Lorenzo Amati INAF - IASF Bologna INAF - IASF Bologna with main contributions by: M. Della Valle, F. Frontera, C. Guidorzi, M. De Laurentis, E. Palazzi with main contributions by: M. Della Valle, F. Frontera, C. Guidorzi, M. De Laurentis, E. Palazzi

Why looking for more cosmological probes ?  different distribution in redshift -> different sensitivity to different cosmological parameters

Recent results from SNLS (231 SNe Ia at 0.15 < z < 1.1, Guy et al. 2010) compared to those of Astier et al (44 low redshift SNe along with the 71 SNe from the SNLS first year sample) Guy et al Astier et al. 2006

 Each cosmological probe is characterized by possible systematics  e.g SN Ia:  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)

If the “offset from the truth” is just 0.1 mag…. (slide by M. della Valle)

 all GRBs with measured redshift (~250, including a few short GRBs) lie at cosmological distances (z = – ~9.4) (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 ? Jakobsson, 2009Amati, 2009

 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 ~5x10 49 – 5x10 52 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 Ghirlanda et al, 2006

 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 spectra typically described by the empirical Band function with parameters  = low-energy index,  = high-energy index, E 0 =break energy  E p = E 0 x (2 +  ) = observed peak energy of the F spectrum  measured spectrum + measured redshift -> intrinsic peak enery and radiated energy E p,i = E p x (1 + z) 190 GRB Jakobsson (2009) Ep The Ep,i – Eiso correlation

 ~260 GRBs with measured redshift, about 50% have measured spectra  both Ep, i and Eiso span several orders of magnitude and a distribution which can be described by a Gaussian plus a low – energy tail (“intrinsic” XRFs and sub-energetic events) 95 GRBs, sample of Amati, Frontera & Guidorzi, A&A (2009)

 Amati et al. (A&A 2002): significant correlation between Ep,i and Eiso found based on a small sample of BeppoSAX GRBs with known redshift BeppoSAX GRBs

 Ep,i – Eiso correlation for GRBs with known redshift confirmed and extended by measurements of ALL other GRB detectors with spectral capabilities 130 long GRBs as of Sept BeppoSAX GRBs

 Swift: reduction of selection effects in redshift  Ep,i of Swift GRBs measured by Konus-WIND, Suzaku/WAM, Fermi/GBM and BAT (values provided by the Swift/BAT team (GCNs or Sakamoto et al. 2008). Swift GRBs

 Fermi: unprecedentred broad-band coverage of prompt emission (~10 keV – GeV) – reduction of biases in measurement of Ep  When computing Ep,i and Eiso based on the fit with Band function (unless CPL significantly better) all Fermi/ GBM long GRBs with known z are fully consistent with Ep,i – Eiso correlation as determined with previous / other experiments, both when considering preliminary fits (GCNs) or refined analysis (e.g., Nava et al. 2011) Amati 2012 Zhang et al. 2012

 the correlation holds also when substituting Eiso with Liso (e.g., Lamb et al. 2004) or Lpeak,iso (Yonetoku et al. 2004, Ghirlanda et al., 2005)  this is expected because Liso and Lpeak,iso are strongly correlated with Eiso  w/r to Eiso, Liso and Lp,iso are more difficult to estimate and subject to larger uncertainties

 the Ep,i– Liso correlation holds also within a good fraction of GRBs (Liang et al.2004, Firmani et al. 2008, Frontera et al. 2012, Ghirlanda et al. 2009): robust evidence for a physical origin and clues to explanation BATSE (Liang et al., ApJ, 2004) Fermi (e.g., Li et al., ApJ, 2012)

Ghirlanda et al  No evidence of evolution of index and normalization of the Ep,i – Eiso correlation with redshift

 strong correlation but significant dispersion of the data around the best-fit power- law; the distribution of the residuals can be fit with a Gaussian with  (logEp,i) ~ 0.2  the “extra-statistical scatter” of the data can be quantified by performing a fit whith a max likelihood method (D’Agostini 2005) which accounts for sample variance and the uncertainties on both X and Y quantities  with this method Amati et al. (2008, 2009) found an extrinsic scatter  int (logEp,i) ~ 0.18 and index and normalization t ~0.5 and ~100, respectively

“Standardizing” GRB with Ep,i-brightness correlations  2004: evidence that by substituting Eiso with the collimation corrected energy E  the logarithmic dispersion of the correlation decreases significantly and is low enough to allow its use to standardize GRB (Ghirlanda et al., Dai et al, and many)

 the Ep-E  correlation is model dependent: slope depends on the assumptions on the circum-burst environment density profile (ISM or wind)  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 ) Nava et al.., A&A, 2005: ISM (left) and WIND (right) ISMWIND  BUT…

 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 ?

