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A new method optimized to use Gamma Ray Bursts as cosmic rulers | | C. Firmani
; G. Ghisellini
; G. Ghirlanda
; V. Avila-Reese
; | | Date: |
18 Dec 2004 | | Journal: | Mon.Not.Roy.Astron.Soc. 360 (2005) L1 | | Subject: | astro-ph | | Affiliation: | 1,2), G. Ghisellini , G. Ghirlanda , V. Avila-Reese ( INAF - Osservatorio Astronomico Brera, Italy, IA-UNAM, Mexico | | Abstract: | We present a new method aimed to handle long Gamma-Ray Burst (GRBs) as cosmic rulers. The recent discovery of a tight correlation between the collimation corrected GRB energy and the peak of the gamma-ray spectrum has opened the possibility to use GRBs as a new category of standard candles. Unfortunately, because of the lack of low-z GRBs, up to now this correlation is obtained from high-z GRBs with the consequence that it depends on the cosmological parameters we pretend to constrain. Hopefully this circularity problem will be solved when, in a few years, the low-z GRB sample will be increased enough. In the meanwhile we present here a new Bayesian method that eases the aforesaid circularity problem, and allows to introduce new constrains on the cosmological (Om,OL) diagram as well as to explore the universe kinematics up to z~3. The method we propose offers the further advantage to make handy the problem of the (Om,OL) loitering line singularity which inevitably appears when standard candles with z>2 are used. The combination of GRB with SN Ia data makes the popular LambdaCDM cosmology more consistent with the Hubble diagram at a 68% confidence level. For a flat cosmology we find Om=0.28pm0.03 for the combined GRB+SN Ia data set. Correspondingly, the transition redshift between cosmic deceleration and acceleration is z_T=0.73pm0.09, slightly larger than the value found by considering SNe Ia alone. We briefly discuss our results also in terms of non--LambdaCDM dark energy models. | | Source: | arXiv, astro-ph/0501395 | | Services: | Forum | Review | PDF | Favorites | |
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