1. GRB physics and cosmology with spectrum-energy correlation
Lorenzo Amati
INAF – IASF Bologna (Italy)

2. Outline GRB: standard scenarios and open issues
Spectrum-energy correlation and its implications
GRB cosmology with spectrum-energy correlation
Future perspectives

3. Standard scenarios for GRB origin
LONG
SHORT
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
likelycollimated emission
energy budget up to erg
short duration (< 5 s)
clean circum-burst environment
old stellar population

4. Standard scenarios for GRB phisics
ms time variability + huge energy + detection of GeV photons -> plasma occurring ultra-relativistic (G > 100) expansion (fireball or firejet)
non thermal spectra -> shocks synchrotron emission (SSM)
fireball internal shocks -> prompt emission
fireball external shock with ISM -> afterglow emission

5. Open issues (several, despite obs. progress)
GRB prompt emission physics
most time averaged spectra of GRBs are well fit by synchrotron shock models
at early times, some spectra inconsistent with optically thin synchrotron: possible contribution of IC component and/or thermal emission from the fireball photosphere

6. Afterglow emission physics
consistency with synchrotron predictions found e.g. for GRB
deviations in the X-ray band from synchrotron: found for GRB (Harrison et al. 2001) and GRB (in ‘t Zand et al. 2001).
they are consistent with relevant Inverse Compton on the low energy photons

7. Early afterglow ( 1 min ≤ t ≤ hours )
new features seen by Swift in X-ray early afterglow light curves (initial very steep decay, early breaks, flares) mostly unpredicted and unexplained
initial steep decay: continuation of prompt emission, mini break due to patchy shell, IC up-scatter of the reverse shock sinchrotron emission ?
flat decay: probably “refreshed shocks” (due either to long duration ejection or short ejection but with wide range of G) ?
flares: could be due to: refreshed shocks, IC from reverse shock, external density bumps, continued central engine activity, late internal shocks…
~ -3
~ -0.7
~ - 1.3
~ -2
10^2 – 10^3 s
10^4 – 10^5 s
10^5 – 10^6 s
( 1 min ≤ t ≤ hours )

8. GeV emission
CGRO/EGRET detected VHE (from 30 MeV up to 18 GeV) photons for a few GRBs
VHE emission can last up to thousends of s after GRB onset
average spectrum of 4 events well described by a simple power-law with index ~2 , consistent with extension of low energy spectra
GRB ,measured by EGRET-TASC shows a high energy component inconsistent with synchrotron shock model
Recent AGILE detection of 2-3 >500 MeV photons

9. Prompt optical emission
GRB990123: first detection (by ROTSE) of prompt optical emission
optical light curve does not follow high energy light curve: evidence for a different origin (reverse shock ?)
GRB (RAPTOR) contrary to GRB990123, the optical light curve follows the high energy light curve: evidence for same origin (internal shocks ?)r

10. the challenging “naked eye” GRB080319B: complexity and energetics
Bloom et al. 2008

11. Circum-burst environment
evidence of overdense and metal enriched circum-burst environment from absorption and emission features
emission lines in afterglow spectrum detected by BeppoSAX but not by Swift
Swift detects intrinsic NH for many GRB afterglows
optical (Lya) NH often inconsistent with X-ray NH
prompt
afterglow
Amati et al.,Science, 2000
Antonelli et al., ApJ, 2001

12. Collimated or isotropic ?
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 ?

13. GRB/SN connection
are all long GRB produced by a type Ibc SN progenitor ?
which fraction of type Ibc SN produces a GRB, and what are their peculiarities ?
are the properties (e.g., energetics) of the GRB linked to those of the SN ?