 A tight correlation between Ep,i, Lpeak,iso and time scale T 0.45 was also claimed, based on still small number of events and proposed for standardizing GRBs (Firmani et al and others)

 … but Rossi et al and Schaefer et al. 2008, based on BeppoSAX and Swift GRBs, showed that the dispersion of the Lp-Ep-T 0.45 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

Ep,i – Eiso “Amati” 02 Ep,i – Liso 04 Ep,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 LisoEiso Lp,iso tb,opt + jet modeltb,optT0.45 =  Ep – “intensity” (or “spectrum-energy”) correlations

 Eiso is the GRB brightness indicator with less systematic uncertainties  Lp,iso is affected by the lack of or poor knowledge of spectral shape of the peak emission (the time average spectrum is often used) and by the subjective choice and inhomogeneity in z of the peak time scale  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 T 0.45, inhomogeneity on z of T 0.45 ) and substantially reduces the number of GRB that can be used (e.g., #E p,i – E   ~ ¼ #E p,i – E iso )  recent evidences that dispersion of E p,i -L p,iso -T 0.45 correlation is comparable to that of E p,i - E iso and evidences of outliers / higher dispersion of the E p -E  and E p -E iso -t b correlations

Ep,i – Eiso “Amati” 02 Ep,i – Liso 04 Ep,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 LisoEiso Lp,iso tb,opt + jet modeltb,optT0.45 =  Amati et al. (2008): let’s make a step backward and focus on the Ep,i – Eiso correlation

Ep,i – Eiso “Amati” 02 Ep,i – Liso 04 Ep,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 LisoEiso Lp,iso tb,opt + jet modeltb,optT0.45 =  Amati et al. (2008): let’s make a step backward and focus on the Ep,i – Eiso correlation

 does the extrinsic scatter of the E p,i -E iso correlation vary with the cosmological parameters used to compute E iso ? Amati et al GRB D l = D l (z, H 0,  M,  ,…)

 a fraction of the extrinsic scatter of the E p,i -E iso correlation is indeed due to the cosmological parameters used to compute E iso  Evidence, independent on SN Ia or other cosmological probes, that, if we are in a flat  CDM universe,  M is lower than 1 Amati et al Simple PL fit Amati et al. 2008

 By using a maximum likelihood method the extrinsic scatter can be parametrized and quantified (e.g., Reichart 2001, D’Agostini 2005)   M can be constrained to (68%) and (90%) for a flat  CDM universe (  M = 1 excluded at 99.9% c.l.)  significant constraints on both  M and   expected from sample enrichment Amati et al (real) GRBs 70 (real) (sim.) GRBs

 analysis of the most updated sample of 137 GRBs shows significant improvements w/r to the sample of 70 GRBs of Amati et al. (2008)  this evidence supports the reliability and perspectives of the use of the Ep,i – Eiso correlation for the estimate of cosmological parameters  m (flat universe) 68% 90% 70 GRBs (Amati+ 08)0.04 – – GRBs (Amati+ 12)0.06 – – GRBs 114 GRBs 137 GRBs

GRB

Adapted from Amati+ 12 and Ghirlanda  the simulatenous operation of Swift, Fermi/GBM, Konus-WIND is allowing an increase of the useful sample (z + Ep) at a rate of GRB/year, providing an increasing accuracy in the estimate of cosmological parameters  future GRB experiments (e.g., SVOM) and more investigations (physics, methods, calibration) will improve the significance and reliability of the results and allow to go beyond SN Ia cosmology (e.g. investigation of dark energy) 300 GRB Perspectives Perspectives  Expected significant enlargement of the sample in a few years

 Several authors (e.g., Kodama et al., 2008; Liang et al., 2008, Li et al. 2008, Demianski et al , Capozziello et al. 2010, Wang et al. 2012) are investigating the calibration of the Ep,i - Eiso correlation at z < 1.7 by using the luminosity distance – redshift relation derived for SN Ia  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  Drawback: with this method GRB are no more an indipendent cosmological probe  Calibrating the Ep,i – Eiso correlation with SN Ia Kodama et al. 2008Wang et al. 2012

~ -3 ~ -0.7 ~ ~ -2 10^2 – 10^3 s10^4 – 10^5 s 10^5 – 10^6 s ( 1 min ≤ t ≤ hours ) Swift team  (observational gap between “prompt” and “afterglow emission” will be filled by Swift in > 2004)  Investigating correlations involving afterglow properties

