 02Ep,i – Liso
04Ep,i – Lp,iso“Yonetoku”04
Ep,i – E“Ghirlanda” 04
Ep,i – Eiso-tb“Liang-Zhang” 05
Ep,i – Lp,iso-T0.45“Firmani” 06
Eiso<->Liso Eiso<->Lp,iso
tb,opt + jet model tb,opt T0.45=
Ep,i – Eiso“Amati” 02Ep,i – Liso
04Ep,i – Lp,iso“Yonetoku”04
Ep,i – E“Ghirlanda” 04
Ep,i – Eiso-tb“Liang-Zhang” 05
Ep,i – Lp,iso-T0.45“Firmani” 06
Eiso<->Liso Eiso<->Lp,iso
tb,opt + jet model tb,opt T0.45=
The genealogy and nomenclature of spectrum-energy correlations
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
Amati et al. 2008
Simple PL fit70 GRB
By using a maximum likelihood method the extrinsic scatter can be parametrized and quantified (e.g., D’Agostini 2005)
M can be constrained to 0.04-0.40 (68%) and 0.02-0.68 (90%) for a flat CDM universe (M = 1 excluded at 99.9% c.l.)
Amati et al. 2008
releasing assumption of flat universe still provides evidence of low M, with a low sensitivity to
significant constraints on both M and 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
Amati et al. 2008
70 REAL
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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 -2 L1/2 t-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
Drawbacks: lack of settled physical explanation
physical explanations of the Ep,i – Eiso correlation in alternative GRB scenarios
‘Cannonball’ model (Dar et al.) ‘Fireshell’ model (Ruffini et al.)
Drawbacks: lack of calibration
differently to SN Ia, there are no low-redshift GRB (only 1 at z < 0.1) -> correlations cannot be calibrated in a “cosmology independent” way
would need calibration with a good number of events at z < 0.01 or within a small range of redshift -> 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.)
possible further improvements on cosmological parameter estimates by exploiting self-calibration with GRB at similar redshift or solid phyisical model for the correlation
Amati et al. 2008
70 REAL 70 REAL + 150 SIMUL70 REAL
+ 150 SIMUL
70 REAL
Luminosity-Variability correlation (Reichart et al., Guidorzi et al., Rizzuto et al.)
Combining spectrum-energy correlations with other (less tight) Combining spectrum-energy correlations with other (less tight) GRB correlations (e.g., Schaefer 2007, Mosquera Cuesta et al. GRB correlations (e.g., Schaefer 2007, Mosquera Cuesta et al. 2008)2008)
Luminosity-time lag correlation (Norris et al.)
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)
Very recently, several authors (e.g., Kodama et al., 2008; Liang et al., 2008, Li et al. 2008) calibrated GRB spectrum—energy correlation at z < 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 M and but with this method GRB are no more an indipendent cosmological probe
Calibrating spectrum-energy correlations with SN IaCalibrating spectrum-energy correlations with SN Ia
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 > 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)
GRB as tracers of star formation rate and cosmic beaconsGRB as tracers of star formation rate and cosmic beacons
GRB can be used as cosmological beacons for study of the IGM up to z > 6 and the evolution of their host galaxy ISM back to the early epochs of the Universe (z > 6)
EDGE Team
The future: what is needed ?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
2008: main contribution expected from joint Fermi + Swift measurements
Fermi/GBM (8-30000 keV) -> increase in number and accuracy of Ep measurements; Swift -> z estimate for simultaneously detected events; Fermi/LAT -> 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 BAT+KON+SUZ 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%) -> 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, … )
2008: main contribution expected from joint Fermi + Swift measurements
Fermi/GBM (8-30000 keV) -> increase in number and accuracy of Ep measurements; Swift -> z estimate for simultaneously detected events; Fermi/LAT -> 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 BAT+KON+SUZ 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%) -> 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, … )
2008: main contribution expected from joint Fermi + Swift measurements
Fermi/GBM (8-30000 keV) -> increase in number and accuracy of Ep measurements; Swift -> z estimate for simultaneously detected events; Fermi/LAT -> 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 BAT+KON+SUZ 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%) -> 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, … )
In the > 2014 time frame a significant step forward expected from SVOM:
spectral study of prompt emission in 5-5000 keV -> 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 -> 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 -> test of correlations and calibration for their cosmological use
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
Under study: GRB as cosmological beacons with EDGE/Xenia
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
