Gamma Ray Bursts are the most extreme extragalactic astrophysical sources: their isotropic emitted energy is in the range 10^51 to 10^55 erg and they are detected to very high redshift. Their high power makes them the best candidate class of sources to probe the deep universe and its evolution.

The large dispersion of the isotropic energy of GRBs is highly reduced if it is corrected for their collimation angles but it is still too large to make them standard candles.

The discovery of a correlation between the burst peak energy and their collimation corrected energy allows instead to assign to each GRB its proper energy. This correlation makes GRBs standard candles to be used in observational cosmology similarly to SN Ia to test the cosmological models. GRBs, being detected at larger redshift with respect to the expected limit of SN Ia (i.e. z ~ 1.7), can probe the distant Universe structure and dynamics.

The original sample of GRBs (15) which allowed to discover the E_gamma - E_iso correlation and to study for the first time the Universe with GRBs is continuously increasing.

In this page we mantain an updated version of the correlation and of the constraints on the cosmological parameters by adding new GRBs.

Scope Methods Publications People Links
Peak Energy  versus total energy updated [.ps image]
Peak Energy vs tot. energy updated
Black symbols (32 GRB + 2 XRF) represent the bolomentric isotropic energy (Eiso) of GRBs with measured reshift and prompt emission spectrum. Red Symbols (15 GRBs) and green symbols (4 GRBs of the latest update) represent the bolometric collimation corrected energy (Eg) for those bursts with estimated jet break time. Blue and green arrows (8 GRBs + 1 XRF and 2 GRBs of this update) represtent the upper/lower limits for Edue to upper/lower limits on their jet break time

Eiso    [erg]
Ep*(1+z)   [keV]
t_b [days]
Angle  [deg]
Egamma [erg]
GRB 021004
2.33 (3.3+-0.4)E52
8.5+-1.0 (3.6+-0.9)E50 
GRB 030323
3.37 (3.0+-0.8)E52
> 4.8
> 7.8
> 2.8E50 
GRB 040924
0.859 (9.5+-[1.0])E51
> 1.0
> 6.9 deg > 6.8E49 
GRB 041006
0.716 (4.0+-[0.4])E52
0.16+-0.04 2.98+-0.44 deg (5.4+-1.7)E49
GRB 050525 (*)
0.606 (9.6+-1.0)E52
135+-8 0.4+-0.1 3.86+-0.57 deg

(*) The First Swift GRB !

Epeak - Eiso  Correlation 
Rank corr. coeff. = 0.8571     Null Hyp. prob. = 5.76e-09
  [Epeak/100 keV] = (3.0 +-1.0) [Eiso / 1.0E53]^(0.56+-0.02) 

Chi2=7.4 (26 dof)
Epeak - Egamma  Correlation 
Rank corr. coeff. = 0.9422      Null Hyp. prob. = 2.92e-09 
  [Epeak/100 keV] = (3.0 +- 1.1) [Egamma / 3.6E50]^(0.7+-0.04) 

Chi2=1.33 (16 dof)

Constraints on the cosmological parameters Omega matter and Omega Lambda obtained with the sample of GRBs alone (red contours), with the 156 SNIa (blue contours) and combining GRBs and SNIa (filled region). The contraints of the CMB data are also reported. Dashed lines correspond to the sign changing of the cosmic acceleration at different redshifts.  [.ps image]
Constraints on the parameters w0 and w´ of the
equation of state of the universe obtained with GRBs (red contours), SNIa (blue contours) and GRBs combined with SN Ia (filled regions). The balck point represents the standard cosmological constant model. The dotted line corresponds to the statefinder r=1. [.ps image]

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