 A correlation between the time, Ta, and the luminosity, Lx, of the end of the “plateau phase” in GRB X-ray afterglows is being investigated (Dainotti+ 2008,2010)  A three-parameters correlation between Ep,i, Eiso and Ex,iso has been recently reported (Margutti et al. 2012, Bernardini et al. 2012)  If confirmed and refined by further analysis, these correlations may be complementary to the Ep,i – intensity correlation for standardizing GRBs Dainotti et al Margutti et al. 2012

Chandra & Frail 2012  In the “Swift era”, radio afterglow emission is being detected for about 30% accurately (< a few arcmin) localized GRBs (~93% in X-rays, ~75% in optical/NIR)  Most detections by VLA / EVLA (Frail et al, Chandra et al.); several detections also by WSRT, ATCA, GMRT; a few by VLBA.  The canonical long-duration GRB radio light curve at 8.5 GHz peaks at three to six days in the source rest frame, with a median peak luminosity of erg s −1 Hz −1.  The typical mean fluxes at 8.5 GHz in days from the GRB range from ~100 to ~900  Jy. Peak fluxes may reach 10 mJy The SKA contribution The SKA contribution  Radio properties of GRBs

Chandra & Frail 2012  Scintillation: fundamental probe of ultra-relativistic expansion of GRB sources  Test of afterglow models unbiased, w/r, e.g., to optical observations (dust extinction, contamination by SN and host galaxy light  Relevance of radio observations of GRBs Frail et al. 1997:

Chandra & Frail 2012  Scintillation: fundamental probe of ultra-relativistic expansion of GRB sources  Test of afterglow models unbiased, w/r, e.g., to optical observations (dust extinction, contamination by SN and host galaxy light)  Properties of circum-burst environment  Late time non relativistic phase expansion (LC and SED): afterglow physics and determination of the blast-wave energy independent of the initial jet collimation  Statistics of orphan afterglows: inference on maximum jet opening angle  Relevance of radio observations of GRBs

Chandra & Frail 2012  Scintillation: fundamental probe of ultra-relativistic expansion of GRB sources  Test of afterglow models unbiased, w/r, e.g., to optical observations (dust extinction, contamination by SN and host galaxy light)  Properties of circum-burst environment  Late time non relativistic expansion phase (LC and SED): afterglow physics and determination of the blast-wave energy independent of the initial jet collimation  Statistics of orphan afterglows: inference on maximum jet opening angle  Relevance of radio observations for GRB cosmology

 Scintillation: fundamental probe of ultra-relativistic expansion of GRB sources  Test of afterglow models unbiased, w/r, e.g., to optical observations (dust extinction, contamination by SN and host galaxy light)  Properties of circum-burst environment  Late time non relativistic expansion phase (LC and SED): afterglow physics and determination of the blast-wave energy independent of the initial jet collimation  Statistics of orphan afterglows: inference on maximum jet opening angle  Relevance of radio observations for GRB cosmology Soderberg et al. 2011

 High sensitivity + high angular resolution + short reaction time + broad band: measurement of GRB source size and expansion velocity through ISM scintillation; accurate location of GRBs in host galaxies; early radio afterglow: physics (reverse shock, transition from optically thick to optically thin synchrotron emission, …); kinetic energy and jet opening angle from SED fitting; host galaxy radio emission  High sensitivity: increased number and accuracy of GRBs radio calorimetry; detection of very high z GRBs (up to z 10 ?); study of SFR up to very high z; nearby (z <1 ) low-luminosity GRBs and GRB/SNe;  Broad FOV: significant number of orphan afterglows -> constraints on distribution of GRB jet opening angles and, hence, of energy budget  SKA for GRBs Chandra & Frail 2012 Shivers & Berger 2011

 High sensitivity + high angular resolution + short reaction time + broad band: measurement of GRB source size and expansion velocity through ISM scintillation; accurate location of GRBs in host galaxies; early radio afterglow: physics (reverse shock, transition from optically thick to optically thin synchrotron emission, …); kinetic energy and jet opening angle from SED (X, opt., IR, radio) fitting;  High sensitivity: increased number and accuracy of GRBs radio calorimetry ; detection of very high z GRBs (up to z 10 ?); study of SFR up to very high z; nearby (z <1 ) low-luminosity GRBs and GRB/SNe;  Broad FOV: significant number of orphan afterglows -> constraints on distribution of GRB jet opening angles and, hence, of energy budget  SKA for cosmology with GRBs Chandra & Frail 2012 Shivers & Berger 2011