14. short / long classification and physics
Swift GRB : a long GRB with a very high lower limit to the magnitude of an associated SN -> association with a GRB/SN is excluded
high lower limit to SN also for GRB (and, less stringently, XRF )
In the spectral lag – peak luminosity plane, GRB lies in the short GRBs region -> need for a new GRB classification scheme ?
Gehrels et al., Nature, 2006

15. Alternative scenarios
EMBH / fireshell model (Ruffini et al.)
CannonBall (CB) (Dar et al.)
Precessing jet (Fargion’s talk), stochastic wakefield plasma acceleration (Barbiellini et al.), ns-quark star transition, …
Short GRB as SGR giant outburst at high z

16. The Ep,i – Eiso correlation
GRB spectra typically described by the empirical Band function with parameters a= low-energy index, b= high-energy index, E0=break energy
Ep = E0 x (2 + a) = observed peak energy of the nFn spectrum

17. from redshift, fluence and spectrum, it is possible to estimate the cosmologica-rest frame peak energy, Ep,i, and the radiated energy assuming isotropic emission, Eiso
isotropic luminosities and radiated energy are huge; both Ep,i and Eiso and span several orders of magnitude
Ep,i = Ep x (1 + z)
log(Eiso)= 1.0 , s = 0.9
log(Ep,i )= 2.52 , s = 0.43
(Amati, MNRAS, 2006)

18. Amati et al. (2002) analyzed a sample of 12 BeppoSAX events with known redshift
we found evidence of a strong correlation between Ep,i and Eiso , highly significant (r = 0.949, chance prob %) despite the low number of GRBs included in the sample
Ep,i = kEiso
(0.52+/-0.06)
Amati et al. , A&A, 2002

19. only firm outlier the local peculiar GRB 980425 (GRB 031203 debated)
analysis of an updated sample of long GRBs/XRFs with firm estimates of z and Ep,i (41 events) gives a chance probability for the Ep,i-Eiso correlation of ~10-15 and a slope of 0.57+/-0.02
the scatter of the data around the best fit power-law can be fitted with a Gaussian with s(logEp,i) ~ 0.2 (~0.15 extra-poissonian)
confirmed by the most recent analysis (more than 70 events, Ghirlanda et al. 2008, Amati et al. 2008)
only firm outlier the local peculiar GRB (GRB debated)
Amati et al. 2008

20. 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

21. Implications of the Ep,i – Eiso 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 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)
e.g., Ep,i  G Tpk  G2 L-1/4 in scenarios in whch for comptonized thermal emission from the photosphere dominates (e.g. Rees & Meszaros 2005, Thomson et al. 2006)

22. jet geometry and structure
XRF-GRB unification models
viewing angle effects
Uniform/variable jet
PL-structured /universal jet
Uniform/variable jet
PL-structured /universal jet

23. The Ep,i – Eiso correlation and sub-energetic GRB
GRB not only prototype event of GRB/SN connection but closest GRB (z = ) and sub-energetic event (Eiso ~ 1048 erg, Ek,aft ~ 1050 erg)
GRB031203: the most similar case to GRB980425/SN1998bw: very close (z = 0.105), SN2003lw, sub-energetic

24. d=[g(1 - bcos(qv - Dq))]-1 , DEp  d , DEiso  d(1+a)
the most common explanations for the (apparent ?) sub-energetic nature of GRB and GRB and their violation of the Ep,i – Eiso correlation assume that they are NORMAL events seen very off-axis (e.g. Yamazaki et al. 2003, Ramirez-Ruiz et al. 2005)
d=[g(1 - bcos(qv - Dq))]-1 , DEp  d , DEiso  d(1+a)
a=1÷2.3 -> DEiso  d(2 ÷ 3.3)
Yamazaki et al., ApJ, 2003
Ramirez-Ruiz et al., ApJ, 2004

25. GRB , a very close (z = 0.033, second only to GRB ), with a prominent association with SN2006aj, and very low Eiso (6 x 1049 erg) and Ek,aft -> very similar to GRB and GRB031203
but, contrary to GRB and (possibly) GRB031203, GRB is consistent with the Ep,i-Eiso correlation -> evidence that it is a truly sub-energetic GRB -> likely existence of a population of under-luminous GRB detectable in the local universe
also XRF is very weak and soft (sub-energetic GRB prompt emission) and is consistent with the Ep-Eiso correlation
Amati et al., 2007

