lorenzo amati inaf - iasf bologna inaf - iasf bologna with main contributions by: m. della valle, f....

Lorenzo AmatiLorenzo Amati

INAF - IASF BolognaINAF - IASF Bologna

with main contributions by: M. Della Valle, F. Frontera, C. Guidorzi, with main contributions by: M. Della Valle, F. Frontera, C. Guidorzi, M. De Laurentis, E. Palazzi M. De Laurentis, E. Palazzi

Cosmology with Gamma-Ray Bursts: Cosmology with Gamma-Ray Bursts: status and perspectivesstatus and perspectives

Why looking for more cosmological probes ?Why looking for more cosmological probes ?

different distribution in redshift -> different sensitivity to different cosmological parameters

z

MoL dzzzkkSkHczD0

5.0325.05.0 ''11|| ||1

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

Guy et al. 2010

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 = 0.033 – ~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 ?Are GRB standard candles ?

Jakobsson, 2009 Amati, 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 ~5x1049 – 5x1052 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, E0=break energy

Ep = E0 x (2 + ) = observed peak energy of the F spectrum

measured spectrum + measured redshift -> intrinsic peak enery and radiated energy

Ep,i = Ep x (1 + z)

190 GRB

Jakobsson (2009)Ep

The Ep,i – Eiso correlationThe 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. 2011

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. 2008

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 correlationsStandardizing” 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)

ISM WIND

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 T0.45 was also claimed, based on still small number of events and proposed for standardizing GRBs (Firmani et al. 2006 and others)

… but Rossi et al. 2008 and Schaefer et al. 2008 , based on BeppoSAX and Swift GRBs, showed 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

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 – “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 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 evidences of outliers / higher dispersion of the Ep-E and Ep-Eiso-tb 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=

Amati et al. (2008): let’s make a step backward and focus on the Ep,i – Eiso correlation

does the extrinsic scatter of the Ep,i-Eiso correlation vary with the cosmological parameters used to compute Eiso ?

Amati et al. 2008

70 GRB

Dl = Dl (z , H0 , M , ,…)

a fraction of the extrinsic scatter of the Ep,i-Eiso correlation is indeed due to the cosmological parameters used to compute Eiso

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. 2008

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 0.04-0.43 (68%) and 0.02-0.71 (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. 2008

70 (real) GRBs 70 (real) + 150 (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 – 0.43 0.02 – 0.71

137 GRBs (Amati+ 12) 0.06 – 0.34 0.03 – 0.54

70 GRBs 114 GRBs137 GRBs

Adapted from Amati+ 12 and Ghirlanda+ 2007

the simulatenous operation of Swift, Fermi/GBM, Konus-WIND is allowing an increase of the useful sample (z + Ep) at a rate of 15-20 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

300 GRB

PerspectivesPerspectives 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. 2010-2011, 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. 2008 Wang et al. 2012

~ -3

~ -0.7

~ - 1.3

~ -210^2 – 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. 2012 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 1031 erg s−1 Hz−1.

The typical mean fluxes at 8.5 GHz in 5 -10 days from the GRB range from ~100 to ~900 Jy. Peak fluxes may reach 10 mJy

The SKA contributionThe SKA contribution Radio properties of GRBs


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:


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



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


Relevance of radio observations for GRB cosmology


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


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 < 1 at >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 15-20 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 ?But… is the Ep,i – intensity correlation real ?

Band 2008Sakamoto et al. 2011

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 (1997-2003), ~230 in the Swift era (2004-2012)

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 15-150 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. 2008

No evidence of evolution of index and normalization of the correlation with redshift

The Gamma-Ray Burst phenomenonThe Gamma-Ray Burst phenomenon sudden and unpredictable bursts of hard-X / soft gamma rays with huge flux

most of the flux detected from 10-20 keV up to 1-2 MeV, with fluences typically of ~10-7 – 10-4 erg/cm2 and bimodal distribution of duration

measured rate (by an all-sky experiment on a LEO satellite): ~0.8 / day; estimated true rate ~2 / day

shortlong

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

Establishing the GRBs cosmological distance scaleEstablishing the GRBs cosmological distance scale

prompt

afterglow

~ -3

~ -0.7

~ - 1.3

~ -210^2 – 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 980425, a normal GRB detected and localized by WFC and NFI, but in temporal/spatial coincidence with a type Ib/c SN at z = 0.008

bumps in optical afterglow light curves and optical spectra resembling that of GRB980425

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 1054 erg in a few tens of s !)

fundamental input for origin of long / shortGRB 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 GRB980425 (very low redshift z = 0.0085, sub-energetic, inconsistent with most other GRB properties)

GRB 980425

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.):

Ep,i = Ep,obs x (1 + z) , tb,i = tb / /1 + z)

Dl = Dl (z , H0 , 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 ?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: 15-20 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 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

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 L1/2 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


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 1031 erg s−1 Hz−1.

The typical mean fluxes at 8.5 GHz in 5 -10 days from the GRB range from ~100 to ~900 Jy

The SKA contributionThe SKA contribution Radio observations of GRBs

lorenzo amati inaf - iasf bologna inaf - iasf bologna with main contributions by: m. della valle, f....

Documents

redshift ep

measured redshift

redshift distribution

swift grbs

break energy ep

low redshift sne

short grbs

sne ia