Conclusions and perspectives  Given their huge radiated energies and redshift distribution extending from ~ 0.1 up to > 9, GRBs are potentially a very powerful cosmological probe, complementary to other probes (e.g., SN Ia, clusters, BAO)  The Ep,i – Eiso correlation is one of the most robust (no firm evidence of significant selection / instrumental effects) and intriguing properties of GRBs and a promising tool for cosmological parameters  Analysis in the last years (>2008) provide already evidence, independent on, e.g., SN Ia, that if we live in a flat  CDM universe,  m is 99.9% c.l. (  2 minimizes at  m ~ 0.25, consistent with “standard” cosmology)  the simulatenous operation of Swift, Fermi/GBM, Konus-WIND is allowing an increase of the useful sample (z + Ep) at a rate of GRB/year, providing an increasing accuracy in the estimate of cosmological parameters  future GRB experiments (e.g., SVOM) and more investigations (physics, methods, calibration) will allow to go beyond SN Ia cosm. (e.g.,dark energy EOS)  Radio observations by SKA will give a significant contribution by providing unique clues to the physics, energy budget and beaming angle of GRBs

Backup slides

 different GRB detectors are characterized by different detection and spectroscopy sensitivity as a function of GRB intensity and spectrum  this may introduce relevant selection effects / biases in the observed Ep,i – Eiso and other correlations But… is the Ep,i – intensity correlation real ? Band 2008 Sakamoto et al. 2011

? OK

 Amati, Frontera & Guidorzi (2009): the normalization of the correlation varies only marginally using GRBs with known redshift measured by individual instruments with different sensitivities and energy bands Amati, Frontera & Guidorzi 2009

 Detection, arcmin localization and study of GRBs in the GeV energy range through the Fermi /LAT instrument, with dramatic improvement w/r CGRO/EGRET  Detection, rough localization (a few degrees) and accurate determination of the shape of the spectral continuum of the prompt emission of GRBs from 8 keV up to 30 MeV through the Fermi/GBM instrument

 When computing Ep,i and Eiso based on the fit with Band function (unless CPL significantly better) all Fermi/ GBM long GRBs with known z are fully consistent with Ep,i – Eiso correlation as determined with previous / other experiments, both when considering preliminary fits (GCNs) or refined analysis (e.g., Nava et al. 2011) Amati 2012 Zhang et al. 2012

 selection effects are likely to play a relevant role in the process leading to the redshift estimate (e.g., Coward 2008, Jakobbson et al. 2010)  Swift: reduction of selection effects in redshift -> Swift GRBs expected to provide a robust test of the Ep,i – Eiso correlation

 Swift era: substantial increase of the number of GRBs with known redshift: ~45 in the pre-Swift era ( ), ~230 in the Swift era ( )  thanks also to combination with other GRB experiments with broad energy band (e.g., Konus/WIND, Fermi/GBM), substantial increase of GRBs in the Ep,i – Eiso plane Pre-Swift: 37 GRBs

 Ep,i of Swift GRBs measured by Konus-WIND, Suzaku/WAM, Fermi/GBM and BAT (only when Ep inside or close to keV and values provided by the Swift/BAT team (GCNs or Sakamoto et al. 2008, 2011): Swift GRBs are consistent with the Ep,i – Eiso correlation Red points = Swift GRBs Slope ~ 0.5  (logEp,i) ~ 0.2 Gaussian distribution of data scatter

Sakamoto et al. 2011BAT (Swift/ Official Catalog)

 the Ep,i– Liso correlation holds also within a good fraction of GRBs (Liang et al.2004, Firmani et al. 2008, Frontera et al. 2009, Ghirlanda et al. 2009): robust evidence for a physical origin and clues to explanation BATSE (Liang et al., ApJ, 2004) Fermi (e.g., Li et al., ApJ, 2012)

Ghirlanda et al  No evidence of evolution of index and normalization of the correlation with redshift

The Gamma-Ray Burst phenomenon  sudden and unpredictable bursts of hard-X / soft gamma rays with huge flux  most of the flux detected from keV up to 1-2 MeV, with fluences typically of ~10 -7 – erg/cm 2 and bimodal distribution of duration  measured rate (by an all-sky experiment on a LEO satellite): ~0.8 / day; estimated true rate ~2 / day short long

 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 erg/cm2 in keV) a cosmological origin would imply huge luminosity  thus, a “local” origin was not excluded until 1997 ! Early evidences for a cosmological origin of GRBs

 in 1997 discovery of afterglow emission by BeppoSAX Establishing the GRBs cosmological distance scale prompt afterglow

~ -3 ~ -0.7 ~ ~ -2 10^2 – 10^3 s10^4 – 10^5 s 10^5 – 10^6 s ( 1 min ≤ t ≤ hours ) Swift team  (observational gap between “prompt” and “afterglow emission” will be filled by Swift in > 2004)