26. GRB was a very long event (~3000 s) and without XRT mesurement ( keV) Ep,i would have been over-estimated and found to be inconsistent with the Ep,i-Eiso correlation
Ghisellini et al. (2006) found that a spectral evolution model based on GRB can be applied to GRB and GRB031203, showing that these two events may be also consistent with the Ep,i-Eiso correlation
sub-energetic GRB consistent with the correlation; apparent outliers(s) GRB (GRB ) could be due to viewing angle or instrumental effect

27. Recent Swift detection of an X-ray transient associated with SN 2008D at z = , showing a light curve and duration similar to GRB
Peak energy limits and energetics consistent with a very-low energy extension of the Ep,i-Eiso correlation
Evidence that this transient may be a very soft and weak GRB (XRF ), thus confirming the existence of a population of sub-energetic GRB ?
Modjaz et al., ApJ, 2008
Li, MNRAS, 2008

28. Ep,i – Eiso correlation and short GRBs
only very recently, redshift estimates for short GRBs
all SHORT Swift GRBs with known redshift and lower limits to Ep.i are inconsistent with the Ep,i-Eiso correlation
intriguingly, the soft tail of GRB is consistent with the correlation
GRB : no SN, first pulse inconsistent with correlation, sfto/long tail consistent: evidence that two different emission mechanisms are at work in both short and long GRB, with different relative efficiency in the two classes (thus generating also intermediate)
Amati, NCimB, 2006

29. GRB-SN connection and the Ep,i-Eiso correlation
GRB and other GRB with firmest evidence of association with a SN are consistent with the Ep,i-Eiso correlation
GRB : the long GRB with a very deep lower limit to the magnitude of an associated SN is consistent with the correlation too
GRB : stringent lower limit to SN magnitude, inconsistent with correlation, but it is likely short
XRF / SN 2008D: possible very low energy GRB, possibly consistent with with the correlation
Further evidence that GRB properties are independent on those of the SN
Amati et al. A&A, 2007

30. GRB cosmology with Ep,i – Eiso correlation
GRB have huge luminosity, a redshift distribution extending far beyond SN Ia
high energy emission -> no extinction problems
unfortunately, they are not standard candles !
but need to investigate their properties to find ways to standardize them (if possible)

31. Standardizing GRB with 3-parameters spectrum-energy correlations
the Ep,i-Eiso correlation becomes tighter when adding a third observable: jet opening angle (qjet -> Eg = [1-cos(qjet)]*Eiso (Ghirlanda et al. 2004) or “high signal time” T0.45 (Firmani et al. 2006)
the logarithmic dispersion of these correlations is very low: can they be used to standardize GRB ?
jet angle inferred from break time in optical afterglow decay, while Ep,i-Eiso-T0.45 correlation based on prompt emission properties only

32. Methods (e. g. , Ghirlanda et al, Firmani et al. , Dai et al
Methods (e.g., Ghirlanda et al, Firmani et al., Dai et al., Zhang et al.):
Ep,i = Ep,obs x (1 + z)
Dl = Dl (z, H0, WM, WL, …)
general purpouse: estimate c.l. contours in 2-param surface (e.g. WM-WL)
general method: construct a chi-square statistics for a given correlation as a function of a couple cosmological parameters
method 1 – luminosity distance: fit the correlation and construct an Hubble diagram for each couple of cosmological parameters -> derive c.l. contours based on chi-square

33. method 2 – minimum correlation scatter: for each couple of cosm
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

34. 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

35. Drawbacks: lack of solid 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

36. 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), resulting in slightly reduced contours w/r to simple (and circularity free) scatter method (using Lp,iso-Ep,i-T0.45 corr.)

