LONG GAMMA–RAY BURST PROMPT EMISSION PROPERTIES AS A COSMOLOGICAL TOOL

 

C. Firmani,³ V. Avila–Reese,² G. Ghisellini,¹ and G. Ghirlanda¹

 

¹ INAF–Osservatorio Astronomico di Brera, via E. Bianchi 46, I–23807 Merate, Italy (giancarlo.ghirlanda@brera.inaf.it, gabriele.ghisellini@brera.inaf.it)

² Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70–264, 04510 México, D. F., Mexico (avila@astroscu.unam.mx) 

³ INAF–Osservatorio Astronomico di Brera, via E. Bianchi 46, I–23807 Merate, Italy and Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70–264, 04510 México, D. F., Mexico (firmani@merate.mi.astro.it)

 

Received 2007 January 11
Accepted 2007 February 1

 

RESUMEN

Se usa una estrecha correlación entre 3 propiedades de la emisión 7 de los Estallidos de Rayos Gamma (ERGs) con corrimiento al rojo z conocido (Firmani et al. 2006a) para constreñir parámetros cosmológicos (PCs) en el diagrama de Hubble (DH) con una muestra de 19 ERGs en el amplio rango de z = 0.17 — 4.5. El problema de la circularidad se resuelve con un enfoque bayesiano. Encontramos que la cosmología de concordancia ACDM es consistente con los datos de los ERGs a nivel de varias pruebas. Si suponemos el modelo Λ, entonces = y el caso plano está dentro del la. Suponiendo planitud, obtenemos , y fijando Ω_m= 0.28 obtenemos la ecuación de estado de la energía oscura , estando el caso ACDM (w = —1) dentro del la. Dado el bajo número de ERGs útiles no se puede aún constreñir bien la evolución de w = w(z), pero encontramos que el caso w(z) = —1 (ACDM) es consistente al 68.3% CL con los ERGs. Demostramos cómo un amplio rango de z's en la muestra usada (como es el caso de los ERGs) mejora la determinación de los PCs en el DH.

 

ABSTRACT

Recently, a tight correlation among three quantities that characterize the prompt emission of long Gamma–Ray Bursts (GRBs) with known redshift z, was discovered (Firmani et al. 2006a). We use this correlation to construct the Hubble diagram (HD) with a sample of 19 GRBs in the broad range of z = 0.17 — 4.5, and carry out a full statistical analysis to constrain cosmological parameters (CPs). To optimally solve the problem of circularity, a Bayesian approach is applied. The main result is that the concordance ACDM cosmology is fully consistent with the GRB data at the level of several tests. If we assume the Λ cosmology, then we find and the flat–geometry case is within la. Assuming flatness, we find , and fixing Ω_m =0.28, we obtain a dark energy equation of state parameter , i.e. the ACDM model (w = —1) is within 1σ. Given the low number of usable GRBs we cannot yet constrain well the possible evolution of w = w(z). However, the case w(z) = —1 (ACDM) is consistent at the 68.3% CL with GRBs. It is shown also how a broad range of z's in the used sample improves the determination of CPs from the HD, which is the case of GRBs as distance indicators.

Key Words: COSMOLOGICAL PARAMETERS — COSMOLOGY: OBSERVATIONS — DISTANCE SCALE GAMMA RAYS: BURSTS

 

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ACKNOWLEDGEMENTS

We thank Giuseppe Malaspina for technical support, and Jana Benda for grammar corrections. We are grateful to the anonymous referee for a through and constructive report that helped to improve the content of the paper. VA–R. gratefully acknowledges the hospitality extended by Osservatorio Astronomico di Brera. This work was supported by PAPIIT–UNAM grant IN107706–3 and by the Italian INAF MIUR (Cofin grant 2003020775002).

 

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