 GRB , a normal GRB detected and localized by WFC and NFI, but in temporal/spatial coincidence with a type Ib/c SN at z =  bumps in optical afterglow light curves and optical spectra resembling that of GRB  1997: accurate (a few arcmin) and quick localization of X-ray afterglow -> optical follow- up -> first optical counterparts and host galaxies -> GRB-SN connection: Galama et al. 1998, Hjorth et al. 2003

 1997: accurate (a few arcmin) and quick localization of X-ray afterglow -> optical follow-up -> first optical counterparts and host galaxies  optical spectroscopy of afterglow and/or host galaxy –> first measurements of GRB redshift

 redshifts higher than 0.01 and up to > 8: GRB are cosmological !  their isotropic equivalent radiated energy is huge (up to more than erg in a few tens of s !)  fundamental input for origin of long / short GRB COSMOLOGY ?

 definite evidence that short GRBs DO NOT follow the Ep.i – Eiso correlation : a tool to distinguish between short and long events and to get clues on their different nature (e.g., Amati 2006, Piranomonte et al. 2008, Ghirlanda et al. 2009)

 the only long GRB outlier to the correlation is the peculiar GRB (very low redshift z = , sub-energetic, inconsistent with most other GRB properties) GRB

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

 fit the correlation and construct an Hubble diagram for each set of cosmological parameters -> derive c.l. contours based on chi-square  Method (e.g., Ghirlanda et al, Firmani et al., Dai et al., Zhang et al.) : E p,i = E p,obs x (1 + z), t b,i = t b / /1 + z) D l = D l (z, H 0,  M,  ,…)

 several authors (e.g., Kodama et al., 2008; Liang et al., 2008, Li et al. 2008, Tsutsui et al. 2009, Capozziello & Izzo 2010) calibrated the correlation at z < 1.7 by using the luminosity distance – redshift relation derived from SN Ia  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  but with this method GRB are no more an independent cosmological probe  Calibrating the Ep,i – Eiso correlation with SN Ia

 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 adapted from Salvaterra et al. 2008

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

 present and near future: main contribution expected from joint Fermi + Swift measurements  Up to 2009: ~290 Fermi/GBM GRBs, Ep estimates for ~90%, ~35 simultaneously detected by Swift (~13%), 13 with Ep and z estimates (~10% of Swift sample)  2008 pre-Fermi : 61 Swift detections, 5 BAT Ep (8%), 15 BAT + KONUS + SUZAKU Ep estimates (25%), 20 redshift (33%), 11 with Ep and z estimates (~15% of Swift sample)  Fermi provides a dramatic increase in Ep estimates (as expected), but a only small fraction of Fermi GRBs is detected / localized by Swift (~15%) -> low number of Fermi GRBs with Ep and z (~5%).  It is difficult to improve this number: BAT FOV much narrower than Fermi/GBM; similar orbits, each satellite limited by Earth occultation but at different times, … )  Summary: GRB/year in the Ep,i – Eiso plane

 In the > 2014 time frame a significant step forward expected from SVOM:  spectral study of prompt emission in 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

 GRB prompt emission physics  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) Implications of the Ep,i – intensity correlation

 physics of prompt emission still not settled, various scenarios: SSM internal shocks, IC-dominated internal shocks, external shocks, photospheric emission dominated models, kinetic energy / Poynting flux dominated fireballs, …  e.g., Ep,i  -2 L 1/2 t -1 for syncrotron emission from a power-law distribution of electrons generated in an internal shock (Zhang & Meszaros 2002, Ryde 2005)  e.g., Ep,i  Tpk  2 L -1/4 in scenarios in whch for comptonized thermal emission from the photosphere dominates (e.g. Rees & Meszaros 2005, Thomson et al. 2006)

 Up to date (Sept. 2011) Ep,i – Eiso plane: 131 long GRBs, 4 XRFs, 13 short GRBs  identifying and understanding sub-classes of GRBs

Chandra & Frail 2012  In the “Swift era”, radio afterglow emission is being detected for about 30% accurately (< a few arcmin) localized GRBs (~93% in X-rays, ~75% in optical/NIR)  Most detections by VLA / EVLA (Frail et al, Chandra et al.); several detections also by WSRT, ATCA, GMRT; a few by VLBA.  The canonical long-duration GRB radio light curve at 8.5 GHz peaks at three to six days in the source rest frame, with a median peak luminosity of erg s −1 Hz −1.  The typical mean fluxes at 8.5 GHz in days from the GRB range from ~100 to ~900  Jy The SKA contribution The SKA contribution  Radio observations of GRBs