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)
END OF THE TALK
BACK UP SLIDES
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
Debate based on BATSE GRBs without known redshiftDebate based on BATSE GRBs without known redshift
Swift / BAT sensitivity better than BATSE for Ep < ~100 keV, slightly worse than BATSE for Ep > ~100 keV but better than BeppoSAX/GRBM and HETE-2/FREGATE -> more complete coverage of the Ep-Fluence plane
Band, ApJ, (2003, 2006)
CGRO/BATSE
Swift/BAT
Swift GRBs and selection effectsSwift GRBs and selection effects
Ghirlanda et al., MNRAS, (2008)
fast (~1 min) and accurate localization (few fast (~1 min) and accurate localization (few arcesc) of GRBs -> prompt optical follow-up with arcesc) of GRBs -> prompt optical follow-up with large telescopes -> large telescopes -> substantial increase of substantial increase of redshift estimates and reduction of selection redshift estimates and reduction of selection effects in the sample of GRBs with known effects in the sample of GRBs with known redshiftredshift
fast slew -> observation of a part (or most, fast slew -> observation of a part (or most, for very long GRBs) of prompt emission down to for very long GRBs) of prompt emission down to 0.2 keV with unprecedented sensitivity –> 0.2 keV with unprecedented sensitivity –> following complete spectra evolution, detection following complete spectra evolution, detection and modelization of low-energy and modelization of low-energy absorption/emission featuresabsorption/emission features -> better estimate -> better estimate of Ep for soft GRBsof Ep for soft GRBs
drawback: BAT “narrow” energy band allow drawback: BAT “narrow” energy band allow to estimate Ep only for ~15-20% of GRBs (but to estimate Ep only for ~15-20% of GRBs (but for some of them Ep from HETE-2 and/or Konusfor some of them Ep from HETE-2 and/or Konus
GRB060124, Romano et al., A&A, 2006
all long Swift GRBs with known z and published estimates or limits to Ep,i are consistent with the correlationall 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 beforethe 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 -> the Ep,i-Eiso correlation is Swift allows reduction of selection effects in the sample of GRB with known z -> the Ep,i-Eiso correlation is
passing the more reliable test: observationspassing the more reliable test: observations ! !
Amati 2006, Amati et al. 2008
very recent claim by Butler et al.: 50% of Swift very recent claim by Butler et al.: 50% of Swift GRB are inconsistent with the pre-Swift Ep,i-Eiso GRB are inconsistent with the pre-Swift Ep,i-Eiso correlationcorrelation
but Swift/BAT has a narrow energy band: 15-but Swift/BAT has a narrow energy band: 15-150 keV, nealy unesuseful for Ep estimates, 150 keV, nealy unesuseful for Ep estimates, possible only when Ep is in (or close to the possible only when Ep is in (or close to the bounds of ) the passband (15-20%) and with low bounds of ) the passband (15-20%) and with low accuracyaccuracy
comparison of Ep derived by them from BAT comparison of Ep derived by them from BAT spectra using Bayesian method and those spectra using Bayesian method and those MEASURED by Konus/Wind show they are MEASURED by Konus/Wind show they are unreliableunreliable
as shown by the case of GRB 060218, missing as shown by the case of GRB 060218, missing the soft part of GRB emission leads to the soft part of GRB emission leads to overestimate of Epoverestimate of Ep
Full testing and exploitation of spectral-energy correlations may be provided by Full testing and exploitation of spectral-energy correlations may be provided by EDGE in the > 2015 time frameEDGE in the > 2015 time frame
in 3 years of operations, EDGE will detect perform sensitive spectral analysis in 8-2500 keV in 3 years of operations, EDGE will detect perform sensitive spectral analysis in 8-2500 keV for ~150-180 GRBfor ~150-180 GRB
redshift will be provided by optical follow-up and EDGE X-ray absorption spectroscopy (use redshift will be provided by optical follow-up and EDGE X-ray absorption spectroscopy (use of microcalorimeters, GRB afterglow as bkg source)of microcalorimeters, GRB afterglow as bkg source)
substantial improvement in number and accuracy of the estimates of Esubstantial improvement in number and accuracy of the estimates of Epp , which are critical , which are critical for ultimately testing the reliability of spectral-energy correlations and their use for the estimates for ultimately testing the reliability of spectral-energy correlations and their use for the estimates of cosmological parametersof cosmological parameters
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
Phillips’s relationship is calibrated on the “tardy” component luminosity-decline rate relation might change with redshift??? Metallicity? (Nomoto et al. 2003
Dominguez et al. 2005)
bmaM dB 15
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?