37. “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)
Recent evidence that the dispersion of the Lp-Ep-T0.45 correlation is significantly higher than thought before and comparable to the Ep,i-Eiso corr.
Campana et al. 2007
Rossi et al. 2008

38. 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
Simple PL fit
70 GRB
Amati et al. 2008

39. By quantifying the extrinsic scatter with a proper log-likelihood method, WM can be constrained to (68%) for a flat LCDM universe (WM = 1 excluded at 99.9% c.l.)
releasing assumption of flat universe still provides evidence of low WM, with a low sensitivity to WL
significant constraints on both WM and WL (and likely on dark energy EOS) expected from sample enrichment and z extension by present and next GRB experiments (e.g., Swift, Konus_WIND, GLAST, SVOM)
completely independent on other cosmological probes (e.g., CMB, type Ia SN, BAO; clusters…) and free of circularity problems
70 REAL
70 REAL SIM.
Amati et al. 2008

40. 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)
Ep estimates for some Swift GRBs from Konus (from 15 keV to several MeV) ant, to minor extent, RHESSI and SUZAKU
NARROW BAND
BROAD BAND

41. 2008(-2011 ?): GLAST (AGILE) + Swift:
accurate Ep (GLAST/GBM = keV) and z estimate (plus study of GeV emission) for simultaneously detected events
by assuming that Swift will follow-up ALL GLAST GRB, about 80 GRB with Ep and z in 3 years
AGILE and GLAST: second peak at E > 100 MeV ? (e.g., IC like in Blazars)

42. In the 2011-2015 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
substantial increase of the number of GRB with known z and Ep -> test of correlations and calibration for their cosmological use

43. GRB as cosmological beacons: EDGE/XENIA (under study)
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)
EDGE Team

44. End of the talk

45. Backup slides

46. Gamma-Ray Bursts
most of the flux detected from keV up to 1-2 MeV
measured rate (by an all-sky experiment on a LEO satellite): ~0.8 / day
bimodal duration distribution
fluences (= av.flux * duration) typically of ~10-7 – 10-4 erg/cm2
short
long

47. The GRB phenomenon: VHE
CGRO/EGRET detected VHE (from 30 MeV up to 18 GeV) photons for a few GRBs
VHE emission can last up to thousends of s after GRB onset
average spectrum of 4 events well described by a simple power-law with index ~2 , consistent with extension of low energy spectra

48. afterglow emission (> 1997): X, optical, radio counterparts

49. … and host galaxies Long Short GRB 050509b
host galaxies long GRBs: blue, usually regular and high star forming, GRB located in star forming regions
host galaxies of short GRBs (very recent): elliptical, irregular galaxies, away from star forming region (but still unclear)
Long
Short
GRB b

50. in 1997 discovery of afterglow emission by BeppoSAX
first X, optical, radio counterparts, redshifts, energetics
GRB , Metzger et al., Nature, 1997

51. 1998: GRB/SN connection
GRB , a normal GRB detected and localized by WFC and NFI, but in temporal/spatial coincidence with a type Ic SN at z = (chance prob )
further evidences of a GRB/SN connection: bumps in optical afterglow light curves and optical spectra resembling that of GRB980425

52. circum-burst environment
evidence of overdense and metal enriched circum-burst environment from absorption and emission features found in a few cases

53. >2005 prompt – afterglow Swift era
BeppoSAX era
prompt
afterglow

54. Conclusions - I
The Ep,i-Eiso correlation is the most firm GRB correlation followed by all normal GRB and XRF
Swift results and recent analysis show that it is not an artifact of selection effects
The existence, slope and extrinsic scatter of the correlation allow to test models for GRB prompt emission physics
The study of the locatios of GRB in the Ep,i-Eiso plane help in indentifying and understanding sub-classes of GRB (short, sub-energetic, GRB-SN connection)

55. Conclusions - II
Given their huge luminosities and redshift distribution extending up to at least 6.3, GRB are potentially a very powerful tool for cosmology and complementary to other probes (CMB, SN Ia, clusters, etc.)
The use of spectrum-energy correlations to this purpouse is promising, 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,…)
need calibration with a good number of events at z < 0.01 or within a small range of redshift
need solid physical interpretation
identification and understanding of possible sub-classes of GRB not following correlations

56. Tests and debates

57. 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

58. Ghirlanda et al., MNRAS, (2008)
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)

59. 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

60. 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

61. very recent claim by Butler et al
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: 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 , missing the soft part of GRB emission leads to overestimate of Ep

62. 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 keV for ~ 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

