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Lorenzo Amati INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Bologna

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:

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Lorenzo Amati INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Bologna

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  1. Cosmology with Gamma-Ray Bursts Lorenzo Amati INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Bologna XLIV Rencontres de MoriondLa 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 –> 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 / 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, z=0.0085) • 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 – 1052erg-> 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 -> 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. log(Ep,i )= 2.52 s = 0.43 “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 -> 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

  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, A&A, 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 -> 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,obsx (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 -> 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 -> 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 < 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. Eiso<->Liso Ep,i – Eiso “Amati” 02 Eiso<->Lp,iso Ep,i – Liso 04 Ep,i – Lp,iso “Yonetoku”04 tb,opt + jet model tb,opt T0.45 = Ep,i – Eg “Ghirlanda” 04 Ep,i – Eiso-tb “Liang-Zhang” 05 Ep,i – Lp,iso-T0.45 “Firmani” 06 The genealogy and nomenclature of spectrum-energy correlations

  21. Eiso<->Liso Ep,i – Eiso “Amati” 02 Eiso<->Lp,iso Ep,i – Liso 04 Ep,i – Lp,iso “Yonetoku”04 tb,opt + jet model tb,opt T0.45 = Ep,i – Eg “Ghirlanda” 04 Ep,i – Eiso-tb “Liang-Zhang” 05 Ep,i – Lp,iso-T0.45 “Firmani” 06 The genealogy and nomenclature of spectrum-energy correlations

  22. Using the simple Ep,i-Eiso correlation for cosmology • Based on only2 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., D’Agostini 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

  25. 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 < 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.)

  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 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 WM and WLbut 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 > 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 > 6 and the evolution of their host galaxy ISM back to the early epochs of the Universe (z > 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) -> 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, … )

  36. 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, … )

  37. 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, … )

  38. 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

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

  46. fast (~1 min) and accurate localization (few arcesc) of GRBs -> prompt optical follow-up with large telescopes -> substantial increase of redshift estimates and reduction of selection effects in the sample of GRBs with known redshift • fast slew -> observation of a part (or most, for very long GRBs) of prompt emission down to 0.2 keV with unprecedented sensitivity –> following complete spectra evolution, detection and modelization of low-energy absorption/emission features -> 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., A&A, 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 -> 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 > 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

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