Differerent progenitors / explosion mechanisms ?
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
LONG
energy budget up to >1054 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 (< 5 s) clean circum-burst environment GRBs in the outer regions of the host galaxy
SHORT
Very recently (Kodama et al., 2008; Liang et al., 2008) calibrated GRB spectrum—energy correlation at z < 1.7 by using the cosmology independent luminosity distance – redshift relation derived for SN Ia (RIess et al, 2007)
Obtained significant constraints on both M and but with this method GRB are no more an indipendent cosmological probe
Combining spectrum-energy correlations with other (less tight) Luminosity correlations in GRB (Schaefer 2007)
GRB can be used as cosmological beacons for study of the IGM up to z > 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 > 6)
GRB as cosmological beaconsGRB as cosmological beacons
EDGE Team
Gamma-Ray Bursts: the brightest cosmological sourcesGamma-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
shortlong
possible further improvements on cosmological parameter estimates by exploiting self-calibration with GRB at similar redshift or solid phyisical model for the correlation
Amati et al. 2008
70 REAL 70 REAL + 150 SIMUL70 REAL
+ 150 SIMUL
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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”
Amati et al. 2008
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(flat)
(e.g.,Chevalier & Polarski, Linder & Utherer)
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 – E~ 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-E and Ep-Eiso-tb correlations (but see talk by Ghirlanda)
Ep,i – Eiso correlation vs. the other spectrum-energy correlations
Complementarity to other probes: the case of SN IaComplementarity 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
The Hubble diagram for type Ia SNe may be significantly affected by systematics -> need to carry out independent measurement of and
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 (z=6.3 Kuwai et al. 2005, Tagliaferri et al. 2005) -> interesting objects for cosmology
SNe-Ia are currently observed at z<1.7: 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 z~7-8)
No need of correction for reddening
Different orientation of the contours
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 m, 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: Swift+GLAST/GBM, SVOM,…)
auspicable solid physical interpretation
identification and understanding of possible sub-classes of GRB not following correlations
ConclusionsConclusions
Complementarity to other probes: the case of SN IaComplementarity 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
The Hubble diagram for type Ia SNe may be significantly affected by systematics -> need to carry out independent measurement of and
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 (z=6.3 Kuwai et al. 2005, Tagliaferri et al. 2005) -> interesting objects for cosmology
SNe-Ia are currently observed at z<1.7: 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 z~7-8)
No need of correction for reddening
Different orientation of the contours
The Hubble diagram for type Ia SNe may be significantly affected by systematics -> need to carry out independent measurement of and
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 (z=6.3 Kuwai et al. 2005, Tagliaferri et al. 2005) -> interesting objects for cosmology
SNe-Ia are currently observed at z<1.7: 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 z~7-8)
No need of correction for reddening
Different orientation of the contours
Complementarity to other probes: the case of SN IaComplementarity 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)