63. extending to high energies (1-2 MeV):
due to the broad spectral curvature of GRBs, a WFM with a limited energy band (< keV) will allow the determination of Ep for only a small fraction of events and with low accuracy (e.g., Swift/BAT ~15%)
an extension up to 1-2 MeV with a good average effective area keV) in the FOV of the WFM is required
-> baseline solution: WFM + GRB Detector based on crystal scintillator
accuracy of a few % for GRB with keV fluence > 10-6 erg cm-2 over a broad range of Ep ( )
Pow.law fit
Pow.law fit
WFM: 2mm thick CZT detector, eff. Area~500 keV, FOV~1.4sr
WFM + GRBD (5cm thick NaI, 850cm2 geom.area)

64. extending to low energies (1 keV)
GRB was a very long event (~3000 s) and without XRT mesurement ( keV) Ep,i would have been over-estimated and found to be inconsistent with the Ep,i-Eiso correlation
Ghisellini et al. (2006) found that a spectral evolution model based on GRB can be applied to GRB and GRB031203, showing that these two events may be also consistent with the Ep,i-Eiso correlation
missing the X-ray prompt emission -> overestimate of Ep

65. In some cases, Ep estimates form different instruments are inconsistent with each other -> particular attention has to be paid to systematics in the estimate of Ep (limited energy band, data truncation effects, detectors sensitivities as a function of energies, etc.)
include X-ray flares (and the whole afterglow emission) in the estimate of Ep,i and Eiso

66. e.g., , ,

67. Swift has shown how fast accurate localization and follow-up is critical in the reduction of selection effects in the sample of GRB with known z
increasing the number of GRB with known z and accurate estimate of Ep is fundamental for calibration and verification of spectral energy correlations and their use for estimate of cosmological parameters (sim. by G. Ghirlanda)

68. consider BATSE 25-2000 keV fluences and spectra for 350 bright GRBs
Ep,i = K x Eisom , Ep,i = Ep x (1+z), Eiso=(Sx4pDL2)/(1+z)
Ep,i-Eiso correlation re-fitted by computing Eiso from 25*(1+z) to 2000*(1+z) gives K ~100, m ~0.54 , s(logEp,i) ~ 0.2, Kmax,2s ~ 250
-> Smin,ns = min[(1+z)2.85/(4pDL2)] x (Ep/Kmax,ns)1.85 (min. for z = 3.8)
2 s
only a small fraction (and with substantial uncertainties in Ep) is below the 2 s limit !
Adapted from Kaneko et al., MNRAS, 2006

69. Open issues (several, despite recent huge observational advancements)
Prompt and afterglow emission mechanisms: still to be settled
early afterglow (steep decay, flat decay, flares): to be understood
GeV / TeV emission: need for new measurements to test models
X/gamma-ray polarization: need of measurements to test models
short vs. long events: emission mech. and GRB/SN connection
sub-energetic GRB and GRB rate: to be investigated -> SFR evolution
collimated emission: yes or no ?
spectrum-energy correlations and GRB cosmology: explanations and test
… and more !

70. jet angles derived from the achromatic break time, are of the order of few degrees
the collimation-corrected radiated energy spans the range ~5x1040 – 1052 erg-> more clustered but still not standard
recent observations put in doubt jet interpretation of optical break

71. long weak soft emission is indeed observed for some short GRBs
confirmation of expectations based on the fact that short GRBs are harder and have a lower fluence
spectra of short GRBs consistent with those of long GRBs in the first 1-2 s
evidences that long GRBs are produced by the superposition of 2 different emissions ?
e.g., in short GRBs only first ~thermal part of the emission and lack or weakness (e.g. due to very high G for internal shocks or low density medium for external shock) of long part
long weak soft emission is indeed observed for some short GRBs
Ghirlanda et al. (2004)

72. Polarization
no secure detection of polarization of prompt emission (some information from INTEGRAL and BATSE ?)
polarization of a few % for some optical / radio afterglows
radiation from synchrotron and IC is polarized, but a high degree of polarization can be detected only if magnetic field is uniform and perpendicular to line of sight
small degree of polarization detectable if magnetic field is random, emission is collimated (jet) and we are observing only a (particular) portion of the jet or its edge